SLC over concrete flagstone in hallway question....

[DavieA]

Hi All, after a short time off the tools my first job back and im having a head scratching moment:lol:. I was looking at a concrete flagstone hallway in a house approx 100 years or there abouts, the flags are uneven and far from level in anyway however quite stable. They are approx 1-1.5inches thick and about 15-20inches square. The customer wants a level floor for her carpet as you can feel the uneven flags through the carpet at the moment.

I intend to use weber floor flex as there is a run in the center of the property that requires to be built up, from what I can see the flags have possibly had some sort of finish which looks like paint. The paint is sound and not flaking and obviously between the flags are the joints which I think will allow the slc to fill up and lock the screed to the flags but do the flags need the paint removed and if so any suggestions on the best method? I don't really want to use a grinder due to the dust involved.

My thought was if the paint was sound id be good to go however if it needs taken back to the concrete then would I need to prime again?


Thanks again all:smilewinkgrin:

Dave

 

[Andy Allen]

is there a DPM under the flags..?

 

[DavieA]

I thought someone may ask, to tell you the truth I'm not 100%.The flags seem sound and there are no signs of moisture of damp smell. Also they look original from there condition and settling so I believe they are original. They have been covered with carpet until now and the owner is just looking for a flat surface for relaying carpet.

 

[Ajax123]

Take up the flags and sell them as reclaim then put a screed in instead. It's positively sacriligeous to SLC over old flag stones IMO...

 

[DavieA]

I hear you Alan, I did mention that but the homeowner doesn't want to go down that route and so asked if I could just sl the floor. The flags aren't very desirable Imo, too small but suppose one man's rubbish.... and all that. My current thoughts are the stone is free from movement, paint cannot be scrapped off, isn't flaking and sound so cannot see any real issues. But as always the wealth of knowledge on this forum will soon confirm this or point out error.

Thanks for the info

 

[Ajax123]

I suppose your only issue really then is damp. As has been asked...is there a DPM. If not rising damp will cause any SLC to blow albeit it might take a while.

 

[DavieA]

I'd of thought that if rising damp was present that there would be signs of that, but the flags feel dry and not damp, no smell, no signs of mold or staining etc. But I am not an expert in concrete unlike you guys so I will take your advice all day. Do you have any advice on determining whether dpm is present and on what I have discussed is it too big a risk?

 

[Ajax123]

I'd of thought that if rising damp was present that there would be signs of that, but the flags feel dry and not damp, no smell, no signs of mold or staining etc. But I am not an expert in concrete unlike you guys so I will take your advice all day. Do you have any advice on determining whether dpm is present and on what I have discussed is it too big a risk?

Rising damp won't show necessarily on old flags as the floor will be in equilibrium. If its on a limecrete base it becomes breathable. It's how we used to build. That said the paint would probably show signs but it may be an old paint as well. A rudimentary damp meter would give you that answer.

 

[DavieA]

Yeah the paint looks a fair age, but sound and bonded well. I have a moisture meter if that's the same as a damp meter?

 

[Ajax123]

Yeah the paint looks a fair age, but sound and bonded well. I have a moisture meter if that's the same as a damp meter?

Yep that's the gizmo...

 

[DavieA]

Cheers Alan I'll see what reading I get. Any advice on acceptable range for flags? I've only used it on plaster before tiling.

 

[Ajax123]

Acceptable range to put SLC down is 75% rh. Not sure what that is in percentage bu guessing it will be around 2 to 3 %. How does your meter measure. Des it give a number or does it give green amber and red?

 

[DavieA]

It's this one and measures in % Moisture Detector MD Brennenstuhl black / yellow: Amazon.co.uk: DIY & Tools.