To epoxy or not to epoxy?

[TitanTea]

When I go to put the new wood stringers and bulkheads in do I just epoxy them in and then epoxy and mat over or should I glue them in with an adhesive and THEN epoxy and mat over them?

 

[Capt'n Chris]

Re: To epoxy or not to epoxy?

What you use to secure them will depend on what material you're using to build them.

 

[TitanTea]

Re: To epoxy or not to epoxy?

Wood stringers/bulkheads

 

[RICHARD5]

Re: To epoxy or not to epoxy?

My most recent job was a stringer and deck rebuild on my brother's jet boat.

I used 5/4 Mahogany for the stringers and cross members. I bed the stringers and cross pieces in thickened ester resin and smoothed the squeeze-out to form a fillet. There was some light grinding required to shape the fillet. Then I used 3 layers (2", 5", 8") of 8 oz cloth centered on the fillet. The 2" strip went against the fillet. I cut the cloth flush to the top of the stringers.

The cross members (3 pieces per station) mated to the stringers with mortise and tenon and epoxy. Masking tape was used to prevent excess epoxy from contaminating exposed wood surfaces.

All wood got 4 coats of spar varnish before any fiberglassing. I scuffed the varnish with 120 grit and cleaned with acetone just prior to laying in the glass.

After glassing, everything below decks got 2 coats of boat kote.

The deck was 19/32" AC Birch ply and received 4 coats of spar varnish on the underside and topside. All cutting and fitting was finished before applying varnish. The plywood edges received two coats of slow cure ester resin before the varnishing. Deck is secured with 1 5/8" monel screws.

My brother wanted no adhesive securing the deck against my advice.
Before the deck went down I ran water down the bilge to check how it would flow. I felt this was neccessary because I also rebuilt the engine stringers and changed the engine box per his specifications. I added a bilge pump and alarm.

This boat has 600HP and will be subject to pounding and vibration. I'm satisfied my work will stand up.

 

[ondarvr]

Re: To epoxy or not to epoxy?

When I go to put the new wood stringers and bulkheads in do I just epoxy them in and then epoxy and mat over or should I glue them in with an adhesive and THEN epoxy and mat over them?

You don't want to use mat with epoxy, use cloth or something like 1708.

You can bed them in many different ways, but the bedding is used more to keep the plywood stringer from contacting the hull than for bonding it for strength.

You can put epoxy, construction adhesive or strips of foam under it to keep it off the hull, all are normal methods.

 

[scott11]

Re: To epoxy or not to epoxy?

You can bed them in many different ways, but the bedding is used more to keep the plywood stringer from contacting the hull than for bonding it for strength.

You can put epoxy, construction adhesive or strips of foam under it to keep it off the hull, all are normal methods.[/QUOTE]

I am also doing my stringers and transom in my boat. I have been reading from others about how they bedded their stringers. What is the reason for this? I noticed when taking the old ones out of my boat that they had no bedding under them but they also werent fully wrapped in fiberglass cloth. It seems like the factory took alot of shortcuts when constructing my floor but then again it has lasted 30 years without proper storage so thats not too bad.

 

[F14CRAZY]

Re: To epoxy or not to epoxy?

I used epoxy thickened with cabosil to bed in the stringers and bulkheads and removed the excess to form fillets. I've found that ideally, the fillet should harden up with some glass, so like some 4'' tape wouldn't be bad to go with it. Let that all harden up, then proceed to glass

 

[ondarvr]

Re: To epoxy or not to epoxy?

[qoute]
I am also doing my stringers and transom in my boat. I have been reading from others about how they bedded their stringers. What is the reason for this? I noticed when taking the old ones out of my boat that they had no bedding under them but they also werent fully wrapped in fiberglass cloth. It seems like the factory took alot of shortcuts when constructing my floor but then again it has lasted 30 years without proper storage so thats not too bad.[/QUOTE]

For a long time stringers in production boats weren't bedded and many aren't now. Every now and then when stringers aren't bedded the plywood can create a hard spot where it contacts the hull, the glass flexes around this hard spot and "may" crack. Bedding them in epoxy, or any type of putty, spreads the load over a larger area. Softer constrution adhesives space the plywood off the hull.

 

[scott11]

Re: To epoxy or not to epoxy?

Ok that makes sense. What other products are there other than epoxy to bed them in? Im not totally sure but i think i remember people saying 3m 5200 is a good product to bed and make fillets. Im just looking for any possible ways to save a few bucks if possible.

 

[TitanTea]

Re: To epoxy or not to epoxy?

Good stuff.So basically you don't want the wood stringer just naked and sitting on the hull in needs to be in some epoxy (if that is what you are using) Is there are rule of thumb for the thickness of the epoxy the stringer needs to sitting on? Ok lastly help me out here please what is fillet? Not sure what that is in boat building but fish wise I'm there... I got the old floor out and found no bulkheads just a single stringer with a couple of what looks like hull reinforcement...here are some pics of my 1986 Thundercraft trihull rebuild...

 

[ondarvr]

Re: To epoxy or not to epoxy?

1/4 inch is the normal gap.

Its just a radius where the hull and stringer meet so the glass will conform to the shape, glass doen't like sharp corners. It can be made from many things (wood, foam, putty, fiberglass, etc) and putty is very common.