SITE BOOK - Plaster systems - British Gypsum
SITE BOOK - Plaster systems - British Gypsum SITE BOOK - Plaster systems - British Gypsum
Technical support: T 0844 800 1991 F 0844 561 8816 E bgtechnical.enquiries@bpb.comExpanded metal lath / beadsPlaster should only be applied to galvanised steel or epoxycoated stainless steel. Before plastering, all cut edges,damaged metal lath, staples, nail heads and ends of tyingwire should be bent inwards and adequately protected bygalvanising, painting or by applying a thick coat of lacquer.Machine applied plaster requires the use of spray lath.Replastering walls - generalThistle Uni-Finish is designed for the finishing andre-finishing of a wide range of backgrounds, from low tohigh suction and from low to high levels of key (e.g. texturecompounds, old finish plasters, fillers, plasterboard,moisture resistant board, paint i.e. gloss, emulsion, satin,vinyl, gypsum undercoat plasters, tile adhesive, concrete,cement boards and Glasroc H TILEBACKER.Thistle Uni-Finish - problem backgroundsCertain paint finishes: Thistle Uni-Finish is tested for useon common interior decorative paints. There are certaincoatings that Thistle Uni-Finish will not adhere to, theseinclude exterior grade paints, anti-graffiti and self-cleaningpaints.Textured finishes: British Gypsum cannot guarantee thebond between the painted textured finish and thesubstrate, or Thistle Uni-Finish applied to unpaintedtextured finishes.Sand & cement / lime backgrounds: Some sand &cement / lime backgrounds have extremely high suction,especially in buildings built before 1930. Pre-treatmentwith Thistle GypPrime is recommended before re-plasteringthese backgrounds.Crumbling backgrounds: Thistle Uni-Finish will providelimited consolidation of slightly crumbling backgrounds butwill not solve the problems of flaking or loose backgrounds.Thistle Dri-Coat is recommended for application followinginstallation of a damp proof course. In other re-plasteringsituations, the Thistle plaster designed for the equivalentnew background should be used (normally Thistle BondingCoat or Thistle Hardwall). The following general pointsshould be noted:– No plaster should be used below ground level ashydrostatic pressure can give rise to direct waterpenetration. A suitable tanking treatment must bespecified in this situation.– Heavy salt contamination in the background can causepersistent damp problems. Buildings such as oldfarm-houses, stables and barns not originally built with adamp proof course, or buildings that have been exposedPlaster systems9419
www.british-gypsum.comPlaster systems9420to storage of chemicals, are particularly at risk from thisproblem.Thistle Dri-Coat should not be used in these situationsunless a proper survey shows that the risk from salts isminimal. An independent wall lining may be a bettersolution. Chimney breasts are another area where saltdeposits may be heavy.Replastering walls - following damp proof coursetreatmentThistle Dri-Coat is the only British Gypsum plasterrecommended for this application. The source ofpenetrating or rising dampness must be identified andeliminated. The existing plasterwork should be hacked offto a height at least 0.5m above either the new damp proofcourse or the last detectable sign of dampness. Where theold plaster is gypsum based, it must be completely removedfrom the area to be replastered. Ideally, replastering withThistle Dri-Coat should be delayed as long as possible toallow the background to dry out. After chemical dampproof injection, old mortar joints which are the site of thehigher salt concentrations should be thoroughly raked outand the face of the brickwork brushed with a wire brush.Before replastering work is carried out, any salts brought tothe surface of the background during drying should becarefully removed.Angle beads must not be fixed with gypsum basedmaterials, use Thistle Dri-Coat.The background must be clean, sound, and free from dustand efflorescence. Where only residual moisture is present,Thistle Dri-Coat can then be applied. Low suction or smoothbackgrounds, such as engineering bricks, should be treatedprior to plastering with a water-resisting bonding aid whichshould be plastered in accordance with the manufacturers’recommendations.Where the background is dry, it is important to controlsuction with the application of water. This prevents rapiddrying of the plaster which would impair its strength.Replastering walls - general applicationWhere the wall to be replastered is damp, replasteringshould be delayed as long as possible to allow thebackground to dry out. Any source of penetratingdampness must be identified and eliminated. Beforereplastering, any salts brought to the surface of thebackground during drying should be carefully removed.The background must be clean, sound, and free from dustand efflorescence. Where only residual moisture is present,Thistle undercoats can then be applied.
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Technical support: T 0844 800 1991 F 0844 561 8816 E bgtechnical.enquiries@bpb.comExpanded metal lath / beads<strong>Plaster</strong> should only be applied to galvanised steel or epoxycoated stainless steel. Before plastering, all cut edges,damaged metal lath, staples, nail heads and ends of tyingwire should be bent inwards and adequately protected bygalvanising, painting or by applying a thick coat of lacquer.Machine applied plaster requires the use of spray lath.Replastering walls - generalThistle Uni-Finish is designed for the finishing andre-finishing of a wide range of backgrounds, from low tohigh suction and from low to high levels of key (e.g. texturecompounds, old finish plasters, fillers, plasterboard,moisture resistant board, paint i.e. gloss, emulsion, satin,vinyl, gypsum undercoat plasters, tile adhesive, concrete,cement boards and Glasroc H TILEBACKER.Thistle Uni-Finish - problem backgroundsCertain paint finishes: Thistle Uni-Finish is tested for useon common interior decorative paints. There are certaincoatings that Thistle Uni-Finish will not adhere to, theseinclude exterior grade paints, anti-graffiti and self-cleaningpaints.Textured finishes: <strong>British</strong> <strong>Gypsum</strong> cannot guarantee thebond between the painted textured finish and thesubstrate, or Thistle Uni-Finish applied to unpaintedtextured finishes.Sand & cement / lime backgrounds: Some sand &cement / lime backgrounds have extremely high suction,especially in buildings built before 1930. Pre-treatmentwith Thistle GypPrime is recommended before re-plasteringthese backgrounds.Crumbling backgrounds: Thistle Uni-Finish will providelimited consolidation of slightly crumbling backgrounds butwill not solve the problems of flaking or loose backgrounds.Thistle Dri-Coat is recommended for application followinginstallation of a damp proof course. In other re-plasteringsituations, the Thistle plaster designed for the equivalentnew background should be used (normally Thistle BondingCoat or Thistle Hardwall). The following general pointsshould be noted:– No plaster should be used below ground level ashydrostatic pressure can give rise to direct waterpenetration. A suitable tanking treatment must bespecified in this situation.– Heavy salt contamination in the background can causepersistent damp problems. Buildings such as oldfarm-houses, stables and barns not originally built with adamp proof course, or buildings that have been exposed<strong>Plaster</strong> <strong>systems</strong>9419
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