PVA (Polyvinyl acetate) is one of the most common products used in building and DIY/ home renovation.
Unfortunately PVA is often recommended for uses where it will not be suitable at all!
There are two types of PVA currently in use for building/home repair uses, one is the standard PVA which can be used internally and the other one is external PVA, which can also be used outside.
PVA and Plastering
PVA is mainly used to provide a barrier when plastering over existing coats of plaster or paint, by applying a watered down coat of PVA to the existing plaster it prevents the existing plaster from sucking out all of the moisture from the new plaster being applied. Without applying the PVA first to the existing plaster the new coat of plaster would dry too quickly and would cause it to crack.
External PVA can be used for a similar purpose outside, for example when rendering.
PVA and Tiling
PVA should never be used as a tiling primer in wet areas, you should always use a primer that has been specified by the tile adhesive manufacturers. Using PVA as a tiling primer in wet areas is asking for trouble. When dried PVA comes into contact with water it returns to a liquid state again, this could mean that your tiles will loose contact with the wall and will fall off! It is normally safe to use PVA as a tiling primer in kitchens as they are not exposed to the same amount of moisture that a Bathroom is.
PVA and Painting
When a wall has been recently plastered do not use PVA to seal the wall before painting it. PVA is not meant for this purpose and by doing this you can cause lots of problems as you are actually sealing any moisture left in the plaster. If you need to paint newly plastered walls then you should use a mist coat of diluted emulsion paint or a paint that is specifically designed for this purpose such as Dulux trade supermatt or fastmatt.
PVA and sealing
PVA should never be used to seal stone, brick or concrete outside. If the stone, brick or concrete requires sealing then there are dedicated sealers that can be used. Under no circumstances should you use PVA as it is not suitable.