So, your canvas car roof needs a new roof. You are putting a new canvas roof on it. But, you have to penetrate the roof in a bunch of places for:
- Trolley pole wiring
- Pole hooks
- Roof walks
- Vents
Etc. etc.

How does that work? How do you seal the roof around those areas? The point of a canvas roof being that it can float around while the roof twists as the car goes down the track - right? How does it float without hanging and tearing at all these penetrations?

If you go with EPDM does that change anything?

In practice I believe the canvas will move very little over the roof itself. So you stretch it as tight as feasible, then start cutting holes or fastening down saddles and what not, and the canvas is anchored at those points. It will still stretch a little when it has to. It's a pain, especially if you have things like cables that have to go through the canvas during installation, but somehow it works. Use lots of caulk.

As for newer materials like EPDM I couldn't say.

If you are going through the trouble to replace the canvas roof, whether it be with canvas or EPDM, for gosh sake, replace the tack moulding! All the work of prepping the roof, stripping off old canvast, streaching it, won't make a bit of difference if the canvas or EPDM doesn't have a good, solid survace to attach to.

It seems that most people who have been using EPDM on roofs have been gluing it down, anyway, so this negates any movement relative to the roof beyond what the material can stretch.

With canvas, most the penetrations tend to happen either close to the edge (smoke jacks, toilet vents) or near the car center line, so the canvas is only constrained "mid span" so to speak, so is still free to move over the greater portion of the roof.

The two Milwaukee streetcars in the collection at IRM have an interesting detail in this regard, both cars had illuminated signs or something added at some point in their career, and the wiring was run exposed on the arch roof, penetrating the roof mid way down the curve, half way between the trolley boards and the tack molding. The wires were run straight down the roof, perpendicular to the track, below the level of the penetration, where they turned 180* in a "J" shaped arrangement. This allowed a flap of canvas to be tacked in caulk over the hole in the roof, with the opening for the wire on the downward side, where it would shed water. This would be easy to do with a piece of EPDM glued over the hole, with the space around the wire pumped full of elastic sealant.

You have a choice with EPDM as to whether you glue it down in its entirety, or just around the perimeter and at penetrations. There's more ability to "slide around" if you do it just where it is aboslutely needed.....but given that both membranes are weakest in abrasion, do we really want to allow for the greatest slideability in either case?

I've put on canvas by bedding it into gloppy white roof coating, stretching and tacking as I go, then imbedding a couple coats while still wet, then covering with an additional coat or two drying between. Top coating can be done in acrylic paints tinted to your preference. It's easy to apply patches using this method too.

EPDM seems more robust for cars in service and kept outdoors, and is also very easy to patch - glue it right onto the break. Light colored membranes do best for obvious reasons.

If your roof is twisting and racking a lot going down the line, i think you have both structural and roadbed problems to solve......

dave

There is a company in Media, PA that makes a roofing product originally for tin roofs of buildings, but has been used on railcar restorations. The system consists of a paint like primer, then an adhesive material that you roll on, then imbed a fiberglass mesh into it, then apply another coat of the adhesive type material, let it dry, and then apply a finish coat of the color that you want. The company advertises in the National Preservation magazine.

Fred Heilich

Bob,

On canvas roofs I have worked on, for the items going on the roof which are being clamped on like cleats, after the canvas has been stained push a welding rod up from under the roof at each bolt hole. Someone on top of the roof rubs chalk on the protruding canvas. Then a razor blade is used to cut a bolt size hole in the canvas. The bottom of the cleat is heavily coated with white lead paste, or modern equivalent, and the cleat is bolted down. On larger items like large wires or pipes, the hole to be cut in the canvas has a circle of tacks driven around it first. The hole is cut and then a copper or tin plate flashing is coated with white lead paste is tacked down. The flashing is usually some sort of a cone soldered to a circular sheet formed to the curve of the roof. Al made all of these for 1005. On roofs from frugal properties like Key System, the flashings were made from several layers of canvas with lots of white lead paste. Then the roof and all the attachments are painted with another coat of canvas stain to blacken, or what ever color, the flashings.

The SN caboose had a rubber roof on it that was many years old. After working with that roof, I would not use rubber on a rail car roof. My view of the world is from a place where the cars are keep indoors when not being used.

I used black Awl-Grip with the flattening agent on our metal flashings. Looks lots better than gloss.

I know. :)


Well, the ancients did not glue it down. They certainly could have easily. But they didn't. In fact they laid felt under the canvas, perhaps to protect it from nails/corners and perhaps to give it abrasion resistance, but definitely to have the opposite effect of gluing it down. The paint would have had the effect of gluing the canvas to the felt, but not necessarily to the wood.

Now WHY did they do that? "Them who don't learn from history are doomed to repeat it".


Many groups have testified right here on how carbodies flex. Makes sense to me, I've had an automobile with T-tops, not to mention, LOL, speeders*. Canvas roof implies wooden roof, if not wooden car. Steel/wood cars are basically a steel bathtub, that has no reason not to flex. Maybe only a fraction, but the roof is not structurally strong enough to stop it. So it must move.

My hunch is the movement dissipates via microscopic movements all over the roof, e.g. in the tongue/groove. When that is defeated by rigidizing the roof (e.g. with fiberglass), the motion is concentrated in places less well equipped to handle it, i.e. the weakest point.


*Speeder cabs are built with specific devices to allow for roof/body flex. When some clever customizer defeats those devices and tries to force the car to be rigid, it breaks the car somewhere else. I see it all the time.

I've also seen the rigid and brittle fiberglass roofs fail due to movement of the substrate.

I've also seen wooden cars resided and reroofed without tightening the loose tension rods that hold everything together. No matter what you use this is going to work loose or fail due to too much movement.

What about the galvanized iron flat seam soldered patchwork roofs? I've found them on some of the old wooden cars I've dealt with.

dave

On the roofs i have put new canvas on, only about 20% has a felt or paper underlayment. The underlayment was probably installed to reduce the visibility of the seams under the canvas and to keep the canvas, which moves on the roof, from wearing on wood edges. Before installing the wood it has to be properly prepared. If new wood is being installed, it should be primed on all surfaces before it is installed After installing new wood or preparing existing wood start with setting all the nails quite deep. Then I use Abatron wood epoxy to fill the nails and other depressions. Then heavily belt sand the roof to curve the roof boards to the contour of the roof. I have seen bonnets sanded so heavily by the car builder as to remove half the wood thickness. After sanding reprime and paint the entire wooden roof. I use a cream colored gloss alkyd enamel as the top coat on the wood so it's looks like the white lead the car builders used.

One reason for all the painting and sanding of the wood is to kill any splinters that might get into the canvas while it is being slid around to position it. The other reason for all the priming and painting is that if the car is going to be out of doors much the heat from the sun will try to dry out the top side of the wood causing it to cup. This cupping will result in the wood joints being visible, it will loosen some of the nails and the raised joints which will wear on the underside of the canvas. Also the painted roof boards will not absorb the oil in the canvas stain out of the canvas. This is important as the oil is what makes the canvas water proof.

I have seen canvas roofs originally installed both by St Louis and American where the canvas was laid in soft white lead. The white lead with the canvas pattern still embedded in it is still on the roof boards. I assume this is another effort at getting a smooth canvas roof. Most of the old canvas roofs I have removed were original to the car. This is evidenced by the tack patterns in the roof boards. I have discussed with with Donald Curry at Seashore and this is also his experience. I attribute the long life of these canvas roofs to all the white lead the car builders used. I suspect the toxicity of the lead prevents canvas destroying organisms from rotting or eating the canvas.

All rail cars are flexible. If you look at stress strain curves for steel you will see that where there is stress there is strain. What that simply means is any load on steel will result in it deflecting. I have ridden on the roof of CCT 7 around the loop at WRM. As the car starts into the super elevation a 60 foot long wrinkle developers diagonally across the roof. When the car comes out of the curve the wrinkle goes away. CCT 7 is an all steel interurban baggage car with two doors in each side and a wooden roof. I assume a coach without the two large baggage doors would be somewhat more ridge, but it will still flex.

Canvas roofs were durable and appropriate for rail cars. But they must be properly installed and recoated with canvas stain if they start to dry out.