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fifthwheel5 · 26-12-2018, 22:29

Kia ora everyone, all the way from sunny New Zealand,

I am not a boat owner, but you all seem to have such strong knowledge of fibreglass that I thought you may have some better ideas than I do!

I am currently remodelling an old fifth-wheel (articulated trailer) that used to be used as a mobile clinic. It has a mystery rust-coloured, chemical-smelling brown ooze coming down from several old rivet holes in the ceiling. I've attached a photo for your viewing pleasure. As you can see, it looks to be quite oily.

The roof is fibreglass and seems to have been neglected for a long time. Beneath that, it has spray foam insulation, and what I believe is a plywood/fibreglass ceiling.

I took out some internal walls by grinding off the rivet heads. This has left Not all of the rivet heads are oozing, which gives me some hope. There are also no other sign of water damage, such as yellow stains or visible water tracks.

I wondered if anyone out there had seen this happen to them before and knew what on earth it might be?

Thanks very much!

coopec43 · 26-12-2018, 23:43

I'd be a bit concerned?

https://www.youtube.com/watch?v=0Hh5MYv7lWc

Benz · 27-12-2018, 04:58

Looks like rust. There may have been water intrusion that rusted the rivets and they're oozing it all out.

coopec43 · 27-12-2018, 05:01

Quote:

Originally Posted by Benz

Looks like rust. There may have been water intrusion that rusted the rivets and they're oozing it all out.

I'd go along with that but from experience it is very hard to trace the source of a leak so maybe it is tannin from rotting ply?

guyrj33 · 27-12-2018, 09:09

That liquid could also be the result of osmotic blistering of the fiberglass, commonly known as blisters.

Elie · 27-12-2018, 09:18

If it smell like vinegar you have an osmose problem.

Dooglas · 27-12-2018, 10:41

Uniflite boat hulls, manufactured with hetron fire retardant, are admittedly a special case - but, as the chemical reacts and breaks down, the affected fiberglass oozes a thick brownish liquid from blistered areas. Any chance this fiberglass was treated with a fire retardant? This specific issue is not a result of osmosis, but of an actually chemical reaction in the resin.

Sailorman Ed · 27-12-2018, 11:02

firthwheel,
is it cored? degrading balsa or ply could produce a brown stain. I seriously doubt it is osmotic residue.

Taipe · 27-12-2018, 12:08

Now that you have removed a ceiling panel, if you have not already done so, you are going to want to remove a few square inches of insulation around one of the stained drips in order to get a good look at the underside of the fbg roof. I think you will find the answer. Either a fungus has figured out how to use rainwater to help it digest the foam insulation/wood paneling, or it is as others have pointed out, a chemical fire retardant used in the fbg production lay up. Hopefully it is just the former, in which case it is just a matter of redoing the rivet (or substituting it with a threaded fastener) with a good all-weather uv resistant sealant on the topside such as 3M 4200.

bletso · 27-12-2018, 13:48

Quote:

Originally Posted by coopec43

I'd go along with that but from experience it is very hard to trace the source of a leak so maybe it is tannin from rotting ply?

The way I have found to be effective is the drill a hole in the underside near the leak, inject compressed air, (5-10 PSI), and soap the outside. boy do leaks appear! You can be surprised how far away a leak can be in a cored deck!