I had remembered that Paul was building his very large layout using spline roadbed so before he could even order lunch I was pounding him with questions. Paul is a smart and patient fellow and was glad to share with me his experience laying what seems to be miles of Masonite spline roadbed, or more properly called hardboard spline roadbed.
He uses 3/16" hardboard but prefers the 1/4" which Home Depot didn't have at the time. His layout is HO and HOn3, so I focused on the HO. I had worried about hardboard because down South the humidity is terrible and the board has a tendency to warp. He has had no difficulty at all with it, so here in Utah it should do fine. He cuts the strips to 7/8" for the spline. For standard gauge track he uses 8 splines bonded together with yellow carpenter's glue. Paul mentioned that he heard that others had used hot glue but both of us wondered how it stayed hot enough for the bonding of a long section. Yellow works for me.
His risers are 1x4 lumber, but he says he would go with a 1x3 if he were to do it again. To start the construction he fastens the riser to the benchwork with a clamp. He then sets the height and it is ready. Next he puts a nail in the center of where the curve is going to go and lays the first spline. The next spline is offset from the first by 3-6" so that the joints don't line up. The spline is glued in place. The next spline is offset as well and glued. You place four splines this way.
Shown here are the spline made with 3/16" hardboard, the ballast shoulder which is a half of a spline cut along the middle at 45 degrees and three splines glued together. Click to enlarge.
Next you move the nail to the outside of the four splines you just installed and start putting splines on the other side in the same offset fashion. This is continued for another four splines. Then, to make the ballast shoulder on this primary roadbed, he takes on spline and saws it in half longways at a 45 degree angle. The angle pieces are glued on to each side of the road bed.
He clamps the assembly with a large amount of clamps, one every few inches. I have some samples of roadbed that he cut out on one section. They are very strong. Once the roadbed is dry he drills a hole for mounting on the riser. The riser is then checked for position and slope, then screwed down to the riser. The riser is then mounted to the benchwork with three screws to keep it in place.
I've got quite a few pictures of his fine spline roadbed and I'll post those tomorrow.
Paul...please make corrections and suggestions! I had a lot of tea at lunch and am not sure if I got all the notes on the cocktail napkin right.