Chimney lining options – Isokoat

Should your flue be in a poor state of repair there are many chimney lining options to consider. The ideal flue is the correct size for the appliance, well insulated and robust. Sometimes, however, there are limits created by the existing structure. Typically, there is a flue that has served an open fire that is failing. To prevent it leaking the flue needs lining but most of the lining options will reduce the cross sectional flue area and this is likely to cause the fire to spill smoke and fumes.  In cases like these the lining of the flue needs to be with a material that will cause the minimum reduction in flue area.

Our choice of material, when confronted with a limited flue size and absence of alternative or additional flue area, is to turn to the Isokoat flue coating and renovating system developed by Isokern. It has been used by thousands of installers in Europe since the 1950’s and is a pumice based compound that will seal the flue and also stabilise the internal structure of the flue. (It will not however have any structural impact on the stack as a whole). Neither Isokoat nor other thin materials will offer any significant insulation to the flue and thus the products of combustion may cool more quickly in a flue lined in this way and are more likely to condense in the upper flue and leave soot and tar deposits. It is important therefore with an uninsulated flue to keep it routinely and thoroughly swept.

There are other materials that reduce the flue area less than using a circular liner including a relatively new system called Furanflex . Despite assertions this material struggles to reach the the corners of the existing flue and also to maintain a consistent flue area on any tight bends.

Where Isokoat is the chosen option we apply the material as far as possible by hand having carefully prepared the surface to receive this material by replacing failing bricks and ensuring that there is a suitable stable surface to take the Isokoat.  Where the flue size is limited the Isokoat is applied under pressure with a winch and tight fitting pad. This combination forces the material into the cracks and fissures, sealing them, re-pointing the joints and strengthening the flue wall. Mineral fibre reinforcement in the Isokoat ensures that the wet material will not pour or leak away through larger cracks, but will be forced into and fill and bridge them. The coating is built up using between two and four applications to provide a smooth, gas tight flue which will withstand the effects of flue gases for years to come. The flue is fully repaired and sealed with virtually no reduction in size; very important if the correct flue size is to be maintained for the appliance served by the chimney.
Isokoat repair process

The Isokoat repair process

A hand cranked winch assembly, A, is temporarily secured to a special steel bristled brush, C, which has been made to dimensions larger than the chimney flue shape, whether square or rectangular.

The steel bristled brush supports first a heavy duty sponge section, D, and then a hessian, or similar membrane, E. As the assembly is drawn up the flue, measured quantities of the unique ISOKOAT filling material, F, are systematically poured into the top of the flue and rests on the membrane, E.

The weight of the ISOKOAT filler, combined with the pressure exerted onto the wall of the flue by the upward moving brush and former assembly, forces the ISOKOAT into cracks, gaps or fissures in the flue wall. The procedure is repeated until we are satisfied that the chimney is fully repaired.

This process ensures the chimney flue system is hardly reduced allowing the maximum size for the removal of harmful gasses from the appliance in the fireplace.

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