A little off-topic, but...damp prevention

[Deadeye]

There is a wide range of experience here, amateur and professional, so...

Victorian end terrace house. Roof in good condition (replaced 2 years ago).

Rear elevation rendered at bottom (ground floor) but bare brick above; pointing not great. Chemical DPC injected at foot ~10 years ago. Render finish to windows poor and the top "edge" where it goes back to being plain brick is scrappy and flat. Looks like a bad job.

Side is brick (solid wall), repointed well in top half, painted below on ground floor. No DPC

Front elevation rendered; no DPC

All walls come down to paved ground; no soil and below floor level. Airbricks clear.

There is quite bad damp on the side and back and a bit at the front round the base of the door. The paint of the side is flaking off and some of the brick feels soft in places.

What to do? Options - from various people who've come and sucked their teeth include (but not limited to):

- French trench all round. I've heard mixed reports

- Injection DPC again - also mixed reports. This is the go-to solution of damp companies, whose business is, after all, to sell injection DPCs

- Repoint rear and try to get a proper drip line onto the rendered part

- Render the back and side fully

- paint sealant on the bricks then paint; again seen warnings against this

At the moment I'm inclined to fully render/re-render the back and side, but interested in advice!

Thanks!

 

[rogxwhit]

Am I picking up that it's non-cavity construction?

 

[Adam W.]

Take off render and re-point in lime mortar if the bricks are good enough. Cement render on Victorian brick is known to cause damp problems and is generally regarded in the conservation industry as shiz.

Here's some SPAB blurb.....https://www.spab.org.uk/advice/lime-renders-vs-cement-renders

 

[Deadeye]

Am I picking up that it's non-cavity construction?

Yes, solid wall (Victorian)

 

[Deadeye]

Take off render and re-point in lime mortar if the bricks are good enough. Cement render on Victorian brick is known to cause damp problems and is generally regarded in the conservation industry as shiz.

Here's some SPAB blurb.....https://www.spab.org.uk/advice/lime-renders-vs-cement-renders

Thank you.
Unfortunately the render seems to remove the brick face when chipped away (we scratched some off when fitting an extractor fan to the kitchen) so I fear that might just end up in re-rendering

 

[sammy.se]

Hi,
Sorry to hear you are having damp problems. I live in a similar, single skin Victorian brick house. Please see my thread here:
Damp in Victorian house dining room

1) Firstly, you almost certainly have a slate DPC. Lots of people say you don't have one in old houses, but 99% of the time it's there.
2) The way our houses are built, they need to breathe. It's the way they are designed and it's the reason they have lasted hundreds of years (or 120 years in our case).
3) for them to breathe, you can only use lime or chalk paint, both inside and out. You can only use lime plaster/render, inside and out.
4) The solution to your problem is simple, but also a pain: Remove all cement and paint; remove all gypsum based plaster internally (on the external walls you have a problem with)
5) Re-render internally with Lime.
6) Externally, re-paint with lime paint, or leave bare bricks.
7) Check your gutters and down pipes and drains. Even a trickle of water gets into the bricks (they are sponges), then get stuck between cement and modern paint, with no where to go. (All this 'micro porous' claims of modern paint isn't up to the needs of buildings like ours)
8) check for leaks inside, e.g. a water mains under your floor boards
9) How low is ground level outside? It needs to be 6"/150mm below your original slate DPC. If it is, great. If it isn't you'll need to fix that (see my thread)

Hope this helps.
What I am saying sounds counter intuitive, but it's the only right solution.
I'm happy and damp free for 2 years now.
Happy to speak with you on the phone if you want to learn more about my damp journey.

sammy

 

[Adam W.]

Thank you.
Unfortunately the render seems to remove the brick face when chipped away (we scratched some off when fitting an extractor fan to the kitchen) so I fear that might just end up in re-rendering

You can always re-render the bricks with lime render.

 

[rogxwhit]

I can't offer any answers but have a few randomly connected thoughts. I've come across solid brick walls that seemed to be in a semi-engineering brick that presumably is less porous than ordinary brick. So rain will have a harder time getting in but equally internal moisture will have a harder time getting out? Yours sounds softish? But solid walls will in any case tend to be colder (on the inside) and thus there's an increased condensation risk. Condensation is a common source of dampness. So I'm glad that your airbricks are clear. Have you checked the floor joists where they contact / enter the external walls?

A French drain at least could do no harm, but could well be waste of time. DPC injection is in my opinion snake oil, and would have no effect whatsoever on condensation dampness. Avoid.

A possible answer that is sure to be completely out of court for practical reasons could be external insulation. But I'd be wary of internal insulation, which can easily exacerbate condensation risks.

Choice of 'solutions' might relate to the porosity of your bricks, & thus the changing moisture gradients within the wall thickness? Cement render is usually a bad deal because of (1) breathability and (2) hairline cracks that suck rainwater in.

Sorry for woffling on. I hope something can be worked out.

 

[Spectric]

Rendering over solid walls with cement just stops them breathing and holds moisture in. As Adam has said lime mortar.

 

[Deadeye]

I can't offer any answers but have a few randomly connected thoughts. I've come across solid brick walls that seemed to be in a semi-engineering brick that presumably is less porous than ordinary brick. So rain will have a harder time getting in but equally internal moisture will have a harder time getting out? Yours sounds softish? But solid walls will in any case tend to be colder (on the inside) and thus there's an increased condensation risk. Condensation is a common source of dampness. So I'm glad that your airbricks are clear. Have you checked the floor joists where they contact / enter the external walls?

A French drain at least could do no harm, but could well be waste of time. DPC injection is in my opinion snake oil, and would have no effect whatsoever on condensation dampness. Avoid.

A possible answer that is sure to be completely out of court for practical reasons could be external insulation. But I'd be wary of internal insulation, which can easily exacerbate condensation risks.

Choice of 'solutions' might relate to the porosity of your bricks, & thus the changing moisture gradients within the wall thickness? Cement render is usually a bad deal because of (1) breathability and (2) hairline cracks that suck rainwater in.

Sorry for woffling on. I hope something can be worked out.

The bricks are London stocks I think; rather porous. It's all a bit of a mess - some painted (and ?sealed); some bare; some rendered. I'm really hoping to not have to completely re-render owing to budgetary consideraitonis as much as anything else!

 

[sammy.se]

Just don't re render with cement.

 

[pgrbff]

Thank you.
Unfortunately the render seems to remove the brick face when chipped away (we scratched some off when fitting an extractor fan to the kitchen) so I fear that might just end up in re-rendering

Cement render over the years cracks, only microcracks but it allows water in and once behind soaks in to the bricks and can't get out. If you do remove render and re-render, use a soft hydraulic lime mortar that breathes. French drains do work, they allow air to circulate rather than having wet top soil transmit water to the brick.

 

[davethebb]

Deadeye,
You don't say how high the damp goes up the walls, or how it is appearing, so assuming it is only a couple of feet or so it sounds like penetration from the local ground level. Is the damp affecting the joists?

It is likely the paint that was probably applied to resolve the problem in the first place but has now failed is allowing water to penetrate and not come out. The water is probably water runoff from the wall and splashing from the paved area (and possibly a small amount of rising dampness from moisture under the paved area local to the wall).

Firstly, I would remove all the paint from the wall up to about 1 mt or more from ground level, and if you can create a 400-300mm gap between the paved surface and the wall, dig down at least 300mm or so and then leave it for a year. Buy a cheap moisture meter and take readings inside and out and log then to see if it is making a difference. You need to leave it to see if it helps but also the wall needs to dry out anyway before you do anything else. This will probably resolve your problem.

Moving forward try and prevent the problem first by removing splashing at ground level, if you can't then you may need to replace the paint with something like lime and lime wash but backfill the 400-300mm void with gravel and a membrane (small plants may help as well as the reduce the splashing).

 

[pauljhaigh58]

Hi I have used a product called belzona 5122 I think used on listed buildings/ stone on very exposed areas
Pointing /substrate has to be sound first .it’s a clear liquid and is waterproof and breathable if you contact them with your problem they can advise found them very helpful (I am not connected to this company) and you can apply there products yourself or get there contractors hope this helps

 

[Limey Lurker]

Paint on the side wall will stop any moisture that gets into the brickwork at the top and sinks through the bricks, getting out except to the inside.

 

[MikeJhn]

I remember back in the 60's at Brixton School of Building they had various bricks types built into small walls in troughs of water to show that rising damp does not exist.

Most damp on solid walls is caused by something other than rain penetration, a knowledgable "Building Surveyor" or "Structural Engineer" would be able to pinpoint the problem, like leaking gutters, down pipes, or splashing from hard standings, you don't state where the damp is in the walls, but lack of internal ventilation can also cause damp in any type of wall construction.

 

[MikeJhn]

Ho done my normal thing and looked at the "Similar threads" list on the bottom left of a page and answered a post that it two years old, oh well still relevant.