Help you boat builders, cabinet makers part 2

[western traveler]

I have mahogany trim being cut and coming soon to lap my roof seams to walls. The material is being trimmed to 1/2” thickness for the wall piece radius’s. They will be 1 1/2” width.
The roof pieces are going to be four 1/8” X 2” strips as that was the best for bending this material.
The plan is to attach the wall pieces flush to the top before overlapping the roof strips to equal 1/2” X 2” X 2” trim.
I have always planned to use epoxy and micro balloons for both but I have also considered 4200 Sika Flex for the radius trim.
Opinions on the ability of T-50 staples penetrating the 1/8” bottom piece of mahogany and 6oz cloth or should I use short crown staples instead for that bottom strip? I feel the additional strips should be okay with the T-50 staples and epoxy mix to get to 1/2”
Thoughts please on both…

[Pmullen503]

I guess I would use sealant. This is going to be a high maintenance item; subjected to UV and potentially pooling water. I would trust sealant over an epoxy joint unless you plan to glass cloth the entire assembly once in place.

[KCStudly]

I would avoid staples here, both for appearance sake and to optimize sealing. Use structural thickener, not fairing filler. Temporarily clamp, tape or otherwise hold trim in place while curing. Epoxy bond alone should be more than adequate if prepared properly. If possible, apply side pieces first just slightly proud of top, plane, router or sand flush, then do same with top trim; leave hanging off side a hair and plane, router, or sand flush. Then route a radius on outside edge so your final sealer coats don't break down on a sharp edge.

Round over inside edge of top trim, and bottom edge of side trim before installation, for the same reason.

[KCStudly]

Could also bond and screw down the trim and plug screw holes, like you plan to do on bottom edge trim.

[western traveler]

Pmullen and KCStudly

Thanks for the input!
Yes, the plan was structural thickener.

I was thinking the crown staples would assure a good bond to the glass on the bottom strip and T-50 staples to be pulled after cure on the additional strips but hated the thought of penetrations anywhere on the roof. I hadn’t considered clamping them using the side trim for a cleat. I could attach side trim to both port and starboard sides and clamp wood strips across the roof to assure a flat lamination.

Great tip to leave them proud and router flush! Sometimes the obvious escapes me…
Also plan to round the edges of all the trim.

Another question;

If I glue the roof strips down with structural epoxy thickener and successfully bond them all, would it still be advisable to epoxy dowels down through or should the bond be strong enough to stay in place? I hadn’t even considered that but great point.

Ralph

[KCStudly]

With proper preparation of the surfaces to be bonded, using thickened epoxy, like West System with some 403 filler mixed in, you'd have a hard time getting them apart w/o destroying something.

Bare wood to bare wood, or bare wood to cured fiberglass (better yet "green" fiberglass) will bond very well. If the wood is an oily species the mfg will likely advise to wipe with solvent damped rag... not soaking wet (acetone) shortly before bonding.

"Green" epoxy has not fully cured to its full hardness. Depending on brand and weather factors (mostly temperature) standard or slow curing epoxy can take only 4-6 hrs to set, but the chemical reaction won't be done sometimes for 24 hrs up to several days. Best to do secondary operations during this window to take advantage of the chemical bonding process.

In my area using the West System, I always seem to get amine blush, that waxy substance that "floats" to the top, so to speak. Due to logistics and time requirements, I never seem to be able to do secondary operations in the sweet spot between firm enough, but not set yet. So when I come back the next day I always wash amine (water and abrasive "greenie" pad, wipe with paper shop towels and allow to air dry for a bit). Even if the cure is still a little green, I don't risk it.

If your cabin wall and/or roof surfaces are fully cured, filled and/or fared, just wash amine off and sand 50 or 80 grit to prep for a mechanical bond. If they are fully cured weave without filler coats, I would sand any "wet" (over saturated glassy areas... which there really shouldn't be) and scuff the heck out of the rest of it with a fresh, dry, greenie pad. Make sure to vacuum or wipe any sanding dust off. Acetone damped towel is okay, let it dry a bit before next step.

[western traveler]

KCStudly,
Thank you for that detailed explanation. I am using RaKa and their adhesive additives and will try to avoid all roof penetrations. Where I have used it so far has turned out strong. Will do another test piece before proceeding.
Ralph