Advice please on re-plastering a Chimney Breast

[JonHeath]

Hi all,

Looking for a bit of advice here. I have a few damp spots on a chimney breast in a bedroom. I've tackled this a number of times from the outside with a new cap on the chimney, re-pointing the whole chimney stack, ventilation improvements etc. I just can't get rid of these spots.

So I'm tackling it now from the inside now. I've hacked the plaster off where the chimney breast is (where the brick is single). There's no obvious damp issue when looking at the brickwork. My plan is to batten, and then plasterboard this section keeping a gap between the brickwork. I could possibly used foil backed board and/or tank the wall for belts and braces. Is that needed?

This will then stick out further than the existing plaster either side. Rather than hacking off all that plaster either side and boarding that I was going to maybe build up the existing plaster out. What is the right product to build the plaster out by another 10-15mm? Is that the right thing to do or should I board those areas (dot and dab) as well? Once everything is back to the same level I'd then get the whole lot re-skimmed by a pro, and re-attach skirting / coving.

If there is any other alternative products or ideas I'm very open to suggestions. I've attached a couple of pictures if that helps.

Thanks
Jon

 

[Alastairreid]

Is it vented at the bottom? is the cap on the chimney vented?

 

[JonHeath]

Yes it’s vented top and bottom with external air bricks. Also the cap is vented.

I’ve spent a lot of time on the outside. Now the plaster is off you wouldn’t even know there was or had been any damp. For whatever reason there must be moisture in the chimney and it’s picking the weak spot in the breast.

I’m comfortable that creating a small cavity by using battens to get the plasterboard off the bricks will sort the issue. What I’m looking for is some advise on bringing the other areas of the wall back to be level with this once I’ve done it. Thanks.

 

[Alastairreid]

I would try a render basecoat with waterproofer in it and skim the full wall to finish.

 

[JonHeath]

Thanks. So you wouldn’t bother trying to board it off the wall at all? I was going down that road as it felt like belt and braces. I only want to do this once.

Do you have any recommendation on render and waterproofer? Standard Sand and cement? What about some of the tanking slurry options like Sandex?

 

[bobasd]

why not post a photo of the external, projecting chimney breast?

the old bed room fireplace opening seems to have been bricked up - was the flue swept before bricking up? you might have to open the flue for another, better sweeping.

presuming your bed room is on the first floor then has any flue from any lower floor fireplace been swept - and vented if needed?

there's no need for your elaborate propositions, simply render back up with a mix of 4:1 sand and lime and a remedial skim finish. dont use any gypsum plaster.

 

[JonHeath]

Here's some photos (below) of the external from the work we did in the summer. The stack was re-pointed, lead work checked, capping replaced to rule that out, ventilation already was in place.

The chimney has been sealed since I bought the house 9 years ago, so not sure if it was swept. Yes the bedroom is on the 1st floor. The fireplace is sealed up on the ground floor too.

Sorry if they seem elaborate but knowing that there is still some slight moisture in the chimney my gut reaction was to create a cavity and batten plasterboard off the wall.

If I am going to just refill the gap with sand/lime render then are you confident any slight moisture that is still in the chimney will not come through the render eventually? Is this something you've done before to solve this type of issue?

 

[bobasd]

you have two flues in the c/breast.
there's only one terminal pot to be seen on the stack: its on the left hand side ie.the L/H flue - your air bricks are in the right hand flue.
flues in a chimney breast and stack are separated by a feather.
there's no way of knowing which flue is serving which fireplace just by looking at the c/breast so your airbricks could be almost useless until you know which flue they are venting

you need another terminal for the R/H flue, and you need to open up and sweep both flues as recom above.

the flaunching is inadequate - there should be an all round overhang to discharge water away from the stack. google pics.

what do you mean by capping?

am i "confident" - maybe read my past posts for what they are worth?
the S&L render will give you some years of damp free decorations perhaps many providing the flues are swept and vented.

the tower didn't appear to be tied-in - even with stabilisers i tie towers in.

 

[Alastairreid]

Thanks. So you wouldn’t bother trying to board it off the wall at all? I was going down that road as it felt like belt and braces. I only want to do this once.

Do you have any recommendation on render and waterproofer? Standard Sand and cement? What about some of the tanking slurry options like Sandex?

Sand and cement render with a plasticiser/waterproofer additive applied as a basecoat will help prevent moisture wicking through the brickwork from the flue.

 

[JonHeath]

Thanks for the info.

Looks like the previous occupant has decided the other flue (with no terminal) has adequate ventilation with the two airbricks, and the other flue has adequate ventilation with just the capping cowl. When I was referring to replacing the "capping" I was talking about I replaced the cowl that you can see on the pictures.

I've never had a chimney flue swept. I'm presuming they need access from the bottom, which doesn't exist? How would you recommend opening up the flues to be swept? I do have a weird looking small door thing on the ground floor on the exterior. Not sure if this gives access. See the picture below. The ground floor section of the chimney exterior is actually enclosed in part of a workshop building I have on that side of the house. So this small door thing is in my workshop.

I'm not sure what you're referring to when saying the tower isn't tied in? Could you elaborate please.

Happy to do work needed on the exterior but I'll be honest, I'd rather wait on that until Spring when it starts to get a bit warmer. What's your view on doing the rendering now and leaving the additional ventilation and flaunching until Spring? Also one final question. Is there much difference between rendering with Sand & Lime versus Sand, Cement and Waterproofer as the other poster suggested. I'm guessing the lime solution would allow the wall to breathe whilst Cement & Waterproofer would be more of a barrier. Would either be OK? Thanks.

 

[JonHeath]

Sand and cement render with a plasticiser/waterproofer additive applied as a basecoat will help prevent moisture wicking through the brickwork from the flue.

Thanks for the reply. When you say applied as a basecoat you've lost me. I was thinking your option was to do a sand/cement render with waterproofer mixed in. This would replace the plaster I've hacked off. So would be around 10mm thick. I'd then have the whole wall skimmed again.

 

[Alastairreid]

Thats it, take the render flush with existing, let it dry, pva the whole face of the wall, let it dry, pva again, let it go tacky then skim.

That door is a soot box, the flue can be cleaned from the top and debris removed from the box.

The waterproofer in the sand and cement will prevent moisture passing through into the finished plaster.

the lime plaster will allow the moisture through and wall to breath but excessive moisture will stain the wall. hence my suggestion.

Bob was making an observation that the tower scaffold was not tied into the gable whilst in use.

 

[JonHeath]

Thanks for that Alastair. I'm tempted to go with the Sand/Cement/Waterproofer option and do further remediation on the chimney next year when the weather improves.

Regarding the scaffolding tower, it was tied to the chimney stack. You can just about see the blue rope on the pictures. Maybe not the preferred method, but we try our best as amateurs!

 

[Alastairreid]

Regarding the scaffolding tower, it was tied to the chimney stack. You can just about see the blue rope on the pictures. Maybe not the preferred method, but we try our best as amateurs!

Its all as they say...Academic now.....Bob likes to point those things out.

 

[bobasd]

open the bricked up/blocked off fireplaces and sweep the flues from below - that way you can definitely remove all the free soot and debris, and wire brush the fireplace walls if needed.
or, you can open the flues from the outside by removing bricks, just like you installed the air bricks.
whatever, make sure to empty the soot box.