Damp Sub Floor - The Saga Continues

[theboldbadger]

We live in a Victorian semi. When we moved in i immediately identified a problem with damp under our subfloor. The ground (and it is literally soil under there) is coated with a white mould and Is damp to the touch.

Luckily we have between 3-5 foot of crawl space height depending on where you are in the house so I can easily get down there for surveying.

In the first survey I identified one area at the back of the house where water was actually puddling, I knew this wasn’t a good sign.

Long story short, after months of false starts we identified that when running the downstairs bathroom tap or flushing the loo we could see water trickling into the puddle.

We found that the old cast pipe was displaced when joining to the clay pipe, whilst it was only by 150mm or so it was enough for some of the waste water to seep into the soil under the house, probably making an underwater channel and working its way to the lowest point where this puddle is, roughly 6 metres away. It’s hard to know how long this problem has been going on for but it could be 40 years or more possibly.

Once the pipes were fixed we ran all the taps in the house again, flushed the loos etc and there is no more immediate running water coming into the puddle.

Next we decided to clear the water from the puddle and at the same time we dug it
into a deeper hole to allow more water to run into the hole and act as a drain of sorts, which we could then clear out.

Digging this hole quickly turned into an absolute nightmare as we basically disturbed the smell of 40 years worth of poo, revealing a pile of sewage water that has been there a very long time.

We bagged it all up into rubble sacks and got rid of it. We were then left with a hole that could probably hold roughly 25 lites of water…. And here’s where I’m now stuck and looking for help.

In the 4 weeks since the digging of the hole I have been back down to check if it is still puddling 3 times. On each occasion there has been at least 10 litres of water pooling in the hole which I’ve cleared out each time. The banks of the hole are seeping with damp. The soil is a clay soil so it is very hard for water to drain from it.

My initial thoughts were that the water filling is a good sign as it is just the water draining from the soil and in to the drain. Eventually (or so I thought) the water will stop flowing to the drain and the whole area will dry up.

I’m now not so sure as the volume of water to me seems too much to be explained by a draining effect, and is showing no signs of slowing down. However, you can’t see it flowing by running taps or loos, it’s like a constant seep.

Today we went under the floor again, this time with the idea to put a hole-y bucket into the hole with a submersible pump to pull the water out more easily. We needed to dig the hole a bit deeper to get the bin in and when we started digging we got down about 2 1/2 feet and suddenly hit a clay pipe!

Now this clay pipe is much smaller than a waste clay pipe, probably 25mm diameter. And weirdly it seems have 40mm lengths and then a collar, but the collar is not tightly fitted. In fact you can spin the pipe around in the collar and move it about. It like it’s not meant to be sealed. Now bear in mind this pipe has nothing to do with our water works (water in or waste out). I’m now totally confused and wondering if this pipe has something to do with the dampness inflow. Possibly as well as the soil pipe issue we have now fixed. It also seems crazy that there is a random clay pipe so far beneath the soil.

I guess my questions are:

1. I’m not a drainage expert. Does the amount of water I’m talking about seem normal? Is the hole acting as a drain as I initially thought? Will it eventually stop seeping from the soil and dry up if I keep clearing the hole? Bear in mind this may have been leaking slowly for many many years.

2. Has anyone seen an old clay pipe like the one we found? Any ideas what the victorians or Georgians used these for?

3. Any other theories or tips to fry the area out?

Any help much appreciated.

This is the pipe we found at the bottom of our hole

This is the clay soil once dug out. You can see how wet it is.

 

[tell80]

1. Do you have pics of the earlier repair to the "old cast iron pipe" transition? Who did the work?
2. The recently discovered clay pipes could be drainage tiles for draining ground water - they were laid loose fitting in short lengths. But who laid them, when?
3. Drainage tiles end by discharging into a sump or a ditch or a stream, and occasionally (& very illegally) into a manhole.
4. Are you on a hillside? Do you have retaining walls?
5. It might be expensive but tracer cable can be inserted into the tile . The tracer will show where the pipes come from and go to.
6. The "white mould" is a salt, its harmless.
7. Do you have ample air bricks?
8. Probe the joists , look for rot and condensation.

 

[theboldbadger]

1. Do you have pics of the earlier repair to the "old cast iron pipe" transition? Who did the work?
2. The recently discovered clay pipes could be drainage tiles for draining ground water - they were laid loose fitting in short lengths. But who laid them, when?
3. Drainage tiles end by discharging into a sump or a ditch or a stream, and occasionally (& very illegally) into a manhole.
4. Are you on a hillside? Do you have retaining walls?
5. It might be expensive but tracer cable can be inserted into the tile . The tracer will show where the pipes come from and go to.
6. The "white mould" is a salt, its harmless.
7. Do you have ample air bricks?
8. Probe the joists , look for rot and condensation.

Thanks. Tracer cable is a good idea.

This is a photo of the old transition before it was fixed. The clay in this section has now been replaced with plastic and we’ve tested to ensure it’s no longer leaking. The site of the puddling is about 6metres from here under the house.

 

[theboldbadger]

Yes it’s on a slope, not massive but from the driveway it runs downhill towards the house

 

[tell80]

Are you on mains drainage or a septic tank? Any manholes visible?
The downhill position of the house suggests that you will always have excessive ground water, & that the drain tiles were laid to relieve the excess.
A long term observation is needed but it could be that you will have to channel the sub-area soil to a pumped sump?
I dont see any air bricks in the pic.
You have a number of gullies - where are they draining to, and where are they tying in needs a drainage map.

 

[blup]

You need a drain survey including tracing the drainage tiles to check for condition and route.

Blup

 

[JohnD]

When you find one broken clay gulley, you can reasonably expect that there are more. It's good practice to dig along until you are confident you have found and replaced all the damaged bits

The digging can be arduous, but the job is not complicated, and reasonably pleasant in summer

A camera survey will save time