I used treated timber gravel boards as used for the bottom of fencing panel. All joints screwed. Track (Peco SM32) was laid directly to the boards with brass pins. Given a good coat of water based fence paint before track laid. Then an extra coat about every 3/4 years when the fence panels re-done. The track was lifted about 4 years ago but the boards still serve as a shelf for potted plants after something over 20 years.

While it is not so good to look at I chose not to use felt and/or ballast as this way it dries off quickly. (Allen Morgan)

I had to rebuild a large part of my outside line last year as gales and wood weakness actually severed the line in a couple of places. The line runs about 3 to 4 feet above ground level so the wind could get underneath it. Reflected long and hard on what material to use for the relay and eventually decided on 1 inch thick decking board. This was based on the fact that I had used the material for large garden planter boxes over several years and it had stood up to the damp very well. So far it has worked well and given a robust and level track bed. It is covered by mineralised felt both for appearances and also to protect it from the worst of the water. The only issue is that for the turnouts that operate outside I have had to use surface mounted Tortoise point motors as I wasn't happy with the thought of mounting them under the board and getting the right throw. I have been impressed with the stability of the decking boards and reckon they have provided a cost effective solution. (David Corrin) I use Decking Boards Martin with great success.(Joseph Booth )

My first outdoor baseboard was made from B & Q WBP (Weather and Boil Proof) 9mm plywood, painted and with torched on roofing felt. It lasted about 12 years before disintegrating. I replaced the wood with the same and it didn't last 3 years. (Chris Simpson)

I used 19mm marine ply covered with roofing felt, the felt was wrapped over the edge of the ply and fixed with felt nails along the edge of the ply. The edges of the felt finish just below the underside of the ply so that any water draining off doesn't contact the ply itself. A hardwood strip was fixed along the edge with brass screws through small square wood spacing blocks to allow the water to drain off between the felt and the hardwood strip. Make sure any joins in the felt are overlapped and sealed, also seal any holes provided for wiring. It was done 16 years ago and the track was recently relaid for 45mm dead rail operation. I replaced the felt with new because some of the stone chippings had disappeared and the new track didn't need any wiring holes, but the timber underneath was still perfectly sound. (Phil Hindley)

I have used a thing called Buffalo Board which is a plastic coated laminated product. It is used in the heritage railway sector as flooring for coaches and is deemed particularly effective in toilet areas which would indicate a high tolerance of moisture. I have only had it in use for twelve months or so and thus far all seems well. (Martin Long)

A more expensive product is the re cycled plastic based board and beam material marketed by Filcris. It can be cut and shaped by them to what you want and is easily screwed for joints. It would appear to need little by way of maintenance once set down.

I know of folk who have used this and are pleased with it but it is quite pricey.(Martin Long)

Yes Filcris are the ones many people use Martin. The main issue they don't mention is with expansion, which can be greater than wood. So allowances have to be built in. (Mike England)

I've had Filcris board on my outdoor track for 5 years now and no issues with it. Easy to cut, drill and screw. I haven't experienced the expansion issues that some allude to, I do have small gaps between the boards. (Tim Humphreys)

Having used the Filcris material I would say stay clear, the expansion and contraction from season to season is quite dramatic. I made the bases and laid the track in the spring 4 years ago (140ft) some is on a brick base ( about 25ft) the rest is on the Filcris system, from the initial laying the base expanded through the summer and some of the joints between the track lengths split, as the autumn and winter came on I found that the contraction again was dramatic, so much so that at the moment (2nd Feb) it is more like a zig-zag. (Bill Rankin)

I now have replaced my outdoor baseboards with 11mm OSB, and am relatively happy with it. All I have done is paint it with fence paint. After two years it shows no sign of distress.(Chris Simpson)

It certainly isn't to be recommended for a ground-level line, where it may be sitting in water, but OSB3 is intended for humid conditions (e.g. bathroom floors). I have used it to replace partially-rotted softwood planks on the elevated portion of my line. It is covered with roofing felt, so just the underside is exposed to the humid atmosphere. It doesn't sag at all. This section has been in place for just 18 months, but I have other outdoor structures in OSB3 which have been in place for much longer. (Tony Peck)