small trickle of water above fireplace lintel

[Ouch77]

Stripped the render off the fireplace in the diningroom over the weekend to find a small wet spot just above the concrete lintel. The water appears to originate from within the chimney cavity and is seeping through a mortar joint.

The fireplace itself was blocked up years ago (previous owner) and a small hole (missing brick) was left at the bottom for air, however cautious exploration has revealed a lot of broken concrete lumps that suggest it's not getting a lot of air through.

It's in internal brick chimney stack, twin flue of an asymmetrical design, and the dining room fireplace is offset from the main rise, appearing to be connected via a diagonal rise.

There is no evidence of damp anywhere else in the house.

We've no intention to resurrect the diningroom fire, and will be batten & boading over the chimney breast, clearing and re-instating the vent at the bottom, however I want to resolve this small damp spot first - anyone got any suggestions on how I can tackle this?

 

[JohnD]

ventilate top and bottom. See if rain is getting in, and correct if so.

 

[Ouch77]

ventilate top and bottom. See if rain is getting in, and correct if so.

Assuming I clear the vent at the bottom, are you suggesting I put another air vent in at high level (say about 2m) - this would be above the point where the the offset joins into the main rise.

If the rain is getting in - I assume it is, due to the fact it's been raining recently, how would I correct this? Different chimney pot?

 

[JohnD]

Condensation usually causes damp, not trickles. Rain causes trickles.

You can have it capped and the flaunching or flashing repaired if rain is getting in, but you have to ventilate it top and bottom to prevent condensation.

The ventilators can be where convenient, such as under the ground floor or in the living room; and you can have an airbrick near the top of a capped chimney. I mean top and bottom of the chimney, not just two ventilators in the same room. You need airflow.

You can ventilate the top in a loft, but this would be dangerous if in future someone didn't know, and re-started using the chimney

You can even have the top of a chimney removed down into the loft, and the roof reinstated and tiled. IMO this is the best, but most expensive, method

 

[Ouch77]

It's a twin flue chimney, and I wish to retain the living room fireplace as a functional fire, so removing the chimney top is not really an option.

Is the chimney pot not sufficient ventilation for the top of the chimney? The ground floor is concrete, so no under-floor ventilation.

I'm guessing that the quantity of rain that would usually drop straight down a chimney is usually quite small, and natural ventilation and latent heat within the building is enough to evaporate this off. In my case something obviously isn't right, either excessive water is getting in (will have to get onto the roof to check the flashing) or it's not being evaporated off.

Could the fact that there's an angled slope on the bottom of the flue contribute to this problem - perhaps it's directing the rain that falls down the chimney to one spot?

 

[JohnD]

round here, we've had 3 inches of rain in a couple of days, so maybe recent rain has been unusual

if the chimney is ventilated top and botom it should keep reasonably dry

you can get a sort of umbrella cap to shield the pot from rain but allow airflow, but I have no experience of these

 

[Nige F]

umbrella cap in clay is ok but it`s acually a downdraft cowl : you need an elephant`s foot - clay - vent seriously. they won`t laugh@you in the builders merchants. and while youre up@ chimney - pour loads of grangers proofing or other waterproofer around the bottom of pots - worked for me

 

[Ouch77]

You're all sounding very much like i need to climb up on the roof. Oh dear...