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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Ground floor damp proof course or lack of.
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. |
#2
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Ground floor damp proof course or lack of.
Mark S. wrote:
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? What "compound" did you put on it? Did you do ant preparation/treatment apart from scabbling it off? 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. "The skim". What's that, the "compound"? The black stuff is hopefully bitumen emulsion. 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? :-( If the surface is coherent, use bitumen emulsion again. If it's not, take it back until it is, or dig it out & replace. Just managed to save some money to get some work done on it too. Shouldn't be expensive. What's the "project"? |
#3
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Ground floor damp proof course or lack of.
Mark S. wrote:
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. Your new membrance gcan go on top,it doesnt need to be 1" down. Salt only shows up when water evaporates, leaving the salts behind. Top the slab with a sealer and it wont dry, so no salts form. Concrete likes being wet, as long as its not wet & frozen. NT |
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Ground floor damp proof course or lack of.
On Wed, 12 Oct 2005 22:48:37 +0100, Chris Bacon
wrote: Mark S. wrote: 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? What "compound" did you put on it? Did you do ant preparation/treatment apart from scabbling it off? 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. "The skim". What's that, the "compound"? The black stuff is hopefully bitumen emulsion. 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? :-( If the surface is coherent, use bitumen emulsion again. If it's not, take it back until it is, or dig it out & replace. Just managed to save some money to get some work done on it too. Shouldn't be expensive. What's the "project"? The floor was breaking up when I'd taken the carpets and lino up. The top inch or so was hollow and crumbling and lifting off. I took the this top inch off over the whole downstairs floor. There's a concrete slab underneath except between the two was the bitumen type stuff which is what was the damp course. I used self levelling compound over the whole floor to keep the dust down and make it less of a pain to keep swept etc. Bits of this have lifted off leaving the salt deposits under them. If you put something on the floor and leave it there's a "damp" patch under it when you move it. Do I repaint the floor with a bitumen paint and will that fix it or just dig the whole lot out and re-lay it in the normal way with proper layers, insulation etc. The project is the house... Mark S. |
#6
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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 |
#7
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Ground floor damp proof course or lack of.
Mark S. wrote:
The floor was breaking up when I'd taken the carpets and lino up. The top inch or so was hollow and crumbling and lifting off. I took the this top inch off over the whole downstairs floor. There's a concrete slab underneath except between the two was the bitumen type stuff which is what was the damp course. Is the floor slab a) coherent and b) flat and reasonably smooth? I used self levelling compound over the whole floor to keep the dust down and make it less of a pain to keep swept etc. Bits of this have lifted off leaving the salt deposits under them. If you put something on the floor and leave it there's a "damp" patch under it when you move it. Probably the damp-proofing was breached when you removed the screed. Do I repaint the floor with a bitumen paint and will that fix it or just dig the whole lot out and re-lay it in the normal way with proper layers, insulation etc. I'd be inclined to remove the top (again), hire a multi-headed concrete floor scabbler, run that along, clean up, apply bitumen emulsion "as it says on the tin", and re-screed. How long did the previous job last, I wonder? 50 years? |
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