Fasteners and Fiberglass for a Plywood Squaredrop Build

[MojaveD]

Is a polyester body filler (such as bondo short strand) okay for filling screw holes and seams?

 

[Tony Latham]

Is a polyester body filler (such as bondo short strand) okay for filling screw holes and seams?

Of course, polyester resin is the goo in Bondo, which isn't as great an adhesive as epoxy. Will it work? Probably.

Since you're using epoxy, just make up some extra-thick epoxy with a thickener such as wood dust or, better yet, microballoons, as discussed.

Tony

 

[MojaveD]

Sounds good, thanks for that Tony.

When wetting out fiberglass on vertical surfaces, should the epoxy mixture be thickened a bit?

David

 

[Pmullen503]

Sounds good, thanks for that Tony.

When wetting out fiberglass on vertical surfaces, should the epoxy mixture be thickened a bit?

David

No. You should apply only enough epoxy that can be absorbed by the cloth and the substrate underneath. You should squeegie off any excess resin before it sets up to make sure the cloth is down tight against the substrate.

Apply subsequent coats after the first starts to gel but before the it fully sets up. A foam roller works well. Spread those coats out as far as possible so they don't run. These coats will take MUCH less epoxy than the first coat so don't mix up too much.

A light held at an angle to the surface helps in getting it even. You want a more or less uniform sheen.

 

[MojaveD]

Thank you PMullen503. When I finish an area and return days/weeks later to work an adjoining area, will I need to abrade the edge of that cured epoxy to give the next section adhesion?

Will an overlap of 6oz glass be obvious, or does that disappear under the epoxy?

TIA,

David

 

[KCStudly]

Overlaps will be obvious, but if you sand the cured edge to a taper, after laying the next piece over the taper you can sand that back, too. Just be generous with the overlap and expect to have to use some fairing filler. I was never able to dedicate the super long periods of time to wet out substrate, wet out cloth (preferred method is on a plastic sheet flat on a work bench then have a few people help you move it to the work piece holding the plastic sheet taut... check my build for "poor man's prepreg"), then fill the weave in multiple stages all in one session, so I had to do a lot of amine washes and greenie pad prep while trying to catch it the next day when it was still a little "green". Mostly I ended up (and it hasn't ended yet due project stalling) using fairing filler to fill the weave. You want the glass to be laid up with the specified saturation by weight for your cloth spec, before you lay on more to fill, so it tends to be a very lengthy process on big sheets.

 

[MojaveD]

Thanks KC, your build looks like a work of art. Do you advise fiberglassing the whole underside of the camper? I saw where your side FG wrapped underneath. Wondering if my build will endure being flipped belly up.

My build is super basic and hopefully functional (just need a space to sleep for camping) so in the end I’ll be okay with fabric weave and seams showing. I plan to paint it with a flat exterior enamel. I also hope to get it campable by this winter.

Here’s my progress so far:

 

[Pmullen503]

Nice looking trailer. I STRONGLY suggest you cover the entire surface with cloth and epoxy, not just the joints. Even a light 4 oz. cloth and epoxy will stabilize the wood surfaces and give a uniform base for paint. You'll wish you had after a couple years.

 

[KCStudly]

I did not do the bottom of my cabin in glass because when I started my initial intent was to do PMF. Still contemplating going back, sanding all of the incompatible TB2 and bondo off and redoing in epoxy/glass. Mostly because I have no plan to include drip edges at the cabin to trailer frame joint (see GPW's teachings and lessons about rot due to no drip edges).

Even if you can't tip your cabin all the way over on it's roof or sides, at least tip it up part way so the surface isn't completely vertical. It helps a bunch. Just be careful to roll/squeegee/dapple brush any drips or runs out before they start to gel. When my cabin was still in raw foam and I didn't have the confidence to roll it on it's side for fear of creating more dents and gouges, I still tipped it up a little which, IMO, made it go much better reducing drippings wasted onto the cardboard flats I had spread along the floor of my work area. Even after partitioning the size of my side wall layup down to from the aft end of the side door to the aft end of the galley, while working lengthwise first from the top down, by the time I worked my way lower, some of the heavy drips or runs from above had started to gel and left fat rich areas were the weave floated a little and I couldn't get it to press down flat. I didn't want to sand through the strands of weave to fair these areas down, so required more fairing compound over a larger area to hide the highs.

Still, there would have been a huge amount of wasted resin hitting the floor and/or the application time would have soared if I hadn't tipped it at all.

 

[KCStudly]

Duplicate post. Something weird is happening. When I attempt to post it seems to go, but then when I reopen on my phone the text is still in the compose window.

 

[MojaveD]

Will every screw hole require thickened epoxy, or would neat epoxy fill those, if horizontal?

 

[Tony Latham]

Will every screw hole require thickened epoxy, or would neat epoxy fill those, if horizontal?

Thickened epoxy will work great; liquid, not so much. I suggest dabbing it first with straight epoxy first, so the wood doesn't pull out epoxy from the goo.

Tony

 

[KCStudly]

Screw head looks to be above the surface. If so, you won't be able to fair out the filling and it will leave a lump. Are they 82 deg flat heads?

 

[MojaveD]

Thickened epoxy will work great; liquid, not so much. I suggest dabbing it first with straight epoxy first, so the wood doesn't pull out epoxy from the goo.

Tony

Aha, would this apply to filling gaps as well? I’ll need to do some filling and filing.

 

[MojaveD]

Screw head looks to be above the surface. If so, you won't be a to fair out the filling and it will leave a lump. Are they 82 deg flat heads?

KC, they’re below surface, but I can see how that first pic could be confusing. Here’s another, along with the screws I used.

 

[Tony Latham]

would this apply to filling gaps as well?

Yes.

Tony