Concrete floor repair

[beejay12]

We live in a 1962 build semi detached with concrete ground floors. Construction looks like concrete poured level with the DPC in the walls, with a screed layer on top. The screed is spaced away from the walls by about an inch and is about half an inch thick. On top of that were some plastic tiles stuck down with a black bitumen-looking glue. No evidence of a DPM anywhere. Been told this is typical of the era!

There are a couple of patches where the concrete is damaged. The screed in these areas is no longer attached to the underlying concrete and could be lifted by hand. The concrete underneath is "crumbly". I can scratch it with a chisel and almost rake it away, it just seems to have broken up. These areas also look and smell damp. The areas each run along most of the wall and vary from afew inches wide to up to a foot at most.

The rest of the floor seems fine. There are some thin cracks in the screed (~2mm wide) but the screed itself is hard and tightly attached to the underlying concrete.

Anyway, I'm planning to repair these damaged areas of the floor as so, does it sound like a good way to go?

dig out the damaged areas
Fill with new concrete
replace the screed, using some batten to maintain the same gap away from the wall, was thinking of using some self levelling in several layers to build it up.
Paint on a liquid DPM, including the first course of brick in the wall, so it goes over the DPC

I'm curious as to whats caused this in the first place, hopefully we can just repair the damaged areas and the floor will be ok?

 

[^woody^]

First find out if the properties are in an area and of a type which experience sulphate attack of the ground floor slab.

Otherwise I can't see why you would want to renew patches of the floor slab instead of just the screed. If there is a problem with the slab then it may need renewing, not patching

 

[pinenot]

Sounds like a reasonable plan. If the screed de-lamination and concrete break up, is bad enough might it be better to think of something more upgrading forbye repair of same?

Hacking of the screed and and scrabbling the concrete sub-base would provide a good base. By applying the liquid dpm, as described, you could then go on to fitting a floating floor, with insulation! just a thought...pinenot

 

[beejay12]

Just to update the thread, I've had a sulphate test done which gave a low Class 2 result. However the test did show that the slab is only about 50mm thick with a thick layer of sand underneath, he didn't find much in the way of hardcore down there. The surveyor was of the opinion that theres no issue with sulphate but the thin slab and poor fill underneath is causing the damage we've found. We'll have a think how we proceed from here

If we repair it as I was thinking, would there be any benefit in digging out the sand in the area being repaired so the concrete repair ends up being a reasonable thickness?

 

[lymmranger]

Your floor slab construction is typical of the time your property was constructed....

thin concrete (with no DPC below) then "bitumen" sticking down "marley" tiles.

It is the bitumen and tiles which is your DPC!!!!!!

where they are "missing" you have NO DPC

You need to address this..........

Ideally - a liquid DPC followed with a screed, or "asphalt the whole floor" - smelly!

......modern construction is a DPC before the concrete