Filling a crack in a wall, preventing rising damp in new mortar

[MisterBoy]

We've discovered a crack/gap in our solid brick external wall the bottom few courses of bricks. It was previously hidden until we prepared the house for repainting and appears to be historic/stable but at the bottom is a good finger width wide and in hindsight the position lines up with a very damp area inside... We had thought the DPC had failed but now think water is simply getting through the hole between bricks on the first course as rain pools here.

Pointing it seems an obvious solution but won't regular mortar allow rising damp? Is there some simple additive you can put in concrete in such cases? We've used waterproof render before but I've no idea what is special about it.

 

[JohnD]

Walls are normally made of bricks and mortar. Neither of them "causes" damp.

"Rising damp" is a vague term and there is usually some particular reason for excessive water in a wall. Very often a leak. Post some pics, inside and out. Show all nearby drains and downpipes.

If you have lime mortar, it often washes away from a long-term leak such as a broken drain, leaving gaps in the mortar.

 

[MisterBoy]

Well not sure I agree with that. It's a 1860 Victorian solid brick house... rising damp is pretty much a feature because while bricks and mortar don't cause damp, they are permeable. Traditionally, you just decorated around it and accepted it Now we have DPCs precisely because rising damp is a common issue.

DPC was retro-fitted at some point but if I put in new mortal vertically from the ground up, past the height of the DPC, that will surely act as a bridge for water, wicking it up past the DPC and longer-term causing a way for water to get in. We all know how good water is at finding any little way in

I'll try to get a photo later.

 

[JohnD]

It sounds like you have silicone injection, which is not much good.

Damp courses only became compulsory in 1875 so your house may not have one.

Water does not rise very far up clean bare brickwork, with no plaster or render to help it.

The photos will be useful.

 

[MisterBoy]

I guess that's one reason they panelled walls - I thought it was because the brickwork was wet and they wanted to hide it but sounds like actually it's as much because bare brick meant the water couldn't get very far.
Plaster is a nightmare for damp, to state the obvious. One tiny point of ingress seems to be all it takes

 

[MisterBoy]

Managed some photos though it's under scaffold so not the best quality.
The crack is a few feet long but only widens very near the ground. It 'jumps' to the right the very last course which is where there's actually a gap right where water runs past.

The bricks to the left were part buried and their mortar seems pretty badly eroded as well. There was a dry stone wall here which is a) why that bit isn't painted b) why we didn't see it sooner. We thought the damp was simply due to the dry stone wall up against the house.

The render looks really bad at the base because we started removing loose bits. Not sure that external render isn't making it worse!

We don't think there is active movement at least.