Penetrating Damp in Victorian House

elenapopaphoto

stuart45 said:

Is there any debris in the cavity?

Builder says there shouldn't be, but we're going to have this checked next. thank you!

elenapopaphoto

Doozergirl said:

elenapopaphoto said:

Apodemus said:

I'm not sure that the ACO drain was the best option - assuming what we are seeing is an open plastic drain with a grid cover.  That will do a good job with any surface water but might be leaving you with damp soil and ground water against the wall at a higher level than your internal floor.  I would have thought that a decent french drain would have been better although that might have had to be located slightly further out from the foot of the wall, to avoid your minimal foundations.

Even if everything was fixed properly, it might take a good few months for the wall to dry out, so I wouldn't necessarily give up hope just yet.  A rough rule of thumb is often given as a month for every inch of thickness in the wet wall. and you probably have at least eight or nine inches of concrete block there to dry out.

Doozergirl said:

As above, but I'll be more brave than Apodemus and say that the ACO drain definitely isn't appropriate.  For the same reasons.  You cannot have anything touching the wall above the floor level. 

You need a French drain, with the ground level immediately adjacent to the wall at 150mm below floor level.  Your patio can be higher but it must definitely be sloping away from the house.  If the patio isn't sloping away then you can use the  ACO drain, but it MUST be below your floor level.  

You won't destabilise foundations because that ground level can't always have been that high or it would always have been soaking wet. It's almost always subsequent landscaping that causes the problem. 

Thank you both for your input. I should probably add that the trench beneath the ACO drain was filled with cement. So there is only cement underneath the plastic, then the clay. Does that make any difference at all? Will we have to undo all this and install a French drain? 

In a word, yes.  There should be nothing touching the wall beyond 150mm below what would be the original DPM, your floor level.  It doesn't matter what it is.  Concrete, paving, Aco drain, soil, foliage.  Nothing.  
 

That's a bummer. You'd think a seasoned builder would know better than to add another layer of concrete on top of an already too high patio (to 'level it off'). Our original request was for all the concrete to be removed but as you know, he said the thing about foundations being too shallow for that. My instinct has always been to never layer stuff on top of something that isn't quite right. Guess I should have listened to my instinct
Thank you so much for your insights.

elenapopaphoto

Doozergirl said:

tacpot12 said:

Doozergirl said:

tacpot12 said:

Do you know if the floor has a DPC under it? You might be able to see the polythene sheet around the edges of the floor. 

 If it doesn't, then you have another problem. If there is no DPC under the floor and none in the walls, you might be better off knocking the extension down and restarting with proper foundations. Although this will be expensive, it will cure the problem and give you complete confidence that that part of the house will be dry. You will also be able to improve the insulation under the floor and in the walls, to get better efficiency. 

That's a bit extreme!  As long as a house can breathe, the lack of a DPM isn't the end of the world.  There will be many, many kitchens without DPMs without serious issues.  The main problem here is the ground level being higher than floor level.  

Yes, I realised that it was a bit extreme, but the OP did say that they had already had advice not to drop the patio level as it may destabilise the building. If the floor has no DPC under it, damp is going to be a persistent problem. I agree that making sure both the inside and outside walls can breath will help in the absence of a DPC, but the OP has been waiting a long time for this to happen already, and the ACO drain was put in to make things better so it was already a problem even before the ACO drain was installed. I just wonder if remediation to the walls is really capable of sorting this out. 

I've always wondered how watertight the ACO drains are when clipped together. It is possible that some rainwater is leaking from the drain into the foundations and not being taken to the sewer?

The ACO drain has been fitted entirely incorrectly in the wrong place.  I suspect the builder is talking rubbish about the foundations being a problem.  I've said this all above, but that extension was not built with the ground level as it now appears.  

Back in the days before DPMs, houses did not have them at all.  If the floor is able to breathe, they shouldn't be a problem.  I can see what the main problem is.  If the excess water ingress stops, under the floor will also eventually dry out enough to not be a major problem. A liquid DPM could always be laid to the floor to protect any new flooring above it - knocking the thing down shouldn't even be a consideration.  

Checking that all the water from the drains goes to the right place is a very good idea. 

We have painted the concrete floor with two layers of bitumen paint, but I suspect this won't do much unless we fix the patio height problem, correct?

FreeBear

elenapopaphoto said:  It is a 1900 Victorian terrace, with a rear two storey 'extension' that was added to all houses in the neighbourhood, but not sure when - could be 30s, could be 50s.

Have a look at historical OS maps from 1900 onwards, and you should be able to pin down when the extension was added to within 10 years or so. Start here - https://www.old-maps.co.uk/ - Your local records office (main library ?) may have more detailed maps available.

1930s construction would have had a DPC incorporated in to the wall - It will most likely be level with the bottom of the door frame (now buried by the drainage channel). I would be very surprised if there wasn't a foundation of some sort. Although I wouldn't expect it to be very deep. 150-200mm below the DPC would be my guess.

If there really isn't a DPC at the base of the wall, then having gypsum plaster internally is going to be a problem - The stuff doesn't like to be wet for a prolonged period of time. The gypsum is water soluble, and the plaster turns to a powdery mush fairly quickly. One of two ways to combat this...

Strip off the gypsum plaster and slap a waterproof render on the wall up to a height of 1m - It will mask the problem for a few years before it needs doing again (so not a cure). Who ever does this will recommend injecting snake oil a chemical DPC...

Alternatively, strip off gypsum plaster and replaster with lime - Whilst it still doesn't cure the problem, it will tolerate being damp and won't turn to a mush. If you want to add a bit of colour, mix some pigment in to the top coat rather than slapping paint on.

stuart45

elenapopaphoto said:

stuart45 said:

Is there any debris in the cavity?

Builder says there shouldn't be, but we're going to have this checked next. thank you!

You might also find that water is entering the cavity from further up the wall, and when it runs to the bottom has nowhere to run out. 

elenapopaphoto

FreeBear said:

elenapopaphoto said:  It is a 1900 Victorian terrace, with a rear two storey 'extension' that was added to all houses in the neighbourhood, but not sure when - could be 30s, could be 50s.

Have a look at historical OS maps from 1900 onwards, and you should be able to pin down when the extension was added to within 10 years or so. Start here - https://www.old-maps.co.uk/ - Your local records office (main library ?) may have more detailed maps available.

1930s construction would have had a DPC incorporated in to the wall - It will most likely be level with the bottom of the door frame (now buried by the drainage channel). I would be very surprised if there wasn't a foundation of some sort. Although I wouldn't expect it to be very deep. 150-200mm below the DPC would be my guess.

If there really isn't a DPC at the base of the wall, then having gypsum plaster internally is going to be a problem - The stuff doesn't like to be wet for a prolonged period of time. The gypsum is water soluble, and the plaster turns to a powdery mush fairly quickly. One of two ways to combat this...

Strip off the gypsum plaster and slap a waterproof render on the wall up to a height of 1m - It will mask the problem for a few years before it needs doing again (so not a cure). Who ever does this will recommend injecting snake oil a chemical DPC...

Alternatively, strip off gypsum plaster and replaster with lime - Whilst it still doesn't cure the problem, it will tolerate being damp and won't turn to a mush. If you want to add a bit of colour, mix some pigment in to the top coat rather than slapping paint on.

This is interesting - thank you. I had a look and to my surprise, it looks like the 'extension' was already there in 1900, which I assume means the likelihood of any DPC having been installed at that point is low? Just goes to show how many self proclaimed experts have wrongly guided us during the purchase/renovation of this house. 

Yes, you are absolutely right. the wall inside was only just recently plastered - roughly 3 months ago - and there is already a crack, slight swelling and layer of white fuzzy stuff which I assume is salt. I'm just baffled at my builder who clearly thought doing all this was a great idea.

Thank you very much for your suggestions. My gut feeling is we will have to wreck the patio again to lower it as much as possible - when/if we can afford it. What a waste of money this has been so far...

Apodemus

Ok, I think you need to go back to the drawing board and get a fresh pair of eyes on your property!  It didn't quite make sense before:  A terrace where all the houses had similar rear "extensions"; concrete block walls, with brick window surrounds and corners; a 30s or 50s extension with no foundations...

Now that we know the "extension" was there by 1900, perhaps in fact it is part of the original house (which is why they are all the same along the terrace).  We can, perhaps then postulate that the wall is not concrete blockwork, but brick, with a later cement render (or at least that it was originally built as brick and parts remain).   This may also help to explain the window issue - was one of these openings originally a door, which was blocked up?   Do you know any of the neighbours well enough to be able to ask about their houses for comparison (while obeying local lockdown rules, of course! ).

So the first thing I'd do is start investigating the actual structure a bit more.  I'd attack some of the interior gypsum plaster and expose a lot of the damp wall to see if it really is all concrete blockwork.  if nothing else, getting the gypsum off will help the wall structure to dry out. If that shows up brickwork, then you could look at removing the exterior concrete render - although this is unlikely to come off cleanly and might need to be replaced by a lime render. 

As mentioned above the high ground level is probably still your biggest problem, but if you've got a sodden brick wall faced with cement render and gypsum plaster, it will take an age to dry out even once you sort out the ground level.  You may need to let that wall breathe. 

elenapopaphoto

Apodemus said:

Ok, I think you need to go back to the drawing board and get a fresh pair of eyes on your property!  It didn't quite make sense before:  A terrace where all the houses had similar rear "extensions"; concrete block walls, with brick window surrounds and corners; a 30s or 50s extension with no foundations...

Now that we know the "extension" was there by 1900, perhaps in fact it is part of the original house (which is why they are all the same along the terrace).  We can, perhaps then postulate that the wall is not concrete blockwork, but brick, with a later cement render (or at least that it was originally built as brick and parts remain).   This may also help to explain the window issue - was one of these openings originally a door, which was blocked up?   Do you know any of the neighbours well enough to be able to ask about their houses for comparison (while obeying local lockdown rules, of course! ).

So the first thing I'd do is start investigating the actual structure a bit more.  I'd attack some of the interior gypsum plaster and expose a lot of the damp wall to see if it really is all concrete blockwork.  if nothing else, getting the gypsum off will help the wall structure to dry out. If that shows up brickwork, then you could look at removing the exterior concrete render - although this is unlikely to come off cleanly and might need to be replaced by a lime render. 

As mentioned above the high ground level is probably still your biggest problem, but if you've got a sodden brick wall faced with cement render and gypsum plaster, it will take an age to dry out even once you sort out the ground level.  You may need to let that wall breathe. 

Thank you so much for taking the time to get back to me. I think we (and several others) were fooled into thinking the rear wing was added to the house much later because of the cement blocks in question. I've attached a few photos here - the house isn't rendered on the outside, just painted, and you can see the outline of the blocks through the paint if you look carefully. I also posted a photo of a vent hole so you can see the material. There are several other holes drilled into the wall that look the same. So it's made out of these blocks, but stitched together at the corner (and window surrounds) with bricks. This is only for the rear wing, the rest of the house is all brick. The neighbours looks exactly the same.

One of the windows was indeed a door back in the day, but it had been bricked up badly by a previous owner. They had also bridged the air cavity in the process of installing a window there, but my builder claims to have cleared it out. 

Does this mean that the interior gypsum plaster is ok to stay, and we should concentrate efforts into lowering the patio level? Or should we have lime plaster everywhere regardless?

I'm not really sure how we could change the slope of the patio so that it slopes away from the house - the house is on a hill in two directions, so the garden slopes upwards from the house, and so does the neighbours' house. You can tell from one of the photos. Any suggestions? Or would the slope not matter if we had a French drain put in?

Thank you so much again.

Doozergirl

You may well need the ACO drain in your french drain because of the hill, just at a lower level so it isn't breaching anything. It would be cheaper than lifting an entire patio and would get excess water away.   

Keep an eye that it doesn't get blocked, with regular maintenance.  

stuart45

It does not look like blockwork to me. It looks more like render with Ashlar marks, which was quite common. Done with a straight edge and a bent nail to look like stonework.