Chimney Bricks flaking

[AnthonyL]

What is happening to my chimney stack bricks and why?

It is a non-working chimney though I don't know if that has always been the case.

How do I fix it?

[alan_m]

Porous bricks that have got wet and the the water has frozen spalling off the front of the bricks. Some attempt has been made in the past to stop this by painting the surface.

It's not obvious how that tall mast is secured but perhaps its not doing your chimney any favours as you also seem to have cracks running through the centre of bricks.

[Steve Walker]

If it's not used, why not just remove it? Bring it down to just above the flashing level and fit a vented cap?

[alan_m]

Actually it's possibly not a structural crack but part of the next brick about to spall but the flake of brick is being held on by the paint.

New paint may prevent water entering the surface of the brick but old paint that is failing may let water in behind the paint layer and then prevent it from evaporating. One problem with painting a wall/brickwork to prevent water ingress is that regular maintenance is then required to maintain the paintwork.

There is another section further down the chimney that is showing failing paint, probably because the brick behind is also spalling.

If that chimney is to be repainted a repair could be attempted by first removing any obvious failing paint. Soak the surface of the bricks that have spalled with a water seal and use a sand cement render just to fill the missing surface layer on those bricks - then repaint. Possibly rake out and replace any dodgy pointing which may also let water in to the top of the brick. I did this 30+ years ago on my current house for a few bricks that had minor surface spalling and have noted no further deterioration or failure since.

Water Seal

If you are not going to DIY consider getting in a company that use alternative surface coatings that are meant to last maintenance free 25+ years. Or, as others have indicated, in not used remove the chimney above roof level.

[jon]

Light a fire and dry out the bricks.

[Brian Gaff (Sofa]

When I had a large rota aerial on the chimney the chimney was great, but after the lot had to come down due to age and all the lashing wires removed, a couple of years down the line and it needed work. So aerials can be good or bad for constructions. I guess we do tend to ignore chimney stacks when getting the house decorated. The guys who I engaged to do the coating of the walls did not want to know about the chimney stack. It is now rendered but painted only with normal outdoor paint. Brian

[Brian Gaff (Sofa]

Round here due to it being a conservation area in a lot of places, the chimney has to stay. Brian

[Muddymike]

Cheap bricks tend to do that. Rebuild with better bricks is the only permanent solution.

Mike

[Jimmy Stewart]

engineering bricks

[AnthonyL]

No firepace - but the chimney isn't capped - so getting damp from the inside, paint flaking, water getting behind the paint, cold weather, freezing, winds, aerial vibration. Is that fitting the picture?

Most of the similar properties are not painted at all, the whole of ours is.

[Chris Hogg]

And in that vein, is there an airbrick or other form of ventilation at the bottom end of the chimney where the fireplace used to be, to help keep it dry, or is it sealed completely?

But as others have said, the underlying problem is poor quality bricks.

[Harry Bloomfield, Esq.]

alan_m brought next idea :

With not very good paint, or maybe not even proper paint for the job.

[AnthonyL]

If there was an airbrick it's been plastered over.

Most of the estate uses the same bricks, same house design and and look around at their chimneys doesn't show the problem but most of them are not painted. I'd be sceptical about the bricks being poor as a cause.

The area is a smoke free zone so no-one is using their chimney's for solid fuel though I don't know if anyone is using them as a flue for a gas fire.

This house has had some wierd things done - I've mentioned elsewhere I blame the Italians who were the owners before the ones I purchased from. The side of the house, as the photo shows, as an extension so the outside of the chimney is now on the inside of the extension.

I think I'm going to have to get someone to have a more professional look at it.

[Chris Hogg]

Bricks can be classified by their frost resistance, amongst other things: F2 - Frost resistant, suitable for all applications; F1 - moderately frost resistant, OK for use where they don't get too wet; F0 - not frost resistant and only suitable for internal applications.

It looks to me like the builder had some F0 bricks left over and decided to use them up. Nearby properties may have had better bricks. Only F2 bricks should be used for chimneys.

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[alan_m]

Or it is the result of painting.

A bare brick will get wet but also dry out. A brick that is behind a layer of failing paint may get wet because water runs down behind the layer of failing paint (a crack where the paint is at the pointing) and then is prevented from drying out by the paint being an waterproof layer.

A brick wall can prevent water ingress to a house although it does soak up some water when it rains but, say, as a result of a broken gutter or dripping overflow pipe the same wall can get much wetter and become saturated leading to internal damp problems.

[Chris Hogg]

Yebbut frost resistant bricks don't spall, by definition, painted or otherwise. If they spall, they're not frost resistant.