chimney stack/water ingress/waterproof paint?

gutovicky

Hello,   I have 2 related questions.    Please can you advise?

My bungalow [built 1970] has a chimney passing through the centre of the building, with a smallish stack on the roof.
The brickwork of the stack is bare.  The brickwork passing through the loft is mostly covered in a light cement render. 
 
I have recently noticed that, during prolonged/heavy rain, the chimney, as it passes through the loft space, gets a little damp at its upper end [to about 2' below roof level] - enough to make the render a little darker there  [....so water, getting into the chimney stack outside, must be seeping downwards through the brickwork.  I don't think it's a flashing problem....].

1.  Should I be alarmed?  Or is it usual for the bare brickwork of a chimney stack to 'allow some water in' during spells of heavy rain - and this dampness just evapourate away when the rain stops?

I had a local (& reputable) roofing company provide a quote for re-pointing the external chimney stack and re-cementing its flange-cap.  
This company also advised having the chimney stack painted with 'waterproofing paint'....  

2.  What are your feelings about using waterproofing products/paints on bare, external brickwork?    

Thank you, Vicky
 

stuart45

Built in 1970, you probably don't have a tray fitted. 
Chimney DPC Tray being fitted. - Bing video
Some damp will often penetrate the brickwork, but will often dry out before it gets to ceiling height. As chimneys aren't used so much nowadays, they don't dry out as well. Getting it pointed and new flaunching will help.

FreeBear

Waterproofing paint on brick is a waste of time. Moisture will get trapped inside, and when it freezes, the brick will spall.

If you have had the fireplaces removed, get some caps fitted to the pots - This will stop rain from getting inside the flue. Pots that are still in use would benefit from a cowl being attached.

jrrowleyws

Do you use the chimney? If not, consider taking it down to below roof level and tile over where it was. Then you won't have an issue again!

DougMLancs

we had the same problem @gutovicky so we did what @jrrowleyws suggests and it's been fine since. Made more room and less shade for the solar panels too 😁

gutovicky

Thank you all for the feedback!!

I agree, I should ideally get the external stack re-pointed and its top re-flaunched.
I agree, I've always thought using waterproofing paint on external brickwork is a bad idea - sadly, it definately makes me think twice about using that company (there is other fascia & soffit work to be done).

Yes, agreed, if I got rid of the chimney, I wouldn't have the problem! But I was hoping to install a small woodburning stove in the near future…. …which would help reduce the lingering dampness from prolonged rain presumably.

BTW, does anyone know… if I employed a (Hetas) company to install a suitable flue-liner for a woodburner, would you expect them to 'tidy-up' the chimney - at least re-new the flaunching - as part of that job?

Thanks for your tips as usual, Vicky

FreeBear

BTW, does anyone know… if I employed a (Hetas) company to install a suitable flue-liner for a woodburner, would you expect them to 'tidy-up' the chimney - at least re-new the flaunching - as part of that job?

They would only do it if you specified it as part of the job. Depending on the size of the chimney, it could take most of the day to repoint.

jrrowleyws

gutovicky said:

Thank you all for the feedback!!

I agree, I should ideally get the external stack re-pointed and its top re-flaunched.
I agree, I've always thought using waterproofing paint on external brickwork is a bad idea - sadly, it definately makes me think twice about using that company (there is other fascia & soffit work to be done).

Yes, agreed, if I got rid of the chimney, I wouldn't have the problem! But I was hoping to install a small woodburning stove in the near future…. …which would help reduce the lingering dampness from prolonged rain presumably.

BTW, does anyone know… if I employed a (Hetas) company to install a suitable flue-liner for a woodburner, would you expect them to 'tidy-up' the chimney - at least re-new the flaunching - as part of that job?

Thanks for your tips as usual, Vicky

Some hetas installers are more experienced than others at chimney maintenance and repair. Some just install liners and stoves. Find a good one and I'm sure you could get a chimney refurb done at the same time. It's not going to be cheap though, grind out and repoint will take at least a day depending on size of your chimney and you'll need scaffold up to and around the chimney. 

You could still take the stack down below roof height and then have a steel double walled flue protruding from the roof for your wood burner. Again, not a particularly cheap option.