How to tile over outdoor level slab?

[Redstar1]

Hi,

I've got a 6m x 6m courtyard slab adjoining the house that is basically level except for a corner that has a small dip that can be filled with self-levelling product.

I'm told its a big no-no to not have a 1:100 fall so what do I need to do to lay tiles on this area?

I did consider a low deck but I think over time the gaps will fill with dirt.

Any other options for a plain concrete slab?

Buy a big squeegee?

[MitchellMc]

Welcome to the Bunnings Workshop community @Redstar1. It's splendid to have you join us, and many thanks for your question about tiling a slab.

To achieve the required drainage on your courtyard slab before tiling, one effective method is to apply a cement slurry followed by a thin layer of cement to create the necessary slope. Start by mixing a cement slurry, which is a thin, watery mixture of cement and water, and apply it evenly over the surface of the slab. While the slurry is still wet, pour a layer of fresh cement on top and screed it to spread it evenly, ensuring the fall slopes from the highest point to the lowest point of the slab. This will create a gentle slope that directs water away from the area. Once the cement is poured, use a float to smooth out the surface and ensure a consistent slope before allowing it to cure. Once the cement layer has set, you'll have the right fall for proper drainage, and you can proceed with tiling over the surface. To ensure good tile adhesion and durability, it's important to use a suitable outdoor tile adhesive.

If you're considering alternatives, a raised deck is another option that provides good drainage and a level surface. The step up onto the raised deck could create a nice outdoor feature.

Please let me know if you have any questions.

Mitchell
 

[Redstar1]

Thanks MitchellMc,

Starting with the Cement slurry - is it a consistency like a thickish whitewash & applied with a stiff broom.

Then with the slope layer @ 1:100 for the 6m width that's starting at 65mm to something like 5mm or 60 to feathered 0mm?

Using only GP cement https://www.bunnings.com.au/bastion-20kg-general-purpose-cement_p0760481 or a mix like bagged premix concrete https://www.bunnings.com.au/bastion-20kg-premix-concrete_p0760291 or bagged mortar?

Is it useful to add a "Bondall" product to the 2 steps?

I'll do some (movement) cuts into the slab that line up with the grout lines (using coloured silicone) @ 3m grids - is this adequate?

And finally, what size notching tool for the adhesive - eg 10mm & adhesive applied to just one surface or both (back battered)? 

Regards,

[MitchellMc]

Hi @Redstar1,

For the cement slurry, it should have a watery consistency, similar to a thick paint or a wash. It’s used as a bonding agent to help the new layer of cement adhere to the existing slab. Applying it with a stiff broom or brush is ideal to ensure good coverage.

As for the slope layer at a 1:100 fall, you're correct that the drop should be gradual. For a 6m width, the total drop should be around 6cm, from the highest to lowest point. You’re aiming for a start around 60mm at the high point, tapering down to 0mm at the low point, which sounds like a good plan. Feathering the edges smoothly will help to avoid any sharp transitions.

When it comes to the cement mix, while General Purpose (GP) Cement would work, but I’d recommend using a pre-mixed concrete given the thickness. If you want to improve adhesion further, adding a bonding agent like Bondcrete can be a good idea, especially for ensuring a strong connection between the existing slab and the new layer. If you do use Bondall, follow the manufacturer’s instructions on how to mix it with the slurry or the cement.

I'm not entirely sure what these movement cuts are that you intend to install. Typically, if there are two slabs that have an expansion joint in between them, you'd position a "grout" line above it and use a silastic for that joint between the tiles to accommodate the movement of the two different slabs. For a single slab, I haven't heard of adding cuts to the slab; you'd simply tile over it as it's one solid base.

Finally, for applying tile adhesive, you’ll likely need a notched trowel with a 10mm notch, which is common for outdoor tiling. The adhesive should generally be applied to the surface where the tile will sit, not both the slab and tile (unless you're back-buttering larger tiles or specific situations require it). Make sure to spread the adhesive evenly and apply it in small sections to avoid it drying out before you lay the tiles. 

Please let me know if you have any questions.

Mitchell