Homasote the undisputed gold standard!
Homasote is the gold standard, especially if you are hand laying track, which takes a considerable learning curve, but gives you much better looking track. Homasote gives you unparalleled support of the ties, holds a spike better than anything else, and has exceptional sound deadening capabilities.
also some folks say why have road bed at all? real railroads have ballast to support the track above the surrounding ground level and provide drainage. this will be very noticeable on a main line, and less so on sidings and yards. Unless you are modeling a poorly built short line, the track will set on a grade with a raised profile, and representing that profile, and the sound deadening capabilities are what we use roadbed for.
I have said that homasote is the best, and of course, I'm correct in this, but there are some issues with homasote that must be dealt with in some fashion, or it's use is impossible or will lead to disastrous results I will cover them here.
#1 Availability.
I live in a town with more than 100,000 people in it. Only once have I bought a sheet of homasote here, and it isn't here now. from what I understand it's main use now days is to fill places for expansion cracks when someone is pouring concrete. You can by homasote that has been milled into the proper roadbed profile From the California roadbed company. It is called Homabed, and it comes with half a box pree slotted to make it easy to curve. on request you can get the whole box slotted, or the whole box straight. you can also by blanks for under switches. good stuff, and I have gor good service from them.
#2 expansion and contraction.
Many folks have had very ugly experiences involving the expansion and contraction of homasote. It is often assumed that this problem is due to heat expansion, and while homasote does expand with heat, it does it at about the same rate as the plywood in rests on, and so that is not a problem. The problem comes from moisture. homasote is basically pressed paper mache. If there is humidity in the room, it will suck it up, and hold it for what seems to be forever. when it sucks up the moisture it expands on all axises, and this can be a serious problem. It is a problem however with a simple and easy solution. When the homabed (or sheet homasote, or strips cur out of sheet homasote) is glued to the plywood , before anything else happens, paint every exposed edge of the homasote with paint. I use the craft acrylic paints, painting the roadbed grey. you can use house paint, anything, any color, the important thing is to get two heavy coats on every exposed surface, to seal the Homasote so that moisture can't get in. For this reason I wouldn't recoment homasote over spline roadbed, unless there was plywood over the spline roadbed, cause you don't want that exposed unpainted homasote down there between the spines sucking up moisture.
OK, that is my spiel about homasote. Next lets discuss cork. Reading the posts there seems to be three themes; cork is wonderful, cork is OK, and I'm never using that stuff again. What no one seems to have pointed out is there are two types of cork material.
The first appears to be a sheet of natural cork, which has been cut to shape for our use. from my experiece, this stuff is ok under flex track (I like to paint it too (it helps get a better look when it is ballasted), but it is unsuitable for handlaying switches, as it doesn't hold a spike well enough.
The second type of cork material looks like a composite material . it looks like a bunch of cork has been ground up, and it has been cast into shape in a black rubbery material. this stuff is denser than the plain cork, supports the track better, is less likely to degrade, and hold a spike better than the plain cork but not as well as the homasote.
down in my staging yard I have used some WS foam under flex track in one section of the yard. Another section is salvaged from a previous smaller staging yard, and has homabed. the sound difference is huge, there is a lot of rumble on the foam, and only the click of metal wheels on the homabed.
for those interested in hand laying track I am doing a tutorial on building switches over in the logging mining and industrial section on Bill and Tom's excellent adventure. Questions about hand laying track will be answered there. There is also a lot of photos of my interesting track nearby in logging in east TN on the DG,CC,&W RR in 1928
whatever roadbed you use, even none at all have fun with the trains that is what we are here for.
Bill Nelson