Wet patches on concrete floor

[WendyG]

HAPPY NEW YEAR EVERYONE

Having had the property for 10 years and lived with the odd "damp patch" on the floor of a large outbuilding attached to the kitchen (used as utility with fridge/freezer and washing machine (dryer is in another building across the yard) and all the dross necessary to carry out constant repairs to an old neglected property.  There are two radiators but these have never been used for the last 10 years and are turned off.   No heating.

The building was used as a "shop" some years before by the previous owner and has a floor comprised of large concrete slabs.  Very recently we have noticed varying size areas of "glistening" wet rather than smaller dark slightly damp patches.   The roof has been replaced so not coming from above and not coming from below as we first thought, as a small hole drilled through the grout produced dry material.  Most of the floor is bone dry.  The walls are not damp apart from one or two minor areas of a few inches.

If anybody has any ideas we would be most grateful as at the moment we are totally baffled.

WendyG

[Bugsy]

We had a cat once that used to do that ;)

[Chancer]

What you have described sounds more like a tiled floor (the grout reference) can you confirm please, I think I may know what it is.

[pachapapa]

If it is "glistening" wet then that indicates condensation.

The funny weather has probably contributed, new years day warmest since 1884, with the floor temperature being several degrees colder than the ambient air. C is correct in that tiles will offer a surface favourable to localised codensation.

In a word the condensation surface must have a temperature lower thanthe "dew-point", so relative humidity, high recently as well, will increase the chance of condensation.

Normally an effect encountered in spring time when the floor temperature increment lags, but been a funny winter.

[sid]

Chancer, I can't bear the suspense!  [:-))]   What do you think it is?  [blink]

Our gite, which is closed during the winter, suffers from a damp patch mostly shown up in the grout; I've always assumed that it's "rising damp" as the tiled floor is very unlikely to be damp-proofed (membrane) as it's so old. The patch dries up once we open up for the summer and the ground is drier anyway. In previous years there has been a musty smell, but for the past 2 winters we've kept a small window open downstairs (too small to climb through!) and a skylight open upstairs, which allows a small throughflow of air. The damp patch has been noticeably smaller and there is no mustiness. A "VMC" would presumably have the same, or better, effect?

[WendyG]

Hi

Thanks for replies.  The floor has large "concrete" tiles/slabs, which have been grouted - the grout is absolutely dry below the very top surface.  Reading posts think it is likely to be condensation as has been very mild and muggy here.

Appreciate you taking the time to answer.

Will have to air as and when possible and look forward to the summer.

WendyG

[Chancer]

My suggestion if it was tiled was going to be dewpoint condensation.

Re the other posting about one damp patch on a tiled terre battu floor, it may just be that the material under that part is less insulating than around it, my floors have sable à lapin over the terre battu but in some parts it has virtually no depth.

My mystery moits patches appear in spring and autumn during humid weather on certain areas of floorboards on the first floor, I have knocked down all the dividing walls now but I believe that the patches correspond to rooms where dogs were locked up for long periods of time and had either wee"d on the floor or died and decomposed, I know for sure that some did, either it is a ghosty spectral thing or more likely there are salts, probably urine that have leeched into certain planks and not others, every year the damp patches appear in the same places and they still stink to high heaven.

A good few years ago after some detective work I resolved a leak problem that was salt based, I would often find a pool of water on the floor of my garage yet could find no leak in the roof above, I was a racing driver and had hung the laurels that I had won from the rafters, most of them just dried out and turned grey except for the one above the phantom pool of water which remained fresh and green, it had been treated with some kind of saline solution and when the weather was damp it would be running with the humidity it had attracted most of which dripped onto the floor.

[AnOther]

Snail trails ?

[Chancer]

I had those in my UK place last winter, the floorcovering (then) was Heuga tiles, they were covered with a spiders web of snail trails, some even leading up the upholstered chairs.

I only ever found one culprit but he must have been pretty busy.

[sid]

Aha, Chancer, a case of resting on your laurels! [:D]

I hadn't considered condensation, but it is a definite possibility. The solution appears to be better ventilation during the winter months, at least as far as our case is concerned.