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Peter Taylor
 
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Default Ground floor damp proof course or lack of.


"Mark S." wrote in message
...
A while ago I took off the top inch of loose concrete on the ground
floor of my project.

I levelled it with compound to cover the dust/roughness more than
anything else.

It's been left about 12 months and there's a few patches where the
compound has lifted off and there's what I suspect is "salt"
underneath?

I think the damp course was a layer of tar like paint that had been
under the skim level that had become detatched/broken up.

Is it possible to fix it using anything within the inch or so that's
"spare" or is it a job I really could do without doing that needs
doing? :-(

Just managed to save some money to get some work done on it too.

Mark.


Mark - what you have is a concrete slab with a liquid damp-proof membrane,
probably Synthaprufe or similar, applied on the top surface and then covered
with 1" cement/sand screed. This used to be common practice years ago, but
is never recommended these days as it always fails in the way yours has.
The screed will never bond properly to the membrane and in time will break
up. A reinforced screed at least 2½" thick is needed, but I guess you can't
raise the floor level.

The salts tell me the membrane isn't effective - i.e. dampness is getting
through it. Unless you do something about this the dampness will always be
there to ruin any floor coverings you put down and give your house a damp
smell and feel.

Your options a
1 Clean off everything above the membrane, apply more coats of bitumen,
and renew the 1" screed. You could use fine mesh or, better, polyester
fibres to reinforce the screed, but it won't bond to the bitumen. This is
the simplest option, but it's not going to last.

2 Break up the concrete slab, dig out and lay new insulation, new
polythene sheet membrane and a new concrete slab with 65mm screed on top.
This would be the "proper" job.

3 Another option, but quite expensive, is to scabble off all the old
bitumen, lay a 1" thick quick-hardening epoxy screed such as Ronacrete
http://www.bpindex.co.uk/manf.html?id=1254 and apply a surface damp-proof
membrane on top like Biscem SDPM
http://www.biscem.co.uk/crossproduct...iscem-sdpm.asp
This will be much quicker than laying a new slab, but it will cost you an
arm and a leg.

Peter