Re: Tar roof References needed

I have been involved with railway preservation for more than 30 years and I have never heard of tar-covered canvas roof. But then I may not have heard of everything.
Canvas covering of wood roofing is usually painted or otherwise sealed. Since it is on a wood roof usually on a wood car it all has to move and give. So you never want to paint the canvas so much that it is stiff and will not flex.
I would suggest that you go over to the Railway Preservation News website and post your inquiry at its bulletin board called "interchange." A number of experienced people monitor this board and you can probably get some good information.
Brian Norden