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Suction control is one of the most important things a plasterer will learn. 99% of all background substrates will have varying degrees of suction. Most amateur/DIY plasterers will be caught out by background suction, most will put it down to not laying the plaster on the wall quick enough, but most of the time its down to lack of knowledge and poor preparation.
What is suction? At its basic level the substrate will pull the moisture out of the newly applied plaster, leaving it dry, brittle and unworkable in minutes. Most professional plasterers with some years under their belts will be able to determine the levels of suction from any substrate simply by looking at it. Of course we all get caught out from time to time.
How to control suction from walls and ceilings. Once you have determined that you need to control background suction its all about knowing what product will work the best, most plasterers will use PVA (Polyvinyl Acetate). There are loads of different brands on the market varying in price as well as quality. All manufacturers recommend diluting the PVA with water and using this as a priming coat. After application it will have to be left for a minimum of 12 hours to do its job properly, even though it could feel touch dry in 30 minutes. Some people recommend multiple coats, but in my opinion I do not recommend it. After the priming coat is thouroughly dry, most plasterers will use another coat of PVA called the Bonding Coat, this again is watered down but not to the degree of the priming coat, this again is applied and can not be plastered onto until the PVA feels "touch tacky".
Controlling suction with primers and stabilisers. Again there is various brands on the market, British Gypsum make a product called Gypprime, yellow in colour and costs around £70 for 11 ltrs, this product can be diluted and British Gypsum state that it will do around 600 sqm per tub. It can be applied either with a brush or roller and even sprayed, but this is a professional product financially out of reach of most keen DIYers. Artex stabilex is another water based primer/sealer, which is white in colour and sells for around £12 for 5 ltrs, this product is one of my personal favourites. It also can be applied by a brush or roller and will work faster at sealing a substrate than PVA. There are also oil based stabilisers on the market but again they will need at least 12 hours to dry and these carry a powerful odour.Remember these products are only primers/sealers not a bonding agent thats a whole new topic in itself.
Last of all there is good old H2O yes water, although this will not seal a substrate and is not a bonding agent, applied in the right amount it will slow it down long enough for the plaster to be applied and is free! (well sort of).
The above information only touches on the beginning of what is to be learned about suction control, it takes a whole career in plastering to fully understand it, but I hope what I have touched on helps in some way.
What is suction? At its basic level the substrate will pull the moisture out of the newly applied plaster, leaving it dry, brittle and unworkable in minutes. Most professional plasterers with some years under their belts will be able to determine the levels of suction from any substrate simply by looking at it. Of course we all get caught out from time to time.
How to control suction from walls and ceilings. Once you have determined that you need to control background suction its all about knowing what product will work the best, most plasterers will use PVA (Polyvinyl Acetate). There are loads of different brands on the market varying in price as well as quality. All manufacturers recommend diluting the PVA with water and using this as a priming coat. After application it will have to be left for a minimum of 12 hours to do its job properly, even though it could feel touch dry in 30 minutes. Some people recommend multiple coats, but in my opinion I do not recommend it. After the priming coat is thouroughly dry, most plasterers will use another coat of PVA called the Bonding Coat, this again is watered down but not to the degree of the priming coat, this again is applied and can not be plastered onto until the PVA feels "touch tacky".
Controlling suction with primers and stabilisers. Again there is various brands on the market, British Gypsum make a product called Gypprime, yellow in colour and costs around £70 for 11 ltrs, this product can be diluted and British Gypsum state that it will do around 600 sqm per tub. It can be applied either with a brush or roller and even sprayed, but this is a professional product financially out of reach of most keen DIYers. Artex stabilex is another water based primer/sealer, which is white in colour and sells for around £12 for 5 ltrs, this product is one of my personal favourites. It also can be applied by a brush or roller and will work faster at sealing a substrate than PVA. There are also oil based stabilisers on the market but again they will need at least 12 hours to dry and these carry a powerful odour.Remember these products are only primers/sealers not a bonding agent thats a whole new topic in itself.
Last of all there is good old H2O yes water, although this will not seal a substrate and is not a bonding agent, applied in the right amount it will slow it down long enough for the plaster to be applied and is free! (well sort of).
The above information only touches on the beginning of what is to be learned about suction control, it takes a whole career in plastering to fully understand it, but I hope what I have touched on helps in some way.
