External Paint Issues

[MontyMonty]

We have recently moved into a 1960s bungalow on the south coast. It is generally in a very good condition. The external walls are half brick half pebbledash. The bungalow has cavity wall insulation.

I am planning to repaint the pebbledash walls. They are white at present but we are changing to a cream colour. However after some rain recently I recently noticed a dark patch had appeared on the external wall between the front two windows. On closer inspection the paint was what I can only describe as soft. If you run your finger along the wall it leaves a yellow residue. When the wall dries the dark patch disappears. But again if you rub the wall you get a powdery yellow residue.

Can anybody advise on what they think the issue may be. Could it be a damp issue? Although there doesn't appear to be any damp on the internal wall. Or is it just some poor quality paint or painting?

Grateful for any advice.

 

[opps]

How big is the patch. It might be rust. I have, on a couple of occasions, seen rust marks in newly dashed walls. In theory, a spot prime with an oil or shellac based finish should suffice- but it is not guaranteed to work.

 

[MontyMonty]

Hi opps. It's a relatively large space. Around three foot across by six foot high.

Just run my finger along it again. It leaves a white residue on my finger and a yellow streak on the wall. The yellow streak disappears after a short while. All very odd.

 

[opps]

Can you take photos from further out?

I agree that it sounds odd- for what it is worth- I am a decorator

 

[MontyMonty]

Apologies for the delay in replying.

I went to take a picture but as the weather was dry the wall looked blemish free.

I'm going to use a stabiliser and then paint the wall with a good quality masonary paint.

Incidentally, the (empty) bungalow next door has a similar issue in exactly the same spot. Some of the neighbours seem to think it is a problem caused by the cavity wall insulation.

 

[MontyMonty]

If it was felt the cavity wall insulation was a potential issue with the wall would it be better to use a water seal rather than a stabiliser? And can you use masonary paint over water seal?