Penetrating damp - how do you remedy it before insulating?

It appears there are a number of sources for the moisture
The electrician came today; when he removed the wet socket, the mortar at the back is wet. I think it’s penetrating in from outside .
We inspected outside and around the window, (sited above the socket to the left), there is a hole in the mortar and the seal around the window is heavily degraded.
In addition to this - the radiator pipes under the window are in the plaster wall - which are another potential cause of moisture being drawn in - Learned that info at the #LloydHamSchool​:grin::muscle:t3: So we’re getting that sorted.

Quote - cndensation drips down. I think we have that problem too, because the beading for the laminate was wet on the floor. Also I attached a picture of the paintwork to show how the wall is affected…

We know both the walls in that affected corner are exterior cold walls and are sometimes wet when we wipe them down to get rid off the blackspot mould.
The important thing for now is the electrics have been made safe and the socket fully removed from the wall.

Our next stop is get a new window fitted - we know we need one.anyway - and inspect and repair the pointing.
After that we’ll watch and see what happens.
I wonder about insulating those walls or replacing the plaster with other to prevent the cold wall condensation situation.

It’s the hallway and stairs underneath - these areas and the bedroom are on the gable end and front corner face of the house.

As the damp in the walls is clearly not rising damp there should be negligible salts dissolved in it, so there shouldn’t be an urgent need to replace the plaster. As you have identified the window/wall join, a hole and dodgy pointing I suggest waiting for those to be remedied. Use a dehumidifier in the affected room and wait as long as your patience holds out for any improvement.

When repointing include plasticiser and waterproofer in the mortar mix or use

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I’ve just noticed that you have older plaster with a modern skim coat. The base may be vapour open and the skim is not. That could be contributing to an accumulation of damp, as the original Victorian structure would have “breathed”.

And this brings about the question that’s I’ve been debating with myself
Do we go back to original breathable ?
OR do we use the modern less breathable materials to make this old house watertight? Would this route require us to move away from breathable materials altogether?
Do the Stormdry products block and seal the pores in the bricks…and will the plasticisers for the cement do the same ?
And if they do, does that mean we insulate with a non-breathable material and plaster over that with foil backed plasterboard or such like.
I know the paint hasn’t helped the case for breathing - it’s vinyl silk.

I think we have original lime plaster in the back room around the window - it’s the only window that doesn’t suffer a condensation problem.

What would you do?

The easy questions first. The Stormdry products do not block the pores, unlike sealants. This brings me to my first post above where I distinguished between sealants and waterproofers. Tests show that about 2% of “breathability” is lost. Sealants loose about 98% to 100% breathability if I remember correctly.

Any building has to be watertight, as in liquid water, but see below about vapour.

Now the trickier bit!

A structure that was designed to “breathe”, although unintentionally, needs to breathe unless a very skilfully designed and executed conversion plan is carried out by absolute experts. Breathing buildings can be airtight ones at the same time. This is because what these breathing buildings “breathe” is water vapour, not air.
It is a common belief that buildings need air but that isn’t so.

So, how is airtight and breathable possible at the same time? Easy peesy. The gaseous molecules of air are mostly larger than water molecules, so all you need to do is make your home airtight with layers that water can get through (so will hydrogen but we can ignore that) but atmospheric gasses can’t.

Although modern products are available that do this there are traditional ones that coincidentally do too. Or maybe it isn’t coincidence. Our ancestors would have discovered what products lead to a lasting comfy home by trial and error without understanding the science.

As luck would have it, 2cm or more of lime plaster or lime render meet the requirements. Assuming no gaps or cracks. In practice you need gaps to get in and out of and to let the light in, so special attention needs to be given to joins. Also, you can’t quite touch floorboards with the plaster as the boards expand and contract and damage the plaster, but get as near as possible and seal the gap with a suitable modern product. I suggest laying some cardboard on the floorboards and plastering to them and then after removing the cardboard add flexible sealant.

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:heart:The scientific explanation ! Thankyou


So, how is airtight and breathable possible at the same time? Easy peesy. The gaseous molecules of air are mostly larger than water molecules, so all you need to do is make your home airtight with layers that water can get through (so will hydrogen but we can ignore that) but atmospheric gasses can’t.

Now have the answer :muscle:t3::100:

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Do you have a picture of the exterior? An angle up to the eves/gutter would be ideal. Is it on the weather side of the building?

A draft passing through the electrical box along cracks surround the cables or chase to the floor system could be significant, usually this effect is much worse with dot and dab.

What’s in the room below the outlets?

Have you taken any measurements, with a hydrometer or thermal camera? You can detect drafts with a warm wet finger - so it needn’t be high tech.

At the moment there isn’t enough to make an informed decision. Although all measures would be worthwhile if you’re going for significant quantities of IWI.

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Hi Frank, my apologies, I’ve been missing my notifications.
We definitely need to get a closer look along the pointing on the gable end and front elevations . And you are right about gaps around power inlets , these are apparent at lower level. Also some of the bricks are blown, a problem I wonder might have been exacerbated by the old lime pointing having been replaced with cement and ugly black febtone.
We have a definite plan for the internal of the bedroom though and it is a new window and the external walls to be completed in lime.
I’m also rolling up my sleeves to argue against trickle vents for this bedroom.

Additionally, we’re not going add IWI , just a good layer of lime , maybe Diathonite. I need to do some costing first.

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I came across this retrofit advice that might be pertinent to this thread.

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I’ve looked back through the thread and read this with renewed interest.

As a general rule for both dampness and airtightness measures, and IWI you really need to avoid sockets on external walls. In fact it is best to avoid all fixtures and fittings on external walls, inside or out. That’s not to say that you mustn’t have them but huge amounts of extra planning and precautions are required.

Having experienced this with our plug socket - I agree. 100% they can be a thermal bridge on an external cold wall. In addition to plug sockets on dry walls, it’s making me think about metal handles on upvc doors and windows.
@lloydham posted about a very wet internal door handle on his A+ rated door. With the very valid question
’should this happen?’
My window fitter spoke of letter boxes and door handles in relation to them failing the thermal performance of all the other specialist materials used on windows and doors.

I don’t have a letter box in my thermal envelope.
Fortunately for me I can access my letterbox without getting wet in the rain even though it’s about 1 metre from the thermal envelope.

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Hi Carla,
On my new door i did not have a letter box, i had a letter box outside and i did not have to retrain the postman he used the box from day one, it was just at the right hight.
On the new building i will be blocking up the letterboxs ( not getting a new door yet)and putting boxes outside.

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Even a small thickness of insulation can reduce energy loss a lot as well as eliminating condensation. The comfort improvement is even greater because the wall is no longer acting as a ‘cold radiator.’ So if you can possible afford the Diathonite I would go for it. Back to Earth have a good article on the benefits of a 2cm thick wood fibre product. Plus a good installation video. Though in your case I think I’d prefer the Diathonite solution if it’s no more costly.

Given the age of your house, you’re very likely right about the blown bricks being caused by repointing with a cement:sand mortar. I have the same problem. If you do insulate internally, that may make the problem worse because the wall outside the insulation will be even colder and wetter in winter than before. Repointing with a lime mortar seems to be the solution. It has to be the right sort of lime. It seems that the heritage industry’s tendency to say “lime good/cement bad” over-simplifies a complicated subject. The best source of real data that I have found is this paper by Straube, Fig. 2 & Tables 4.1/4.2 of which indicates that even modest amounts of hydraulic lime have a big beneficial effect on cement mortar permeability.

If it’s a gypsum skim coat then it should be pretty vapour permeable. As I understand it, gypsum plaster is not considered to be a great finish in traditional buildings because “breathability” has three attributes: being (i) vapour permeable, (ii) capillary active and (iii) hygroscopic. According to this paper, (see table on p.13 for a summary) gypsum plaster has a similar vapour permeability to lime plaster. But because it has high capillarity, gypsum plaster soaks up water easily. I think that its low hygroscopic capacity and medium speed of hygroscopic take-up mean that it then dries out slowly compared with lime plaster. I’m a bit nervous to advise on something I’m only just finding out about, but I think that retaining a gypsum skim coat should be fine if its in the sandwich between the original wall and “breathable” internal insulation. But the paint should probably be removed if it may be a vapour barrier

That is an interesting paper. It was published almost 20 years ago so I would hope that it has been well peer reviewed I wonder what the consensus was. I would be nervous about putting a less permeable hygroscopic layer in the midst of a permeable structure. Stripping paint from the existing wall skim before attaching a new layer is likely to damage the skim anyway, so the problem may resolve itself.

As an afterthought, in @pottyone72’s case we don’t know for sure what is under the skim. It is known to be lime plaster at certain locations. Whether other plaster has been totally replaced is unknown.

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I have wondered about this .

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@pottyone72, this is relevant to your comments about damp and mould in fuel poor households:

Roadmaps for fuel poverty and retrofit: we know what needs to be done so why can’t we do it? With Tania Jennings (Chair of the Association of Local Energy Officers, London)
Zero Ambitions Podcast

Listen on Apple Podcasts:
‎Zero Ambitions Podcast: Roadmaps for fuel poverty and retrofit: we know what needs to be done so why can’t we do it? With Tania Jennings (Chair of the Association of Local Energy Officers, London) on Apple Podcasts

or find the episode for end of November’23