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Ground floor damp proof course or lack of.



 
 
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  #1  
Old October 12th 05, 11:30 PM
Mark S.
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Default 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.
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  #2  
Old October 12th 05, 11:48 PM
Chris Bacon
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Posts: n/a
Default 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  
Old October 13th 05, 12:02 AM
[email protected]
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Posts: n/a
Default 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

  #5  
Old October 13th 05, 12:48 AM
Mark S.
external usenet poster
 
Posts: n/a
Default 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  
Old October 13th 05, 01:48 AM
Peter Taylor
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Posts: n/a
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 2" 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  
Old October 13th 05, 11:39 AM
Chris Bacon
external usenet poster
 
Posts: n/a
Default 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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