Sooting
As sooting penetration of the casing stones is a fireplace with water, tar and acids called, leading to brown spots, partly unpleasant odor. It arises from condensation of condensable components of the combustion gases. As a result of sooting, the chimney wall joints may break free from frost , escaping hot smoke gases and flying sparks can then rather ignite the dry wood of the roof structure.
The flue gases from a combustion system are cooled down on the way through the fireplace and the chimney . If these temperatures do not reach high enough temperatures due to the way the boiler or fireplace is operating , they can still cool down inside the chimney to below the dew point temperature of the substances in the flue gas. The condensable compounds contained in the exhaust gases (for a detailed list, see condensate ), especially water vapor , volatile unburned hydrocarbons and acids, condense as a result.
The cooling of the flue gases also reduces the buoyancy and, associated with it, the chimney draft , which gives the flue gases a longer residence time in the chimney and promotes further cooling.
Sooting can occur with incorrect planning of condensing and low temperature heating systems, even with longer chimney sections through unheated rooms (storage tanks) or irregular, sporadic firing with solid fuels . The flue gases have a high proportion of water vapor and relatively cool exhaust gas. As a remedy, acid-proof pipes made of stainless steel , plastic or ceramic are usually pulled into existing chimney pipes (for more on this see condensing boiler ).
Free sulfuric acid from the condensate affects the cement and the carbonate-containing aggregates in mortar , chimney stones and plaster. Among other things, the lime contained in the cement is converted into gypsum and ettringite . The reaction products "float", that is, they swell , and shatter the building material . In addition, the wet wall structure can also be impaired by frost bursts in winter .
In the case of heating with solid fuels, sooting can be triggered by unsuitable fuel, such as varnished or impregnated wood, chipboard or similar materials whose combustion can produce acids and other chemical substances. Firewood that is not sufficiently seasoned and therefore damp also contributes to this, as the moisture condenses in the fireplace.