Ground preparation and track laying - phase 1

There are many different ways to support track in the garden, and I spent a considerable time reading about the pros and cons of concrete versus raised timber versus loose chippings etc. without coming to a conclusion as to which was best for me. It was only after visiting several other railways of 16mm Narrow Gauge Association members that I decided that I would lay a concrete foundation for the track. I decided to tackle my proposed line in three phases, starting with the long double straight and loop on the left of the plan. The first stage was to mark out the bed, and then remove the turf and soil down to a depth of 4 to 6 inches.
The straight section would run beside concrete edging slabs that were dead level, but the loop would need a 1 in 80 gradient up and back to keep the track a couple of inches above the surrounding grass. To achieve a constant gradient, I secured a piece of metal to one end of my 2 feet spirit level. This protruded 3/10ths of an inch. I hammered a series of wooden stakes along the centre line of the track at 2 feet intervals. Placing the spirit level from one to the next gave me an even 1 in 80 gradient. The top of the stakes corresponded to the top of the proposed concrete bed.
Next came the supports for the shuttering which would be used to contain the concrete. These were of 3/4 by 1 1/2 inches timber, hammered either side of the wooden stakes. The distance between the supports was set at 4 1/2 inches, the required width of the concrete on the single track sections. On the curve I set the outer support to be 1/10th of an inch higher than the inner to provide a suitable camber for the track. Along the double straight, the supports for the wider track bed were level, using the concrete edging as a reference.
The shuttering to contain the concrete was made from 4 to 6 inch wide strips of hardboard. These were easily curved to the desired shape, and secured to then supports with screws. There is an excellent website put together by Tony McCormack which provides a huge amount of advice and information on laying concrete, walls, paving etc. which I found invaluable and would thoroughly recommend to anyone contemplating such works.
The soil under the track bed was thoroughly compacted and covered with a one inch layer of scalpings (road hardcore) to provide a very firm base for the concrete. This was left to dry out and harden for a few days.
The loop and straight needed 135 feet of shuttering. The total time it took me to get this far was 4 days, working in a very warm and dry September.
The shuttering was covered with two coats of shutter release agent sprayed on with a small handheld garden sprayer. This is a waxy paraffin and thin oil mixture obtainable from builders'merchants which helps to prevent the concrete bonding to the shuttering. Waterproof gloves, goggles and a breathing mask were very necessary during the spraying.
I hired a concrete mixed for a day. I used a screeding concrete mix of 2 parts water to 3 parts cement to 12 parts concreting sand. This worked out at 5 litres of water, 7 1/2 litres of cement and 30 litres of sand for each mixer load. This produced a very smooth and free flowing concrete without any large stones. I chose this mix so that I should be able to drill into it easily later for the track fixing screws. The concrete was poured to the top of the shuttering, compacted with a strip of wood, and then smoothed level with a float.
I placed a strip of flexible board every 8 feet or so. These separates the concrete into sections, and should allow thermal expansion and contraction without cracking the concrete. It should also make it a little easier to remove a concrete section in the future if necessary without damaging the adjacent track bed. The top of the strips was set about 1/2 an inch below the concrete surface. A few days later these were covered with a waterproof sealant.
The shuttering was removed after 24 hours to reveal the concrete bed. This has a very smooth surface and fine structure due to the repeated compating and use of concreting sand with no stones.
Track laying commenced with the points for the junction since these needed to be accurately aligned. The Peco SM-32 track was screwed into plastic plugs which were in holes drilled into the concrete. A 2mm gap was left between the rails on each yard length of track to allow for expansion in hot weather. The test train to check the levels consisted of my slowest and least powerful battery locomotive, and most free running van. The locomotive changes engine pitch on the slightest gradient, and the van rolls into the locomotive on any down gradient. Fortunately, the gradients were all where they were expected, and not in between!
The track layout was designed with the majority of the curves having a 5 feet radius. To ensure nice even curves, I used a 5 feet radius gauge from Railwood Products (Bob Wood has now retired but these are still available in a range of sizes for 0/16mm and G/45mm tracks from Marcway Products, 598-600 Attoxhall Road, Sheffield S9 3QS. Phone - 0114 2449170). The track on the loop was recovered from my previous line, and the accumulated gunk between the chairs and the rails meant that the relatively gentle curves could be easily bent by hand and held their radius.
As mentioned before, the concrete track bed was laid with a camber on the curves, the outside being 1/10th of an inch higher than the inside. This should aid running through the curves. The effect on the track can be clearly seen here on the curve branching to the left.
After a prolonged spell of wet weather which thououghly soaked the soil, I hammered 6 inch tall wooden lawn edging along the side of the concrete. This protuded just above the edge to about rail height so that it would help contain the ballast.