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Paving over existing concrete - advice please
John P - 20/8/19 at 03:48 PM


Leading up to our bungalow is a concrete path around 4 feet wide and roughly 20 ft long. At the bungalow it meets a wider path / patio which is around 6 ft wide x 20 ft long.

It's made of concrete which is solid, fairly smooth and has a good fall to take the water away but doesn't look that good and also doesn't match up with another path or the front steps so I'd like to go over it with some 450 x 450 paving slabs to match the rest.

I've pressure washed the surface and it's now very clean so I was going to simply lay a cement and sand screed over the surface and bed the slabs on that.

On-line I've found it recommended lay a screed made up of 5 parts sharp sand to 1 part cement 35 mm thick but can't really understand why it needs to be so thick. Also why is sharp sand used as if it were brickwork it would be building (soft) sand which I would have thought would stick to the slabs better?

I was hoping to lay a screed more like 15 mm thick using some admix in the sand and cement as this would significantly reduce the amount of mortar I have to mix up by hand and also make the job quicker and easier but obviously I don't want to create problems in the future.

Any advice?


macc man - 20/8/19 at 06:15 PM

I had a similar concrete base and I used building sand and cement 4:1 mix. Might be advisable to pva the existing base and each slab back as you lay them. Mine have been down over 10 years and still secure.

SJ - 20/8/19 at 07:13 PM

I recently re laid my patio over concrete. I did the cement as thin as I could. The previous slabs were just on sand.

Both work well.


Benzine - 21/8/19 at 11:24 AM

Originally posted by macc man
Might be advisable to pva the existing base and each slab back as you lay them.

We did that at our last job, can't remember the brand but it had a blue/purple tint to it and was specifically for slabs. One of the electricians asked what it was as a builder was brushing some on. "It keeps the moles from coming through" "oh, okay" believed him and walked off