One quick and easy way to build a railway in the garden is to make it out of timber. You can fairly easily bang some timber posts into the ground, and fix a plywood top to them, cutting the plywood to size and shape to get the curves you need. However, there are one or two things which you need to be aware of.
What sort of plywood?
First, there are lots of different sorts of Plywood you could use, some are better than others.
- OSB - (Oriented Strand Board) This is the stuff used to board up broken windows, and is also used to make shed roofs. It's very cheap, and looks like lumps of wood squashed and glued together. Actually, that's exactly what it is. It has been proven by The Building Research Establishment that this material will lose 40% of its strength if it gets wet. If you are going to use OSB, then you'll need lots of wood preserver and bituminous glue, on the edges and a covering of roofing felt to try to keep it dry. It will also need supporting underneath with battens.
- Exterior Grade plywood or 'WBP' - (Weather and Boil Proof plywood) This is a great material to use. As its name suggests, it's designed to withstand the weather. The glue used to make it is water resistant. Even though it's designed to be used outside, protecting it from the elements is still a good idea, to make it last longer; either by painting, varnishing, or covering with roofing felt.
- Marine Ply is designed to be immersed in water, and made with a waterproof adhesive. However, when used on boats, it is only propery protected when covered with a generous number of coats of varnish. It tends to have a nice finish to it on one side, and can be expensive.
- Shuttering Ply, as its name suggests, is used in the construction industry for making boxes which are about to be filled with concrete. The ply is discarded when the concrete has set. It's rough faced, and not designed for long-term exposure to moisture.
- If after reading this you've decided that Plywood isn't such a good idea, a board material called Cape Pyrok is available. it's a cemented particle board which is Fireproof, inert, strong and very heavy. It's difficult to cut to curves, mind you, and might make you wish you'd gone for the brick-laying approah instead!
All plywood will bow unless properly supported. I have a set of baseboards made of 22mm Shuttering Ply, which are supported every 4 feet (approx 1.2m). Some of these are still straight after being left out untreated for over a year, but some are starting to bow, and need attention. Treated battens running the length of the board would help here, and something about 2-3 inches (50-75mm) deep will probably be enough.
Soak the boards in a perserver like Cuprinol for ten to fifteen minutes per side before installing them (to do this, you'll need to make a waterproof tray to do the dunking in).
Paint the edges of the plywood with a bituminous paint. It will stop the water seeping in, which could otherwise cause the plywood to de-laminate.
With wood perserver alone (i.e. no roofing felt), WBP is known to last for over ten years in a garden railway.
Generally, you can improve the weatherproofing of a plywood base by covering the ply with roofing felt (a bituminous felt material covered in fine gravel).
Adding roofing felt to the armoury against the weather is a great trick. Not only is it exactly the stuff for keeping the rain out, because it's a roofing material, but it is also covered in little grey gravel shippings which pass for ballast or slate waste (slate waste is used as a sub-base material on some Welsh narrow gauge railways, being readily available.).
The aim with the roofing felt is to keep the wood dry, more than to keep the rain off. You will probably fix the track through the roofing felt to the plywood, thereby breaching the waterproofing in places. The bituminous material will close around the nails or screws to some extent, but if the felt is merely nailed or stapled in, there can be air pockets between the felt and the plywood, where water can gather. This problem can be minimised by glueing the felt to the ply with roofing adhesive. The stuff you apply with a heat gun or blowtorch is best (and hey, getting the blowtorch out is going to be fun! just be careful not to set fire to anything in the process!)
The roofing felt should be folded down the sides of the plywood to protect the edges of the ply, but should not be folded underneath, where it could allow more rain to gather. Instead, it should be left hanging down, allowing the water to drip off. A railway built using this technique has lasted over 15 years.