Fiberglass over XPS

[Westley]

Okay - to continue the conversation, here's a post I made under FRP:

Feedback please?

Yes, it's my understanding that the "P" stands for plastic.

But it's also my understanding that they include polyester resin in the definition of plastic.

So, I thought that in the mfg process, the FRP is made using fiberglass and polyester resin.

I do know that if sanded in prep, FRP and epoxy will stick together super well and bond with cured laminated fiberglass like used in boat making, which I think is cured polyester resin and fiberglass.

I haven't tried bonding FRP with XPS, yet, but I did bond 1708 fiberglass with XPS using epoxy resin. The result seems very strong for just one laminate.

I have a supply of FRP that I scrounged. It's the type used on the roof of the over-the-road trailers. I've used a little of it and find it to be very strong and bonds well. It's quite flexible and about 1/8" thick or less.

I used two of the XPS 150 sheets from Home Depot for the experiment, each 2'x2' X 1" thick. I roughed up the surfaces with a RO sander, 40 grit. The fiberglass/epoxy is in the middle of the sheets of XPS. When cured, I trimmed and squared the edges on my table saw.

With the resulting 2" thick panel is suspended by the edges, laying flat, I can stand on it, bounce, and it holds my 220 lbs just fine.

I don't know if that's a sufficient test or not. There may be other issues with 150 XPS, such as heat and perhaps delamination from stress, or perhaps expansion/contraction from temp changes, leading to delamination. The XPS is not strong stuff, and if there is failure it will be the XPS that gives way, not the epoxy/fiberglass.

[tony.latham]

So, I thought that in the mfg process, the FRP is made using fiberglass and polyester resin.

FRP is plastic with fiberglass mixed in with it. It's not cloth. Much like the glass-reinforced nylon that your trusty drill is made from.

Tony

[Westley]

Yes, The FRP I've seen looks like it has strands of fiberglass going in all different directions. There may be some made with cloth or continuous strands or matt or woven in some manner. FRP itself is not the same as fiberglass cloth. FRP is far more rigid than fiberglass cloth.

I think the FRP used in bathrooms is far different stuff compared to that used to skin RVs (Filon). UV protection for one and strength for another.

Also, I'm sure the FRP used for roofs on the over-the-road trailers is far different than the bathroom stuff.

Here:

https://en.wikipedia.org/wiki/Fibre-reinforced_plastic

https://bedfordreinforced.com/why-frp/how-frp-is-made/

https://www.livescience.com/60682-polymers.html

From what I think I know, the FRP made for bathroom walls may be suitable for the inside of a camper, but I wouldn't use it on the outside, especially where some structural strength is counted on.

Also, the folks at the building supply stores are going to recommend some sort of FRP glue for attaching the stuff. From what I read, that glue never hardens up, but stays flexible, gooey, which is fine for walls that don't move down the road. Frankly, I wouldn't use the bathroom FRP, nor the FRP glue on a camper build. And if I did use it on the inside, I would sand it and epoxy it to the wall, then prime and paint it with some good two-part boat paint.

But then, I don't know how I could hold it in place on a vertical wall until the epoxy set. Initially I was thinking applying it to a wall laying horizontal during the build phase, making a structural panel, which is the way I plan on using the FRP I have.

Fiberglass cloth can be used to apply to a vertical wall.