Old house, concrete slab, engineered wooden floor - I have questions

The usual guidance for old houses is to let them breath and don't try and seal stuff in / out.  I wouldn't try and seal that slab under anything that won't breath.

@wwaswas the best thing you could do first would be to get a moisture % reading of the concrete slab. Do you know anyone in the trade that could lend you a decent one (not a £9.99 jobbie from eBay)?

It’s likely that even if your readings are within tolerance for an engineered oak floor, any decent supplier/fitter would be insisting on a liquid DPM given the age and unknown provenance of the slab.

yes they do work and instead of sealing the moisture in, they just control the release to a level that the material can withstand.

Youll also need to consider whether the slab needs a levelling/smoothing compound. In which case, it’s a simple case of liquid DPM/primer (same material) and compatible levelling compound.

thanks DD

It's an Extech MS055 - so not bargin basement I got it to give me a reasonable idea of what was going on with the floor and scare myself by testing the walls but it's not 'pro' level.

I've DIY'd a few floors now and had planned to do it with this one but the floor thing worries me and I think if I pay someone to do the whole job I can blame them if there's issues, maybe?

What's a reasonable rate per sq m, maybe, for this sort of job? (room's small - 16 sq m)

Personally with a ceiling that low I would be thinking of digging it down deeper to get more ceiling height.  I know somone who did that in a similar aged house.  got another 8 inches of height

Independently, probably £35/sqm to include DPMing.

Through a supplier and employed or subbed fitter, getting on for maybe £45-50/sqm but probably more comeback. Obvs floor on top but that varies wildly.

Personally with a ceiling that low I would be thinking of digging it down deeper to get more ceiling height. I know somone who did that in a similar aged house. got another 8 inches of height

I've had loads of emails offering me ways to get an extra 8 inches. Let me forward them on.

Thanks again DD - I'll contact some local flooring co's.

TJ - I'd be worried about digging down - there's literally no foundations, the building floats on a couple of big oak beams at ground level. I've got used to ducking after 3 years so the head injuries aren't happening so regularly 🙂

I think what the folk I know did is underpin then dig down.  Expensive job   Its a very old house and the new floor level is below ground level

It was just a thought - it will be very expensive but will make the house nicer and more valuable

it will be very expensive but will make the house nicer and more valuable

TJ makes a great point - even if its expensive to do, if you dont do it, it'll come off the value of the house if you ever come to sell it - hobbits never pay top dollar for their properties. I'd be storngly inclined to dig it out, get some insulation in there and do it properly. if you can do some of the donkey work it might not cost the earth either!

you are going to have parties for short people to be able to use that room once you start adding any meaningful floating floors on top.

stick with carpet (if its not mouldy)

What petrieboy said. Dig down and see what's there, maybe a new basement to be discovered in an ancient burial crypt and cave system.

You say it’s on a flood plain, when was the last time it happened?

maybe sticking with a carpet or perhaps ceramic wood effect ‘planks’ might be a less risky option? Perhaps with some extortionate to run lecy under floor heating?

have a good look (in person) at some karndean. Some of their wood-effect stuff is honestly indistinguishable from wood at the height you look at in from, and would cope much better than real wood (even engineered) in a damp environment.

I had similar - my house is at least 100 years newer mind, relative new build. Engineered wood floor that previous owner installed ended up like a wave machine as you trod on one bit the wave would ripple along the floor it was that buckled. Burnt well in the burner mind.

I sealed it with epoxy, worked well. Never sure whether it was the right thing to do, but it did the job of stopping moisture coming up. It was one of those 2 can systems from a specialist damp place. I probably still have the cans if you're interested.

Akin to what benpinnick says, it probably isn't level.

We floated an engineered wood click system onto the existing concrete in our place as we didn't have the time to redo the floor or the money to install underfloor heating if we did. Certainly wasn't going to put a moisture meter near it, ignorance and all that 😆. Our floor does the rippling thing in places.

From removing the fireplaces and looking in alcove cupboards, there is a high probability our concrete floor was poured over the original flags, which offers us an alternative floor to relay or more headroom in the future (no steps needed here to paint the ceiling).

From removing the fireplaces and looking in alcove cupboards, there is a high probability our concrete floor was poured over the original flags, which offers us an alternative floor to relay or more headroom in the future (no steps needed here to paint the ceiling).

Ha, colleague of mine has just taken up some horrific fake wood patterned lino type tiles sat on a poured, levelled floor that was put down by the previous owner.

They found the original, immaculate solid oak floor, hand finished out of 50mm thick and 100-120mm wide planks, all cut to butt up to each other. Only issue is the points where the plastic sheet under the levelling compound leaked, so they're having to sand and wash the levelling compound out of the wood before they refinish and wax the whole thing (it's pretty much the entire upstairs of the original house ~80sqm.

Limecrete slab is the proper way to do it. https://www.lime.org.uk/products/sublimer-insulated-limecrete-floor.html

An electrical resistance meter will not give you a damp reading. They are normally the tool of snake oil salesmen and are designed for testing moisture in wood. You need a carbide test to confirm moisture content.

If the walls are on oak beams, they are likely to be rotten next to the concrete slab. Anything that prevents moisture evaporating through the floor is bad news.

As above, if it's on a flood plain, what's the flood risk on the EA website. No point spending money on a new floor if it's at risk of being flooded.

As a structural engineer, I'd be very concerned about digging down to get headroom, you'd likely undermine the walls and have both physical and building regs problems. Note that Building Regs don't generally apply retrospectively unless you make a major modification - so what you have is legal, mess with it and you could need to meet modern standards which would be impossible. It's possible that the concrete was laid over the original flags, so removing it could be viable; it might be worth taking up a small area to see.

Is it listed? That might restrict what you'll be able to do.

Thanks all.

Last flooding was just over 20 years ago and there has been mitigation by EA and it's officially a 'low risk' area now (although I had to check as I thought it was higher).

I'm reluctant to start digging out the floor for all sorts of reasons - potential cost and risk to building structure being main ones (I'd want a structural engineer involved at the leasdt). It's the only room in the house with a very low ceiling - the rest are ok for me at 6'1" (albeit that upstairs rooms are half in the roof so only have height in the centre). It's the lounge so not a room people spend long periods standing or moving around in and losing 10-15mm over carpet+underlay isn't that big a deal.

Meter I used is one of the ones that does some sort of magic scan rather than using two prongs but I was going to get a chemical test done too.

Rest of downstairs floors are all reclaimed French oak like this so in terms of risk a £1.5k-£2k engineered floor is going to be neither here nor there if it comes to another flood and reinstatement costs.

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we have a large dog and trying to keep a carpet clean in a rural area is a battle so a hard floor seems a good idea. Will check out Karndean etc but an opportunity to add some insulation would be useful even if it was only a few mm as a part of a damp proofing underlay.

Will get a couple of flooring people in for some quotes.

I'm sure this is fine...

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I had a concrete layer in one room in my old house (1790s) with a layer of bitumen over it to seal it, then carpet over the top. It was the recommended way of damp proofing in the 1970s, I’m told. The general effect was under floor cooling… sub optimal in chilly Yorkshire.

Dug it up and insulated then put a wooden floor over the top. Massive difference. No oak beam complications though.

Looks like you've got the proper hygrometer in a box, make sure you read the instructions and let it stabalise. Also, worth moving it around to get readings in different locations. 79% RH (as indicated in your photo) is above the critical 75%RH value. For more info see https://www.concrete.org.uk/fingertips-document.asp?id=778

Just to add that the applied damp-proof membranes generally seem to work.

I’m sure you’ve done your homework but are you absolutely certain your existing floor is concrete? We live in a slightly newer (circa 1700) rubble built cottage and our floors pre-renovation were carpeted over earth, which is fairly typical of its age. They were smooth & appeared concrete but that was just years of compacting.

Thanks Mildred - it's certainly a screed finish, whether that's over a proper slab or just covering whatever there's before I'm not sure. It looks in good condition so it's on a stable base, in any case. I've got a picture of the room from an article written in the 1920's somewhere - I'll try and dig it out.

Found it. This is the room from 1927. I think from looking at the floor covering near the dresser where it's not been walked on the squares that can be seen are where there are quarry tiles underneath. I suspect someones just skimmed across the top of those later on but I might be wrong. We'll know when the existing carpet is fully lifted I guess.

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