Victorian Damp Proofing or Bodge?

[Jamesinnewcastle]

Hi All

First time here and first time solver of damp issues so please be gentle!

I have a terraced house built in 1902 and the lounge smells strongly of damp which the owner has ignored for many years. The paint has bubbled on one wall which backs onto a yard which is concrete. There are two 'damp' areas on the wall. The house has cavity walls.

Now I have found a large hole in the concrete seal surrounding a 1st floor toilet waste pipe and its cistern overflow pipe which has either broken away or never been there in the first place. The missing part of the seal is hard to see from the yard as the missing part is between the big pipe and the wall. I assume that this is the main cause of the damp as rain can easily enter the wall cavity and it lines up with the main damp patch inside.

There was also a 'nice patio' where earth was very close to the bottom of the wall which always keep the gap between the patio and the wall dark with damp - I've cleared that back and now the concrete is always dry and light grey.

Also (through reading things on the internet) I have routed away all the nice plastic waterproof paint covering the outside wall that was stopping the mortar from 'breathing'.

Hopefully this will have 'cured' the source of the damp problems - stay with me, there is a question coming!

I've taken up the floor boards and determined the general wall construction as shown in the attached drawing and photo. There are some items that I have guessed at, like the plastic sheet jumping beteen the two sets of bricks so if you think the drawing may be wrong please say.

My question is about the general design of the wall and how it does do whatever it does to protect against damp? It seems to me that the plastic sheet is some sort of damp proofing but I can't find any reference to this design on the internet. Can anyone tell me if this was a standard practice and/or direct me to a reference document please? I want to know what I should do if anything to aid keeping the damp at bay. I assume that I should clear all the debris that has dropped down from the walls into the plastic 'bag' (for want of a better word). Also there is one air brick in the wall concerned and three on the other side of the room - should these have air vents on the inner walls of the cavity to let air under the floor? I think that the plastic will block any such air flow.

Was this plastic a bodge that should be removed?

Cheers
James

 

[vinn]

Unless you have opened up the cavity you cant know how things are inside it? It would probably be a good idea to open up the cavity and be certain of how things are inside it.
The ground level is too high could you post a photo of the external wall at low level.
Besides the plastic sheet, can you point out the internal and external DPC's?
The air brick is useless - its the sub-area not the cavity that should be getting through ventilation.
Approx three air bricks would be needed for a rear elevation.

Any gaps around the soil pipe for instance can be filled with a semi-dry sand and cement plug.

Is the wall in the photo the only wall with damp issues?

 

[Jamesinnewcastle]

Hi Vinn

Thanks for the reply, there are a few more details that I didn't mention at first as it would have made a very long post!

For some reason there is a brick missing from the inner brick course (leaf?) of the wall in question. It is below floor level and while the occupant has lived in the house for over 8 years the missing brick may be the result of someone previous exploration of the damp (I suspect it was freshly covered over when the house was sold). I rescued a good deal of what looked like damp soil from this hole. I confess I haven't looked into the cavity very far - I will do this when I get access again.

The houses in the area are build on a slight hill with the yard upper most - now you mention it I have drawn my illustration by starting off with a 'standard' sort of layout - in fact the yard concrete is higher that the floor inside. I'll change the drawing.

Both the inside and outside brick courses have the twin plugged holes that indicate the pressure injected DPC I believe - I can't see any other membranes, though I might not know one if it bit me!


"The air brick is useless - its the sub-area not the cavity that should be getting through ventilation." I agree that's why I wondered if the scheme was a standard design or if it is a bodge.
Approx three air bricks would be needed for a rear elevation.

This is the only wall with damp issues.

I'll add some outside and more inside pics.

The one showing the waste pipe in the corner looks wet with damp but thats just water I had added - it shows the only air brick in the wall in question. The injection holes are in the upper row of the black painted bricks and in the white bricks over the air vent.

The piles of detritis showed in the indoor photos show the big pile of damp/dark 'soil' where the missing brick is.

You can see on one photo that the 'patio' is still leaking water but it can't now reach the wall!

Cheers
James

 

[vinn]

I suspect that the plastic sheet was installed to protect the tails of the joists. They might have had previous wet rot difficulties. In fact, that whole floor might be a replacement floor.
What are the joist tails resting on?
What space is below the joists to the oversite soil? 150mm?

Its necessary to take out a number of bricks to make an access hole to the cavity.

Injected DPC's are a waste of time in my book - especially when you have bridging from the high ground, and perhaps inside the cavity.

You have created a channel against the yard wall but where is that water going to drain to?

To simplify: Membranes are in sheets - DPC's are in rolls about 100mm wide.

 

[Jamesinnewcastle]

Hi Vinn

To answer your questions:

"I suspect that the plastic sheet was installed to protect the tails of the joists. They might have had previous wet rot difficulties. In fact, that whole floor might be a replacement floor." - This comes back to whether or not this plastic sheeting is a standard building technique - would it have been done when the house was built or is it a definite modification in the past 100 years? I suspect the injected DPC is later given the general technology. There is a section of the floor in the corner adjacent to the wall that has much wider floorboards than the rest and I so I guess that these must have been replacements at some point since there is a definite join 'line' across one of the joists, but of course when and why is a mystery.

"What are the joist tails resting on?" - The joists are resting on low brick courses, one course pretty much at the end of the tails. The joists seem to be isolated from the bricks by either thin slates in some places or what seems to be Lino in others. I say lino in that it is the same thickness and breaks in the same way as Lino.

"What space is below the joists to the oversite soil? 150mm?" - The joists sit on two rows of bricks so probably a bit more than 150mm. I note that the soil under the floor is quite dark, next time I get in I'll collect some and see if it is damp.

"Its necessary to take out a number of bricks to make an access hole to the cavity." - What would I be looking for in the cavity?

"You have created a channel against the yard wall but where is that water going to drain to?" - The wall meets a smaller wall at right angles, at the end of that wall is a drain - I plan to angle grind a very small slope in the concrete floor along the length of the wall to lure the rainwater away from immediate contact and hopefully to slope gently to the drain. I have monitored the way the water stands after a few bucket fulls of water and while it does not run fast, it does drain to a thickness that dries after about an hour.

I'll see if I can get more pictures today.


Cheers
James

 

[Gerrydelasel]

This comes back to whether or not this plastic sheeting is a standard building technique - would it have been done when the house was built?

Did they have plastic sheeting in 1902?

 

[Jamesinnewcastle]

Hi Gerry

I'm always surprised by what they had in the 1900's. I just Googled it and 'plastic' was invented in 1907 (Bakalite)! Probably it is a later modification then, however the owner may not be so clear as to the age of the property, I'll check. Second Google - Polythene was invented in 1933 and it would have been a good few years before becoming commercially available. The house is one of a good few rows build for the mines up here in the North East.

So still the question as to whether the scheme is a usual one or just an improvisation? I am told by my friend that he has seen something like it on 'Homes under the Hammer' but that's not really much eveidence!


Cheers
James

 

[Gerrydelasel]

So still the question as to whether the scheme is a usual one or just an improvisation? I am told by my friend that he has seen something like it on 'Homes under the Hammer' but that's not really much eveidence!

It is usual to install polythene around the ends of joists after wet rot, yes.

(Polythene was not readily available to the public until well after WWII. My grandfather is a retired plastics materials physicist and never tires of telling us about the first poly' washing up bowl her bought for my grandmother in the 1950s. It was yellow. It was expensive. She still has it.)

 

[joeinlondon]

Seems early for cavity wall. I would guess the problem is the high concret level out side. It my 1870s house the was a bitumen damp course which had been built over . By taking down below this level it helped a lot.

Later interventions affecting the performance of historic buildings are commonly responsible for damp problems around the base of buildings. Where possible these should be tackled before further remedial work is considered. damp masonry could take many months to dry following the elimination of the source of moisture.
Common later interventions include:
• external ground level raised above internal floor level
• raised flowerbeds built against external walls
• undrained hard surfaces built up against the base of walls
• trees and shrubs growing against buildings, encouraging moisture to dwell against the wall of the building and damaging subterranean drainage systems
• inappropriately designed rainwater drainage systems, such as down pipes that discharge at the base of the building
• inappropriate cementitious render or pointing encouraging a build-up of moisture within the fabric by directing rainwater into the building or discouraging evaporation.

http://ihbc.org.uk/context_archive/95/bagg/julian.htm

http://www.spab.org.uk/advice/technical-qas/technical-qa-20-rising-damp/

 

[vinn]

James,
Maybe if you removed the concrete bed from the channel and dug down a little and filled with stones you might create a kind of French drain?
Ignore the plastic/Pvc issues. Stay relevant on page.
The cavity might be blocked with debris bridging any inner DPC.
The sub-area needs all the ventilation it can get.

 

[JohnD]

An old house, with a damp patch near some plumbing, when the other walls are not damp, immediately draws the mind to plumbing leaks.

It is quite normal for the old salt-glazed clay gullies, bends and pipes to be cracked and broken in the ground, especially at the bends and sockets, and for the water supply pipe to be leaking.

Are there any red worms in the damp soil?

Have you got a water meter?