Inspect your Chimney Breast! What to look out for when checking your chimney breast.

Inspect your chimney breast. An odd statement to most, I imagine. However it is something that you should do occasionally, just to be sure that everything is OK. There are problems with your chimney breast that can become quite serious, and it pays to know how to check your chimney breast, and what to check your chimney breast for. As always, if you are worried, get the chimney swept by a certified chimney sweep and ask his advice.
The problems with modern chimneys, that is to say post 1965 are fairly limited. As long as there is nothing obviously wrong with them, they are usually OK, although one useful tip is to run the palm over the breast when the fire has been alight for a while and check for hot spots, especially low down.
The older chimney breasts are where the problems tend to lie, and it is a good idea to inspect your chimney breast regularly each year so that if there is a problem, the remedial work will not be so grave. The chimney breast will often show signs of staining or damp patches, especially on bedroom chimney breasts as it is mostly bedroom chimneys that are sealed off, and this reflects a problem that stared inside the flue, and which has been a long time in developing.
When you burn anything, there will always be acid formed. The flue gases contain a lot of water, and this combines chemically with the products of combustion. You get carbonic acid because burning carbon releases carbon dioxide, and carbon dioxide plus water gives carbonic acid. Likewise, any sulphur in the fuel gives sulphurous and sulphuric acids, and nitrogen in the air that feeds the fire gives nitric and nitrous acids.

This is why you shouldn’t burn plastic like PVC on the fire as it has quite a high chlorine content, and causes a lot of hydrochloric acid.
All these acids condense out on the inside of old Victorian style chimneys (Pre 1965, yes, I know she had been dead 65 years then, but they were still making them that way.) These chimneys were lined with cement mortar, and the acids will strip that away over the decades, before eating their way into the mortar between the bricks.
Goodness knows that’s bad enough, but as these acids eat into the mortar, they leave salt deposits behind, and therein lies the cause of the damp patches. Salt is hygroscopic, i.e. it pulls water out of the air. In a normally functioning chimney, air flows up the chimney, and this air pulls water out of the liner and an equilibrium is reached, where the salt pulls the water in and the air flowing up the chimney pulls it out.

This equilibrium could in theory go on forever, but what so often happens is that the householder gets tired of all the expensive warm air rushing up the chimney and decides to close it off. Now there is no air running up the chimney to keep it dry, and the salt has the atmospheric water all to itself. This is why a proper closure of the chimney involves getting it swept by a certified chimney sweep, sealing it at the bottom, filling the flue with vermiculite or perlite, and sealing it at the top.

If it isn’t sealed like that, and so many aren’t, then the atmospheric water keeps coming in from the outside, and the salt moves further and further into the stack, until it reaches the chimney breast surface. At that point it can then pull water in from the room, and people often report that the damp patches grow and shrink in accordance with the weather. Staining is often a warning sign that creosotes etc, are riding the water from deep inside the flue.

The cure is surgery. All the stained plaster needs to be removed, for a significant distance around the area, and replaced by waterproof plaster. Do take the advice of a qualified builder about this.

On a final note, it never hurts in older properties to get into the loft once in a while and look for any problems that may be occurring in the loft section of the chimney. It isn’t common, but making sure that everything looks OK gives peace of mind.

To recap.
1. If you are worried, get a certified sweep in and pick his brains.
2. Know what to look for, chimney breast stains etc.
3. Don’t ignore any problems. They are always best dealt with promptly.