Damp floor

Hi,

I would appreciate some direction if you can, as there is so much information online that I am not sure where to start.

I have a small cloakroom under the stairs. Externally, the wall is the part of the house which gets the most rainfall.

Until recently, the floor was covered with carpet. When I removed it, because I am considering tiling it, I realised that the floor is not in a great state (uneven surface and crumbling in parts). Furthermore, it smelled of damp and the top eft corner of the room felt wet (it is where most of the rainfall hits on the other side).

Should I start by applying a concrete sealer? Or a concrete hardener / sealer? Do you have a product to recommend?

Should I also use a self levelling compound after that, to fill the holes and make the surface more level? Or something else? Again, if you could recommend a product that would be amazing.

Or do you think that the problem may warrant more significant work? Should I not worry too much about it or should I be more concerned?

Thank you very much.

Clean it up and put a carpet down again. OR

take it up and do a ardex NA moisture system.

I’d say that’s a magnesite subfloor which means it won’t have a damp proof membrane underneath it and you can’t put one above it.

Thank you very much @dazlight

I am looking into magnesite subfloors now. Most sources are suggesting to have it removed, which presumably would cost a lot. They are also saying that sometimes asbestos was used in the mix, which sounds pretty scary. I hope this isn't the case here.

I think I need to confirm that it is magnesite first e.g. using a gas flame and assess the situation. I have also ordered an asbestos test kit to be on the safe side.

Hi,

I thought I would provide an update, in case someone reads this thread in the future.

I did the following two tests:

1. Held some of the material against a gas flame for a while. Magnesite is meant to glow. It didn't.
2. Tested the electrical conductivity of the material, using an electronic damp meter. Magnesite is a good conductor and as such is meant to give very high/ almost full readings even when dry. I got medium readings.

While the above suggest that it is probably a pigmented screed rather than magnesite (even though the visual resemblance is uncanny) I sent a sample to a lab to check for asbestos. It is a small price to pay (around £25) for peace of mind. Luckily, the results came back negative.

Having given this some further thought, I plan to arrange a survey by a damp proofing specialist, before going further. I don't want to cover any potential issues, which might come back and bite me in the ass.

Thanks for thinking of others.

You could always contact a big Mfrs such as Ardex for a recom product? Attach this thread.
You dont say what floor coverings or what fixtures you might intend to use?
Theres a little condensation but no big deal. The whole issue is no big deal.

Hold fire on any D&T salespeople.

Can you post a pic of the outside wall surface at ground level?
Are the adjoining floors - same stuff - suspended - solid concrete?

Hi @tel765

Thank you for the reply, that's very kind. Interesting stuff!

I was hoping it is just condensation, trapped by having carpet on top of it, but the fact that there was a corner where the floor was actually wet and the fact that it is crumbling in parts made me a bit suspicious.

I believe that the whole of the downstairs has the same material, but in other rooms that is covered with laminate (or at least I think it is laminate, it could also be LVT). Regarding this room, my preference would be to tile it or – if it would be more practical considering the situation – to use LVT.

I attach a photo of the outside wall. It is next to the drive and the house is on a slight slope, which would mean that this particular wall is the worst for rainfall. I have looked for imperfections in the wall and couldn't find any. I attach a photo. (There is a shadow in the photo which makes it look as if there is a dip – in reality it's quite flat).

Cheers.

There are hardly any damp signs on the interior walls except for condensation mould.
Is there an air brick vent in the c/room?

The outside shows a construction that I've only seen now and again.
Is it original or remedial work done to hopefully prevent penetrating damp?
Is it the same construction all around the house?

1. the window sill & frame is set too low or it suggests that the red brickwork came up too high?
2. the brick half wall has a DPC(?) below the brick ledge but no sign of a DPC at the base.
3. brickwork was sometimes painted to prevent damp?
4. does the red brick end at ground level or is it sitting on some kind of plinth - the pic is hazy in the shadow.
5. Is there a cavity in the wall?
6. is the outside ground level lower than the inside FFL?

Thanks again for your time @tel765

I attach fresh photos – daylight definitely helps...

You are correct that there was no noticeable condensation on the walls, only the floor. I tend to have the cloakroom door open for ventilation – however the floor was covered with carpet until a few days ago. There is no radiator and no air brick vent. The walls are cavity walls but the cavity is small, not full depth.

Regarding the outside of the house – it is the same all around. I don't know if it's remedial work I'm afraid, as it's predates me buying the house. Most houses in my area have the same painted brick – I live in a coastal town in the North of England, so it could be done to protect from the harsh weather & humidity. The red brick ends at ground level. The outside ground level seems to be level with the inside, not lower. I'm afraid I can't answer the question regarding DPC but it sounds like you may be on to something regarding the base...

Looking closer today, I did spot some small holes close to the main wet area (last picture), though probably not enough to account for the issue.

Cheers.

There was only shadow line - no DPC below the brick ledge.
At the bottom courses there's previous indications of attempts to deal with low level damp
1. you can see DPC injection holes.
2. smeared on attempts at repointing and a gap in the pointing can be seen.

The GL and the FFL being equal across what might be a solid wall is not good news.
Some dig French drains others install Aco drainage but penetrating damp on a hillside can be v. difficult to barrier against.

Thanks @tel765

When I bought the house, I had a full survey done and specifically asked them to confirm the type of wall. The reason for that was that the EPC certificate said "assumed solid walls" but I could see that there were air brick vents outside without any holes visible inside the house. The result of the survey was that the walls are cavity walls but that the cavity is pretty small (hence the EPC certificate, as they base it on the width of the wall). I could be wrong about GL and FFL, they seem to be on the same level to me but I haven't measured it precisely.

I wonder if what you are suggesting is the reason that the previous owners hadn't covered that room with anything (it was me who put the carpet down 2 years ago), so that it can dry out and, if so, where that leaves me regarding my plans. Perhaps there is a good breathable option to cover the floor with?

Maybe instead of an expensive damp proof specialist, I should get a local tradesman to take a close look at it in real life and advise on any work that needs doing before adding anything to the floor. At the risk of sounding silly though... I am not sure what type of trademan is most suitable for looking at this.

Final update, in case someone reads this in the future.

I managed to get someone to look at this. He suggested that I could either ignore the issue (as it did not seem to be causing major issues) or, if I wanted to do something about it, that would mean digging up the old floor, putting a damp proof membrane down and then covering it again. It would cost around £700, which is understandable considering the work involved, but as this is a tiny storage room / cloakroom under the stairs, paying that amount and then paying for tiles etc seemed like a lot of money for such a small room, if it's not causing issues to the rest of the house.

The tradesman did suggest I could cover it with tiles and that it could last for years before I have an issue but it didn't seem wise to me to have dampness trapped underneath the tiles, without an escape route for ventilation. In the end I covered the floor with thin breathable carpet and also bought a good dehumidifier for the room.