Cracks in concrete floor

sjoh0961

Hello.

We've recently bought a house (ca. 1930), which has concrete floors on the ground floor. There are some thin, but long cracks in one room, in particular, but there is nothing that is particularly out of level.

In one part of that room, there is a more-recently concreted area, where the fireplace was. Around some of these cracks, especially near the fireplace, there is a small amount of damp that is just about visible/detectable by touch. It wasn't apparent before, but is there now, after the ridiculous amount of rain we've had.

We're in London, on clay.

Trying to decide whether it's just something to cope with in an old house, that probably won't notice with a carpet down, or whether we are in trouble and need to get a surveyor in, and will end up ripping floors up for thousands of pounds?

Can anyone give any advice/suggestions/reassurance, please?

Thanks a lot.

Tim

RDG

Without seeing the floor I can only hypothesise about the cracks from what you have said.

It sounds like some of the cracks are full depth and that water is seeping through (but I cant be sure without looking at it). The best thing to do is leave that area exposed and monitor it. If it dries out when there is no rain and then gets damp when there is then you may want to tink about getting it repaired.

From what you have said it sounds like the floor is fine and you dont need to remove the whole thing. The repair could be a simple as using a high viscosity resin, but that would depend on the crack width.

If you want to take some photos and pm me a link to them il have a better idea.

Leif

What happened to the fireplace? Obviously a chimney is a way in for damp if not sealed. My house has a transparent plastic membrane 5" beneath the top layer of floor screed. It comes to the surface at the edges of the room, and where the fireplace is, where it appears around the edges of the constructional hearth. So I assume the constructional hearth could be without a DPM, and hence could get damp from the soil below. Could that be the issue?

sjoh0961

Yes, it wouldn't surprise me if that's the issue. Previous owner seems to have had a habit of doing any jobs badly and, presumably, cheaply. So that would presumably leave me with having to take out the concrete where the hearth was, and redoing it to a better standard? Any ideas on that?

RDG

So theres no damp along the long thin cracks? If not then it is probably that the hearth area is cast straight on the ground but the rest of the floor isnt.

I take it that that the edge of the hearth area is the cracks your talking about? These will be joints rather than cracks, as the concrete was jsut poured straight into fill the void. As I said before you could have these sealed without any destructive work. The concrete itself is probably fine and fit for purpose so ripping it out wouldnt gain very much.

Again without seeing it I cant say for sure whats best.

sjoh0961

RDG wrote: »

So theres no damp along the long thin cracks? If not then it is probably that the hearth area is cast straight on the ground but the rest of the floor isnt.

I take it that that the edge of the hearth area is the cracks your talking about? These will be joints rather than cracks, as the concrete was jsut poured straight into fill the void. As I said before you could have these sealed without any destructive work. The concrete itself is probably fine and fit for purpose so ripping it out wouldnt gain very much.

Again without seeing it I cant say for sure whats best.

I'd like to show some photos, but I can't work out how, as I have to link to them, rather than just attach them to the post, but I only have them saved on my desktop.

There is some damp coming up in the joints between the hearth area and floor, and there is one area where damp is coming up through a crack in the original concrete, but this is very close to the hearth.

RDG

Use a site like flikr to put your photos online and then you can link to them once you have 10 posts.

It maybe that the unprotected area below the heath is allowing water to run along the bottom of the slab and is coming up where the crack is full depth.

My advise would be to monitor it and see if it is related to the moisture in the ground, hopefully we will get a dry period this summer where the cracks may dry out if you can wait?

sjoh0961

RDG wrote: »

Use a site like flikr to put your photos online and then you can link to them once you have 10 posts.

It maybe that the unprotected area below the heath is allowing water to run along the bottom of the slab and is coming up where the crack is full depth.

My advise would be to monitor it and see if it is related to the moisture in the ground, hopefully we will get a dry period this summer where the cracks may dry out if you can wait?

Ok, thanks.

I'm pretty sure it is related to moisture in the ground, given that it was dry when we moved in at the end of March, and then it has come up in the last few days, since the crazy rain began.

If it isrelated, is your advice to get the cracks repaired? How would I go about that?

Also, there is one place I've found where the concrete has pushed up a few mm. This is in a different room. Is that likely to be indicative of a worse problem?

sjoh0961

Sorry, I'm not used to posting on forums, and I'm having a bit of a 'mare with the formatting.

Tim

warmhands.coldheart

Chances are there may be no DPM under the concrete so leading to rising damp. Also in olser houses the cement/screed floors don't tend to be as thick as they would put in now-a-days and also sub-base of compacted stones/hardcore which is usual now-a-day wasn't always put in in those days either especially where sub-soil was clay.

Personally I'd rip the lot up but then it will cost but in the longterm if you put insulation etc in when re-instating you could make the money back..

RDG

With the cracks and joints it may be ok to just seal them up with a reasonable thin sealant, like i said a high visocosity resin would be ideal - but the floor needs to be dry at the time of sealing or it wont work. This will prevent water to the surface but it will still get in the cracks. Seen as the floor was dry when you moved in I dont think that is a major problem.
A resin system is probably over kill so a water based resin floor paint will probably do the trick as long as it is thin enough to penetrate the cracks and joints.

By raised up what do you mean?

Warmhands does have a good point re insulation, but whether it would pay you back depends upon the floor area and how well insulatted the rest of the house is.