| Acrylic primer vs. PVA primer |
By: Jane Deegan, assistant brand manager of Dunlop Adhesives
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Posted: Friday, October 8, 2010 3:46 pm
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Jane Deegan, Assistant Brand Manager of Dunlop Adhesives, discusses the implications of using a PVA primer as opposed to an acrylic primer to encourage jobbing builders not to get themselves into a sticky situation.
You’ve just had a call from an un-happy customer. Three months ago, you were commissioned to re-tile their newly fitted bathroom suite. Looking back, you prepared the area, primed it, put down your grout and adhesive and did a great job on the tiles – the customer was thrilled with the job. So why, a few months later, has all your hard work gone down the toilet and all your tiles, adhesives in tow, fallen off?
Not commonly know amongst all tradesmen, there is a huge difference between using a PVA primer opposed to an acrylic primer. You’ll all remember PVA glue from primary school. The stuff that, to the teachers’ dismay, ends up all over your hands, but with a touch of soap and warm water it’s soon gone. Fundamentally, that’s what PVA primer is.
Why shouldn’t I use a PVA primer?
When a substrate surface is treated with PVA, it partly soaks in to the body of the substrate and partly sits on the surface in a similar fashion to wallpaper paste. If the PVA surface layer gets wet, it can become “live” again, i.e. it reconstitutes (it becomes “sticky”) and doesn't completely return to its solid state. When the tile adhesive is applied to the wall, the water in the adhesive causes the PVA to become “live” which prevents the adhesive from penetrating the substrate resulting in a poor mechanical grip. In essence, the tiles, grout and adhesive are being held to the wall by a thin layer of PVA.
Why should I use an acrylic primer?
An acrylic primer soaks right into the substrate and stops the sponge like "draw "effect. However, they don't coat the surface in any way because they are an impregnator as opposed to a barrier. Tradesman should know, when using a cement-based adhesive, it should not be applied directly to the plaster substrate as it causes a chemical reaction, a problem known as "Ettringite failure". Using an acrylic based primer will prevent this chemical reaction from happening.*
Some tradesmen will have been told by their peers to avoid splashing out on an acrylic primer when PVA will do – but when you discover from an un-happy customer that all their tiles, including the adhesive, have fallen off their walls, you’ll soon discover acrylic primer is a product worth investing in.
* See: http://bit.ly/d01fnc |
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