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Plasterboard on external (now internal) brick wall

jassco

Distinguished Member
Quick question for those savvy on building techniques. We had a porch built last year, and in fairness he did a good job. Where the external brick was present, he boarded over this using plasterboard that could be painted directly onto, and he used dot and dab to attach the board directly to the brick wall.

A few months back before we had the floor tiled, I noticed some damp in the bottom corner, but assumed this was because he boarded directly down to the concrete floor. So I took off the bottom of the board to create a gap, and that's been fine since.

However now I've noticed that the board, which is painted with good quality white paint, is turning a very subtle yellow anywhere that there is dot and dab, so moisture must be soaking through from the original brickwork. Also looking externally, our pointing (on both the porch and existing house walls) appears damp.

So my question is, was it okay for him to dot and dab onto the external (now internal) bricks, and if so where should we be looking to identify the source of the problem?

Happy to call in an expert, but I could do with knowing which expert is needed
 

busterbenny2001

Distinguished Member
The face of the brick should of really been tanked with a waterproof coating to prevent water ingress before dot and dabbing, we tanked then battened before boarding, not a proffessional but just speaking from experience.
 

jassco

Distinguished Member
Not really a cure but some gloss should cover the yellowing
It's quite a prominent place so wouldn't look very good to have it glossed, and as you say it's not a permanent solution so likely to just rot the boards over time. The boards themselves are only 30cm x 2m so not a huge area we're talking about, so I'm hoping if it's an internal problem then remedial work won't be hard.

@busterbenny2001 when you say tanking, do you mean a waterproof membrane / plastic sheet? And would something like this be possible without taking the ceiling down?
 

busterbenny2001

Distinguished Member
its a paint type substance that goes on the bare clean wall, coating it and preventing any water coming through to your internal finish so applied before studwork and plaster board goes on.

Is your wall single skin?
 

jassco

Distinguished Member
its a paint type substance that goes on the bare clean wall, coating it and preventing any water coming through to your internal finish so applied before studwork and plaster board goes on.

Is your wall single skin?

Nope, it's the main wall of the house which I'm assuming is cavity. I've attached a pic that I'm hoping shows the problem as well, but not sure if it's visible in the photo
1501183030195-353833735.jpg
 

jassco

Distinguished Member
Also, the rest of the porch was built using double skin - outside is brick, and inside is breeze block with an insulated cavity. The other walls have all been fine
 

Chrisfxz

Established Member
Where the porch wall joined the external wall perpendicular he should have stihl sawed in a vertical cut and inserted a dpc. Therefore any moisture in the external leaf of the house wall wouldn't transfer through to the internal face of the porch wall.
 

busterbenny2001

Distinguished Member
As above without knowing exactly what was put in in the way of a dpc its really hard to know the best course of action, however you should be able to sort it without removal of your ceiling, maybe remove board and tank or try to get some dpc in there, get a couple of builders to have a look and compare.
 

Thug

Moderator
Before you do anything I would suggest using a damp detector to make sure it is what you think.
It may be that after it was done you painted too early and the damp seeped through then and discoloured it but you have only noticed as the paint has faded differently in that area.

I'm not an expert either, but would certainly verify what your suspicions are before taking it apart.
 

jassco

Distinguished Member
Before you do anything I would suggest using a damp detector to make sure it is what you think.
It may be that after it was done you painted too early and the damp seeped through then and discoloured it but you have only noticed as the paint has faded differently in that area.

I'm not an expert either, but would certainly verify what your suspicions are before taking it apart.
Cheers, I've got a moisture detector for logs so will give that a go.

Another suggestion I've had is that it's just residual damp from the brick walls (it was built in the winter) that once dried completely will just need painting over. The board went up within a couple of days of the roof being finished and the whole porch being made watertight.
 

Thug

Moderator
Cheers, I've got a moisture detector for logs so will give that a go.

Another suggestion I've had is that it's just residual damp from the brick walls (it was built in the winter) that once dried completely will just need painting over. The board went up within a couple of days of the roof being finished and the whole porch being made watertight.

I was actually thinking of that too, and also condensation behind the board.
If there is any moister it has to get out somehow.
 

hufartd

Established Member
It might not be damp coming through the brick but condensation forming on the cold surface "dabbed "parts on the plasterboard.
Could be cured by removing board andfixing on insulated backed plasterboard fixed with an adhesive foam to prevent cold bridging from cold original outside wall.
 

jassco

Distinguished Member
It might not be damp coming through the brick but condensation forming on the cold surface "dabbed "parts on the plasterboard.
Could be cured by removing board andfixing on insulated backed plasterboard fixed with an adhesive foam to prevent cold bridging from cold original outside wall.
I'd be surprised if it is condensation, as we've had the two side windows open permanently.

My temptation is to try the gloss trick and then paint over the top. Removing the board to do any repair work like tanking will destroy the board anyway, so nothing really lost.
 

hufartd

Established Member
You'll soon find out if you gloss the whole board,you'll see the condensation form on the paint or not .
 

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