Has anyone had any problems with 2 inch foam board sagging between supports? If so how far apart were the supports? Gary
Put in more supports. Two inch foam is not meant to be a structural material. It will naturally start sagging. I am finding that on my lightweight modules I am probably going to need to put in more supports, too. My supports are roughly 16" O.C., with the perimeter also supported. I am going to add some intermediate supports, especially toward the center.
A word to the wise- Use a piece of 1/4" medium density fiberboard UNDER the foam board- and still make sure you have a cross piece every few feet to avoid sag. Do not rely on the foamboard alone since 1. You or someone else may lean on it and it may crack, or 2. You may be using heavy material for whatever on top of it and it may cause it to sag. I learned this, as all things, the hard way.
I have not experienced sags with large sheets of foamboard in more than 10 years. I glue (Liquid Nails) one sheet of 3/4" foamboard to 2" wood slats mounted on 16" centers. When that has cured, I glue a second sheet of 3/4" to the first. This gives a 1-1/2" laminate which is stronger than a single 2" sheet. Also, I peel off the clear plastic sheeting from the foamboard before gluing. This allows the glue to penetrate into the foam.
Something I've been considering for the second level of the next layout is laminating 1/8" masonite to the bottom side of ~ 2" foam to serve as a tension member. This would seem to be a good sag counter, would provide enough strength to allow some land form carving, and stay fairly light weight. I need to experiment. Matt
This is very timely as I am about to redo the table for the GandG. Thank you everyone! Wierd, I never thought to ask.
