Damp problem

[Davethedrum]

Hello,
I have recently bought a terraced house in the North West and am having trouble figuring out what to do about its damp problem. After reading about rising damp and how it is commonly misdiagnosed I am not sure of the right the way forward and would gratefully receive any input. I would rather find a ventilation solution or install a physical DPC rather than use a chemical DPC which I see as a last resort. I was wondering if @pigletjohn would be able to help me?
The floor level is about the same as the ground outside (both at front and back) and the pointing on the front is cement-based. There is a cracked drain at the rear. It has been unoccupied for about 9 months to a year and doesn't have a water meter. I can't tell if it has a DPC but today managed to take some photos of what could be the original one. Any comment on whether this is a DPC would be very welcome. I will find a way to attach some photos.
Thank you for any help you can give. I will be ready to answer any questions.

As the boiler has a pressure gauge, any leaks from the radiator pipes would show up as loss of pressure. If you have no water tanks or cylinder the other probable source will be mains pressure water or drains.

It is possible that you might have a leak from the hot or cold tapwater pipes. As the kitchen floor is concrete it would be fairly typical to have a leak from the supply pipe under there, often at the elbow where it turns up to rise through the floor, encouraged by cavitation corrosion. Leaks under concrete floors can't be seen, but the the floor and the adjacent walls will be wet unless a damp-hiding treatment has been used to conceal it. A leak in this position should be detectable by the stethoscope.

Tapwater pipes are mostly in the wall and ceilings, and tend to show a round damp patch through the plaster, mostly in or near the bathroom or kitchen.

I am sure that your drain gullies are leaking into the ground and that your DPC is bridged at the front at least.

Damp-concealing treatments are a great nuisance. Not only do they fail to repair the source of water, they also hide its location to make it more difficult to find.

The dryzone products might have a place when it is impossible to repair the source of water, such as in some stone walls, but I think your house has a slate DPC and that it will be possible to repair leaking pipes and drains, which I think are the probable sources of water.

p.s.

the picture of your small tank looks like it has water in it. Are you sure it has been decommissioned?

If it has water in it there must be a pipe topping it up, and possibly another pipe still running down into the house.

Hello @PigletJohn,
Thank you for your posts. I forgot to mention that the pipes are copper. Yes, the small tank is decommissioned - the bit that looks like horizontal water in the picture is actually vertical and just a different colour because it's below the old water line.
I'm not sure if the picture with the slate in it www.engineeringadmissionsassessment.com/photos.html is a bit misleading. The slate on the top left of the picture just lifts out and looking around the subfloor void I can't see an obvious continuation of slate. However, I think the felt observed on the house up the street is promising for a DPC (perhaps I am being too optimistic though).
There aren't any round damp patches and no obvious signs of a leak indoors. I am planning to replace the (lead) supply pipe anyway. Unfortunately, just now, a tradesman has cut through an external water pipe so I have had to turn the alley stopcock off which means that the stethoscope and boiler pressure will have to wait a few days. I can ask my plumber to look for leaks as well though.
Do you think this would be a viable plan:

Excavate at front and back at least to the DPC
Repair front gulley
Replace supply pipe
Install air bricks front and back (maybe one of these at front and back as well? www.builders-superstore.co.uk/product/ventilation-fan-sub-floor-mains-powered/)
Replaster with something breathable such as lime. I believe replastering is necessary due to hygroscopic salts but please correct me if I have this wrong.
Use stethoscope/boiler pressure/plumber to check for leaks in the meantime.

The surveyor predicted there wouldn't be a DPC and said that the best approach would be to cut in a physical DPC but I am hoping this won't be necessary given the above and with the above plan.

Thank you again for your help - I am very grateful.

"Excavate at front and back at least to the DPC
Repair front gulley
Replace supply pipe
Install air bricks front and back"

yes, those are all good moves.

I don't think you need a fan. Any wind will help air to blow in one side and out the other.

For the excavation, dig until you see some sign of the original ground level, then another nine inches. You may find the brickwork spreading outwards and getting wider ("footings"), do not dig beneath them. You may find, especially if built with lime mortar, that it has washed away and the joints are nothing but mud. In this case, excavate only a couple of feet width at a rime, hose out the mud, pack the joints with sand and cement mortar, give it a couple of days to harden, do the next couple of feet. As it is below ground level it need not be very elegant, and there is no need for the wall to "breathe". You can get a pointing gun, like a cake icer, to help you ram the mortar into the gap. I don't know if hire shops have them. Cement mortar hardens very well in damp conditions, it does not need to set by drying out.

Do the wall before you dig out the gulley. The hole may be deeper than you expect before you reach an undamaged pipe.

You can fill in the trench in front of the wall with large pebbles or cobbles. These allow free draining of water and do not carry damp by capillarity. You can use clean broken brick or concrete and just put pebbles on the top for ornamention if you want. You are filling it in so you don't fall down the hole, and to prevent earth sliding into it. There must be no fine material smaller than a pebble or it will hold damp.

The height should be nine inches below the DPC, if there is one, to prevent water splashing up in heavy rain. As you are on a slope you may need to terrace or step the front garden in some way.

DPC became common in different towns at different times, mostly about 1875.

It is possible to saw a horizontal slot in a wall and insert a DPC but this is quite rare.

Chemical injections are useless.

In clean, unplastered brickwork, exposed to the air, damp will not usually rise more than two courses, or nine inches. Digging out the base, removing earth and rubbish under the floor, and opening the airbricks will allow ventilaton to evaporate water off the exposed bricks. Repairing the drains and other defects will reduce the amount of water being added to the wall. Damp will stop at the point where evaporation from the surface matches or exceeds water being absorbed. Any plaster or render encourages absorbtion and discourages evaporation, but lime is better than cement or gypsum. Inside the house, plaster above the skirtings, but not behind them. You can space the skirting off the wall with an 18mm horizontal batten along the top and bottom. The plasterer can work to the top batten. Leave the skirtings off until the wall has dried.

p.s.

if you have a damp ground-floor chimneybreast, the problem is slightly different.

Hello @PigletJohn,
Thank you for this detailed post. I can now make some steps to book someone to carry out this work. I am grateful for your input as I was always sceptical of injections/tanking so it’s great to have a different plan.
You have shared your knowledge freely and I am happy to do the same. My main area of expertise is all types of maths and physics tuition, particularly for Oxford and Cambridge entry so if you or anyone you know would benefit from advice in this field please ask me.

Hello @PigletJohn, thank you again for your advice regarding my damp problem. I have people booked to do air bricks and am finding someone to repair the gulleys and lower the ground level. I had a plasterer round who said that he thinks it’s mostly down to the property being unoccupied and it doesn’t need lime. He suggested applying SBR before replastering normally. I’m concerned that the SBR would be the opposite of letting it breathe-please would it be possible to advise me on this? Many thanks again.

I agree with you. it's a rubbery coating. So it's a damp-concealing product, not a cure.

Can you afford to wait and let the wall dry out before replastering? If you improve the ventilation and replace the waterpipe you may reduce the damp enough not to need special products.

Lime plastering seems to be a specialist job, and he might not be skilled/keen on it. This may influence his advice. I've had it done where the main contractor called in a lime specialist for a couple of days. You can put a porous paint on it and will look OK.

p.s.

clean brickwork, with the plaster hacked off, can dry quite quickly if you put a household or desk fan (not a fan heater) blowing on it to speed evaporation for a week or so.

You can also hire big builders' drying out fans, used with dehumidifiers, but I don't think yours is so bad. They are noisy.

pps

I have used similar products in the past to try to tank an outside wall to stop the water getting in, but it doesn't work well. Water can still get into the wall from underneath, through the foundation, so leaving it bare to allow drying out is better, especially if you can trench the ground to expose more bricks.

I know an organisation that used bituminous tanking on the outside of reinforced concrete underground structures before covering up, and they are notoriously damp.

This thread has inspired me to try and fix the damp smell in two areas in my Edwardian terrace house, OP I hope you are able to fix your damp issues. I also live in the NW and have high rainfall, I think this could be contributing to it.

I have a damp smell coming from a cupboard in my kitchen along the side return. To try and fix it, today I have removed a wooden trellis from the wall on the outside, it was painted underneath and the paint was peeling, is this caused by damp? The trellis was installed by owner before the previous one, they moved the outside door in the kitchen, didn't do a very good job with the new brickwork and put the trellis in to cover it up. I think there may be gaps at the bottom of the brickwork, where the step would have been as I've had slugs and mice in the kitchen. I have also removed a wooden step from the outside door in the dining room, adjacent to the damp cupboard. It had ventilation holes in it, however it was mostly blocking an air brick. It smelt damp underneath, I have cleaned the air brick and removed the brick which was propping it up. The brick was in the corner, under the outside of the door and was stopping air getting to both of the outside walls. Does this sound like it could be the fix for the damp?

Other issue is at the front of the house in the living room, some days there is a damp smell. There are no signs on the inside wall. I've just noticed that the drain in the corner has moss on its slope and some plants around it. I'm planning to clean it and cut back the plants right next to the drain and in the bed about a foot from the wall. I've cleared the little weeds growing in the gravel drainage channel next to the wall. This was put in by the previous owners. I was going to get a new front door for the porch as it has a huge gap underneath, I'm reconsidering as I have noticed there are ventilation holes in the original wooden step under the inner front door.

@PigletJohn @dontbenastyhaveapasty Any advice would be great, thank you.

@dollsmouse8

This thread has inspired me to try and fix the damp smell in two areas in my Edwardian terrace house, OP I hope you are able to fix your damp issues. I also live in the NW and have high rainfall, I think this could be contributing to it.

I have a damp smell coming from a cupboard in my kitchen along the side return. To try and fix it, today I have removed a wooden trellis from the wall on the outside, it was painted underneath and the paint was peeling, is this caused by damp? The trellis was installed by owner before the previous one, they moved the outside door in the kitchen, didn't do a very good job with the new brickwork and put the trellis in to cover it up. I think there may be gaps at the bottom of the brickwork, where the step would have been as I've had slugs and mice in the kitchen. I have also removed a wooden step from the outside door in the dining room, adjacent to the damp cupboard. It had ventilation holes in it, however it was mostly blocking an air brick. It smelt damp underneath, I have cleaned the air brick and removed the brick which was propping it up. The brick was in the corner, under the outside of the door and was stopping air getting to both of the outside walls. Does this sound like it could be the fix for the damp?

Other issue is at the front of the house in the living room, some days there is a damp smell. There are no signs on the inside wall. I've just noticed that the drain in the corner has moss on its slope and some plants around it. I'm planning to clean it and cut back the plants right next to the drain and in the bed about a foot from the wall. I've cleared the little weeds growing in the gravel drainage channel next to the wall. This was put in by the previous owners. I was going to get a new front door for the porch as it has a huge gap underneath, I'm reconsidering as I have noticed there are ventilation holes in the original wooden step under the inner front door.

@PigletJohn @dontbenastyhaveapasty Any advice would be great, thank you.

I recommend you start a new thread, otherwise your details will get mixed up with the other one on this thread, and both of you are liable to get confused advice.

Thanks, I've started another thread.

Hello @PigletJohn,
Thank you for your messages. I can let the wall dry out and thought I would include the following pictures as an update now that the affected plaster has been knocked off and the flags have been removed in the yard. In this message are pictures of the back of the dining room which has dry bricks where the damp was highest but a couple of wet patches nearby (marked on the plan as W). The left of the dining room appears quite dry. I have got the desk fans as you suggested. There is no need to comment now if this doesn't change anything - it's more of an update than a query.
Thank you again.

and the left of the dining room and an updated plan.

and the yard outside the back of the dining room.

@Davethedrum

and the yard outside the back of the dining room.

Good to see work in progress.

the ground looks very wet. Hopefully repairing the drain will make a big improvement. If you hose the mud off the wall, you might see a DPC either just below or just above the oldest airbricks. It's common to see ground level raised above the DPC, causing damp bridging, so look out for that. When the brickwork is exposed to the air by digging, you should see it start to dry out. Old mortar may have gone and been replaced by mud. Keep taking pics and this will help highlight any change.

ATB

(must just comment that this is a great and very helpful thread, thank you, PigletJohn)

@BlueMongoose yes it’s been most helpful and I am very grateful. My current theory is that the wet ground at the back made the back dining room wall under the window wet which caused moisture to spread leftwards and upwards on that wall. Then I think the other walls presented as wet because of condensation arising from the first wall and the house being unoccupied (these walls are dry behind the plaster). There might be another (smaller) issue at the front but much progress has been made.

Hello, just to update I have dug down a bit at the back and it looks promising. I found quite a large gap under the kitchen door (arrowed in red), big enough to put my hand in and reach the back dining room wall. This point was also where the damp seemed worst in the dining room. I am hopeful that exposing the base of the exterior wall is going to make a significant difference. Thanks again.

It looks like your garden is drying out well, hope that helps and you are able to fix the issue.

Hello @PigletJohn,
Thank you again for your help. I have dug down a bit more and this has raised a few queries, I hope that's OK. Do you think the bricks are dry enough to replaster? Also, I think I see evidence of a slate DPC between the lowest brick and whatever is below that - please could you let me know if you think that's right? Also, finally I was wondering which course of bricks would be best for the airbrick(s)? The interior floor level is about the same as where the paint starts. Many thanks again.

Possible DPC

@Davethedrum

Possible DPC

It does look a bit like a DPC. You need to dig down some more and it will become clearer. When the house was built the DPC will have been two brick courses (sometimes more) above the external ground level, including paving. Raising the ground level is a very common cause of damp.

As you dig, you may find the old lime water has washed out of the joints. You can hose out the mud and re-pack them. Cement mortar is much more durable below ground, and, below ground, there is no "breathing" to worry about.

The bricks will not be dry enough to replaster yet. But if you are able to expose the DPC and expose the bare bricks you are well on the road go drying the wall.

The airbricks can go either above or below the DPC. They must be below the internal floor so air can circulate well, and at least one brick above ground level to prevent water splashing in.

You may find the bricks spread out as the wall becomes wider below ground level, this is brick footings, a way of making foundations. No prob, but don't disturb or dig below them.