technical manu al table of contents - Jamestown Distributors

Question:
Can you explain the differences in terms of durability, longevity & appearance between
one-part and two-part varnishes?
Answer:
It all depends on the application. One should always match the product and its
characteristics to the job.
First off, let’s compare the basic make-up between the two. Single-part products are
generally more traditional in their formulation. They contain natural oils like Tung or
Linseed balanced with alkyd and/or Phenolic resins as an example. These products rely
on exposure to the air to dry. Two-parts however, are more synthetic (polyesters for
example) and rely on the second part or, the “catalyst” to chemically cure the product.
Each produces a very different type of coating.
Let’s take appearance. If they are quality products, there will be little or no difference
between a high gloss one-part and a high gloss two-part clear finish. The degree of
gloss will be comparable. However, having said that, generally a two-part synthetic finish
will be water clear where as a more traditional one-part will have more of an amber tone
to it due to the natural oils. This difference may give you a slight edge when varnishing
very light woods like ash or oak if retaining the lightness is an issue. Beyond that, there
will be no discernable difference.
One-parts are generally softer and more flexible compared with a harder, more scratch
resistant two-part. On an exterior piece of wood that is constantly expanding and
contracting with the weather, a softer more flexible finish is desirable whereas, on an
interior cabin sole or saloon table where scratch resistance would be a real plus, the
harder two-part would be a better choice. The flexibility in an exterior finish is extremely
important for longevity. Once a finish loses its flexibility and becomes brittle, that is when
the film begins to break down. Two-parts are certainly used on exterior applications as
well however. They certainly give relief over short-term maintenance (hard finish etc.)
but we do believe that single-part finishes will outlast them over the long haul, as in 10
plus years. That is when you really see the difference. In addition, two-parts are more
difficult to repair and remove than one-parts.
There are also single part finishes that are formulated to be to harder than normal.
These contain urethane (harder) resins but still rely on air dry. They can be a great
compromise and suitable for many applications where a two-part is too difficult or
unrealistic to use.
In conclusion, there is very little difference in the appearance between the two. Twoparts
being a harder finish, will hold up better and longer on high wear areas but, may
not last as long as a one-part in other areas like exterior wood. Single-parts have the
ability to offer a compromise in a finish that is harder than some single-parts, but not as
hard as a two-part.
People are experimenting all of the time. We regularly hear of two-parts being applied
over a build-up of single-part or vice versa. These combinations may or may not work