Masonry Chimneys

These can simplistically be divided into three types:

• Victorian

• Pre Victorian

• Post Victorian

Pre Victorians are the inglenooks and the larger flues. By and large these are more immune from problems and only suffer from smoking. See below.

Victorians are usually well designed and thought out, but due to being lined and constructed with a cement/mortar mix they suffer from a number of problems due to this. They seldom smoke.

Post Victorians are those constructed after 1965. They are almost exclusively terracotta lined, but unnecessary bends and design problems (see ‘Throats and Voids’) often cause problems and smoking.

Pre Victorian Chimney Problems

Structurally sound, these are often of claybat construction with a daubed clay lining which can contain animal hair, straw etc. This is very resistant to the acid corrosion from the products of combustion (see ‘Chimney Chemistry’) but chunks of liner will often fall.

The big problem is that these chimneys were usually designed to have a small, smokey fire to cure meat, with the draughts from the house helping to keep the smoke mostly going up the fireplace.

Nowadays we want a small hot fire with no draughts, and because this incompatible with the original design, the fireplace has to be modified, not always correctly (see ‘Hood Sizes and the TARDIS Effect’).

Victorian Chimney Problems

Since the basic design is good, the problems with these chimneys are usually structural.

Victorian chimneys are essentially a square brick tube that is built and lined with cement mortar. This is attacked by the acidic products of combustion (see ‘Chimney Chemistry’) which results in a number of problems, including:

a) The pointing at the top can become so damaged that the stack is essentially bricks in a dust matrix

b) Where the chimney is up the side of the house and has a long unsupported length, corrosion can make the windward side stretch more because it is cooled by the wind and it starts to bend, exactly as though it were bending with the wind.

c) Within the flue, the acid corrodes away the mortar until it eats through between the bricks and causes a hole that fumes can travel through. Once inside the other flue they cool and fall down into the other room. The only real cure for that is to reline the chimney (see ‘Relining’).

Sometimes the corrosion is so bad that the bricks between the two flues come loose and can, in extreme cases fall down the flue or flues. Symptomatic of liner corrosion is the steady fall of particles of liner. This can be continuous or intermittent, and sweeping can sometimes make it briefly worse.

High humidity can affect it, and the size of the falling particles can vary enormously. The particles can look like soot fall, but this is because they are stained black. Their texture is very different though when you rub them between your fingers. This acid corrosion can eat away the cement holding the pot in place, which can cause it to become lose or even fall.

Post Victorian Chimney Problems

Since all such chimneys should have a properly built terracotta lining, none of the corrosion problems should ever rear their ugly head.

The problems usually associated with these flues are those of poor design where flue, fireplace and terminal are not in harmony, the voids are unsuitable and the bends unnecessary and savage (see ‘Bends’).