What is this?

[JBR]

Can anyone tell me what this is and, more importantly, what I can do to sort it out?

When we were buying the house, we had a survey done and were advised to have a damp problem dealt with. This involved injection of a new damp-proof course outside this area and replacement of plaster on the inside.
More recently, this has appeared which I assume is related to the original problem.

 

[KenGMac]

JBR, Hi.

Looks like penetrating damp?

No indication of distress in the plaster below the area affected, so, it should not be rising damp?

The position of the damage, in line with the window Sill could? indicate that the window at one time was wider? [unlikely?]

Has the wall had Retro-fill Cavity Wall insulation installed? indeed, is the wall a cavity construction or solid brick? and what age is the property?

What is the condition of the Mastic around the window externally [a possible long shot but?]

A couple of answers would assist?

Ken

 

[^woody^]

Damp and salts.

You need to hack the plaster off, plus about 200mm past the area, and replaster

Before that, check the cavity, or condition of external solid brickwork and deal with that

If the lower wall was rendered as part of the damp treatment, and this was many years ago (at least 15), then dampness may have reached the top of the render

 

[oldbutnotdead]

Check your gutters (or overflow from header tank)- very good odds there's a leak or a drip hitting that windowsill and it doesn't take much of a drip (over a few months) to cause exactly that sort of damage. Once you've fixed the drip, scrape the bubbled paint off, leave bare for a month (to dry it out) then chuck some emulsion at it. If you're lucky it'll take and you'll be home free.

 

[tony1851]

Welcome back!

As above, it's salts. If you lick the tip of your finger and pick up a little of the deposit, you can taste the salts - usually magnesium salts I think, though I may be wrong.

 

[JBR]

JBR, Hi.

Looks like penetrating damp?

No indication of distress in the plaster below the area affected, so, it should not be rising damp?

The position of the damage, in line with the window Sill could? indicate that the window at one time was wider? [unlikely?]

Has the wall had Retro-fill Cavity Wall insulation installed? indeed, is the wall a cavity construction or solid brick? and what age is the property?

What is the condition of the Mastic around the window externally [a possible long shot but?]

A couple of answers would assist?

Ken

Thanks Ken.
To answer your questions one by one:
- No the window has never been wider.
- The wall is, as far as I know, cavity but there is no cavity wall insulation.
- The main part of the house is c.1920s, but this end of the kitchen was added afterwards. I'm afraid I don't know when.
- The mastic around the window is in good condition as far as I can see. The windows, incidentally, are PVC which may give a clue as to the age of the extension.

 

[JBR]

Damp and salts.

You need to hack the plaster off, plus about 200mm past the area, and replaster

Before that, check the cavity, or condition of external solid brickwork and deal with that

If the lower wall was rendered as part of the damp treatment, and this was many years ago (at least 15), then dampness may have reached the top of the render

Thanks Woody.
The wall is rendered (outside) from top to bottom, apart from two or three courses of brickwork at the bottom, and seems to be in good condition.
I seem to remember that the rendering wasn't touched when the damp treatment was done, only the plaster inside.
I shall not be hacking plaster off, or doing any other work, yet until I know exactly what to do. Also, I'm not sure how to check the cavity.

 

[JBR]

Check your gutters (or overflow from header tank)- very good odds there's a leak or a drip hitting that windowsill and it doesn't take much of a drip (over a few months) to cause exactly that sort of damage. Once you've fixed the drip, scrape the bubbled paint off, leave bare for a month (to dry it out) then chuck some emulsion at it. If you're lucky it'll take and you'll be home free.

Thanks Oldbutnotdead (pleased to hear it, btw!).
There are no gutters directly above that area - it's a gable end, and no water tanks or pipes in the loft either. I haven't seen any regular drips hitting the window sill, other than normal rain water.

I can certainly scrape off the bubbled paint and follow your instructions about leaving it bare to dry out. That certainly seems the easiest thing for the time being at least, but I'd really like to discover the cause first.

 

[JBR]

Welcome back!

As above, it's salts. If you lick the tip of your finger and pick up a little of the deposit, you can taste the salts - usually magnesium salts I think, though I may be wrong.

Thanks Tony. (I've never actually been away: I read new posts on most of these forum areas almost every evening out of interest!)

Yes, a distinct salty taste. Is that good or bad?

 

[^woody^]

Damp and salts.

You need to hack the plaster off, plus about 200mm past the area, and replaster

Before that, check the cavity, or condition of external solid brickwork and deal with that

If the lower wall was rendered as part of the damp treatment, and this was many years ago (at least 15), then dampness may have reached the top of the render

Thanks Woody.
The wall is rendered (outside) from top to bottom, apart from two or three courses of brickwork at the bottom, and seems to be in good condition.
I seem to remember that the rendering wasn't touched when the damp treatment was done, only the plaster inside.
I shall not be hacking plaster off, or doing any other work, yet until I know exactly what to do. Also, I'm not sure how to check the cavity.

Some damp remedial work has render on the inside up to 900mm. That's what I meant.

 

[JBR]

Damp and salts.

You need to hack the plaster off, plus about 200mm past the area, and replaster

Before that, check the cavity, or condition of external solid brickwork and deal with that

If the lower wall was rendered as part of the damp treatment, and this was many years ago (at least 15), then dampness may have reached the top of the render

Thanks Woody.
The wall is rendered (outside) from top to bottom, apart from two or three courses of brickwork at the bottom, and seems to be in good condition.
I seem to remember that the rendering wasn't touched when the damp treatment was done, only the plaster inside.
I shall not be hacking plaster off, or doing any other work, yet until I know exactly what to do. Also, I'm not sure how to check the cavity.

Some damp remedial work has render on the inside up to 900mm. That's what I meant.

From what I recall, they just replaced the plaster but it was some time ago. They may have said something about some sort of 'special plaster', but I'm only guessing. This 'bubbling' is about a metre above the floor.

 

[KenGMac]

JBR, hi, again.

The generally held concept is that rising damp will only capable of rising to a height of about 1m. there are contributors on the board that will probably disagree? I was told that water and Capillary action will only go to 1m.

As for what is occurring to your wall? it appears to look a lot like a blocked cavity? and the cavity bridge has allowed rain water which has saturated the external leaf to get across the cavity and the results is visible on the plaster inside the room.

To confirm this theory? you need to have a look inside the cavity.

Best way i know of achieving this is to hire a "Borescope" and follow the instructions, basically you bore a suitable sized hole in either the inside or outside leaf of brick, the position of the hole will need to be above or below the "Potential" cavity bridge, insert the Borescope, the machine is a tube with a mirror at the end and a bright light attached, you can rotate the tube with the mirror on it and by looking in to and along the tube you can see what is inside the cavity?

if you choose to follow the above, I am not sure as to the correct spelling of borescope, just to boost your confidence in what i am typing here? you should be able to confirm or refute the possibility of a Cavity Bridge?
If the Cavity is not bridged then a quick look at the embedded Sill End may prove useful?

Advantages are that using the above you should get a very accurate Diagnosis of what is causing the problem without hacking loads of holes in the plaster inside or on the external face of the wall. all with minimal disruption, and that is the big bonus??

I suppose there are a load of clips on U tube as to what the device can do??

As an aside I do not work for the firm that manufactures them?

Ken.

 

[JBR]

Thanks Ken.
I'll have a look into that.

 

[JBR]

Do you know how much those borescopes cost, or even how much they cost just to hire?!

I've decided to try what Oldbutnotdead said instead, and have sanded off the bubbling surface. I'll leave it bare for a bit and see what happens. I presume I'm looking out for a damp patch forming.