Damp concrete floor

[Trottersindependenttraders]

We've just redecorated and today pulled up the carpets in preparation for new flooring being laid next week. The carpets in the dining room revealed a concrete floor with very old (we're talking antique!) vinyl tiles and random patches which feel damp to touch. Two patches are close the the airbricks, which upon investigation appear to be above floor level and the other 3 or so are in the middle of the room or by the lounge wall.

The lounge has suspended floors and my worry is that the damp has or will extend to the sub floor timbers.

Chemical damp proofing was done by the previous owner 4 years ago, we've lived here for 3 years and haven't ever seen any damp on the carpets, there's no smell, skirtings are dry and there's no mould growing. I will ask a local builder to come round and look at it but any early thoughts / advice would've most welcome.

how old is the house?

how far from the damp patch is the nearest radiator?

have you got a water meter?

Why do you think one room has a concrete floor and the other is timber?

Of all the people to answer! Thanks for your response Piglet John.

House is 1950's.

One damp patch is close to the radiator, no evidence of any leaks from radiator though. Other damp patches are randomly located.

No water meter, we're still rated.

I don't know if the floor in the dining room was originally concrete or used to be timber. The vinyl tiles have certainly been down for some time!

The house was extended in the 1980's and kitchen is now in the extension which also has concrete floors under the tiles and is next to the dining room.

I'm cross that we didn't spot this before, when we bought our previous house it was damp but it smelt damp and there was mould on the skirting boards. Here there was nothing to suggest what was lurking - the underlay isn't mouldy and the carpet grippers haven't rusted either.

Are the radiator pipes buried in the concrete floor?

Does your boiler have a pressure gauge on it, or a small tank in the loft?

A 1950's house should never have needed chemical damp treatment, because it was built with a DPC, unless somebody heaped earth or a path against the wall.

If you can get into some neighbours' houses that are similar, see what their floors are made of, and if they have damp.

Look in the front garden for the stopcock. It will be where the front gate used to be, and may have been buried or concreted over by some idiot. The pipe will run straight from here to where the kitchen sink used to be. Is that under the damp patch?

Stopcock by the front gate, will have a look in the morning. The sink would originally have been in the dining room (was the kitchen when the house was built) so leak under the floor is a possibility. Would it be in random patches though, following no particular line?

Neighbours have all extended out the back but I'll see if any of them can remember if the old floor was concrete or timber. One neighbour is having a DPC put in now, again you could see damp creeping up the walls and you could smell it.

The boiler does have a pressure gauge yes. Do I need to keep an eye on pressure dropping?

I think that the radiator pipe comes under the floorboards in the living room as there's some boxing in that seems to show that. I'll investigate on the morning though.

Can I rule out condensation in this instance, do you think? And as the house shouldn't have needed a DPC, you don't think anything will have 'failed'?

Thanks so much for your advice. I'm equally baffled and fascinated by what is causing this.

if the boiler has a pressure gauge, and you have not had to keep topping it up, it is not a radiator pipe leak.

Water supply pipe might have been steel. 60 years is a good life for a buried steel pipe. When you have found the stopcock, wait until late night, then get person A to turn it fully off, then open again, then off again, at one-minute intervals, while person B, with the best ears, stands in a perfectly silent house, listening for a soft hiss to start and stop. It is likely to be at a joint, especially the elbow where it used to turn. You can also use an engineers stethoscope, pressed against the pipe, or grip it tightly in your teeth.

A 1950's house is less likely to have a wet floor for other reasons, unless perhaps you are on a hill and rainwater runs under the house. However if you invite into your house a person who sells damp-proofing treatment, you can expect him to tell you to buy damp-proofing treatment.

Thanks Piglet John. Boiler rarely needs topping up.

Tomorrow is find stop tap day!

No hills, we're in a v flat county! I've read plenty of advice from you on here about damp proofing treatments to know they're not necessarily the answer.

I will report back with a thrilling update