Gardening & Landscaping

Damp looking patches on a new patio

Anonymous user 23/02/2024 - 3.41 PM

I have had a Kandla honed Indian sandstone patio laid. About 90 slabs 900x600. They were laid on a full bed and not a dot and dab technique. However on about 12 of the slabs it looks like damp patches on the surface and some have thin layer of the white powder which I’m assuming is the salt coming through.I know I can get the Efflorescence cleaner to remove the salt, but I’m not sure why I’m getting the damp looking patches and what can I do about it. The patio has been down for four days now? No primer was put on the back of the tiles. Thanks in advance for any help

Humphries Construction

Rating: 5 out of 5

5/516 reviews

King's Lynn

Hi Without a proper investigation it sounds like the slabs havnt had a primer on the underside which usually stops this. I always use one and I also use a waterproof additive in the mortar which also helps to prevent this happening.

Answered9 June 2021

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Anonymous user

Hi, the damp patches are 'reflective staining', particularly common in grey sawn/honed sandstone. Caused by an area of the sandtone not having full contact with the bedding layer beneath, either not quite a full bed and or an air pocket. This can happen even when installed correctly and unfortunately shows up alot more or grey sawn/honed sandstone. You won't be able to remove the stain but it will weather/dry out with time. I hope this helps

Answered11 June 2021

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E&E Plumbing and Construction LTD

Rating: 4.6 out of 5

4.6/510 reviews

Luton

The best way to prevent damp patches is for you to use a quality patio sealer or patio sealant the surface becomes water resistant making it far harder for algae and lichens to grow. Make sure you prime it first. Also when mixing the mortar make sure you apply SikaBond SBR+ waterproof to help with sealing not just the slabs but the actual mortar so water can't get in between. I hope that helps you out.

Answered9 June 2021

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