Damp chimney stack

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Hi. We currently have a brick chimney stack which we believe is letting in water / damp. Should we render it and if so what happens to the damp in the chimney or should be cover it in a waterproof sealer and are such sealers / coatings breathable?

Any advise gratefully received.
 
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One of the first things you should check is the quality of the lead flashing that couples the chimney stack to the roof, and at the same time see what the brick pointing is like.
If the chimney isn't used, its best not to cap it but rather install one of those terracotta 'pepper pot' things that sits in the top, but allows air out through holes in the side.
John :)
 
Those pepper pots cause more damp issues than they solve.

Is the OP talking about damp chimney breasts?
 
The damp we are getting we believe is coming down the chimney stack. The chimney is built on top of two brick stepped shoulders and the flashings between these shoulders and the roof seems to be OK. The chimney has two pots on it - one is used with a wood burner and has a vent at the top of it and the other has a terracota cap on it which has holes in it for ventalation. The chimney brick work could be repointed but surely it would be better to either apply a damp proof seal to the brickwork or render. As the chimney has damp in it what happens if you render a damp chimney? Does the damp work its way out into the building below or can you apply a breathable render (lime?)

If we apply a damp proof seal is this breathable as well?

Thanks for the answers so far.
 
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Those terracotta things with holes - pepperpots - cause condensation issues.
 
Why do they cause condensation then?
I thought that these would be better than rain cascading down a filthy unused chimney..... :confused:
John :)
 
Yes thats why we had one fixed in the top of the chimney.

If you reneder the stack - which is already damp - where does the damp go to?
 
Why do they cause condensation then?
I thought that these would be better than rain cascading down a filthy unused chimney..... :confused:
John :)

You are a mechanic and therefore know how a carbie works? Same principal. Those silly things stop the Venturi effect and you get slow air flow and hence condensation.
 
Thing is Joe, slow air circulation is surely better than none at all......
i.e the chimney capped with a slab of stone seems to be a popular move!
John :)
 
The slab of stone works by stopping the airflow. No air flow is good. Good air flow is good. Slow air flow is bad and that's what those cowls give you.
 
OK I'm not able to comment on that one.....we get a few chimney breast damp problems up here courtesy of porous Northumbrian sandstone, so something is needed to dry it out!
John :)
 

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