gable end decorative brickwork - mystery!

[JJ105]

We have decorative brickwork on a gable end period cottage. In 2020 a total renovation was carried out. As part of this a new chimney stack was built, the original roof tiles were taken off, and a new roof membrane laid with the original tiles put back on, lead around stack. The brickwork on gable end was all repointed with a lime mortar. Inside the old plaster was mostly hacked off and the bedroom was then lime plastered. It has always had a little bit of damp evident on patches which come and go which in the last couple of weeks has got significantly worse due to rain.

We thought maybe the patches on the walls (and a surveyor we contacted who didnt end up coming out just told us this was likely what the patches were) was the lime plaster chemically reacting to historic soot of the chimney breast (this was sweeped out in 2020 also before the renovation works) rather than a leak or penetrating damp but now wondering if this was incorrect.

We have run a moisture meter over the damp patches which appeared on the ceiling line inside the bedroom and they read high so suggests a roof leak or water coming in through the mortar? Yet when we go in the roof we cant find a source of a leak on the roof as the timbers are dry.

Has anyone got any suggestions?!

 

[cross thread]

Is the stack open ? What type of pots are on ,is the chimney in use ?

 

[JJ105]

hello thanks for the reply. see attached image has a reclaimed terracotta cowl type, which has a lid on the top. The chimney is not in use

in the bedroom we have a grill in the breast for ventilation at low level and being able to see inside which appears dry to the low level access area, and in the ground floor below it is closed over too with a grill for ventilation.

 

[Mr Chibs]

That stack looks like there could be multiple chimney's. Possibly 4.
You appear to only have 1 vented cowl. If the others are just capped off, this could be a contributor to the damp patches.

To be ventilated it needs a vent in the room(s) and at the chimney pot.

 

[JJ105]

ok i see what you mean. there could be 2 historic flues running up the breast (like this image?) and when the stack was replaced from the roof up. On the orrignal stack there was only one pot

 

[Mr Chibs]

I looks like a large stack to service just 1 chimney pot.

Yes, your illustration is what I'm talking about.

My money is on the fact that the other flues have been capped off and not properly ventilated.

Also I wonder if there is water collecting, above the brick corbeling on the gable end.
Looking at your images again, you have damp ingress either side of the chimney breast.

If you look at your gable end photo, you can see damp brickwork following the line of the chimney flue (below the corbel course).

 

[opps]

Damp meters on plaster are not accurate (timber yes, plaster no). I used to have one, but I threw it away after I noticed that it would show old damp patches as still being wet (when they clearly weren't).