This is a question we have heard time and time again when it comes to newly plastered or plasterboarded walls. Many people are of the belief that they need to “seal” the plaster with PVA before painting. Is this a good idea? Should I PVA my walls before painting them?
Well, we have done the testing. We tested PVA, watered down PVA, Mist coating and just painting straight onto the bare plaster to see what the difference is between each method.
Why PVA could be a bad choice
Using PVA to seal walls has been one of those tips that seem to have always been around. But does it work?
Well, we have set up a little test to try and find out. We have painted this plasterboard with PVA and then emulsioned once dry.
You can see the results for yourself. The emulsion has cracked and flaked and just generally not stuck well to the plasterboard at all. This is because the paint sits on top of the PVA rather than the plaster, this does stop it soaking into the plaster but PVA is not a good surface for the paint to adhere to. This is why it has cracked so much. If bashed or brushed against this paint would most likely crack and would peel over the years.
While this is an extreme result as we painted on thick PVA rather than watering it down the effect can still be the same. Even if it doesn’t happen to this extreme amount why risk it when there are other options available to you?
So what other choices do I have?
Our preferred option is a “mist” coat. This is where you water down some emulsion, often just a plain old white, and paint that on first. This in effect works as your sealer. Due to it being watered down the paint goes a lot further than usual and is really quick and easy to apply. You also have the added benefit of it drying really quick.
Then you have the choice of using a dedicated primer. While these work well it is another cost, which is why I normally just go for the mist coat.
Or you could use a cheap emulsion as your first coat. lots of people buy a large tub of the cheapest white emulsion they can find and use this as their first coat, this can be good if you are doing a lot of painting but it’s not that practical if you are painting a single wall or a small room.
Just paint with your chosen emulsion. This is another choice a lot of people make. While it’s fine and there is nothing inherently wrong with this option you will waste paint. Bare plaster sucks up paint, so you will use a lot of extra paint this way. That’s the main reason I prefer using a mist coat as it cuts down on paint usage.
So here is our test of these options. We got a cut off sheet of bare plasterboard and taped it into three separate sections. On the left-hand section, we would use watered down PVA as a sealant. In the middle, we would paint straight onto the plasterboard. And on the right, we would use a mist coat of watered-down emulsion. Let’s see how these three choices get on.
All three methods leave a similar finish. But as you know from our previous test the paint may not have adhered to the PVA perfectly. Even if it has the finish is no better than the mist coat.
Then the method of just painting straight on with paint used a lot more of the emulsion up while giving the same end result as using a mist coat. This is why we really like to use the mist coat.