How to remove & remedy a failed chemical DPC v2

[drpepe]

Can I try this thread again? thanks to the contributors, but the previous thread got locked for some reason...

Hi - any help would be appreciated...

Terraced house c1901 (central property of 3), which we moved into nearly 3 years ago - our house was originally the left hand side of a pair of semis, with the now adjoining left hand house built some years after ours (c1930s). This adjoining house is approximately 30cm higher than ours (based on comparing doorstep levels). This might be important as it would place their party wall dpc above ours.

I have posted several posts in the past about the lack of underfloor ventilation & high humidity which have been partially dealt with (extra airbricks and clearing out rubble from the underfloor), but the current problem is not directly related to this. The left hand party wall has fairly recently (4-5 years) had a chemical DPC and been replastered to ~1.2m along the party wall in the front hallway. However horizontal damp stains are appearing all along at 1.2m height (see pic for an example).
The pictured wall is under the stairs (I stripped the wallpaper)
View media item 96337
I presume that the chemical DPC has failed or never actually worked, and that what I can see is rising damp being forced out of the wall above the re-plastered 1.2m?

What would be the remedy for this ? Presuming I can't do anything about next door, do I need to allow this wall to breathe or go in the opposite direction and think about tanking?

Any suggestions greatly appreciated!

Read more: //www.diynot.com/diy/threads/how-to-remove-remedy-a-failed-chemical-dpc.445391/#ixzz3qN1K5cMU​

The ground floorplan might be of use:
View media item 77344
The front looks like this (ours is blue door on right):
View media item 96389There's a filled in door (plasterboard, stud) from hall to kitchen on the adjacent wall that also shows damp staining, seemingly spreading across and up from the brickwork into the stud:
View media item 96390
Also see some of my other albums for underfloor pics:
e.g.
//www.diynot.com/diy/media/albums/under-floor-d-s-hall.20730/

Some responses the the queries from the original thread:

• I would guess it isn't a cavity wall, based on nothing more than the fact that the wall used to be an external wall, which our neighbours house was built against, c30 years after our house was built in 1901 (in the 'understair' picture above, you can see the wooden frame to some shelves built into the party wall which used to be a window to the outside).
• A lead water pipe enters the property through the front doorstep - it becomes copper about 50cm into the house. Stopcock is under the front mat well. Neither of us have water meters.
• Virtually all the floor in the hall and rest of ground floor have come up - under floor ground level is pretty high, about 20ish cm from the joists (was much higher but i dug it all out in 2014). The mud is dampish but nowhere near being wet.
• Our property has what looks like a bitumen DPC at the front - presumably this continues around to the party wall. If so it is definitely underground on the neighbour's side as it goes through (under, actually) the garden wall and follows the party wall
• A soil pipe runs from front to back of hallway under the stairs and exits to a gully just outside the front wall of the house. No smell of sewage under there or in the house.
• The kitchen floor (pic below) is original and stinks of damp - along the kitchen party wall (about 50cm wide under the run of units) the floor has been replaced with concrete- possibly an attempt to remedy a damp problem in years gone by?

summary:

1. The damp is clearly 'rising' up the wall above the new chemical and old bitumen DPC and behind the new plaster until it escapes over the top.
2. The underfloor (until recently) was clogged with damp mud and debris. The mud subfloor is still damp. Levels of humidity are very high in the hall (75% plus).
3. Something is also going on in the kitchen - damp smell, slugs.
4. The unconventional construction (original semi converted to terrace), and the ground levels between the houses may be contributing?

So, what to do next? We are planning to build an extension to replace an old conservatory at the back, and open up the rear - we will hope to uncover what is the problem in the kitchen at this point.

After that work, we will start to sort out the hallway - i was thinking to hack off the party wall plaster, let it dry, then replace with something more breathable?

Or do any of you still think we have a leak? If so, how to test this and remedy?

Any thoughts appreciated!

 

[ree]

The lockout was perhaps a warning to squabblers.

 

[cAtLeYx]

An incoming water supply and an above ground SVP in this location - Could this be a coincidence?

 

[drpepe]

An incoming water supply and an above ground SVP in this location - Could this be a coincidence?

What are you thinking?

 

[theprinceofdarkness]

Wow is this a test for building surveyors? Suspect areas:-
Leaking sewer pipe.
Leaking water pipe.
Badly stepped/ over lapped DPC
Neighbours garden soil bridging DPC.
Neighbours under floor soil bridging DPC.
Neighbours sleeper walls bridging DPC.
Garden wall bridging DPC.
Water run off from garden wall wetting wall above DPC.
Failed DPC - has it failed else where? I have not seen a bitumen DPC in a 1901 house, all the ones I have seen would have been slate.
As your neighbours house is higher then yours, the general slope of the ground would be from left down to right. So any of his water would run towards your house and be stopped by any wall. The easiest thing to do is to dig up his garden right in the corner of his front wall and the garden wall. So any water that puddles there would drop below your DPC level. Failing that, dig down your side and knock some holes right through the wall under ground, so as to drop the water level.
Frank

 

[cAtLeYx]

drpepe - Does your neighbour have any issues in this location? You have mentioned the pipe below the floor is a "soil pipe" and that is exits to a gulley - Is this "an open gulley?" or a Manhole? Can you confirm it is a soil pipe and not rainwater? Where on the ground floor does the pipe drop from upstairs?

 

[drpepe]

drpepe - Does your neighbour have any issues in this location? You have mentioned the pipe below the floor is a "soil pipe" and that is exits to a gulley - Is this "an open gulley?" or a Manhole? Can you confirm it is a soil pipe and not rainwater? Where on the ground floor does the pipe drop from upstairs?

This is a couple of pics of the drain outside to the left of the front door. The soil pipe exits the house through this wall (about 6 inches underground). The drainpipe is the one that can be seen in the original picture of my front door. There seem to be 3 entries above ground - 2 with flowerpots on(!), and one which the drainpipe enters, plus the presumed connection for the soil pipe underneath.
View media item 81707View media item 81789This pic is of the radiator on the party wall just inside the front door (left hand side) - you can just about see the black soil pipe.
View media item 77389
It is definitely a soil pipe as I can a) hear it when toilets are flushed and b) follow it under the floor to the kitchen where it is boxed in vertically to the bathroom directly above kitchen (soil pipe rises in the bottom left hand corner of the kitchen as you view the floorplan).

 

[drpepe]

Wow is this a test for building surveyors? Suspect areas:-
Leaking sewer pipe.
Leaking water pipe.
Badly stepped/ over lapped DPC
Neighbours garden soil bridging DPC.
Neighbours under floor soil bridging DPC.
Neighbours sleeper walls bridging DPC.
Garden wall bridging DPC.
Water run off from garden wall wetting wall above DPC.
Failed DPC - has it failed else where? I have not seen a bitumen DPC in a 1901 house, all the ones I have seen would have been slate.
As your neighbours house is higher then yours, the general slope of the ground would be from left down to right. So any of his water would run towards your house and be stopped by any wall. The easiest thing to do is to dig up his garden right in the corner of his front wall and the garden wall. So any water that puddles there would drop below your DPC level. Failing that, dig down your side and knock some holes right through the wall under ground, so as to drop the water level.
Frank

Yes it is a bit of a farce isn;t it?

You're right that any water will collect against the garden wall and be held against our house walls. Both front yards are block paved - i can't see him being happy for me to dig theirs up. Further, the 'rising damp' on the party wall goes all the way from the front the the rear of the house - so even sorting out that front corner won't alleviate the issue.

Any thought on what to do next?

Sand and lime for the interior party wall was mentioned - presumably this would allow moisture to evaporate away and not built up (as it is currently doing) ?

 

[theprinceofdarkness]

I do not believe that lime plastering will solve much. As soon as you decorate the surface you reduce the "breathability" and you really don't want moist air in your house, cos' it eats up your heat as it evaporates.
I would did up that sewer pipe to see what all the spare inlets do. While you at at it, pull the plug on a bath full of water to see if there is any flooding/leaks.
Another thing I would attempt to do is first locate your DPC in the side wall. Measure down , using the front one as reference, if required. Then I would drill a hole as low as possible through the party, use a long drill and go carefully, so you can work out how much blockwork you are going through, and if a cavity exists and also if the hole ends up under your neighbours under floor soil or in fresh air.
One point that has occcured to me, as I had a chemical injected DPC that was successful is, where is the line of holes? Also some underfloor ventilation will help, though not cure the problem (holes under the front door).
Frank

 

[drpepe]

I do not believe that lime plastering will solve much. As soon as you decorate the surface you reduce the "breathability" and you really don't want moist air in your house, cos' it eats up your heat as it evaporates.
I would did up that sewer pipe to see what all the spare inlets do. While you at at it, pull the plug on a bath full of water to see if there is any flooding/leaks.
Another thing I would attempt to do is first locate your DPC in the side wall. Measure down , using the front one as reference, if required. Then I would drill a hole as low as possible through the party, use a long drill and go carefully, so you can work out how much blockwork you are going through, and if a cavity exists and also if the hole ends up under your neighbours under floor soil or in fresh air.
One point that has occcured to me, as I had a chemical injected DPC that was successful is, where is the line of holes? Also some underfloor ventilation will help, though not cure the problem (holes under the front door).
Frank

thanks Frank.

• i can see the dpc on the front elevation (it is below the level of the block paving, but i have dug a trench to expose it and the 3 airbricks located in the front room). If you use assume dpc is same level in the party wall it is well below the neighbour's front step.
• Presumably there are DPC injection holes behind the plaster around skirting level? We have the paperwork for the chemical DPC which suggests that entire hallway wall was treated - the presence of the new plaster supports this.
• I will try the bath emptying thing - although the soil under the hallway seems uniformly damp (not wet), rather than much damper where a potential leak might be.
• When we dug out the subfloor, we put an airbrick under the front step (none was present previously), and cleared the whole subfloor of debris and lowered it slightly. The problem with ventilation is compounded by presence of only one airbrick at the rear to the right hand side of the conservatory (see plan in prev post). The cowboys who built the conservatory just blocked up the existing air bricks, rather than ducting through. Also the kitchen is solid floor.
• Drilling through the party wall and digging out the sewer pipe will have to wait til we get the builders in to do our extension, i think!

 

[cAtLeYx]

A thought.?

 

[drpepe]

A thought.?

View attachment 87539

Great diagram, and exactly how i think the setup is here.

Every wall in the house has a step-out (part of the foundation) as pictured in your diagram. See the picture below of under the front lounge floor - you can see the wall plate sitting on this step.

View media item 77343
If the construction is as your diagram, presumably this is a problem caused by shoddy construction back in the 1930s?

The question is what to do about it? I can't really lift my neighbour's floor to get it tanked or dig his subfloor out so it doesn't bridge my DPC?

 

[cAtLeYx]

Could you confirm if the DPC is evident and at which location? Is there an indication that water ingress is above or below the the assumed DPC?

 

[drpepe]

Could you confirm if the DPC is evident and at which location? Is there an indication that water ingress is above or below the the assumed DPC?

I can see the DPC (black line of ?bitumen) from the outside all along the front wall.
I have also seen it inside, along the foundation 'step' to the interior wall in the hall, and inside the mat well (the front door step is cast onto it) but I admit not having seen it in the party wall. But i haven't actually looked for it there yet - I will do asap.

I don't have any idea of ingress either tbh. All i can say is that there is evidence of damp all along that wall, both in the hall (the damp line pictured, & the stud partition in the doorway), and in the kitchen (damp smell).

 

[Chud]

What I find odd is this picture:

I find it odd as it would indicate to me that your DPC is working as the wall only gets damp from 1.2m upwards...so seeing that I would be wondering if water is coming down the wall then being stopped by your DPC? Is it a continuous damp or does it get noticeably worse in wet weather or any other time?

If you have an old style boiler with a gravity fed system with header tanks etc. up in the loft it may be worth checking that none of the ballcocks are continuously slow'drip filling their tank - if they are it could indicate a pinhole leak in your pipework?? (although why it would go near what was your external wall is another matter but having a house of the same age I wouldn't discount anything without checking it!)