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Patio slab on top of uneven patio slabs - how to

Postby tobzzz » Sun May 15, 2022 1:10 pm

Google and / or YouTube are usually my friend but all I can find is articles/vids on starting from scratch to make a patio.

I have large(ish) existing concrete slabs, many are flat, the occasional few are slightly uneven. Photo included. I feel like this is an excellent and easy starting place for laying new patio slabs on top, rather than trying to dispose of the old slabs and almost starting again.

The existing slabs go between a loose stone wall and a soil border by the house, so raising the height by 50mm or so won’t be an issue with house ventilation - I can’t see any issues or downsides. I have 60 concrete slabs that I won’t have to dispose of.

1/ first, importantly, are there any potential downsides I’m overlooking? Do I need to raise existing slabs for a specific reason?

2/ if okay to lay on top, what approach should I use to level over the existing slabs and then adhere the new patio slabs?

3/ as shown in the photo, I have a lot of weeds or grass between the existing slabs, how do I stop this with the new slabs? Is sand between enough or do I need something else?

I don’t mind hard work and i don’t mind it taking a lot of time, I’d rather this and to get it right than rush it and get it wrong. Thanks.
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Simply Build It

Postby stoneyboy » Mon May 16, 2022 9:12 pm

Hi tobzzz,
Suggest you lift the most uneven existing slate and re-bed them. Then lay the new slabs as you propose, on top using a sand/cement mix but do try to stagger the existing and the new joints.
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