I think most are steel or aluminum frame, maybe a marine grade plywood core for strength, aluminum or steal outer skin, with a rubberized traction surface. I know EBY is using a ramp made of some poly material now. GORE builds an all aluminum ramp... Need to keep it very strong and as light as possible.

Contact Mr. Jackson Gore, he can tell you how he's been building ramps since 1964... http://www.goretrailers.com/

When we purchased a 2H steel BP trailer, in addition to a restoration, I had to rebuild the ramp. It was constructed of a steel angle iron frame with a steel faced exterior skin. The core and exposed interior face was a piece of plywood, with attached lateral strips that helped with securing footing. The plywood was bolted to the steel frame's perimeter.

The original plywood was an inferior grade, and had become rotted and delaminated. In some spots, only the exterior skin prevented holes from being punching through the laminate. The ramp was dismantled to just the bare frame. A new piece of steel skin was then installed into the frame. The inside face was coated with a primer and oil based paint. I purchased a piece of Baltic Birch plywood, 3/4" thick (18MM) and cut it to fit. It was surfaced on one side with two coats of WEST System epoxy to seal that face and edges. After that dried, the epoxied surface was sanded with 30 grit paper to roughen the surface. Additional epoxy was mixed and thickened with Cab o sil and liberally spread over the Birch's surface. The plywood was then placed into the frame, with the wet epoxy against the exterior skin. Additional thickened epoxy was added around the perimeter seam to seal things into place. Various weights were added to hold the plywood against the steel until the epoxy set and cured.

The interior ramp surface was then expoxied as well. It was subsequently painted and oak strips were installed to help with traction. The Baltic Birch plywood is far superior to common lumber yard variants. The 18 MM BB grade has 13 plies of construction, many more than the typical sheathing or cabinet plywood grades most yards sell. There are no interior voids and the surfaces are fully finished. It is very rigid and strong. It is NOT water proof and is made for interior applications. By epoxy coating and encapsulating all its surfaces, it is made water proof.

Today there are many more choices of non skid materials, many of which can be used to improve the surface's traction. Various coatings and rubber/plastic materials can be added. A bed liner material with sand added before it has dried, works well on aluminum running boards; it should be as effective when added to an epoxy finish.

The finished ramp was much stronger and stiffer than the original. We saw the trailer at a show about ten years after we sold it, and the ramp was badly scuffed but fully intact and showing no structural problems. Many of the oak traction strips had been broken and not replaced. The trailer was always stored outside and apparently had little or no preventative up keep after the sale.

This type of construction could also be used in the reconstruction of aluminum doors or ramps, where direct contact of treated materials cannot be used against aluminum.