Fiberglass / coatings experts - need a consult

About 18 months ago I recoated the roof of my pop-up camper with an aliphatic urethane bedliner product. The plastic of the roof was cracking and coming apart, and the bedliner was the best reasonable cost repair. you can read the entire process write-up here with before and after pics.

well, after 18 months under the GA sun with some snow and Damn Cold Weather, I have cracks again. I suspect the basic problem is that the urethane based coating hasn't been able to flex enough to keep up in the low temps.

On the original repair in the worst areas I mixed in fiberglass. I used the nonwoven mat type, basically pulling handfuls of long loose fiber out and plastering it down in the wet bedliner with more bedliner on top. Those areas aren't cracked but that method would be a pain in arse over a large area.

I'm wondering how effective it would be to buy 1/4" fiberglass loose fiber and mix it into the liquid bedliner for the second coat. How much does strength does 1/4" fiber add to concrete or other resin/ coating applications? Any experience? Anyone used loose fiber in some other custom-mixed project?

My other option is buying 4" wide rolls of mat and laying them into wet bedliner, then top coating. That would have more ultimate strength, but I'm not sure it's necessary. It is certainly more of a PITA since the cracks are perpendicular to molded in water channels in the roof and over a couple corners. It's also slightly more expensive. At some point I will start to be concerned about how much weight I've added to the top but I don't think either of these approaches that issue.

I would go with the woven, it -is- many times stronger than the loose stuff.

I would also take a look under the roof. Pull away the headliner and see what it holding it together. I am willing to bet you have some rotten wood up there. Without a stiff (and light) structure to hold the roof together, it is just going to keep cracking.

Boats are built that way.. most use end grain balsa encapsulated into the structure, but in areas of high stress they will use plywood.

Non-woven fiberglass is typically used to build up thickness, so it wouldn't be my first choice. I'd go with woven.

And why are you using bedliner instead of resin and then painting on a gel coat?

Have you considered something like HydroStop? http://www.hydrostop305.com/ It should stay flexible.

yeah...there's no wood. That's the problem. The roof is an outer onepiece layer of molded ABS plastic, a 1" thick layer of cardboard corrugation (EDIT: It's hard urethane foam, not cardboard, sorry), and a one-piece inner layer of molded ABS. It's a dumb design that was recalled and replace IF you were the original owner and WHEN the company was still in business. Now? I'm screwed.

There's no way to remove the inner liner. The foam core is wet. There's no construction that can be done to these roof short of completely re-engineering something from scratch or paying $4,000++ for a new NOS roof (IF you can find one) plus well over $1000 truck freight to ship it. No way I'm investing the time to recreate it or the money to fully replace it for a camper that has a book value of about $4k in the first place and is already 14 years old. I can a 3 year old camper with a better roof system and all the features I want (that mine doesn't have) for $6k or so, but I'd rather not have the payments right now.

I'm trying to create a strong (enough) coating to patch it through a few more years until replacing the camper is a possibility. I really hate it because the rest of the camper works great - heat, AC, the whole nine yards - and the interior is in good shape. And it's paid for.

By the way, I did find a source for 1/2" cut fiberglass as well. that should be twice as strong as 1/4", right?

Dave - see notes about ABS construction. Fiberglass doesn't stick to it, and I've already got one coat of urethane bedliner on it, so I think I'm stuck with urethan now.

Toyman - great system but too heavy, complicated, expensive for this application, plus it won't conform to compound curves where the top wraps over to the sides.

I'm finding some scientific results showing short fiber reinforcement of polyurethane showing over 200% increase in tensile strength (http://www.4spepro.org/view.php?source=003956-2011-11-29) The study linked there uses a different PU resin and much shorter fiber, but I would think some increase would be realized.

Am I correct in thinking that tensile strength is the criteria of concern for a coating over a split substrate that is trying to pull apart? Seems like the coating would be tensile-loaded at that point?

An epoxy resin rather than a polyester should still stick to the ABS surface if you really rough it up. Try and buy a wide roll of the cloth so its easier to apply and just run the E36 M3 over the whole top.

It sounds like you know how to work with fiberglass. Why not just cut off the roof and use it as a mold to make your own fiberglass roof? If the rest of the camper works so well it would be a shame to junk it if there's any (viable and cost-effective) way to fix it.

David