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Observations 18 Years Later #2

These notes and images document the condition of a contra-flow Takka built in Deauville QC during the summer of 1995. The stove has been fired by a client originally from Lower Saxony, every day for 19 seasons.

View immediately after construction

Only hard wood has been burnt. The manifolds and side channels have never been cleaned.
The stove is fired with over air via an outside air duct.


Facing Grey Stanstead Granite. Quarried 60km from the site.
Black granite trim of unknown origin.
Refractory Brick AP Green PCP-C
HTC AP Green Greenpatch 421
Castable AP Green. Type Unknown

All images below have an HD option. Click on image.

The fire box floor. The grate has warped and split but still serviceable. It will though probably need to be replaced in the near future.

General view of the fire box. In good condition and showing little evidence of Bell’s reaction.
The fire box is built in traditional style its walls consisting of a single wythe of brick layed flat. Today most contra-flow fire boxes are built with walls consisting of 2 independent wythes of shiners. This offers a possibility of replacing the inner wythe should the surface of the brick ever become badly spalled.

All three walls have multiple hairline cracks running vertically from head joint to head joint. These micro fissures are caused by thermal stress and probably happened years ago. The fissures have no detrimental effect and the fire box remains stable regardless.

View of the fire box lintel, from inside the fire box. The opening is bridged by a castable refractory concrete lintel poured onto a piece of steel angle bar lintel. In the image the dark area is the steel angle bar. The castable lintel is 3 courses high. A sheet of stainless steel acts as a radiation shield to protect the lintel and the vousoires of the arch in the facing.
Note : The steel sheet is seen here twisted diagonally out of place, to expose the composition of the lintel for the image.

View of the lintel from outside the fire box. The castable element of the lintel has three hairline cracks towards the middle. A masonry lintel 7.5 inches high will slump down negligibly if it cracks in the middle. The angle bar below assures that there is no movement at all.

View from the fire box towards the 3 inch wide throat. Note that this method of construction i.e. skew cut fire box ceiling, corbelling up to a narrow central throat is the traditional Finnish manner of construction which is said to rely upon the Venturi effect for mixing prior to secondary combustion.

Interesting is a comparison with the surface of the material in the fire box of the stove detailed here: Observations 18 Years Later #1 with what can be seen in this example. Both stoves were assessed after 18 seasons of regular use by conscientious clients, heating a similar sized house with similar wood. Neither stove has an upper chamber oven.

The stove shown in the above article, Observations 18 Years Later #2, is fired with over air. The stove detailed in Observations 18 Years Later #1 is fired with under air.

The only other variable is in materials which are not of the same origin. Obviously a considerable variable, making comparative observation of the two cases only vaguely conclusive.

Marcus Flynn


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