Cracks in concrete floor

oz0707

If they're not spreading I wouldn't worry too much. I've just poured a new 66m2 slab and have cut crack inducers into it. If you didn't have a dpm surely the damp would come up through the whole slab?

If so cant you get a damp proof self levelling compound or bitumen?

sjoh0961

Yes, I did worry about the sulfate issue at first, but it looks like that causes wholesale crumbling, rather than just a few cracks. And I don't think it would just suddenly appear in an old house, but I could be wrong. Link doesn't work, btw.

sjoh0961

oz0707 wrote: »

If they're not spreading I wouldn't worry too much. I've just poured a new 66m2 slab and have cut crack inducers into it. If you didn't have a dpm surely the damp would come up through the whole slab?

If so cant you get a damp proof self levelling compound or bitumen?

Yeah, it sounds to me like you're right. It sounds like cracks in the slab are probably old settlement, and the damp seems to be coming up through the joins where the old fireplace has been concreted over, so sounds like I can probably paint over it.

Leif

I assume that is a closed up fireplace. In which case make sure the chimney is capped properly. That is one damp ingress route.

Regarding the sealing, damp proofing companies inject a sealant into walls. I wonder if there are similar substances you could use i.e. not so much a paint, but a substance that soaks into the concrete floor providing a deeper and more durable layer of protection. Just a thought.

I have much bigger floor cracks than those. [I'd insert a blowing a raspberry icon if I could find one .... ]

tony6403

sjoh0961 wrote: »

Yes, I did worry about the sulfate issue at first, but it looks like that causes wholesale crumbling, rather than just a few cracks. And I don't think it would just suddenly appear in an old house, but I could be wrong. Link doesn't work, btw.

You are right - the link doesn't work , don't know why . Yet if you Google "Sulfate damage 703049" the link/document is there !
The affected floor in a photo in that document is worse than yours but has similarities. At least worth a look ( page 6 ) .

sjoh0961

tony6403 wrote: »

You are right - the link doesn't work , don't know why . Yet if you Google "Sulfate damage 703049" the link/document is there !
The affected floor in a photo in that document is worse than yours but has similarities. At least worth a look ( page 6 ) .

Thanks, I've looked now. I think that looks a lot worse than what I've got. And I'm in London, which doesn't seem to have had any problems with sulfate attack. Worrying, though. Another thing to take into account

RDG

Like I said before a water based resin floor coating/paint will do the job of sealing the floor to prevent damp penetrating further.

I am not aware of any products which can penetrate any deeper than a few mm into the surface of fresh concrete let alone some that has been down as long as this probably has. The pour sizes of this concrete will probably be very small by this point in time due to the hydation reaction having continued since it was placed.

Sulfate bearing hardcore is generally a risk in areas where there was a lot of coal mining as it was caused by the use of industrial by products. It causes expansion of the concrete and therefore you get the slab heaving at the cnetre and then cracking. From the pics and our discussion I do not think it is an issue here. The cracks would run either along the slab in the longest direction, as the slab will now be arched. OR they would spread from the centre in all directions as the slab would be humped.