Water spots coming through after painting

[J-Paradise]

Hello,

Last week I painted my spare room and used Zinsser Bulls Eye 1-2-3 Plus on the two external walls as there were issues with damp patches and lots of filling had to be done where the previous owners had a shelving unit fixed to the wall, which only made the damp worse due to lack of airflow.

The issue however is that after two coats of Zinnsser and two coats of Dulux Trade Vinyl Matt, some patches have appeared which I would obviously like to cover up.

I have been running a dehumidifier in the room which has done nothing.
My first thought is to paint over the patches with the Zinnsser again and hope that it block the stains but I don't want to waste my time if this won't work.

On the outside there is rendered wall which I cannot do anything about, I think the main cause of damp in the room previously was condensation which we are going to do our best to avoid.

The photos actually show up the area worse than it looks to the eye, the lighter looking patches can't be seen in person. The issue I have is with the darker wet looking spots.

Any help hugely appreciated.
Thanks in advance.

[dewaltdisney]

I suspect that there is damp locked in. By the apparent age of the property the exrernal walls will be solid rather than a cavity, once damp it can only dry out from both wall faces. The main culprit to look at is the rendering to wall seam at the top as this a likely place for moisture to leach in and with this in mind check the gutters above for overspill and leaks. Check over the render to wall seam carefully as pinholes could allow moisture in. The 123 has sealed the internal wall so any residual mositure is trapped as it cannot dry out from the external face because of the render. I hate to tell you but you may have to sand the area back to plaster to allow it to dry out.

But first things first, check for the moisture ingress.

DWD

[J-Paradise]

Thanks for you reply, really appreciate it.

The guttering above are all fine, however it seems like it is quite damp around where the brick vent is (although this isn't the wall that the damp spots are showing through). There is also my neighbours log storage in front but not covering this area, there is a roughly 10cm gap.

Would it be worth waiting until the summer before sealing between the render and the wall? And what would be best to use to do this?

I'd really rather not sand the area back and start again, I just don't have the time. Is there an option to hide it with paint hoping that it will dry out in the summer or is that just stupid...

Thanks again

[dewaltdisney]

It is always difficult to advise from afar. I had a further thought that that garden wall looks to be joined to the house wall and if it is drawing damp this could work through to the house wall. Damp could either come from the coping on top being cracked or the absence of a damp course? This is of course if the stains are damp, are you sure they have not been caused by candles or some other contamination in that area from inside?

Worth a look.

DWD

[J-Paradise]

Hi and thanks again DWD,

The stains are definitely damp, there was peeling paint and mould in the corner of the room before I re-decorated it.
The height of the damp spots is roughly in line with the air brick as highlighted in the photo below.
I will look into re-doing the coping on the wall that joins onto the house, it needs to be done anyway as it's not very nice to look at.

I'm worried that if I try these things and it doesn't work I will have to wait until I have red-decorated again to find out, or is there another way?

Should my process now be:
1. Seal gap between render and wall (Any recommendations on what to use?)
2. Sand back interior wall to plaster and dry out with dehumidifier.
3. Redecorate

Could this issue simply be caused by the wall being very exposed to the elements and something I may never be able to resolve?

Again, thanks a million in advance

[dewaltdisney]

I wish I could tell you exactly what to do, I can only offer suggestions from the pictures. The damp around that air brick is suspect, is it possible there is a pipe leak inside that area? Where does that air brick go, does it go right through the wall into the room? Very strange....

DWD

[J-Paradise]

Thanks again and apologies for not getting back to you sooner.

I think I'm going to have to resort to taking the plaster off from the inside in order to find out what the issue is being caused by. I'm hesitant to take away the render in the outside as the issue doesn't seem to get worse depending on the weather.
Also a small section seems to have blown on the inside and I worry that this may get worse over time if we don't just knock off a section where the issue is and investigate.

Hopefully not a terrible idea...

Joe

[dewaltdisney]

I think that is the best approach. If that is the only area wirh staining then raking off and checking the substrate will give you've better idea of what is going on. Good luck sorting it

DWD