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17 years later

The heater and cookstove seen here were built in 1994. The cookstove has seen infrequent use. The heater, though, has acted as the sole heat source for the log home of 1,900 square feet, burning between 6 and 8 face cords of hard wood per season.

The fire box loading opening is spanned by a castable refractory concrete lintel. This lintel cracked in the centre resulting in the slight loss of some material around the crack on its lower surface. The crack was repaired, and the slight voids filled with refractory mortar. This repair was made 7 years ago and is still sound.

The refractory brick of the core are generic low duty:
The refractory mortar Duchesne HTC.
Recycled facing brick from 1900 layed in type N mortar.

The whole interior of the fire box and throat have been parged in refractory mortar twice, seven years ago, and 2 years ago.

The heater is fired with under air which, in combination with the relatively cramped fire box, has lead to the degradation of the bricks exposed surfaces. There is no facility to reline this fire box without a re-build, therefore parging was chosen as the most appropriate option at the time. Though looking unsightly, the fire box will be serviceable for some time before more serious intervention would be necessary.

Most of the refractory mortar parging done two years ago has disintegrated. The light patch at the left of the start of the sloped rear wall is a 1 inch deep hole that was patched 7 years ago. The ‘brake off’ of the skew cut brick in the sloped ceiling top of centre occurred at the start of this season.

Detail of the broken skew cut header.

Klinkering, which is indicative of gas attack, is evident in the discolouring of the bricks surface.

View up towards the throat. The parged edge of the repaired castable refractory concrete lintel, that spans the fire box loading opening, is visible at the extreme top of the image. Note that the parged surface of the lintel and the masonry above is relatively intact, due to being washed by secondary air. The rear wall however has lost all its parging.

The parged fire box. The brick are brushed, vacuumed and then wet slightly before applying refractory mortar by trowel.

Once the season has ended, the whole fire box will be cleaned and reparged with a more suitable patching material. The refractory mortar used here as a temporary measure, (Mount Savages Super High Mull) is made for laying brick and is not intended to be used as a patching material.

It is my belief that with a deeper, higher, reline-able firebox, in high duty brick, fed by over air, the destruction seen here would be considerably less over the same time. Today most North American stove builders use over air, and build re-linable fire boxes in high duty brick.

For comparison:
Observations 18 years later
Observations 8 years later
Observations 28 years later N. Senf
Fire Box Rebuild N. Senf

The firebox in late May after a full season's daily use since the above intervention. The thin parging has separated and fallen from the relatively undamaged smooth surfaces of the fire box, but has held well in the two voids, top let centre, and bottom left.

The fire box floor having had the parging almost entirely burnt away.

Marcus Flynn


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