Re: another caboose construction question


Dennis Storzek <destorzek@...>
 

--- In STMFC@..., "Mike M" <train_junkie@...> wrote:

Ya' gotta' love the 'net. That's fascinating Dick, thanks for digging
that up and posting it. Now that I know what cotton duck is, I can see
how it might be described as "canvas" in reference ot freight car
roofs. Perhaps the "Mule Hide" often referred to in freight car
construction was cotton duck treated or coated with some sort of black
waterproof sealant.

Cheers!

Mike Mucklin

If the specification says "cotton duck", I'd say that means raw
natural canvas, painted or otherwise sealed after application. If it
says "Mule-Hide", I suspect they mean whatever treated canvas product
Mule-Hide was selling. Since the ad calls it "waterproof canvas" I'd
suspect it's pretreated with oil or paraffin or something, lake canvas
tarps used to be.

I worked on and with some of these materials back in my railway museum
days in the seventies. I hope Mike can bear with the mention of
streetcars, interurbans, and passenger cars for a moment; we'll get
back to freight cars eventually, cabooses anyway.

The roofs on trolley cars were traditionally wood, since there is a
lot of high voltage equipment up there, and a wood roof is a good
insulator for anyone who has to work close to the live conductors.
Trolley cars were traditionally roofed with natural cotton duck,
because it stretches well; necessary to deal with the compound curves
on the ends. Steam road coaches have less severe curves at the end, so
apparently pre-treated canvas could be used. On some trolley cars the
curvature is severe enough that one needs to wet the canvas to get it
to stretch and let it shrink in place. The roofs are done with the
minimum number of pieces; arch roof cars are typically done with one
piece, if material of sufficient width isn't available, it is seamed
down the middle with a triple stitched seam like a trap. The edges are
turned under and tacked with about a million tacks; tacks on 1"
centers in two staggered rows about ¾" apart was typical. On really
sharp builders photos one can often see the pattern of the tacks, and
sometimes little puckers at the corners.

We used to have quite a bit of debate about whether it was proper to
"tar" new canvas. One school of thought is that canvas should be
finished with oil paint, which was what was typically done on marine
vessels, which is where the membrane system seems to have originated.
Linseed oil is a naturally occurring polymerizing oil that doesn't
harden completely for a long time, the end result of painting with
pigmented oil is a somewhat flexible waterproof membrane reinforced by
the cotton fibers. There is ample evidence that this was done to a
large extent, because there are many examples of Terra Cotta red,
brown, gray, and olive roofs on prototype wood equipment. The argument
against using asphalt emulsions, like car cement, is that the solvents
dry out and the material gets hard and brittle more quickly, then
cracks, which lets water seep into the cracks and rot the cotton
fibers. Nevertheless, I've removed examples of old canvas with asphalt
bleeding through the weave, which seems to prove that this was the
first and only material applied to the new canvas. The purpose of the
treated Mule-Hide product may have been to make the canvas itself less
susceptible to decay. Either way, when roofs got old, the accepted
practice was to mop them with asphalt emulsion to seal the little
leaks and hold them together for a while longer, so older roofs tend
to be black.

One of the things that connects "tar paper" to cabooses in people's
minds is preserved display cabooses. Once `Ol 97's caboose went into
the park, the Parks Dept. treated it like a building, and used
building materials to try to keep it from leaking. I've done a lot of
that myself. When preserved equipment has to sit out in the weather,
the first priority is to keep it from leaking and deteriorating
further, even if the materials aren't 100% correct. We used to use a
product called "pilot roofing" quite a bit; this was 90# smooth felt,
like roll roofing but without the granules. On a flat roof, or one
that curved in only one plane, like an arched roof caboose, this could
work quite well. The biggest problem was the 3' width of the material.
These wood roofs are really quite thin; 13/16" was common, but so was
9/16", and the big roofing nails would split it severely. We would
occasionally run the strips across the car so it was only nailed into
the heavy molding provided for this purpose at the eaves, simply
gluing the seams together with asphalt roofing cement. Coaches were
much more difficult to do with roofing felt, the curved ends had to be
pieced, and the end result looked more like a sheet copper roof as
used on some older passenger equipment, but that's a subject for
another list.

Dennis

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