Resin for general repair

[maa. melee]

Is polyester resin recommended for general above the waterline, interior repairs? My engine compartment was made with the stuff and some FG mat and there has been some rot in the compartment where the boat cover had a small hole, draining rain water onto the confines of a floatation chamber. The plywood lasted almost 20 years with only this small blemish. The plywood side of the chamber delaminated, and I need to cut a new piece of ply, glue it in place, and wet out new FG cloth and paint...What would be an affordable and dependable product?

[Bob Cleek]

Fibreglass and EPOXY resin has replaced fibreglass resin for this application. West System, System 3, any of them will work well. You will have better adhesion and less delamination with an epoxy coating.

[Norman Bernstein]

Personally, I'd always use epoxy... but the professionals who work on 'plastic' boats in my marina use polyester resin, which will stick well to existing polyester resin... but not much else.

A lot depends on the repair. If it's structural and not visible (i.e., inside the hull), I'd go with epoxy. If it's visible and will be gelcoated, I'd go with polyester resin.

[garland reese]

I'm not too sure how it relates to big boats and heavier layups, but there is a viable argument for staying with the original materials, for consistency of structural properties..... at least this is very true for light layups, as differing resins and fiber layups can cause the repair to react differently to stresses, which in turn will cause other stresses on the surrounding structure. I don't think it would be anywhere nearly as profound a difference though, on the heavy layups used on big boats.....my experience is in stuff like rowing shells :rolleyes:

[kulas44]

Polyester resin has no place in the REPAIR of boats today. !!!!!!!!!!!!!!

[JimConlin]

Garland, particularly on light structures like rowing shells, the stiffness of a patch should match that of the original or there will be stress concentrations. To understand this, put a patch of tape on a half-inflated balloon and inflate it further. The edge of the stiff patch will be under great stress. This mostly applies to the choice or reionforcement (glass, carbon, kevlar or whatever).

Regarding the use of polyester resin as a repair adhesive, the issue is whether polyester resin will achieve a reliable secondary bond to old, cured polyester. Everything i've heard is that polyester resin is iffy in this and epoxy is reliable. Polyester resin and tabbing is being supplanted by acrylic adhesives in doing the secondary bonds of manufactured polyester/vinylester based boats.

I've used polyester resin for repairs on glass boats and most of these repairs have held.
Do you feel lucky today?

[maa. melee]

Funny how you can make a boat out of the stuff but it's not advisable to repair it with itself. :D

[Puka]

If it's structural and not visible (i.e., inside the hull), I'd go with epoxy. If it's visible and will be gelcoated, I'd go with polyester resin. I'll go along with that... if it is already made outa poly..
and it is furniture not often wet, I think there is a place for polyester. Price,UV & mod. heat resistance,ease of use in a molding situation are strong points of polyester.

It also burns great if you get it too hot,but it don't go like jello as some epoxy does.(Dark hull colours).
It also good for encapsulating insects in. :D :D

BTW As it is not 100% solids don't expect it perform well over some paints (acrylics, vinyls).Styrene has an appetite for them, and the resultant composite will have a retarded interface.

[Puka]

Funny how you can make a boat out of the stuff but it's not advisable to repair it with itself Depends how big the repair is,your budget,and how long you want it to last.

Epoxy is a better material for repairing polyester fiberglass boats because of its ability to form a stronger mechanical bond to a damaged laminate than polyester resin. Epoxy also provides a better moisture barrier than polyester resin. The average DIY repair below the waterline in poly is an osmosis candidate.

As Jim stated.(didn't see his post.)
Do you feel lucky? I like that!

[ 02-27-2006, 10:33 PM: Message edited by: Puka ]

[maa. melee]

You're right..it will only get more and more expensive the longer I wait to buy some epoxy. For a small repair like this, I'll just spring for some 'poxy. We should all start driving a hybrid so as to save oil for the epoxy production.

[capt jake]

Personally, I'd always use epoxy... but the professionals who work on 'plastic' boats in my marina use polyester resin, which will stick well to existing polyester resin... but not much else. Most of the folks at the repair facilities in the marinas around here will admit that the only reason they use polyester is the 'speed' factor. Time is money, the faster they complete the job, the more money they make.

Oh, BTW, I'd use epoxy. ;)

[Dan McCosh]

Re: the "stiffness" issue. The main factor affecting the stiffness of the laminate is the glass fiber, not the resin. The small difference in mechanical properties between polyester and epoxy wouldn't affect a structure. The bonding and vapor resistance of epoxy makes it superior.

[ssor]

Grinding the damage with 25 grit disks with a taper like you would use to scarf plywood and building up the repair will be more than strong enough using polyester resin. If you have any doubt about how well polyester sticks to plywood, spill some where you don't want it, let it cure and try to peel it up.

The objection that I would have with using epoxy to repair polyester is that once you start with epoxy(which will adhere very well) you can't go back to the polyester(which won't adhere to epoxy). So polyester gel coat over an epoxy repair is out.