screws stripping in old foam core - Fiberglass RV

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Old 09-13-2016, 11:58 AM   #1
Junior Member
Name: Steve
Trailer: 17' Bigfoot
British Columbia
Posts: 4
screws stripping in old foam core

Hey folks, we just bought a 30 yr old bigfoot and paid through the nose for it.
It is a great trailer but it is pretty old and the fibreglass and foam insulation seem to be getting pretty brittle.
After just returning from another sojourn into the wild back of beyond on Vancouver Island I noticed the screws that hold the furnace vent to the outside of the trailer have popped out and I almost lost the chimney.
Does anyone have ideas of what kind of material would bond inside to the foam on the edge of the holes so I can insert new screws? I am afraid some glues might melt the foam insulation.

Just a thought if anyone could refer me to another thread or something.

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Old 09-13-2016, 12:17 PM   #2
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Name: Jack L
Trailer: Bigfoot B-17 CB
Posts: 1,011
I don't think the age of the trailer has anything to do with your issue. You're right that some glues will melt the foam.

Can you reposition the furnace vent to allow new holes to be drilled so you don't have to use the old holes which always get larger with time. Another suggestion would be to use fiberglass putty to fill the old hole, then re drill a small hole for the screw. Backing the existing hole with a thin piece of plywood or using pop rivets instead of screws might be other options.

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Old 09-13-2016, 09:13 PM   #3
Senior Member
Name: K C
Trailer: 1980 18' Sunrader Motorhome and 1971 Trails West CampMite Campster
Posts: 770
over time screws can enlarge the holes in fiberglass.

you can put in screws the next size larger as the fastest and least expensive option.

you can install Rivnuts into the holes and then use a standard machine screw. Be sure to use fresh butly tape against the shell and some bedding compound under the head of the Rivnut and on the screw threads. Using a rivut is somewhat like using a pull rivet except that the rivnut has screw threads inside of it which means you can remove the remove the item you are mounting for easy access.
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Old 09-13-2016, 09:59 PM   #4
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Name: Jan
Trailer: '02 Bigfoot 17'
Posts: 24
Maybe try injecting some epoxy into the holes. Let it cure, drill a pilot hole and insert a new stainless steel screw.

I don't know, but it never occurred to me that old fiberglass shells could be come brittle with age.

If you find a good fix, please post again.

Congrats on your new/old Bigfoot!
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Old 09-15-2016, 06:20 AM   #5
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Name: K C
Trailer: 1980 18' Sunrader Motorhome and 1971 Trails West CampMite Campster
Posts: 770
Screw holes don't enlarge from the fiberglass being brittle. They enlarge because of movement. A little bit of frictional sawing action done by the screw threads over the years. The shell, the screws and things such as vents do not all move in unison. It is subtle but over time some screw holes will enlarge. Not all of them, it depends on how much flexing the shell is doing and what kind of wind loads while driving are on the objects being held in place.

I found quite a bit of that on my 1980 Sunrader where everything was attached with screws, no rivets were used on that FGRV. They did put some blocking behind some of the screws for them to grip into but being particle board it was only slightly better at holding up to friction than foam would have been. Plus of course where it got wet it lost all its screw holding ability.

There were also screws that went into foam insulation right under the roof surface. I had one primary area for that which was the screws holding on the roof rack. In that situation 75 percent of the screws had lost their grip due to oversized holes and were only being secured in place by all the roofing compound piled over them and the bracket feet of the roof rack extending out onto the roof surface.

In areas such as the baggage door, propane compartment door and water heater I was able to access those areas from the interior inside of cabinets and under the dinette benches. I tore out the old blocking and replaced it with new. Where there was no blocking for the screws to grab into I added some. Everything resinstalled with new butyl tape and brand new screws too.
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Old 09-15-2016, 10:32 AM   #6
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Name: Carol
Trailer: 22' Airstream Formerly 16' Scamp
British Columbia
Posts: 11,701
Go to any local marine store or Canadian Tire and pick up some Epoxy putty - very easy to use. Fill in the old holes and let dry and re drill.

J-B Weld Waterweld Epoxy Putty

Pretty sure you will find plenty of uses for it in the future as well. Carry it in the trailer for emergency use. ;-)

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