Damp concrete floor in extension, tiles breaking

TranceNRG

Hi guys, I was wondering if you could provide some guidance dealing with a very difficult situation I'm in.

It's probably going to be a long post to explain the situation so bear with me please.

I have a ground floor 2 bed Victorian garden flat (period conversion) in West London. I bought this flat about a 14 months ago and did a full refurbishment with new plumbing, heating, flooring, bathroom and kitchen.
There's an extension at the back of the house (I think this was probably built in the 80s when the house was converted to 2 flats) that houses the bathroom and the kitchen.

Here are couple of pictures to give you an idea of the layout

House, garden, patio and drians - Album on Imgur

Flat layout

Current situation:

About 6 months ago I started noticing that a floor tile in the bathroom was starting to crack. This gradually got worse with this tile lifting up then spreading to a couple of other tiles around it.

Tiles cracking and lifting up

Last Saturday, I my builder's men came around to have a look. They removed about 6 floor tiles and we found that the concrete floor underneath was quite damp and concrete was crumbling (mostly where the tile first started cracking) and still quite damp nearby as well (though not as much).

Damp concrete floor in the bathroom

The guys weren't really sure what was causing the damp. Initially I was thinking it was a leak from a pipe in the floor but according to them, there weren't any pipes going through the floor in the bathroom and the new pipes installed were in the walls.

There were 3 possibilities for the damp according to them -
1. The water pipe connected to the sink tap or the pipe taking waste water away from the sink (both of them are in the wall) is leaking and this water is going to the floor down the wall and is saturating the floor.
2. water leak from the toilet in to the floor
3. The floor in the extension wasn't made properly and is getting damp

They reckon if it's a leak from the toilet or pipes in the wall, it's easy enough to fix. I'm stressed that the damp in the floor is due do a badly built extension. We left it for a few days to see if it dries out and then go from there.

Background and possible causes

When I bought this flat, the day I got the key, I found that there was a leak from the old bathroom and there was a lot of water on the the bathroom floor and living room floor and all the surrounding walls saturated. If I remember correctly, where the new tiles started cracking was roughly where the old pipe was leaking (they were in a box so we had to break the box and to see the leak and then stop the water mains).

We started renovations about a month later and I remember the walls in the living room near the bathroom had damp patches that didn't dry out so I had to get damp proofing people to hack off plaster and add water proof plaster in the living room.

My builders removed the old floor tiles from bathroom and kitchen. Partition walls in the bathroom and kitchen were also removed and new walls installed. I don't remember much about the concrete floor in the bathroom but I do remember the kitchen floor (after the old tiles were removed) looking a bit damp and the plumber kept saying the floor was quite wet. This guy was there last Saturday and I mentioned about the kitchen floor but he said the kitchen floor did try out mostly eventually.

My building survey at the time of the purchase, highlighted high ground level outside, at the back of the house. Also it was paved right up to the building with no gap.
At the time, I didn't know about damp issues so I didn't think of much of this. But because of the damp walls I had, recently I decided to lower the ground level in time for winter so got a new patio few weeks ago. My landscape gardeners removed the old patio (had paving bricks on one half and concrete slabs on the other), reduced the ground level by 10-20 cm and put in a new patio with a 'french drain' (I am not sure if this was a proper french drain but more about this later).

My landscape gardeners also mentioned that, previously waste water from the plastic pipes outside the bathroom (carrying waste water from the bathroom and kitchen) were let straight on to the old patio (brick paving) and that this water was not connected to a drain. I am not sure how many years it was like this but it's possible this water was going in to the building perhaps causing some of the damp issues. When new patio was installed, my landscape gardeners installed a gully in the patio to collect the water from these 2 waste water pipes.

The flat roof on the extension was really old and was probably leaking as well. I remember there was a lot of mould on the walls in the kitchen and bathroom.

It's worth mentioning that tiles in the old bathroom and kitchen seemed fine and I can't remember seeing any cracks. So this damp floor might not have been there for years (you'd think the old tiles would have cracked if the floor was damp for a long time).

The fact that the tiles started cracking in one area (and the concrete is crumbling around this) plus tiles only started cracking this year suggest that this might be caused by a leaking pipe or toilet but then what caused the kitchen floor to be damp, during renovations? Maybe it was the water from the big leak at the time of the purchase or water leaking from the roof. Maybe there are multiple factors here.

Hope it's not too confusing for you to understand. What do you guys think? What could be causing the dampness in the floor? How should I go about investigating/fixing this?

I guess my worst fear is that the concrete floor in the extension wasn't installed properly and the moisture is rising from the saturated ground. If this is the case, to fix the floor, I'd have to rip out the new kitchen and the bathroom which I don't really want to do!

French drain

OK finally the french drain..I told landscaper gardener I wanted the ground level reduced (with a new patio) and a french drain that went around the back of the house and the extension.

New patio, gully and french drain

But all he's done is leave about a 10-12 cm gap between the house + extension and the patio and back filled it with gravel. So the french drain isn't any deeper than the depth of the patio + type 1 base. I'm guessing this is about 15-20 cm deep maybe less. The new ground level is about 10 cm lower, near the extension and about 20 cm lower near the living room. Do you think the 'french drain' needs to be deeper?

Thank you in advance for your input and apologies again for the long post.

PS: I bought an EcoAir DD122 dehumidifier start of this year because of the damp problems I had. I left this in the bathroom last couple of nights so the floor might dry out but so far I haven't seen a difference. problem is because there's no power socket for it in the bathroom, i have to plug it in the kitchen so I can't close the bathroom door properly hence it's not fully closed. Could I get an adaptor for the shaver socket and plug the dehumidifier in to this?

TranceNRG

I forgot to mention that the floor tiles in the kitchen (bigger tiles) so far haven't cracked but they do seem a bit cold but that could be standard.

Doozergirl

The picture of the back of your house is exactly why I hate "Damp Proofing" Companies.

You have had a new chemical damp proof course installed when your survey already told you that your ground level was high enough to breach the DPC and you had evidence of damp in the house. Instwad of fixing the obvious problem, you have been sold a chemical DPC.

From the photo, someone in the past has put a sort of plinth all the way around the bottom of your rendering. That is causing a complete breach and yet your damp proofing company have sold you snake oil by installing another DPC. It almost certainly didn't need it and they will not have solved the initial problem at all as the new DPC is high above it.

What should have been done is removing that plinth entirely, expose the brick (hopefully engineering) and the DPC and brickwork and then fit bell bead to finish the rendering neatly *above* the DPC, removing the breach.

Then your french drain goes in, with a nice gap and good depth so any ground level by the house is 150mm below the DPC.

You have had continued damp ingress, I can imagine. Is there a visible plastic damp proof membrane anywhere against the extension walls inside the house? You install one inside the house as well before pouring concrete so it sits in a sort of container and damp can't seep up.

Any water held in concrete after an ongoing leak would take ages to dry out - and it won't dry out at all if there is also damp ingress from outside and or up through the floor.

I think there are probably a few things happening there. What I am not an expert on is the behaviour of concrete, but I am a bit surprised by the crumbling if it. I don't know if that is a poor mix or an extreme reaction but it doesn't look like a good base for tiling and wouldn't have been when they went down!

Anyway, the outside of your house is still almost certainly a culprit and needs addressing before anything else.

Your tiles come up and the floors have to dry out - for some considerable period of time - months even! I guess a liquid DPM could go down inside before any flooring next time to just be careful and would aave on some drying time but that crumbling really needs to be investigated first and I'm not entirely comfortable advising that from here.

You really need an experienced builder or a properly independent damp specialist surveyor to oversee this.

TranceNRG

Doozergirl thank you for your long and informative reply. Ahh so you saw the 'great work' of the first damp proofing guy! He was a conman and I went through hell because of him. I found this guy from mybuilder and he had decent reviews. I thought I was doing the right thing.
He was the first tradesman that came around and he left a good impression(unfortunately I didn't get any other quotes). I was completely naive and gave him the job. This idiot didn't hack off any plaster and just injected stuff (I don't even know what he injected as I wasn't home).

The my builders started the refurbishment. 3 months later, some of the damp patches inside the living room weren't drying out so then I had to get another damp proofing company to come out, hack off plaster and replaster with damp proofing plaster.

The floor of the extension was never looked at properly though simply because I didn't know that it was an issue. My builders are partly to blame here. They should have advised me to get it checked if it was damp and they shouldn't have laid tiles on it.

I learnt my lesson the hard way though. I was totally new to all the building stuff at the time but having gone through various painful experiences and after lots of research on the internet, I'm far more clued up these days and if I ever take on another project, would do things differently.

If it ends up being the floor, I think I will ask the builders to remove the tiles on the floor and put down some waterproof membrane and re tile. I am not going to rip out the kitchen. Hopefully the kitchen floor will stay intact.

To answer your question about the concrete mixture, I've been told the top layer is screed so it's not as hard as concrete hence it's crumbling.

This may take some time to resolve in this cold wet weather.

Doozergirl

Your second damp people were snake oil merchants as well.

Damp proofing plaster does not stop the initial problem and it certainly won't stop damp getting to the floors. It may well push it down across the floor if it's trapped.

I remember trying to guide you an awful lot before you even started this process.

TranceNRG

I respectfully disagree. There were damp patches on the living room wall that weren't drying out after 3 months. The walls were probably wet from the time I had a big leak in the bathroom.

My builders went to the neighbours house to see if there were any leaks there and they couldn't find anything. Also there was nothing in the walls that would have been causing the issue. No leaks from the roof. So in the end hacking off the plaster and re-plastering it with waterproof plaster stopped the damp patches and we were able to actually paint the walls and finish the living room.

I haven't seen any damp patches anywhere else in the house .

Obviously I have a a different issue now so this needs to be dealt with.

phil24_7

Well walls can take a couple of years to dry our with incorrect wall coverings (cement render on the outside), or if very damp, or if high humidity...etc.

I have never seen a case that genuinely NEEDS damp proof injection or waterproof interior render (except basement).

With damp you should ALWAYS treat the cause and not the symptom.

phil24_7

If you had damp walls before, have waterproof render on the inside and cement based (largely waterproof) render on the outside then you will likely still have wet walls. Either that or the water would have migrated to surrounding areas (this could even be upwards through capillary action).

Doozergirl

I would also feel inclined to respectfully disagree if I'd spent a fortune on damp treatments that weren't damp treatments at all and still had a problem.

I've been renovating Period property for 17 years. And I'm really good at it because I've been doing it that long and seen it all. A lot of those houses I've lived in. What rendering the internal walls does is hide a problem or allow you to decorate without waiting. It solves nothing.

Your second contractor didn't even see what I can see blatantly from one photo.

TranceNRG

As I said what I think happened was the walls got saturated when there was a leak from the bathroom and it was almost flooded in there before the refurbishment was done. The wet plaster had to be hacked off.

It was simply not an option to leave the walls to dry out for a year.

And again I agree that most damp proofing companies are rubbish however this is in the past and I don't think my bathroom floor is damp because what the damp proofing people did. Where the tiles cracked isn't where the damp patches appeared on the will in the living room.

I think I'm going to ask my builders to remove more tiles around the floor and also dig in there to see if they can see a DPM.

TranceNRG

Doozergirl wrote: »

I would also feel inclined to respectfully disagree if I'd spent a fortune on damp treatments that weren't damp treatments at all and still had a problem.

I've been renovating Period property for 17 years. And I'm really good at it because I've been doing it that long and seen it all. A lot of those houses I've lived in. What rendering the internal walls does is hide a problem or allow you to decorate without waiting. It solves nothing.

Your second contractor didn't even see what I can see blatantly from one photo.

Sorry but this discussion isn't exactly helping my current situation.

The damp proofing guy only looked at the damp walls in the living room as there was no other damp hence the work in the living room. Look I agree this was only treating the symptom but I had a number of people come to have a look and they weren't sure what was the cause. my builders even removed a few bricks and couldn't see any leaking pipes or anything. My bet is the walls were saturated when I had leak before. Only way to remove the wet plaster was to hack it off.
If I had to do it again,I'd get a builder to hack it off and re plaster with waterproof plaster and wouldn't use a damp proofing company again.