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Chimneys & Fireplaces

Damp on chimney breast how do we fix it?

We have just moved into a bungalow and have found damp on the chimney breast, previous owner had just been painting over it! We had a survey done before buying but was not picked up. We have had the lead flashing replaced round the chimney and thought we had cured it and had the wall replastered, but the plaster is not drying and the damp us back. We have a log burner which the previous owner used all the time but we daren't use it in case we crack the new plaster. Help!

4 Answers from MyBuilder Chimney & Fireplace Specialists

Best Answer

The chimney should have cowls fitted to stop rain entering the flies which in turn bring the water/moisture into your house/walls.
If the stove in not certified I wouldn’t use it. I install and maintain stoves and some of the non compliant installations I’ve seen in my time are fire hazards waiting to happen.
Get a Hetas certified professional round to check the installation and flue. No doubt they will be able to help you.


Answered 14th Dec 2019

I would need to see photos to be able to help properly.
Depending on where the damp is, I would check the damp course to make sure its not been bridged or not high enough. Most people mistake condensation for damp. a simple are brick to improve ventilation in the chimney breast could help.
The most likely course maybe vermiculite insulation. This is the material used around the flue inside the chimney once log burners have been installed. some people call it backfill. this stuff retains lots of moisture, if the water gets in at the top of the flue and into the back fill it WILL look like damp.
Chris AKA Mr Sweep Stoves Shop Essex


Answered 14th Dec 2019

Could be one of three things here...
The chimney may require re-pointing or the flaunching/crown around the pot could of broke up causing water ingress, or it could do with a weather/bird guard cowl fitting, if it's an open chimney pot...


Answered 15th Dec 2019

If the flue is lined, then you should check the top of the chimney stack, including the pot, that the flexible liner is clamped to it, and that the flaunching is in tact (the mortar around the pot). Also, check that the cowl is in good shape and correctly fitted.
Just over the hearth and inside the flue, the stove pipe connects to the flexible liner via an adaptor. The stove pipe passes through the register plate and down into the stove. Check that all these pipes run down into each other so that any water finding its way past the cowl and into the flexible liner should end up inside the liner, stove pipe or stove itself.
If this is all done correctly then no water should be getting into the inside of the chimney stack flue. Some reasons why your chimney stack or flue might be letting water in are:
- Cowl not doing its job
- Flaunching has failed
- Flexible liner not connected properly to the chimney pot
- Flexible liner only runs into the chimney and a few feet above the register plate
- Flashings around chimney stack failed


Answered 16th Dec 2019

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