Breathable Kitchen Floor?

[HenryFord]

Hi All, we have an old(1840's) cottage that we are renovating. The kitchen is above what may of once been a cellar (what ever it was is now not accessible, but the design of the house suggests there must be something under the kitchen floor, even its only rubble). When we bought the cottage it had wood laminate flooring in the kitchen. Prior to exchange this flooring was fine, no signs of lift or water damage etc, this was checked regularly over 3 to 4 months. Prior to exchange the water had been turned off for about 3 months (over winter - property unoccupied when we bought). On the day before we exchanged the previous owners turned the water back on, found a leak in the kitchen so put a small bowl under it. We got the keys 24 hours later, entered the property and the kitchen was flooded, and floor ruined....bless em! Anyway, some of this water seems to of seeped under the concrete and there is a small damp patch, which I assume is where it is gradually evaporating from. My problem is I dont want to 'lock' it in with a new floor. Can anyone recommend a solution? Air bricks, breathable floor maybe, or just wack the heating up for a few weeks? Come on 'Builder', I know you'll have a reason and a simple solution for this one. Thanks in advance.

[ladybirder]

I hope he does Henry:-)

[Khandro]

If it is what you say, It sounds as if you have to let it dry naturally by keeping the windows open and/or buying or hiring a dehumidifier which would speed up the process .
Did the laminate floor you removed have any sort of plastic membrane or bitumen layer under it?

[mazie]

we had a similar problem Henry. We bought a cottage nearly 2 years ago that the owner only used every other week-end. The bathroom was amazing, fully tiled and beautiful. We had been in a few months and had to relay the drains. The plumber removed the toilet in the bathroom to do this and the floor under the tiles was rotten. It turned out that the outlet joint under the bath had been leaking for years and we had to rip the floor up, remove all the plaster. Was a nightmare. The old man bought a couple of dehumidifiers to dry it all out before we began putting down a new floor and re-plastering. They worked really well. We got ours from Aldi for £99 each. We now use them to dry the washing. Our cottage was built in 1893. Good luck with it

[HenryFord]

Thanks. Khandro, the laminate floor was the 'fake wood' from B&Q probably. They don't seem to have any backing or bitumen, just interlocking wood effect plastic planks

[The Builder]

Henry, one good thing at least ... you are well rid of that B&Q "pretend" flooring!

There are two ways of looking at this. There is generally nothing wrong with isolating the new (hardwood?) floor covering from the substrate. It's quite common to introduce a damp-proof barrier of some kind before a floor finish is applied. Hardcore or even back-filled rubble under the floor needs no damp-proofing in itself. The new floor is the only thing that needs this to protect it.

In which case, a good through-draught will soon remove most moisture from the substrate. Although, as I said above, it need not be bone-dry. In fact, because it is in contact with the earth below, it will forever contain moisture.

The other way of looking at this is to do as you suggest, and let the back-fill breathe through the floor. However, unless the filled void is subject to crossflow ventilation, breathing will be restricted considerably... rather defeating the object. The only way around this is to introduce e.g. airbricks between the fill and the outside world. Though, I can't tell from here if this is even practicable.

Once airbricks are in place, the new floor would have to be installed in a breathable way... to create air movement through the airbricks and up into the room. Obviously, the new floor covering could not be glued or bedded on bitumen for this to work.

If you did want to go for breathability, I would suggest fixing 25 x 50mm treated battens at 400mm centres to the subfloor (concrete?), then secret nailing the new hardwood floor to these. Not always possible of course, due to the extra height of the finished floor.

[HenryFord]

Thanks Builder. Yes the floor is concrete and outside the kitchen at the rear of the house there is an 8 foot drop, inside the walls of this drop is the unknown quantity and is where the condensation is probably rising into and through the kitchen floor... so could we put air bricks on this outside wall to ventilate?

[HenryFord]

Just to clarify the area under the kitchen may of once been a cellar although far from sure about this, either way the area under the kitchen is a volume of space that must contain somthing, so possibly an old cellar that has now been filled in, or possibly 170 year old rubble...So, if the floor drys I assume it was a temporary thing caused by a 24 leak, and its 'breathed' the moisture out, although I understand it still needs to breath? If I were to seal it in with some sort of DPC where would the damp go...up the walls maybe? Where would I put airbricks, back of house maybe? Can I put airbricks in the kitchen floor? (poss stupid question)...Also we were hoping to tile the kitchen floor, is this going to be possible

[The Builder]

I think you've answered your own question, Henry. If you fancy tiling the floor, then there is absolutely no need to ventilate the void under the tiles. Tiling will effectively seal the concrete anyway.

Venting a floor void is only essential if you have a suspended timber floor (joists and boards), to prevent rot.

For the question of "where does the damp go". It is isolated from the interior of the building, so it stays where it is. If the void was filled and concreted in modern times, then a damp-proof membrane would certainly have been laid over the fill, and the concrete poured on top.

A house of this age would either have had a very rudimentary dampcourse in the walls....... or likely none at all. That is a separate issue, and having the void filled with hardcore would have little effect on the amount of moisture in the walls. I only mention this in case you might be concerned about rising damp.

This might all be academic since poured concrete floors bear directly on a hardcore/rubble base. There is most likely no actual void, so nothing to ventilate anyway.