There are certain things you need to do before you start plastering – you can’t just pick up a trowel and start skimming. The the biggest thing is to make sure you PVA before plastering. Failing to do this could result in a total disaster!
Were going to show you exactly what to do. This article will explain why you need PVA, how to use it and direct instructions on how to mix and seal it to the walls. Its a game changer and were going to show you what to do!
What is PVA
PVA (Polyvinyl Acetate) is basically a glue and adhesive. Joiners/ Carpenters and all DIY fanatics use it for many purposes with many companies making strong strains of the stuff. However Plasterers use it for different reasons.
The other main function to PVA is that its used as a primer. We seal all the walls with PVA (not needed on plasterboard), to make sure we can get a decent finish. It helps bond the plaster to the walls and also gives us time.
What does that mean?
Every wall has its own level of suction. Bricks have a high suction rate whereas plaster board is very low (which is why PVA isn’t needed on boards). When you spread plaster onto brickwork, the material drains all the liquids from the mix resulting in the plaster setting extremely fast and in worst cases, cracking.
The plaster can even fall from the walls without correct preparation! PVA seals the walls and acts as a retardant towards the rate of suction. This stops the mix setting at a rapid rate giving us plenty of time to get that perfect finish. So what do we need:
PVA before plastering
You want to get yourself some decent PVA. We recommend the Unibond products – there mix is thick and acts as a great sealer for plaster. Some companies PVA’s are weak, thin and very poor in quality so get a decent one.
We need to mix the PVA with water because its far to thick to apply as a stand alone material. The general mix for PVA is 3 parts water to 1 part PVA (3:1). However I have used 2:1 before for great results but its considered quite controversial.
How to mix PVA for plastering
We essentially want to apply 2 coats of PVA at a 3:1 ratio to our walls. You apply the first coat, wait for it to completely dry and then apply the second coat. The second coat is slightly different.
You want to roll this on just before you start plastering and wait for it to take up. There is a point in its drying stages where its starts to go quite sticky. This is when you mix your plaster and start skimming.
The best time to start skimming is when the walls are still quite tacking. You definitely don’t want to plaster on wet PVA but sticky is perfect. It provides a good key and bonds with the plaster at a stronger rate when slightly tacky.