Driving rain on brick wall?

Just finished dot and dab straight onto a brick wall (plaster was removed) wall didn't seem damp when I put up thew plasterboards, but now I can see patches (where the plasterboard adhesive is), as a result of last night's and today's rain. The wall is gable end, first floor. The outside brick wall has been painted, the paint is quite old although there is only a small amount of flaking. I'll take a look at the pointing and mortar where the roof and gable meet to see if this could be an issue, but my question is this :

How should I treat the outside wall? Water repellant paint followed by a proper paint? Or paint first then put on the water repellant?

Is this a cavity wall or solid?

Typically, you do not "paint" walls. Is it brick or render or something else?

First identify why the moisture is getting in before any cautious talk of water repellent.

Cavity - both walls are brick. The brick is already painted, not rendered. Paint straight onto brick, so not going to strip back fully, and will have to repaint. I suspect entry is between gable and roof. I will be investigating this and repairing if necessary. But I wanted to know if anyone has been using water repellant and if so which ones and how to apply.

Are you sure it's not cold bridging - condensation of humidity where there are extra cold patches on the wall?

Yes I am pretty sure about that, as it only happened when it started to raint. Also sash windows are currently out and being painted and there is no heating as it's currently being refurbished.

However, today, I examined the pointing, which appeared to be good, as the brick and mortar had been painted and the paint seemed in fairly good nick. But the mortar appears to be shot, it seems like a lime mortar as I don't think cement would break away like it did. So I've spent most of the day raking out the mortar and started the pointing. I am essentially going to point the whole wall as it could be that the rain is getting through the mortar and running down the wall. It must be able to bridge the gap some way I guess?

You could buy an inspection camera, take a brick out wait till it rains and then you should be able to see exactly what is happening.

Thanks Catlad - but I have an update!

So started at 5:30am today to do as much raking out and pointing before the rain was due to set in at noon. Along the way, one of the outside bricks was very loose as most of the mortar was shot, so it need coming out anyway to re-set. Low and behold, I don't have a cavity wall, I thought I did as I knew I had two layers of brick. It appears that the inner and outer brick are butted up against each other, and in the brick I removed, was attached to the inner brick with a bit of mortar.

... so, the rain comes, and I have done most of the inverted V (Gable end) that makes up the two rooms on the first floor where the damp is apparent (side note - one room was dot and dab, the other was render and plaster. When I bought it, it was back to brick - I chose to do one room with render/plaster because it was a bit ski-wiff, and I caouold neaten it up with the render, the other was OK, so I dot and dabbed). The damp "spots" are coming through in both rooms, it manisfests itself as round damp patches at the top of the wall where the adhesive was behind the plasterboard), in the other oo it's pretty random.

I am not sure whether the new rain has made these patches bigger or not, or whether the pointing has helped, but I have taken a picture now as it stands and can compare tomorrow. I *think* it's got worse after the new rain despite the pointing, which is mostly done, but time will tell.

I need to re-paoint the outside wall - any recommendations regarding the best external waterproof type paint or paint with some sealing properties - as it appears any future issues on the outside of the wall can bridge straight across?

I am also worried that any salts that have transpired on the inner wall will remain there - anyone know how long it takes for thes salts to develop - I've only just done the darn wall!

Its common in Lancashire to see gable ends slated, and you could add a bit of insulation at the same time or there are these new silicon renders like K-rend.

It will be condensation forming on the dabs, this is the reason why you shouldn't dot and dab an exterior solid wall in my opinion.

Thanks - I understand what you say about the condensation, but what about therendered/plastered wall which is exhibiting the same issue with more "random" damp paches appearing?

OK - your thoughts about ripping off the plasterboard, putting up some battens and insulating between the board and the brick? Or will there still be an issue where the board meets the batten (will this still be a cold spot).

1. I have checked in the attic and the inner bricks are very dry - not wet penetration so is it likely to be condensation?

2. Would rendering the outside all help? (I hate the idea of this though)

3. Still confused why I am having an issue with the room that has been rendered/plastered straight onto the brick - no condensation could form there, and it's new render/plaster

4. Apart from the recent rain, the only other change is that I have taken out the sash windows, and there is no heating. As this room temperature is more likely to match the outside temperature, I thought this would help things ...

There is a dimpled plastic membrane with plugs that goes on your wall first, then you fix your batons to that and there is insulated plaster board celotex pl4000 that has a vapour barrier.

Thanks you.

A final question if anyone knows the answer?

When my problem occured with damp patches on the plasterboard, it coincided with me taking three windows out in the flat and it raining. I mistakingly thought it was rain getting in, but thanks to you guys, I am pretty sure it is what you call cold bridging, as I don't have a cavity. I also have no heating, as the radiators are being fitted. Now I am wondering whether the problem I see is a result of the combination of no heating, no windows and high humidity coming into the flat from the rain? The "colder" spots on the plasterboard would be even colder as these are bridging to the outside, and the high humidity results in the damp wall on these spots?

Question 1
Am I just hoping, or with the windows put back in, the heating on, might the colder spots no be such as problem?

Question 2
The worset spots are those close to the ceiling. I have an attic above, but with no insulation. Would insulating the attic make the problem worse or better? I am not sure the effect of doping this ...

I can't answer your questions directly, but I can add some weight to your first theory.

When we had buckets of rain last week I noticed that we had heaps of condensation on the internal side of our windows in the mornings.

Now the rain has gone, there is nowhere near as much.

I was intrigued by this and could only put it down to the increased humidity in general.