Prime or PVA before Tiling?

Many people think that PVA is okay as a primer on walls and floors before tiling. This is not the case, as traditionally PVA is a multi-purpose product and not specifically formulated to work with tile adhesives.

First of all let’s think back, we all remember PVA – the glue you used in school to paint all over your hand, then see who could peel it back to get the biggest piece off! Peeled off easy? Washed off easy?

When you treat a surface with PVA it only partly soaks in and sits on the surface of the substrate much in the same way as wall paper paste. If PVA gets wet it becomes slightly live again, it doesn’t completely return to its liquid state but it becomes sticky.

When you spread tile adhesive onto a wall, the water in the adhesive makes the PVA live and stops the adhesive from penetrating the substrate and providing a mechanical grip. Basically your tiles, grout and adhesive are being held in place by a thin layer of PVA.

Tile adhesives work by crystallising when it sets. Once the adhesive starts to set crystals form and expand into any imperfections in the substrate (at a microscopic level) to create a grip. PVA stops this process by creating a barrier between the substrate and the tile adhesive.

Why is Acrylic Primer Different or Better?

Well, acrylic primer is specially formulated to work with tile adhesives. The primer actually impregnates the substrate and stops the sponge like “draw” effect without coating the surface. It does not create a barrier and when wet does not become re-active.

Acrylic primer will also stop the chemical reaction which occurs between gypsum and adhesive known as “Ettringite Failure” (Gypsum is a main ingredient in plaster- but is also found in some cement/anhydrate screeds as it’s a cheaper material than cement. The product used to a light grey, but has now been “tinted” dark grey to appear more like standard cement – correct priming of anhydrate screed would be to hoover the complete surface removing all dust particles and coating the floor with 2 coats of primer-in opposite directions)

Primer:

• Stabilises dusty substrates
• Reduces porosity of surface
• Penetrates background
• Provides adequate key between adhesive and Gypsum
• Superior coverage up to 20m2 per litre
• Approved by TTA Enhances and supports BAL 25yr guarantee

PVA:

• Seals of surface-leaving a skin on the top of a substrate
• Water soluble-dissolves in water
• Re-activates when wet
• Never re-sets, remains sticky
• Clear liquid-difficult to see where you have coated
• Easy to over apply

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