SITE BOOK - Plaster systems - British Gypsum

www.british-gypsum.comPlaster systems9Installation – background preparationGeneralAll surfaces should be reasonably dry and protected from theweather. The suitability of a particular background forplastering should be considered in relation to its strength,suction, bonding properties, shrinkage or thermal movementcharacteristics, water and soluble salt content. Very high orlow suction substrates should be pre-treated. With theexception of skimming with Thistle Uni-Finish the use ofThistleBond-it is recommended for smooth backgrounds,whilst Thistle GypPrime is recommended for very highsuction backgrounds. The high suction of certainbackgrounds can be suitably adjusted by sprinkling withwater.Brickwork / blockworkThe surface must be clean, dry and suitable to receivegypsum plaster. Control suction with water if necessary. Ifsuction is severe the background should be pre-treated withThistle GypPrime.On high suction brick / blockwork the use of Thistle Hardwallor Thistle Tough Coat is recommended.Low suction backgrounds such as some concrete blocks andengineering bricks provide minimal absorption. The jointsshould be raked thoroughly to give an adequate mechanicalkey. Smooth backgrounds should be pre-treated withThistleBond-it.Dense aggregate concrete blocks do not require wettingprior to plastering, but the plaster should be applied withvery firm pressure to ensure intimate contact with thebackground.ConcreteThe surface must be clean, dry and suitable to receivegypsum plaster. Any mould, oils or other agents presentshould be removed from the surface.No-fines concrete does not require wetting prior toplastering.Normal ballast concrete should be given sufficient time tomature before applying plaster. The plaster should not beapplied onto a green background or when any free water isvisible. Mature concrete will require wetting to displace theair before plastering. Clean water should be applied 5 - 10minutes before plaster application.With the exception of skimming with Thistle Uni-Finish,in-situ or pre-cast concrete which is exceptionally smooth, or416