Interior Spalling

[KelvinM]

Hi there

I am about to buy a cottage (old, but not listed). There is a chimney stack where the part behind the fireplace is exposed. I think that historically this may have been outside at some point a single storey extension was built such that this part is now inside of the house. The chimney then goes out of the roof.

On this interior part I have noticed some spalling. I just wanted to get opinions on what may be causing it. I have some possible theories:

1. The spalling could have been from when the full chimney stack was exposed. The dampness and freezing could have caused the weakness in the brick and it is only now it is showing;

2. I think there may be a slight leak where the roof meets the exterior part of the chimney stack. Given the room is very cold, has not been lived in for a while, and the recent freezing weather, the damage could be recent an caused by these factors;

3. At some point the current owner has done cement pointing and tried to render parts of the interior part of the chimney stack. This could be causing a problem. The spalling is now only in a small part of the interior stack so the cement render could be re-directing the moisture (?).

I'm fairly confident that it is not due to movement as the spalling is in a small area and there are no other signs of structural issues.

I'm thinking that the best course of action would be to (i) check the roof and stack and real with any potential leaks; (ii) remove the cement render and pointing; (iii) replace the badly damaged bricks using a lime mortar, and (iv) re-point the chimney stack with a lime mortar to aid moisture evaporation.

Any idea or advice would be appreciated.

Thanks

KM

 

[Abi Cott]

Ideally turn the bricks rather than replacing them.

Damp plus cement pointing sounds like the culprit to me. Whether from a leak or recent unoccupation. The pointing will be holding the moisture in the bricks. If they are relatively soft it's a recipe for spalling.

 

[Zebra]

Your plan of action sounds about right. Is it particularly on the lower, or the upper part of the wall? That might help to indicate the source.

 

[KelvinM]

Thank you for the replies so far. The spalling is in a section between 2 and 3 feet from the ground.

 

[MatthewC]

3. At some point the current owner has done cement pointing and tried to render parts of the interior part of the chimney stack. This could be causing a problem. The spalling is now only in a small part of the interior stack so the cement render could be re-directing the moisture (?).

I'm fairly confident that it is not due to movement as the spalling is in a small area and there are no other signs of structural issues.

I found in my house that they had used a sort mix of VERY hard cement plaster on walls inside, up to a wavy line often about two feet up. What I found was that this had simply forced the water in the wall (due to poor RWG and high ground outside) up to the top of the cement, where the bricks then had spalled badly in places, following exactly the line of the so-called plaster. Happily there was no cement pointing outside, but if there had been I would have replaced it with lime.

I just removed the loose bits and lime plastered over the top, and it's fine (seven years later). Unless they are completely gone I wouldn't bother replacing the bricks, but addressing the causes of the damp usually sorts most things so your plan sounds pretty good to me, provided that you have found the only cause of the dampness! Damaged flashing on chimneys is often a cause.

 

[Flyfisher]

I am about to buy a cottage (old, but not listed). There is a chimney stack where the part behind the fireplace is exposed. I think that historically this may have been outside at some point a single storey extension was built such that this part is now inside of the house. The chimney then goes out of the roof.

We have exactly the same thing; a large chimney stack that had been on the outside of the house for a few hundred years and then partically enclosed by a recent single story extension. The stack had suffered so badly from weathering that when we lit the first fire after the extension was built it filled with smoke - what had previously been leaking harmlessly to the outside was now being trapped indoors! This shows the original state of the stack:

On this interior part I have noticed some spalling. I just wanted to get opinions on what may be causing it.

Freeze/thaw will certainly cause damage but I'd be quite surprised if it has happened since being enclosed. We have many unheated rooms but even so they rarely fall to freezing temperatures during the winter, but then we are in the relatively mild east of the country. I agree about carefully checking the chimney flashing - keeping out the rain is clearly a high priority.

Whatever the historical reasons for the damage, I'd say it should be quite easy to repair and once the house is inhabited again then further spalling is unlikely, even if the brickwork remains damp for a while, because it's unlikely internal temperatures will fall to freezing again.

As far as repair is concerned, I raked out the worst of the loose stuff - including complete bricks, and then gradually rebuilt and re-pointed it with lime mortar. I also used helibars across the larger cracks. Because the final result was to be limewashed it made the job somewhat easier than if I'd been trying to exactly match bricks etc. Also, it was already a pretty 'rough' build so my brickworking skills blended right in! These pics show the repairs and the final limewashed result:

 

[Feltwell]

Nice job FF - after your limewashing that looks really good.

 

[KelvinM]

This is all really great advice. Thank you. And the repairs that you have done look great.

 

[Flyfisher]

Thanks for the kind words - I agree its the limewash that makes the finished job acceptable. It covers a multitude of sins :wink:

For anyone thinking of DIYing a similar job for the first time I'd highly recommend a set of pointing trowels of varying widths. In fact I ground down one of mine to about 1/4 inch width for some joints - they really do make it easy to pack in the mortar between joints. Otherwise, I've found no special tools are required, just a bit of time and patience really.