Tar In Your Chimney: Why It’s A Problem.

Look up inside your chimney. Can you see a shiny black surface coating a large part of the visible area of the chimney? Yes? Then you probably have a tar problem.

What Causes It?

When wood which is not thoroughly seasoned is burnt, the wood is not fully combusted. As it burns it releases quantities of steam from the moisture of the wood. The smoke and steam cool as it rises and condense out on the inside of the chimney, lining the flue with tar. Tar is, of course, a flammable substance and the area at the base of your chimney is likely to be a part of the problem. The higher up your chimney the smoke rises, the more it cools. This means the greatest amount of tar will be found at the top of the chimney, therefore it cannot be easily seen.

Why Is It A Problem?

When tar in a chimney ignites through prolonged exposure to high heat, your chimney experiences a rapid change of temperature. This can cause structural damage to the building. The tars and acids that are deposited in a chimney also corrode the mortar. In some cases this is to the extent where you will be able to lift bricks off the top of the chimney by hand. Should there be a chimney fire, this will undoubtedly increase the risk of fire spreading. Tar and condensates may also leak out of the chimney. They will come through the chimney breast and external wall which will cause discolouration and ruin the decor.

How Do I Get Rid Of It?

Tar is a sticky substance. It is extremely difficult to remove by brushing alone. The amount of tar in any chimney will, of course, vary. So we recommend a 3-step process:

  1. Do you have an older property with a chimney lined with mortar or render? And is the tar stuck to the lining? If so, it may be possible to knock off both the render and the tar together through rotary or power sweeping. This does compromise the integrity of the flue, therefore it must be lined afterwards with a flexible flue liner. An alternative product may be available.
  2. There are a variety of products on the market which you can add to your fire as it burns to release a chemical. The chemical rises up your chimney acts as a catalyst for the tar. This causes it to crystallise and harden. The brittle tar can be removed by sweeping.
  3. If you have a large amount of tar, or if adding a specialised product to your fire has not worked, then a full chemical clean is recommended. This involves warming the flue and using an air compressor with specialist equipment. This applies a strong catalysing chemical to the entire lining of the flue. The process requires 20kW of heat for up to 10 hours. By this time the chemical will have crystallised the tar, enabling it to be removed through sweeping.