September 11, 2010.

John R. Bentley 2010.

brickwork details
Boiler Setting and Firebox
for the steam sawmill engine

The question comes up on occasion about the makeup of the brickwork on this boiler setting. Well first of all, the actual setting is made from heat-blackened steel sheet which has been lined with ceramic blanket insulation. The front and back ends are cut from 3/32" steel plate. Four long stainless steel rods, running the length of the boiler setting hold everything together by means of brass nuts on the outside of the two endplates.

This is very similar to the construction style of the old Stuart 500 Series boilers. The main differences are that I have provided a steel floor, and it is slightly altered at the back since this is a horizontal return tube boiler therefore the lower half of the tube plate must be enclosed.

The brick sides are separate pieces, loosely held in place against the walls of the steel setting to avoid any potential problems from differential expansion. Of course these are not real brick, but they serve to prevent singed knuckles when the metal is hot.

A view of the right side

The wood bin holds the brick wall against the actual steel wall

Bottom of the wood bin showing one of the holes for the locating pins

Stainless steel locating pin

The basic material I used for the panel is Masonite - sometimes called Marsonite or Isorel. It is a hardboard and a completely natural wood fibre product free of glues or resins. I used common pegboard with a regular hole pattern as often seen in home workshops to hold small hand tools on a wall.

I applied Durabond 90 on the smooth side of the pegboard with a plastering knife until the compound oozed through the holes on the back side. I then used the knife to smooth the compound on the back side of the board. This allowed the compound to get a very strong grip on the pegboard. When it was dry and hard, I sanded it smooth and flat on the outside.

Durabond is a chemically-setting type of powdered joint compound used in the home building trade to couple joints between plaster board wall panels. It is very durable when hard, unlike plaster or the sanding type of seam fillers which are comparatively delicate. It is sold as a gray powder which is mixed with water.

I actually made three panels - one to be used as a test piece. My testing method was a bit basic, but nevertheless revealing: I repeatedly threw the completed panel flat against a concrete floor in an attempt to crack the layer of Durabond. It just couldn't be done. There was some very minor damage at the corners, but no amount of force would develop a crack across the surface of the panel.

This shows the unmarked Durabond 90 backing on the board

I marked out the mortar lines with a pencil and ruler, then cut the lines with a knife and straight edge. I used a small three-cornered file to widen and deepen the grooves. The vertical mortar lines were done taking care to avoid going through the horizontal lines. Painting was with almost dry paint applied with very small flat model brush. I used flat Caboose Red and Black - very sparingly from a piece of card used as a pallet. The white colour of the compound was allowed to show through in places. Invariably some of this paint went into the mortar lines, but some quick work at the end with a tiny three-cornered file solved that problem.

The final finish was composed of a couple of good coats of clear satin polyurethane on both sides of the panel to seal it from dampness. This was applied with a normal size brush.

I should mention the plant's baseboard surface. 
My sand colored base was made from thick plywood with clear wood edging applied around the perimeter. I brushed on a coat or two of oil-based satin polyurethane as a sealer (that material goes for miles!).

I acquired ordinary sand and washed it repeatedly to remove salt and that other stuff from the seagulls - as it might not help the adhesion with the modern varnish. It can be dried in an oven pan in the stove. Of course in hot weather it could just put it in a flat pan to dry in the sun.

Back to the job at hand: I masked off the wood edging and applied another coat over the plywood. I put the clean dry sand in a shaker and sprinkled it into the polyurethane. I repeated this with about six coats of fresh urethane then applied a couple of final covering coats without any sand. I wanted enough coats on top to round the grains, so it wouldn't act like sandpaper. Polyurethane dries quickly, so the overall job is not a time consuming process. The sand appears darker in the polyurethane - like wet sand. It seems to have provided a very durable surface for this steam plant since 1997.

A quick look at the firebox:

Painted brass doors were formed over a wood pattern in one piece then bisected

The complete firebox is removable from the front of the boiler setting

Here you can see the ceramic blanket insulating material
It is attached to the walls with wood stove gasket cement

The blowdown pipe is visible at the back
(it should have insulation or a deflector in front)

Here is the complete stainless steel firebox
The fire doors are formed from brass sheet and painted with high temperature flat black paint

Note the angled flue gas deflector plate at the back

The grate rests on these two stainless steel rods (actually one U-shaped piece)

(note that the brick colour is over lighted in these shots to show detail in the dark firebox pieces)

This is the back of the U-shaped rod
It is retained by the head of a stainless hex head bolt

Silver brazed stainless steel grate
- could use a cleaning!

Bottom view

Silver brazed ashpan

Adjustable front damper

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