Damp patch. Bay Window

[Willsgeorge]

I’ve recently moved to a Victorian mid terrace with a Bay Window. I’ve had companies around to look at the damp issue under the window. I was hesitant to go ahead with the work as I was sure there was a reason for the damp situation.
I’ve hacked away all the plaster internally and removed over a foot of soil and stone externally which was right against the wall (up to the air vent) I’m going to leave it to dry out and see what happens?
I’m just looking for advice what to do next? and if this was the right thing do do? Is where I’ve dug too low?
I hope to maybe reduce the level of the front garden to match the where I’ve dug out? Should the red bricks below the white render be hidden? I’ve attached some photos.
Any advice would be really appreciated. Cheers.

View attachment 235915

 

[JohnD]

there is most likely a DPC either just below or just above the original airbrick. Probably slate. You may see it better when you lift the floorboards and clear away the rubbish round the airbrick inside.

it is extremely common for numbskulls to make houses damp by heaping earth and paving against their walls. most likely that was the cause of your damp. The airbrick is also choked.

when you have found the DPC, remove any render or plaster or rubble bridging it, inside and out.

exposing your bricks like that will enable them to dry out. You should see a difference in a week or two. Do not dig beneath them.

you can hose out any mud between the bricks and repack with mortar if you want. I would.

when you refill the trench, use clean, large, free-draining material and use landscape fabric to prevent it getting clogged with mud or clay. Large clean stone or broken brick does not support damp by capillarity.

The reconstructed ground level should be nine inches below the DPC. More is fine.

 

[Willsgeorge]

JohnD Thanks for your advice!

 

[AsleepInYorkshire]

I've got to congratulate you on some great tenacity. You've done well to question the "expert" damp proofing companies. 10/10

I'd like, if I may to augment JohnD's earlier please. If there is a damp proof course, as John has said it will be slate. It's rare but they can fail. If the slates were overlapped or there's been subsidence the slates can crack. Therefore, when carrying out a risk assessment there's a small risk of damp from a failed slate dpc. I stand to be corrected but I think you've exposed the foundation brickwork. As John has said don't dig any further. I suspect you've already worked that out. My remedy is a little different to Johns. It's offered as an alternative that may or may not be of some help.

Once you've established where the dpc is, if there is one, then the ground level on the outside of the house needs to be 150mm below that. But this doesn't stop you bringing the ground level up by other means. I'd suggest a small width timber deck. The deck will allow the ground underneath to be completely empty and it will be supported from a timber bearer fixed to wall with dpc behind it. That's the first part of the plan. The second is to use internal protection to. So we're talking belt and braces. There are systems available that allow the plasterboard to "stand off" from the wall. They create a small cavity between the wall (which may be damp) and the plaster. The damp cannot get to the plaster and the plaster stays dry. Minster Insulation (Jewson Group) have a system (and I cant recall it's name) designed to cope in such circumstances.

AiY

 

[^woody^]

A fundamental problem that you have there is that rain will be penetrating the bricks and running down the wall and being locked into the wall behind that render. This will mean that the moisture will be creating dampness at low level which will move to the internal surface.

Whilst there may be other issues behind why the render was applied in the first place, the render needs to be removed before any damp investigation or remedy is carried out.

 

[Willsgeorge]

Thanks for your reply’s and advice.

I’m worried I might have dug too deep! I guess I can fill soil back in?

Before I hacked off the internal paster the damp marks were rising from the bottom - would this still be a external render issue? The plaster was a yellow sandy/ cement mix - I guess you wouldn’t recommend this for new plaster? I have some more photos below.

 

[^woody^]

Before I hacked off the internal paster the damp marks were rising from the bottom - would this still be a external render issue?

Water percolates down a wall and stops at the DPC, and then is held until it can evaporate. Inexperienced people don't realise this.

That is not to say that there is not a rising damp issues too, but what is certain is that that external render is doing nothing except creating a problem

 

[^woody^]

You may be better off lining the wall with polythene, and fitting plasterboard on battens, and extend the internal window boards. Check the floor joists if they go into the bay wall for rot at the bearings too.

 

[mrrusty]

Personally I think any talk of DPC is a red herring. The red bricks you can see will be the footings for the wall. There are two possibilities for dam in this section of wall. 1) it's going to be the coldest area in the room, so will attract condensation. 2) you still have the original sashes - great! - don't take them out. However, it is quite possible that water is finding it's way through or under the sash cill and running off the back of the stone cill into the wall. I would be checking/sealing any gaps in this area, and then I would do exactly as woody suggests above and extend the internal wooden cill and install insulation backed PB inside the bay with an air gap behind connected to the ventilated underfloor. If you use insulated PB it already has a vapour control layer so you won't need an additional membrane.

I also agree with Woody that the render is probably keeping damp in the wall and preventing it evaporating to the outside.

IMO condensation in victorian/edwardian houses is the prime cause of damp - they were designed to be ventilated with chimneys in every room, and once we seal them up, the warm damp air we create just by living finds all the cold spots - bottoms of solid walls, under bay windows, bedroom external corners etc and causes condensation.

The other challenge is hygroscopic salts - years and years of coal fires cause reactions between combustion products and lime mortars creating salts that are easily activated by wet trades or condensation. Once they migrate to the wall surface they draw more moisture out the air causing efflorescence and damp patches which are easily confused with penetrating damp. Uncapped and unused chimneys are another good source for damp in an old property.

 

[Eccles]

We went about it in a different way altogether in a Victorian house which we were renovating a few years ago:- Remove the plaster (you already did) then hire a specialist to impregnate the line of bricks around 150mm above ground level with silicone based fluid. The guy we used was not that expensive - about £25/hour at the time and it worked fine, just let it all dry out for three days then re-plaster.

 

[HERTS P&D]

You can diy it:

https://www.safeguardeurope.com/products/dryzone-system/dryzone-damp-proofing-cream

Andy

 

[mrrusty]

Impregnated damp proofing. Waste of money. If it's condensation it makse no difference whatsoever. https://www.heritage-house.org/damp-and-condensation/the-fraud-of-rising-damp.html

 

[Willsgeorge]

Thanks for all your help!

I’ve let external front dry out a bit where the red bricks are exposed and just below the air vent. Do I need to fill the back with soil over the red bricks or can I fill the whole area below the air vent with drainage gravel etc? Would there be too much drainage if just gravel?

Thanks!