How to tile over concrete slab?

[FEH]

Whats the best tile adhesive for laying 200x300mm pressed ceramic tiles on a concrete slab please? There is so much choice I am overwhelmed! The slab has been down for 9 months. I'm aiming for a 3mm bed. Not a wet area.

Also, do I need to prep the slab first?

Thanks for your suggestions!

[MitchellMc]

Welcome to the Bunnings Workshop community @FEH. It's brilliant to have you join us, and many thanks for your question about tile adhesives.

For 200 × 300 mm pressed ceramic tiles onto an existing concrete slab, Davco 20 kg Ultraflex Ceramic Tile Adhesive is a very suitable choice. It’s designed for ceramic tiles on concrete. 

In terms of preparation, yes, you do need to prep the slab first. Make sure the concrete surface is clean, dry, free of dust, grease and loose material. Any cracks or hollows should be filled and smoothed first (you can use a concrete patch or levelling compound). If the slab is very smooth or has a light laitance on the surface, getting it slightly keyed with a light sanding or broom finish helps the adhesive bond better.

Once the surface is prepped, you can mix the Ultraflex adhesive to the manufacturer’s instructions and apply it with a 6 mm notch trowel, pressing the tiles firmly into place, which will bed them down to around 3mm. After installation and once the adhesive has set, grout and then seal if needed for your tile type.

Please let me know if you have any questions.

Mitchell
 

[FEH]

thanks Mitchell

I'd love to understand why you suggest Ultraflex. Concrete slab has no chance of flexing.

[MitchellMc]

Hi @FEH,

Great question.

Even though a concrete slab feels completely rigid, it can still experience very small amounts of movement over time from temperature changes, moisture, shrinkage and general settlement. This movement isn’t something you can see or feel, but tiles and grout are brittle, so they don’t tolerate stress well.

Ultraflex is suitable for both rigid and flexible substrates. A “flexible” substrate doesn’t mean something that bends when you touch it, it simply means a surface that can move slightly over time. Concrete fits into that category, which is why a lightly flexible adhesive is recommended. It provides excellent bond strength for ceramic tiles and adds a bit of insurance against cracking and debonding in the long term.

Mitchell