Cracks in slab that tiles are to go on

[Nicko11997766]

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Evening! I'm looking at tiling the floor of an outdoor concrete veranda. It's undercover but gets all weather as it's west faced.
I've been reading that if the concrete has cracks, they will eventually come through the tile.
Is there a recommended membrane or something similar I can apply over the slab before tiles are laid.
Hiring someone is out of the question due to finances and I'm forced to do it myself.
Thanks

[ErrolFlynn]

I’m not a tiler, but here are a few thoughts:

You're wondering if you could put down a layer of something (eg. rubber) that will save the tiles from cracking. Interesting idea. But if this membrane is glued to the concrete on one side and your tiles on the other, then inevitably the tiles will crack because they don't flex.

Even if you were able to do that it wouldn’t be a good thing for brittle tiles to be resting on a soft flexible base.

Solution: dig up the existing concrete and relay it strong enough not to crack, then start tiling.

Something to consider: skip the tiles and paint the surface. Wet tiles can be slippery. Fill the crack, but if it’s the result of roots it’s going to be getting worse. You can buy paint additives that make paving paint slip-proof. Just the thing for a wet surface. If you were feeling artistic you could stick some masking tape down prior to painting to simulate grout and the finished paint job might look a little like tiles.

Unless you consider something like this.

[droog]

Basically no.
Tiles are designed to be stuck down, any differential movement in sections of the substrate will result in breaking of the tile.

However, a concrete slab can have cracks in it and have little to no differential movement between the sections, if there is reo and it is doing its job there should be no movement between the sections. Do you know if the slab has reinforcing ? and have you lived in the property long enough to know if the crack has been there for a long period without further movement ?

A previous house I owned the slab out the front door had multiple cracks, when I eventually bit the bullet and dug it up someone had previously overlaid a 75mm concrete slab over the original cracked and broken slab. If its cracked and moving only option is start from scratch.
If it is cracked but stable fill any holes with a levelling compound and lay the tiles with rubber based adhesive.

[Nicko11997766]

It's a 120yr old house and the slab has always been there, when I moved in. The can't recall if the cracks have moved or not. Not sure about rio. I'd like to assume there is.
Where it has cracked, there is a few low spots on one side of the crack. Just wondering, if I use a bit of mortar to level to the cracks out.. a coat of primer?

[ErrolFlynn]

It’s possible the slab is stable, but you wouldn’t be able to tell. There might be seasonal movements as the soil changes from wet to dry. Those tiny movements may be enough to crack the tiles. Brittle things.

Whatever caused the crack in the first place, it’s very unlikely that either end of the cracked slab is on the same plane. For example, a tree root may have pushed the slab upward, it cracked, and it has stayed in position. At least until the root rotted, then the slab shifted again. The whole slab is no longer flat and tiles sit best on a flat surface. They will look odd if you lay them on an uneven surface, and if severe they may be difficult to lay.

Put a straight edge over the surface and check to see how flat the surface is. Grinding the surface flat might be required. Floor leveller works a treat, but is expensive. If you do any of this and the tiles crack then all of that work and money has been wasted.

Another solution: skip the job for now. Save your money until it can be done properly.