EN (PDF | 1.3 MB) - Wacker Chemie

LASTING PROTECTION FOR BUILDING FABRIC –
WITH SILRES ® BS SILICONE MASONRY
PROTECTION AGENTS
CREATING TOMORROW’S SOLUTIONS

WATER-REPELLENT TREATMENT:
RELIABLE PROTECTION AGAINST
MOISTURE

The term “water-repellent treatment”
refers to the treatment of mineral
substrates, especially facades of fairfaced
masonry and concrete, with
hydrophobic impregnating agents.
The term “impregnating agent” is
frequently used on its own in this
context, since it is considered self-
evident that these agents are hydrophobic,
that is, water-repellent. By
definition, however, “to impregnate”
just means to saturate an absorbent
material with a low-viscosity, capillary-
active liquid.
SILRES ® BS is a registered trademark of Wacker Chemie AG.
Contents
Water-Repellent Treatment: Reliable Protection against Moisture 2
Moisture: Absorption by Masonry and Resulting Damage 4
Water Repellents: A Sure Guarantee of a Comfortable Ambience 8
Silicone Resins: Reliable Vehicles of Water Repellency 2
Silanes and Siloxanes: Stable Compounds 4
Customized Rather than Standardized Active-Agent Concentrations 8
General-Purpose and Specialty Products: Solutions for Every Application 22
WACKER Water Repellents for Maximum Effectiveness 26
Stone Stengthening with Ethyl Silicates 2
Long-Term Studies: Well-Known Reference Objects 6
Your Silicone Masonry Protection Team 40
WACKER at a Glance 4
It follows that impregnations – also of
masonry – do not necessarily imply water-
repellent treatment. They may serve, for
example, to strengthen and consolidate
the masonry, or to imbue it with biocidal
properties.
In this brochure, however, impregnating
agents are understood to be hydrophobic
agents, that is, compounds which confer
water repellency on mineral substrates.
The purpose of water-repellent treatment
is to protect exposed facades from moisture
and attendant damage by applying
a colorless, non-film-forming agent which
prevents capillary uptake of water and
the aggressive substances dissolved
therein. Because the impregnating agent
does not block the capillaries, the substrate
retains its vapor permeability.

MOISTURE: ABSORPTION BY MASONRY
AND RESULTING DAMAGE
4

The mechanisms of water uptake by
building materials are as varied as
the possible forms of damage to the
building. This chapter deals with the
mechanisms of capillary water uptake,
condensation, and hygroscopic water
uptake, as well as the consequences
for the building fabric.
Stone fabric damaged by the effects of
salt and moisture.
When mineral building materials come
into contact with water, they absorb an
amount which depends on their porosity.
The result is various forms of damage,
including:
- Penetration of moisture through the wall
- Cracks caused by swelling and
shrinkage
- Damage caused by frost and
de-icing salt
- Destruction of concrete caused by
corrosion of the reinforcing steel
- Efflorescence and salt damage caused
by hydration and crystallization
- Lime leaching
- Rust stains and curtaining
- Dirt pick-up and curtaining
- Attack by fungi, moss, lichens and
algae
- Chemical corrosion, e. g. binder
transformation caused by acidic gases
(SO 2 , NO 2 )
- Impaired thermal insulation
Algal growth on exposed construction
elements with a high moisture content.
Many of these forms of damage can be
prevented, or at least reduced or kept at
bay for longer, by means of impregnation.
Creation of a water-repellent zone considerably
reduces the uptake of water
and aggressive substances; the masonry
remains dryer, and is consequently less
prone to the kinds of damage referred
to above.
However, this is only true of capillary
water uptake, which is the “natural”
water uptake by building materials when
they come into contact with water –
when a facade is exposed to rain, for
example. There are various mechanisms
of water absorption other than capillary
water uptake, and these include
condensation, capillary condensation,
and hygroscopic water uptake.

Capillary Water Uptake
Capillary water uptake is responsible for
the penetration of large volumes of
water into the building material within a
short time. The amount of water absorbed
depends primarily on the radius
of the capillary pores in the building material.
There are three pore categories:
6
Micropores have a radius of less than
10 -7 m, gel pores less than 10 -8 m. These
small pores do not permit capillary water
transport. Water can only penetrate
these pore spaces in the form of vapor.
Consequently, building materials in
which micropores dominate are practically
impervious to water penetration by
capillary action. They are likewise
difficult to impregnate, since the water
repellents cannot penetrate into these
pores, either.
Pores with a radius of between 10 -7 m
and 10 -4 m are referred to as macropores
or capillary pores. These pores support
capillary action, and are able to transport
water and other liquids in the building
material to a degree dependent on their
capillarity. Building materials with a high
proportion of such pores are generally
well suited for impregnation with water
repellents.
Air pores, as the third pore category,
have a radius exceeding 10 -4 m. These
large pores, like micropores, are unsuitable
for capillary water transport.
Capillary water absorption by mineral
building materials is usually according to
the “square-root-of-time law.” If water
absorption W is plotted against the
square root of the time t, a straight line
is obtained, at least for the initial phase
of capillary absorption. The gradient is
referred to as the water-absorption
coefficient, or often just as the w value:

Fig. 1
y = water absorption [kg/m 2 ]
16
14
12
10
8
6
4
2
0
W = w ·√t
Brick
W water absorption [kg/m 2 ]
w water absorption coefficient
[kg/m 2 h 0. ]
Ettring Tuff
Monks Park limestone
t absorption time [h]
1 2 3 4 5
Sand-lime brick
Clinker brick
Burgpreppach sandstone
Mortar slabs
x = t [h 0.5 ]
Miltenberg sandstone
Engineering concrete
Strictly speaking, the water absorption coefficient
w describes the rate of capillary
absorption characteristic of a particular
building material, but it is frequently used
as a measure of the capillary absorbency
of building materials in general. The water
absorption coefficient is determined as
per ISO 52617.
Fig. 1 shows characteristic water-absorption
curves for different building materials.
The w values range from 0.15 kg/m 2 h 0.5
for the very dense bridge concrete to
11.5 kg/m 2 h 0.5 for the highly absorbent
brick.
Hygroscopic Water Absorption
The presence of soluble salts increases
the equilibrium moisture content of
building materials due to the salts’ hygroscopicity,
i.e. their ability to attract
water vapor. The extent of this hygroscopic
moisture absorption is determined
primarily by the chemical nature
of the salts, by their concentration in the
masonry, and by the moisture content
of the ambient air. Hygroscopic water
absorption is especially serious when
nitrates are present in the masonry.

WATER REPELLENTS: A SURE
GUARANTEE OF A COMFORTABLE
AMBIENCE
Unlike the various film-forming
coatings, building materials that have
been treated with a water repellent
retain their vapor permeability. This is
because organosilicon water repellents
do not seal the pores at the surface
of the mineral masonry substrate, but
form a very thin layer on the pore
walls. Siliconized pores are no longer
wetted by water, and capillary water
uptake is prevented.
8
It may be concluded from the above
comments about the various water-uptake
mechanisms that provided the
building material has pores which do
permit capillary action, or the salt content
– at least in the surface zone – is
not excessively high, capillary moisture
absorption without doubt poses the
most serious problem. In this case,
water-repellent treatment is certainly one
of the best ways to protect the masonry
from moisture damage.
Water repellents need to fulfill the following
requirements:
- Drastic reduction in water uptake
- Retention of high water-vapor permeability
- Extensive penetration
- Adequate resistance to alkalis
- Resistance to UV light
- Surfaces not rendered shiny or tacky,
or caused to yellow
- Environmental compatibility
Unlike film-forming coatings, such as
those based on acrylic, polyurethane or
epoxy resins, organosilicon water repellents
do not seal the pores at the surface
of mineral masonry, but simply form a
very thin layer on the pore walls (Fig. 2).
Fig. 2
a b c
A mineral surface with (a) a hydrophobic
impregnation, (b) filled pores, and (c) a
sealant film.

Water can no longer penetrate in liquid
form into capillaries that have been rendered
water-repellent, since, as a polar
liquid, it is unable to interact with a
non-polar, hydrophobic surface. In other
words, pores which have been siliconized
and are therefore hydrophobic can
no longer be wetted by water.
The degree of wetting can be determined
quantitatively as the contact angle θ.
Untreated surfaces of mineral building
materials are wetted immediately by
water, i. e. the drops of water spread out
and are rapidly absorbed by the building
material (Fig. 3a). If the same building
material is treated with an impregnating
agent, the drops of water are repelled in
the form of beads and do not penetrate
into the substrate (Fig. 3b).
Fig. 3a
hydrophilic material
0°
Wetting of a hydrophilic porous surface.
Abb. 3a
Fig. 3b
hydrophiles Material
0°
hydrophobic material
180°
Wetting of a hydrophobic porous surface.

Water Vapor Can Diffuse
Since the pores in hydrophobically treated
masonry remain open, the building
material retains its vapor permeability, or
“breathability.” Accordingly, the passage
of water vapor is impaired only slightly, if
at all. This is of great importance, since
moisture contained in the building material
can diffuse to the outside in the form
of water vapor without causing any
damage, e.g. blistering and subsequent
spalling, which frequently occur with
thick surface coatings.
0
Water under Pressure is a Problem
Ground water can be a serious problem
in cellars, as can driving rain for highly
exposed facades. The larger the pores
in the building material are, the greater
the problem.
Since the pores are open, a water-repellent
treatment obviously cannot always
protect a building material from ground
water or driving rain.
However, properly applied water repellents
are perfectly sufficient to render
many standard building materials, such
as sand-lime brick, clinker brick and
plasters, resistant even to driving rain
with velocities of 100 km/h and more.
“Properly applied” in this context means,
for example, that the water repellent
produces a hydrophobic zone which is
not merely superficial but extends to a
good depth.
The water repellent must accordingly be
formulated such as to allow maximum
penetration into the building material.
Only then can the effectiveness of the
hydrophobic impregnation be guaranteed
for years or even decades.

SILICONE RESINS: RELIABLE
VEHICLES OF WATER REPELLENCY
Fig. 4
R
2
R
R
OEt
0 Si 0 Si 0 Si 0 Si
0
Si
R
OEt
0
Si
0
0
Si
R
R
EtO
Si
R R R
Molecular structure of silicone resins.
Fig.
Consistency of solid silicone resins.
0
R
0
R
0
Si
R
OEt
The close structural similarity between
fully cured silicone resins and natural
quartz is the reason for the high affinity
of silicone resins for silicate building
materials, and for the exceptional
durability of surfaces treated with
these resins. Silicone resins boast
excellent water repellency, and are
completely resistant to many chemical,
physical and biological influences.
Organosilicon compounds have been
recognized for over 40 years as the ideal
active agents for the hydrophobic impregnation
of absorbent mineral building
materials. However, it is not the ubiquitous
silicone rubbers (joint sealants) and
silicone fluids (release agents and lubricants)
that are used in masonry protection,
but the third important category of
silicones – silicone resins.
Silicone resins are three-dimensionally
crosslinked polymers with a silicon and
oxygen backbone. The silicon atoms
carry organic groups R and functional
groups OR’ (usually, R is a methyl group
and R´an ethyl group) (Fig. 4). The resins
range from liquid to solid depending on
the degree of curing, the molecular
weight and the kind of functional group
(Fig. 5). They are soluble in organic
solvents such as white spirit or alcohols.

When applied to the building material,
these silicone resins react with water, the
remaining alkoxy groups being split off, to
form a three-dimensional, densely crosslinked
polysiloxane which is firmly attached
to the building material by way of covalent
Si-O-Si bonds (Fig. 6).
Crosslinked silicone resin bonded to a
substrate.
A comparison of the molecular structure
of a fully cured silicone resin (Fig. 7a)
with that of natural quartz (Fig. 7b)
makes the close resemblance clear. The
fully cured silicone resin can be regarded
as a quartz structure that has been
modified with organic groups. This close
structural resemblance is the reason for
the high affinity of silicone resins for
silicate building materials, and for the
exceptional durability of the water-repellent
treatment.
Molecular structure of fully cured silicone
resin.
The organic group R confers excellent
water repellency on the silicone resins.
Since they are also fully resistant to
many chemical, physical and biological
influences, the resins’ water-repellent
property is generally maintained for decades,
provided that the water-repellent
treatment is carried out properly, i. e.
provided that the right amount of the
right product for the substrate is applied,
and that the concentration of active
agent is high enough.
Molecular structure of quartz.

SILANES AND SILOxANES:
STABLE COMPOUNDS
The ultimate aim of all hydrophobic
impregnations is to guarantee effective
masonry protection for as long as
possible. This goal was not always
achieved with the organic-solventbased
silicone resins frequently used
in the past, or with water-based
methyl siliconates. Today, silanes and
siloxanes form the basis of modern
water repellents. They can be incorporated
easily in a large variety of
products, and have outstanding
properties.
4
When silicone masonry protection was in
its infancy, there were two main sorts of
water repellents, namely solutions of silicone
resins in organic solvents, and methyl
siliconates in water.

Fig. 8
Fig. 9
OH - /H 2O
[ CH3-SiO3/2 ] CH x 3-Si(OH) 2O -
®
Methyl silicone resin
R
R’O-Si-OR’
OR’
(a)
Methyl siliconate
R
R’O -Si-O- R’
OR’
(b)
Alkyltrialkoxy silane Alkylalkoxy siloxane
2-8
Silicone Resin Solutions and Siliconates
Solutions of silicone resins are only of
minor importance today as water repellents.
On account of their relatively high
molecular weight, they do not penetrate
deeply enough into dense building materials.
Under alkaline conditions, standard
silicone resins are broken open and
methyl siliconates are formed. These are
water-soluble and are leached out of the
facade by rain (Fig. 8).
The silicone resin, along with the water
repellency it confers on the substrate,
thus dwindles with time. Aqueous solutions
of potassium methyl siliconate
(CH 3 -Si(OH) 2 O - K + ) are frequently used for
in-plant impregnation of building materials
of fired clay and fibrous gypsum. Alkali
carbonates are formed as by-products.
However, siliconates are no longer used
for impregnating facades because they
are apt to form a white deposit.
The poor degree of penetration and
insufficient resistance of silicone resin
solutions to alkalis prompted the search
for alternative active agents back in the
mid 1970s.
Silanes and Siloxanes
Better penetration is achieved by using
low-molecular rather than high-molecular
compounds. This discovery marked the
birth of water-repellent agents based on
silanes and siloxanes. As is evident from
the chemical formulae (Fig. 9), the silanes,
on closer examination, are monomeric alkyltrialkoxy
silanes, and the siloxanes are
oligomeric alkylalkoxy siloxanes derived
therefrom.

Resistance to Alkalis – a Criterion of
Durability
The second most important discovery
on the way to developing today’s highly
effective water repellents was how to
influence the resistance of the active
agent to alkalis through use of the appropriate
organic group R. If R is always
a methyl group, the reaction of Fig. 8,
in the presence of alkali, will eventually
lead to a complete loss of hydrophobicity.
But if longer-chain organic groups are
used in place of methyl groups, the
reaction of Fig. 8 can still proceed, even
though this is not easy for steric reasons.
However, the resulting siliconate becomes
increasingly water-insoluble as the length
of the R group lengthens, thus preventing
the siliconate from being leached out by
rain. In consequence, the degradation
reaction is suppressed, and the active
agent remains in the form of a silicone
resin network on the masonry.
6
The iso-octyl group has proved to be
particularly suitable. Silanes and siloxanes
with iso-octyl groups are readily available,
can be incorporated in a large number
of products and exhibit outstanding
properties. Water repellents frequently
contain a mixture of silicone components
with short-chain methyl and long-chain
iso-octyl groups.
Silane and Siloxane Blends
In this way, it is possible to formulate
water repellents that are customized in
terms of properties such as penetration
power, resistance to alkalis, water-beading,
etc. A water repellent for concrete
will require, for example, more silane and
more long-chain organic groups than a
product used to impregnate sandstone
or brick. Whereas concrete is usually
very dense and highly alkaline, sandstone
and brick are absorbent and more or
less neutral.

Specialty Products for Maximum
Effectiveness
There is a whole range of building materials
with properties between those of
concrete and sandstone or brick. These
materials include limestones and sandlime
brick, clinker brick, mineral-based
plasters and paints, aerated concrete,
fiber-reinforced concrete, and many
others. It is thus important to have balanced,
general-purpose products, i. e.
impregnating agents that are acceptably
effective on all standard substrates.
Where maximum effectiveness for a
particular substrate is desired, silanes
and siloxanes may be suitably blended
to formulate a specialty product.

CUSTOMIzED RATHER THAN
STANDARDIzED ACTIVE-AGENT
CONCENTRATIONS
A standard solution will not be able to
confer maximum water repellency on
every type of building material, as
each material has different properties.
Whatever the substrate, whether
high-grade concrete or absorbent
brickwork, the right impregnating
agent in the right concentration is
always needed. Impregating agents
may be used in concentrations ranging
from highly diluted to undiluted.
Among the diluted products, aqueous
water repellents are becoming increasingly
important.
The depth to which the active ingredient
of an impregnating agent penetrates is
directly dependent on the concentration
of the active ingredient. The more a
product is diluted, the less able it is to
penetrate into the building material and
fully occupy the walls of the pores and
capillaries so as to prevent them from
absorbing water. The capillary absorbency
of building materials, for their part,
varies enormously. If, for example, a vertical
bridge-concrete surface is saturated
8
with water repellent by flooding, the highgrade
concrete will absorb 80-100 g/m²
at the most. An absorbent brick or
sandstone facade, by contrast, will easily
take up ten times this amount under the
same conditions. To ensure that the active
agent penetrates to an acceptable
depth into the low-absorbency concrete,
it is thus necessary to use a much more
concentrated product than for the more
absorbent sandstone or brick. In practice,
use is made of undiluted silanes or silane/
siloxane mixtures to render concrete
water-repellent, while for natural-stone
facades it is common to use products
containing only 5-10 % active agent.
Silanes and Siloxanes in Solution
In keeping with their hydrophobic nature,
silanes and siloxanes are soluble to
an almost unlimited extent in organic
solvents. Since, however, contrary to
widespread opinion, silicone active
agents penetrate into the pores of building
materials better when dissolved in
petroleum ether than in alcohols such
as ethanol and 2-propanol, the latter are
only used if there is any risk of the water
repellent’s coming into contact during
application with plastics or paints that
are attacked by petroleum ether.
Otherwise, low-odor, dearomatized
white spirit or synthetic iso-paraffins are
the most commonly used solvents.
Care must be taken that whenever
solvents are used, these are, if possible,
anhydrous. The current trend is definitely
toward solvent-free, that is, water-based
products.

SILRES ® BS SMK – A Triumph over
Difficulties
The first breakthrough was the development
of silicone microemulsion
concentrates (sold under the name
SILRES ® BS SMK).
Silicone microemulsion concentrates are
solvent-free mixtures of silanes, siloxanes
and silicone surfactants, which, on dilution
with water, yield ready-to-use silicone
microemulsions.
The advantage offered by these products
results from the nature of the surfactants
(emulsifiers and co-emulsifiers), which
only function temporarily as such; once
the water repellent has been applied to
the building material, they transform into
hydrophobic active-agent components.
If the particle sizes of emulsions and
microemulsions (Figs. 10a and b) are
compared, it is clear that microemulsions,
on account of the vastly greater particlesurface
area, will require considerably
more emulsifier than emulsions. The use
of conventional surfactants would impair
the hydrophobicity.
The great advantage of SILRES ® BS SMK
products, apart from their being waterdilutable
and easy to handle, is the fact
that they come in concentrated form.
This makes for smaller container sizes,
greatly reduces transport, storage and
waste-disposal costs and lessens environmental
impact.
A disadvantage of SMK technology,
however, is that the microemulsions have
to be used within 24 hours of diluting
them. Their appearance does not change
in days or even weeks, but the alkoxysilanes
and alkoxysiloxanes in the microparticles
hydrolyze and polymerize to
an increasing extent, making it harder
and harder for the active agents to
penetrate into the building materials.
Fig. 10
Water
Oil
a) Emulsion
(Section of droplet)
: Emulsifier : Co-emulsifier
Water
Oil
b) Microemulsion
Comparison of emulsion (a) and silicone
microemulsion (b) particle size.

Impregnating Agents in the Form of
Emulsions
Aside from the product classes already
mentioned, there are silane/siloxane
emulsions which boast both dilution and
storage stability. These emulsions are
diluted with water in a ratio of 1:4 to
1:9, the exact ratio depending on the
type of substrate and the extent of water
repellency required.
The problem of using emulsions for impregnations,
however, as was explained
before, is that, if the products are to
have properties comparable to those of
conventional solvent-thinned impregnating
agents, only low-molecular alkylalkoxy
silanes and siloxanes are suited as
active agents. But these silanes and
siloxanes react with moisture, and therefore
special tricks are needed to stabilize
them.
20
The key to success lies primarily in the
correct choice of emulsifiers, in adjusting
the pH to the optimum value, and in the
chemical nature and thus the reactivity
of the active agents. It is advisable, for
example, to employ ethoxy silanes and
siloxanes rather than their methoxy
counterparts, as the former hydrolyze far
less quickly. The reactivity is, moreover,
largely dependent on the nature of the
organic group attached to the silicone:
long-chain groups, such as the iso-octyl
group, drastically reduce the tendency of
silanes and siloxanes to hydrolyze.
Impregnating Cream
Unlike all other water repellents, impregnating
agents in the form of cream may
be applied without wastage even during
overhead work.
SILRES ® BS creams are best applied
using airless equipment, with which up
to 400 g/m² may be applied in a single
operation.
The impregnating cream penetrates
completely into the substrate within a
period of some minutes to some hours;
the exact time required will depend on
the amount applied. Very high depths of
penetration are achieved due to the long
time the cream is in contact with the
construction material.

GENERAL-PURPOSE AND SPECIALTY
PRODUCTS: SOLUTIONS FOR EVERY
APPLICATION
Wacker Chemie AG offers both longestablished
water repellents and new,
innovative masonry protection agents.
Our product spectrum includes both
general-purpose water repellents and
specialty products for concrete.
22
Wacker Chemie AG has been intensively
researching and developing silicone
masonry protection agents for some fifty
years. A large number of products have
been developed during this time, many
of which are still in use.
However, the constant development of
new water repellents necessitated
streamlining the product portfolio and
adapting it to today’s requirements.
The outcome of these measures is a
clearly organized product spectrum
comprising the two categories: “generalpurpose
water repellents” and “specialty
products for concrete.”
General-purpose products are defined
as those impregnating agents which, in
principle, confer good water repellency
on a large variety of very different mineral
substrates, ranging from highly alkaline,
dense concrete to neutral, absorbent
brick and natural stone.
Specialty products for concrete, by
contrast, are those products that confer
long-term protection on high-grade
reinforced concrete of the type used in
bridge building. These products must be
able to penetrate extensively into the
building material, even into very dense
concrete, and they must show excellent
resistance to attack by alkalis.
Table 1 (p. 25) contains a survey of the
various products, their properties, and
their fields of application.

General-Purpose Water Repellents
The best-known and most frequently
used water repellent is SILRES ® BS
290. When used in the recommended
concentrations of 1:11 to 1:15 (parts by
weight), it produces excellent results on
almost all absorbent mineral substrates.
Particularly worth mentioning are its
resistance to alkalis, its good penetration
power and its outstanding beading effect.
For many types of natural stone, in particular,
there is to date still no alternative
to SILRES ® BS 290. The hydrophobic
silicone resin network forms within a few
hours, even on non-alkaline substrates.
SILRES ® BS SMK 1311 is a well-established,
aqueous alternative to solventthinned
products, and is suitable for a
wide variety of building materials, e. g.
sand-lime brick, bricks and mineral
plaster. It should be diluted in a ratio of
1:10 to 1:14 to suit the substrate in
question. By virtue of its autocatalytic
behavior, SILRES ® BS SMK 1311 reacts
to form the hydrophobic silicone resin
just as quickly as SILRES ® BS 290.
However, on many types of natural
stone, including sandstone, limestone
and stone containing clay mineral, the
effectiveness of the aqueous product
may differ markedly from that of
SILRES ® BS 290. Before treating a large
area of masonry, therefore, it is a good
idea to check the effectiveness of the
water repellent on a test area. Like all
silicone microemulsion concentrates,
SILRES® BS 1311 should only be
diluted with tap water on the day it is
to be processed.
Another of the general-purpose water
repellents, SILRES ® BS 1001, is a 50-%
silane/siloxane emulsion that is diluted
with water to suit the consistency of the
substrate in question. Before the emulsion
is diluted and applied, it is advisable
to stir it briefly so as to ensure that it is
homogeneous. SILRES ® BS 1001 rapidly
confers discernible water repellency on
the building material, although the active
agent takes a few days to some weeks
to form completely. The exact length of
time will depend on the alkalinity of the
substrate.
Since the emulsion breaks once it has
been applied, and there is a pronounced
beading effect as soon as the water has
evaporated, the amount of active agent
leached out by rain during the relatively
long curing period is negligible. Like all
aqueous products based on alkylalkoxy
silanes and siloxanes, SILRES ® BS 1001
is markedly less effective on some types
of natural stone, especially limestone,
than, for instance, solvent-thinned
SILRES ® BS 290. It is therefore always
essential to check its effectiveness on a
test surface.
2

Specialty Products for Concrete
SILRES ® BS 1701 is a 100-% silanebased
impregnating agent that is used to
confer water repellency on concrete and
reinforced concrete. It is usually
applied to the concrete by flooding (wet
on wet) at least twice in undiluted form.
Of course, this water repellent may be
diluted with organic solvents or alcohols
in any mixing ratio desired. It should be
remembered, however, that the more a
given quantity of water repellent is diluted,
the less deep the active agent will penetrate.
Because of its iso-octyl silane groups,
SILRES ® BS 1701 is much less volatile
than other commercial silanes. However,
under certain conditions, evaporation may
cause some loss of active agent. This happens
most frequently when the concrete
is old, of low alkalinity, and is hot and dry
at the surface due to exposure to the sun.
In such cases it is advisable to resort to
an aqueous product, in particular to the
impregnating cream described below.
SILRES ® SMK 2101 is similar in composition
to SILRES ® SMK 1311, but contains
24
substantially more iso-octyl silane. This
enhances its penetration power and resistance
to alkalis. When SILRES ® SMK
2101 is used to treat reinforced concrete,
it should be diluted with water in a ratio
of 1:4. Like all silicone microemulsions,
the diluted product ought to be used on
the same day it is mixed. SILRES ® SMK
2101 is also especially suitable as a
primer for concrete coatings.
Unlike all the other products listed in
Table 1, SILRES ® BS Creme C is not a
liquid. Its thixotropic consistency makes
it possible to apply the product without
wastage even when working overhead.
SILRES ® BS Creme C is best applied
using airless equipment, with which up
to 400 g/m² may be applied in a single
operation. Such quantities often cannot
be applied even in three operations
when conventional low-viscosity products
are used on high-grade concrete.
The impregnating agent penetrates completely
into the concrete within a period
of some minutes to some hours, the
exact time depending on the quality of
the concrete and the amount of impregnating
agent applied. No visible traces of
the cream are left on the surface, and
very great depths of penetration can be
achieved.
Thanks to the very pronounced penetration
depth of several mm, even concrete
with a damaged surface (cracks, spalling)
is adequately protected. Tests have
confirmed that a hydrophobic impregnation
not only protects the concrete from
moisture, but also minimizes pollutant
ingress into the concrete. In test samples
of treated masonry, chloride uptake
is superficial only.
In untreated building material, by contrast,
considerable concentrations of
chloride are detectable even at a depth
of 4 mm (Fig. 11).

Fig. 11 Chloride migration in concrete (strength
0.50
class C / 4 )
Untreated specimens and those treated with
0.45
SILRES
0.40
0.35
® BS Creme C
Specimens conditioned for 0 days in 0 %
NaCl solution
Chloride content (%)
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Depth
Untreated 100g/m 2 200g/m 2 300g/m 2
Amount applied of SILRES ® BS Creme C
0-9 mm 1.1-1.9 mm 2.1-2.9 mm 3.1-3.9 mm
Table
Products and
applications
All-Round Products Special Products for Concrete
Product Properties
SILRES ® BS SILRES ® BS SILRES ® BS SILRES ® BS SILRES ® BS SILRES ® BS
2 0 SMK 00 0 SMK 2 0 Creme C
Appearance Milky, colorless Clear, yellowish Clear, yellowish Clear, yellowish Clear, yellowish Clear, yellowish
Silicone agent Silane/siloxane Silane/siloxane Silane/siloxane Silane Silane/siloxane Silane
Product type 100 % 100 % 50 % 100 % 100 % 80 %
concentrate microemulsion emulsion concentrate microemulsion cream
solution concentrate solution concentrate
Density [g/cm ] 1.05 0.95 0.95 0.90 0.90 0.90
Viscosity [mm2 /s] 20 7 12 2 4 Non-sag
Flash point [°C] 38 25 >100 70 25 74
Diluent Solvent Water Water Undiluted/
solvent
Water Undiluted
Shelf life (months)
Applications
12 12 9 12 12 12
Sandstone
Sand-lime brick
Porous limestone
Marble
Granite
Brick
Mineral plaster
Concrete
Reinforced concrete
Suitable Highly suitable Very highly suitable
2

WACKER WATER REPELLENTS
FOR MAxIMUM EFFECTIVENESS
The most important criteria which
water repellents must satisfy are
reduction in water uptake, penetration
by the hydrophobic active agent,
permeability to gas and water vapor
and a beading effect. In the following
section, these requirements will be
described in more detail, and the
effectiveness of the WACKER products
compared on the basis thereof.
26
Capillary Water Uptake
The most important requirement which a
water repellent must fulfill is a significant
reduction in capillary water uptake. A
common specification is that the amount
of water absorbed by a building material
during 24 hours’ immersion in water be
reduced by at least 80 %.
Depth of Penetration
In order that the reduced tendency to
absorb water may be long-lasting, it is
obviously not sufficient if the water-repellent
effect is limited to the surface of the
building material. It is essential that the
hydrophobic zone extend deep below
the surface, but it is difficult to give a
general answer to the frequently-asked
question as to exactly how deep. Of
course, from a technical point of view,
there is nothing against striving for
maximum possible penetration, but it
must be remembered that this is only
achieved by applying a large quantity of
active agent, which incurs high costs.
For many substrates, a penetration
depth in the order of a few millimeters is
technically adequate and economically
acceptable.

Beading Effect
The third important criterion which water
repellents must satisfy is the production
of a beading effect. This effect is measured
objectively by means of the contact
angle Θ. The following classification is
often used:
Table 2
Rating Very good repellency Contact angle Θ >130°
Rating 2 Good repellency Contact angle Θ 110-130°
Rating Slight wetting Contact angle Θ 90-110°
Rating 4 Pronounced wetting Contact angle Θ 30-90°
Rating Surface completely wetted Contact angle Θ

The Effectiveness of WACKER
Products
Tables 4a and 4b (page 30) show test
results for water uptake, beading and
penetration depth of various products
applied to different substrates. White
spirit with a low aromatics content was
used as diluent for the solvent-thinnable
products, and normal tap water for the
aqueous products. All substrates were
impregnated by means of immersion
(immersion times: 1 minute for mortar
and concrete, 5 minutes for all other
substrates).
The quantities of impregnating agent absorbed
correspond approximately to the
amounts absorbed when the products
are applied to vertical surfaces by flooding
in two wet-on-wet operations.
Water absorption was determined 14
days after impregnation, again by way of
immersion (specimens were covered
with 5 cm of water, in accordance with
EN 12859). This method was chosen
because the hydrostatic pressure exerted
by the covering of water simulates,
to a certain extent, the effect of driving
28
rain, making the procedure more realistic
than the sponge immersion test described
in ISO 15148, in which only capillary
absorption is measured.
To determine the penetration depth, a
specimen of each product was broken
14 days after impregnation and dyed
water was dripped onto the fracture
surface. The hydrophobic zone is not
wetted by the dyed water.
Gas Permeability
The term “gas permeability”, when used
in the context of water repellents, refers
primarily to the impregnated structure’s
permeability to water vapor and carbon
dioxide.
Water-vapor permeability is essential for
allowing any moisture beneath the surface
to dry. It is determined as follows,
in accordance with ISO 7783-2: a sample
of the substrate is cemented above
a saturated salt solution contained in
a cup. The salt solution provides for a
constant and very specific relative
humidity within the cup. In line with the
recommendation given in the standard,
frequent use is made of ammonium
dihydrogen phosphate, with which a
relative humidity of precisely 93 % is obtained.
The cup is kept under standard
conditions at 23 °C and 50-% humidity.
By weighing it repeatedly over a period
of several days, it is possible to determine
how much water vapor diffuses
through the substrate. Since the surface
area of the substrate is known, the
water-vapor permeability, WVP, can be
calculated in [g/m 2 d]. Table 3 shows the
water-vapor permeability of sand-lime
brick specimens (diameter: 90 mm,
thickness: 5 mm).
The liquid products SILRES ® BS 290,
SILRES ® BS SMK 1311 and SILRES ®
BS 1001 were applied by immersion
(immersion time: 5 minutes), and
SILRES ® BS Creme was applied by
brush. Once the WVP measurements
had been completed, the test discs
were broken and the penetration depths
determined. In all of the specimens, the
hydrophobic zone extended through the
entire thickness of the disc.

Table
Mortar slabs Dilution Impregnating- Weight Water-vapor
(water/cement agent absorption loss permeability
ratio) [g/m 2 ] [g/d] [g/m 2 d]
Untreated - - 0.70 110.6
SILRES ® BS 2 0 1:15 455 0.61 95.9
SILRES ® BS SMK 1:14 560 0.59 93.2
SILRES ® BS 00 1:9 480 0.65 102.3
SILRES ® BS Creme C undiluted 300 0.57 89.7
As Table 3 shows, the impregnating agents
reduced the water vapor permeability by
less than 20 %, in spite of the fact that
the specimens had been rendered hydrophobic
throughout their entire thickness,
and that sand-lime brick is a
relatively dense substrate. In the case of
coarse-pored building materials, e. g.
many kinds of bricks, mineral plasters
and aerated concrete, there is no measurable
impairment of water-vapor
permeability whatsoever. Permeability to
carbon dioxide is necessary in order that
carbonated substrates may achieve their
ultimate strength. Determining whether
carbonation is affected by water repel-
lents is most easily done by measuring
the depth of carbonation in treated and
untreated lime mortar specimens. To this
end, phenolphthalein solution is trickled
onto the specimen. On account of their
high pH, zones which have yet to undergo
carbonation show up red, while carbonated
zones are colorless. It is generally
correct to say that silane / siloxane
-based water repellents neither hinder
nor promote the carbonation reaction.
Coatability
The question often arises as to whether
building material surfaces that have
been rendered water repellent can be
overpainted. This question is answered
automatically when one recalls that the
same products as the impregnating
agents discussed here, or similar ones,
are also recommended specifically as
water-repellent primers for protective
coats on facades. Facades that have
been rendered water-repellent can easily
be overpainted with all paints that contain
wetting agents, e.g. silicone resin emulsion
paints, emulsion paints and silicate
emulsion paints. Wetting and adhesion
difficulties are only encountered, as would
be expected, with purely mineral-based
coatings such as whitewash.
2

Table 4a
Sand-lime brick Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 12.9
SILRES ® BS 2 0 1:15 560 1-3 1 0.8
SILRES ® BS SMK 1:14 450 1-2.5 1 0.9
SILRES ® BS 00 1:9 557 0.5-2 1 1.0
Brick Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 18.2
SILRES ® BS 2 0 1:15 2372 >50 1 0.16
SILRES ® BS SMK 1:14 1783 >50 1 0.40
SILRES ® BS 00 1:9 1669 32-48 2 0.50
Clinker-brick Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 2.6
SILRES ® BS 2 0 1:15 125 5-10 1 0.09
SILRES ® BS SMK 1:14 101 5-15 2 0.10
SILRES ® BS 00 1:9 124 4-9 2 0.13
St. Margaret limestone Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 2.4
SILRES ® BS 2 0 1:11 1002 >20 1 1.1
SILRES ® BS SMK 1:9 1375 >20 3 2.0
SILRES ® BS 00 1:4 1213 11-20 3 9.5
Ettring tuff Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 17.8
SILRES ® BS 2 0 1:15 873 8-14 1 1.1
SILRES ® BS SMK 1:9 528 6-8 1 1.4
SILRES ® BS 00 1:4 667 2.5-4 1 1.9
Burgpreppach sandstone Dilution Impregnating-agent Penetration depth [mm] Beading effect Water absorption
absorption [g/cm 2 ] [%] 24h
Untreated - - - 5 5.8
SILRES ® BS 2 0 1:15 370 2-6 1 0.3
SILRES ® BS SMK 1:9 297 1-5 2 1.0
SILRES ® BS 00 1:4 311 1.5-5 3 2.7
Table 4b
Mortar slabs Dilution Impregnating-agent Penetration Beading effect Water absorption Water absorption
(water/cement ratio 0. ) absorption [g/cm 2 ] depth [mm] [%] 24h [%] 28d
Untreated - - - 5 6.9 7.6
SILRES ® BS 2 0 1:11 183 1-3 1 1.2 4.2
SILRES ® BS SMK 1:9 164 0.5-1 2 1.2 5.4
SILRES ® BS 00 1:4 210 1-3 2 1.0 4.0
1:1 216 2-4 2 0.9 3.3
SILRES ® BS 0 undiluted 164 4-7 1 0.6 2.0
SILRES ® BS SMK 2 0 1:4 177 1-3 2 1.0 3.2
SILRES ® BS Creme C undiluted 200* 4-8 2 0.5 1.9
undiluted 400* 8-12 3 0.4 1.6
Concrete Dilution Impregnating-agent Penetration Beading effect Water absorption Water absorption
(grade C 0/ ) absorption [g/cm 2 ] depth [mm] [%] 24h [%] 28d
Untreated - - - 5 3.1 3.6
SILRES ® BS 2 0 1:11 82 1-2 1 0.8 3.1
SILRES ® BS 00 1:1 76 1-2 2 0.5 2.4
SILRES ® BS 0 undiluted 102 3-7 2 0.1 0.4
SILRES ® BS SMK 2 0 1:4 76 1-2 3 0.7 2.6
SILRES ® BS Creme C undiluted 200* 2-8 2 0.1 0.7
*Applied by brush
undiluted 400* 6-12 3 0.1 0.3
00

STONE STRENGTHENING WITH
ETHYL SILICATES
Untreated sand. Fully cured Stone Strengthener
SILRES ® BS OH 00.
As long ago as the th century, it was
suggested that ethyl silicates might
be useful for consolidating, i. e.
strengthening, stone. However, it is
only in the last 0 years that this idea
has been taken up. Several thousand
objects have since been restored
with ethyl silicates, bearing witness
to their enduring effectiveness.
Principles of Stone Conservation
In stone conservation, the microstructure
of the deteriorated stone is stabilized
through the introduction of binder. This
strengthening measure is generally combined
with a hydrophobic impregnation to
protect against further deterioration. The
products used to conserve the stone are
impregnating agents which are applied
liberally so as to saturate the building
material. Once applied, the impregnating
agent reacts with the water in the
capillary pores to form a silica-gel-based
mineral binder (SiO 2 aq).
2
Fig. 2
Kat.
Si(OEt) + 4 H O SiO aq + 4 EtOH
4 2 2
Ethyl silicate Water Silica gel Alcohol
How stone strengthener reacts
The binder stabilizes the building material
by way of covalent Si-O-Si bonds.
On the basis of today’s knowledge, a
stone conservation agent should meet
the following requirements:
- Deposition of fresh, weather-resistant
binder
- Good depth of penetration into the
stone, at least down to the undeteriorated
core
- No crust formation but, rather, a buildup
of a uniform strength profile through
the cross-section of the stone
- No formation of harmful, salt-like
by-products
- No discoloration of the stone surface
Sandstone consolidated with Stone
Strengthener SILRES ® BS OH 00.
- No modification or impairment of important
physical properties of the stone.
This applies in particular to water-vapor
permeability and to thermal and hygric
behavior.
- Optimization of physical properties
such as tensile adhesive strength.

Stone strengtheners based on ethyl silicates
meet these requirements best. This
is why modern stone conservation uses
this class of products almost to the exclusion
of others.
WACKER Stone Strengthener
WACKER currently offers the stone
strengthener SILRES ® BS OH 100. It
contains a blend of different pre-condensed
ethyl silicates and is solventfree.
A neutral, organo-metallic condensation
catalyst controls the reaction
between the ethyl silicate and the moisture
in the stone such that the reaction
proceeds at the optimal rate. Gel precipitation
is 32 %, but may be adjusted to a
lower value if desired, for example by
addition of anhydrous solvent (Fig. 13).
Scanning electron micrographs before
consolidation.
Fig. 13
Precipitation (%)
100
90
80
70
60
50
40
30
20
10
0
Type: SILRES ® BS OH 100
Scanning electron micrographs after
consolidation.
5 10 15 20 25 30 35 40 45 50
Gel precipitation by SILRES ® BS OH 00
stone strengthener.
Time (d)

STONE STRENGTHENERS AT WORK
Processing
Stone strengtheners based on ethyl
silcates are generally applied by spraying
or flooding. Movable parts may also be
treated by immersing them in a bath. In
special cases, compresses can be used
to ensure a maximum period of contact
between the stone and the strengthener.
Important notes
- Freshly treated surfaces must be covered
for 2 to 3 days to protect them
against rain.
- Considerable loss of the active ingredient
by evaporation may occur at
temperatures exceeding 25 °C. At such
temperatures, the freshly consolidated
surfaces have to be protected against
direct sunlight.
- Processing temperatures below 5 °C
cause the stone strengthener to react
very slowly. This may result in discoloration
or glaze on the surface.
- The time needed for deposition of the
silica gel depends on the relative
humidity and the temperature.
Therefore, it is advisable to wait for a
4
week before carrying out any further
restoration work on freshly strengthened
sections. This will allow 90-95 %
of the ethyl silicate to be precipitated.
It takes from one to at most three
weeks for deposition to be completed.
- On no account should water be added
to the ethyl silicate preparation in an
attempt to speed up the reaction. This
can cause extensive surface glazing
that is extremely difficult, if not impossible,
to remove.
Fig. 14
Exterior crust
Former surface
Interior crust
Hardness profile of
deteriorated stone
Hardness profile of
successfully consolidated
stone
Hardness profile of
unsuccessful consolidation
Weathered (silting) zone
Undeteriorated zone
Intermediate zone
Cross-section through deteriorated sandstone
and hardness profiles demonstrating
successful and unsuccessful consolidation.

The Significance of Penetration Depth
The success of stone conservation hinges
largely on the depth to which the conservation
agent penetrates into the stone.
In any event, the stone strengthener
must penetrate through the weathered
zone and replenish the depleted binder
levels with fresh binder. After treatment,
the consolidated zone should not be
stronger than the undeteriorated, intact
core of the stone. Otherwise crusts may
form that can cause the surface zone to
undergo slate-like cleavage.
Fig. 14 illustrates crust formation and
the hardness profiles for successful and
unsuccessful stone consolidation work.
The likelihood of a poor hardness profile
can practically be eliminated by performing
preliminary tests to ascertain the
amount of material needed, the penetration
depth and the required gel deposition
rate.
Applications
Stone strengtheners based on ethyl silicates
are highly suitable for consolidating
absorbent silicate sandstone, calcareous
silicate sandstone and porous tuff.
Suitability tests must be performed in
advance when the stone consists of
pure limestone or is a swellable sandstone
containing clay minerals.
Outstanding results are obtained with all
ceramic, absorbent construction materials,
such as bricks, roofing tiles and terracotta.
Moais on Easter Island

LONG-TERM STUDIES:
WELL-KNOWN REFERENCE OBjECTS
Select examples whose importance
makes them familiar beyond Germany’s
borders serve to illustrate how silicone
resins, the active agents on which all
established organosilicon water repellents
are based, are able to protect
buildings against water and attendant
damage for decades by virtue of their
chemical, physical and biological
stability.
6
Reference objects vividly demonstrate
their successful performance in the field
of building maintenance. Provided that
use is made of the correct products,
that these products are prepared and
applied properly, and that their water-
repellent effectiveness is understood and
assessed in the correct sense, i.e. as a
reduction in capillary water uptake and
not just as a superficial beading effect
which is lost relatively quickly, long-term
protection can be guaranteed.
Kaiser-Wilhelm Memorial Church in Berlin –
natural-stone and concrete preservation.

Munich’s Alte Pinakothek – restoration and
preservation of natural stone.
There are numerous structures which today
provide the best proof that impregnations,
given the correct choice of product and
its professional application – are able to
fulfill their function as a means of protecting
buildings and building materials
against the uptake of moisture and
aggressive substances for at least
twenty years. Examples to be found in
Munich are the Olympic Village, whose
white-concrete curtain walls were treated
in 1972 with a product similar to
today’s SILRES ® BS 290, and the Alte
Pinakothek, on which, in 1975, the first
test surfaces were treated with stone
strengthener and subsequently with
water repellent. When these surfaces
were re-examined in 1995, neither the
strengthener nor the water repellent
showed any reduction in effectiveness.
Another well-known example of both
natural-stone and concrete repair and
preservation is the Kaiser-Wilhelm
8
Memorial Church in Berlin. With the help
of WACKER masonry protection agents,
the ruins of the old church and the concrete
structure which is the new church
were repaired at the beginning of the
1980s and preserved with water repellents.
Successfully, as a recent follow-up
examination showed!
One of the oldest examples of a building
that underwent water-repellent treatment
with organosilicon compounds, although
less well-known than those mentioned
so far, is certainly just as informative:
On WACKER’s production premises in
Burghausen, there is a small building
with a lime-finish facade fully exposed to
the weather. In 1954, a test area was
treated with methyl siliconate, today’s
SILRES ® BS 16. Even today, more than
50 years later, the water repellency is
clearly recognizable when the surface is
sprayed with water.
The Olympic Village in Munich – in-plant
concrete impregnation.

4
Lime-finish surface impregnated with
methyl siliconate, in 4.
Testing the same lime-finish surface for
water repellency by the Karstens tube
method, in .
In the Karstens tube test, the untreated
plaster absorbs 5 ml of water in 10 minutes,
while the water-repellent surface
absorbs practically nothing – an amazing
finding after more than 50 years!
These examples go to prove that silicone
resins, the active agents on which all
established organosilicon water repellents
are based, are able to protect buildings
and structures against water and attendant
damage for decades thanks to their
excellent chemical and physical stability.

YOUR SILICONE MASONRY
PROTECTION TEAM
40
This brochure gives you an insight into
the technical aspects of masonry
protection and introduces you to the
SILRES ® BS range of products.
If you require a more detailed description
of these products, please consult the
corresponding data sheets. You may
also find our product overview useful,
which presents WACKER’s entire portfolio
of silicone products for masonry
protection.
For us, however, the most important information
channel remains our personal
contact with you, the customer. Because
this is the only way we can address
your individual needs. And because the
tailored solutions we offer to specific
problems are not covered by any single
brochure.
Supplier of the year 2006.
WACKER is recognized for its superb
product quality, service and technical
support to the gypsum industry.
Our technical support staff know all about
our products and their properties, but
they also know all about your production
processes and the ensuing requirements.
We’ll be only too pleased to help.
Your Silicone Masonry Protection Team
WACKER SILICONES Services:
-Technical service
- Inspection and testing of coatings with
and without SILRES ® BS
- Selection of the appropriate additive and
the right dosage

42
Wacker Chemie AG
Hanns-Seidel-Platz 4
81737 München, Germany
info.silicones@wacker.com
www.wacker.com
6187e/10.06