I have always used the floating method for road bed and would recommend it. I never use wood in direct contact with the ground, it rots and attracts critters. For building bases I use 1/4" James Harde backer board on the ground. It is a cement material, I use masonry blades to cut it. Some of it has been in place for over five years. It could work for your purpose but I've never used it for that.
Good luck, Rob
For more related information, check out the other posting in this forum on "plastic roadbed".
I would strongly recommend against the use of plywood, treated or not, whether on the ground or elevated. Check out the latest issue of GR (August); Jack Verducci's article (starting on page 76) shows a good example of a building base which used marine plywood, and even that disintegrated over time. "THE problem" is that plywood suffers from all the problems of any wood, only the problems are amplified since the laminations are simply thinner sections which deteriorate even faster. It used to be all exterior plywood had to have water-proof glue; that changed a number of years ago....now it's water-resistant at best. All plywood will eventually absorb water, delaminate, warp, and become a serious maintence problem that can only be fixed by total replacement.
For roadbed I am a very strong supporter of the traditional 'floating' style, similar to prototype practice; track on a solid and very well drained bed of stone/gravel.
As for any structures, I either use solid plastic with heavy paint applications to block UV, or solid concrete. I have built a few wood trestles, but I heavily treated them with creosote (not available in the US but it is available in Canada at your local Canadian Tire store). Creosote is the same stuff prototype track ties are treated with and works incredibly well, so long as you take all the precautions of not getting it on yourself or clothing....adds a realistic railroad arome too! :) The one trestle was built using 3/4" hardwood doweling for the piling posts. I made each post about 10-12" longer than is visible to sink into the ground. Once each bent was assembled, i filled a pail with about 12" of creosote and sat the bent into that for 3 days, so that it had a chance to soak to the core. Those have now been in the ground for 4 years. I dug around one of them recently to see how they were standing up, and there's no visible signs of any deterioration (yet).
Creosote is the only thing I have found that will preserve wood for a much extended period of time, but I still give them a 'touch up' every 2nd year.
Good luck.......
Odessey
From my limited and painful experience I would not suggest using plywood. I am on the 'wet' coast, mind you, so all experiences differ. Warping, laminate separation and really wierd noise in those locations where the track is 'public'. What I mean by that is the noise of a train passing over it just doesn't sound right. Having said that, I do use some plywood base out of sight and earshot to provide a more consistant base for out-of-sight switches into a storage yard. I have heavily treated the plywood with wood preservative to try and avoid previous problems. Can't tell you if it will work as I only did it recently.
I have also tried cedar 2x6" (rots in about 4 years) pine 2x6" (Rots really quickly) and always come back to rock or concrete. For a 'tunnel' section, I replaced 2x6 with 8x16x2" thick concrete pavers, to avoid weed growth and the like. Again this is fairly new, but it sounds better and should last a while.
James http://railway.skeenapacific.ca
It will probably delaminate over time. You might be able to get a little more time by carefully sealing the edges and both sides.
Walt
I am thinking of using pressure treated plywood as a roadbed for my layout in Saskatchewan.
The base is clay soil and I expect to use 6 inch wide plywood for good support and to keep any growth away from the track.
I plan to glue ballast to the plywood for "realism".
Anyone tried this ?
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