Core repair


I have removed wet core from the inside.
I have some questions as to how epoxy in the new core and then glass over it. ( I have watched a few YouTube's, but still have questions...)
Anyone willing to talk on the phone? DM me
Thanks, Pete
Deck. Port side next to main hatch. There is / was a crack. I epoxied in a piece of glass to reinforce, epoxied the outside to seal it.
Some show using a filler with the epoxy to put the core in, then supporting it.
Also saw that the balsa needs a good coating of epoxy. Should that be with filler (West 403) or just epoxy?
I follow Boatworks Today on Youtube. Due to a shoulder issue he has opened the channel to answer viewers questions. request is to submit video questions to be incorporated into a episode. Past episode covered technics on hanging glass on vertical /over hanging surface.

Project questions:

Inverted fiberglass:
They make it look easy!! Maybe it is.
Wet the surface, wet the glass cloth, roll in, wet the core put it in. Glass over everything.
I didn't watch, but that's pretty much true. I was always very deliberate in the beginning; faster working later with more experience.
It's not an absolute requirement that you use the identical core material for repairs. I had some small areas of damage under jib tracks in the cockpit, and used plywood of the proper thickness after opening up the area with a hole saw. Worked well.
Anytime you do an external repair you must remove the gelcoat (exterior color material). In a impact damage situation the gel coat often hides the full extent of the damage. Repairs typically do not stick to cured gelcoat especially epoxy.
I prefer epoxy repairs vs. polyester resin repair. Your J24 was built with polyester resin. Polyester works very well in an at once, all in one, monolithic layup. Polyester however does not like to adhere to itself very well in a post secondary bond situation. Epoxy on the other hand is an adhesive. You will find out the hard way that it sticks to whatever it touches.
The balsa core should be coated before placing it into the layup. This assures sufficient resin for a proper bond as the end grain is quite absorbent. Whenever possible match the materials that you are removing. Different materials will flex differently and that introduces stress points. Don't second guess the design engineers.
Its not rocket science but it does require patience. Formulate a procedure for the repair especially the replacement, its neater that way. If you are sloppy you will pay the price in grind and sand time similar to drywall mudding. Thickeners can be your friend as it offsets the effects of gravity (or is it density). All of West Systems Epoxy thickeners are excellent. Each has its place in the process. When in doubt use 406. Thickened epoxy is no replacement for the fibers in cloth. If you need to fill a void where core is not used use hunks of cloth saturated in resin not just thickened epoxy.
A good quality (brand name) wax paper can be a godsend as well. It allows you to lay up materials and deliver them to the repair all at once. Wax paper also can keep a layup from sagging and allows you to shove it back in place with your hands before it sets up. On an overhead repair wax paper with a foam cushion propped into place can help solve the gravity problem. Overhead repairs from the underside hide the repair and eliminate the nonskid repair.
Be very aware of heat build up. Both polyester and epoxy cure chemically and one byproduct is heat. A little too much heat and it will "foam", excessive heat and you will have a fire. On a big repair I often use a plastic garbage bag filled with water placed on the repair to act as a heat absorber.
I believe West Systems is the most replicable epoxy. Its the same every batch, every mix. The only variables are the addition of thickeners which act as insulators and temperature changes how it reacts and cures. The ambient temperature is your biggest variable. This is rocket science and will take you a lifetime to understand. In very warm temperatures stick with small batches, small areas of repair.
The good news is, what ever you screw up you can grind out and do over. The biggest problem you will have is if you get real good at it. EVERYBODY will want your "help" on their little problem.
Further, after Dale's comments (and this is just my own experience and what I've learned by doing): My thought about it being unnecessary to use identical core materials could be qualified. I used plywood in a few places to get the appropriate thickness, but they were only areas about 2-1/2 inches in diameter under fasteners for the genoa tracks, where the core was wet but not rotted, and it was fine in the long-term. I agree that you shouldn't willy-nilly use something like that in a larger area or it will become apparent over time and maybe result in a new problem. Foam coring materials may be less likely to cause a problem if used in place of balsa core. I suspect problems are more likely if your core is stiffer than the original.

A piece of wetted-out cloth overhead that might otherwise fall off shortly after being put in place will stay there if covered with some sheeting. Like Dale says, waxed paper will do. I ultimately settled on using polyethylene sheet as it leaves nothing behind (no chance of wax), won't tear, etc. Heavier gauge like 6 mil helps with picking it up to apply it after wetting it out; thinner material like <1.0 mil 3M masking film is useful for conforming to complicated shapes (with some wrinkles though), and it's good overhead because of its low weight. It all clings together and keeps it from falling off somehow (like magic).

In my experience epoxy will always bond to polyester just fine, assuming that it's clean (use acetone) and properly abraded. And though some would say that gel coat won't adhere well to epoxy, that's not so, in agreement with what the West System people say. It's just a matter of proper preparation: cleaning and abrading. Make sure you clean any amine blush that forms on the cured epoxy with clear water and a Scotchbrite pad as step one.

Polyester (like gel-coat) will usually bond to properly prepared gel-coat fairly well, but it's not really an adhesive like epoxy is and might ultimately come apart.

Finally, epoxy should never be the final surface, un-coated. It needs to be coated with gel coat or paint. It will otherwise ultimately degrade under UV from sunlight and become porous.

This book, downloadable free from Gougeon Brothers (West System) is the bible as far as I'm concerned. I've used it for almost 30 years:
Fiberglass Boat Maintenance | WEST SYSTEM Epoxy
It says "First Edition: 2014", but I bought the print version in 1996, I know. It was a life experience, driving from Philly to Baltimore every weekend for 6 months that year to work on the boat. I won't forget.

The one thing I'd quibble with is the 'bent nail' method of opening an existing hole of core material for filling, in section 7.2.1. Even done with a great deal of care, there were wet areas and deterioration 10 or so years later. I think the epoxy just doesn't wet out sufficiently in such circumstances. I go a different route now. I'd just drill it oversize 3/16 or so from above with a brad point bit, not through the lower skin of the laminate, and then fill it and re-drill for the fastener. If it's a high-load situation, I'd use a backing plate of some sort, or at least a fender washer.

I'll say it again: Good J/24s can be had these days at very reasonable prices. If you want to go sailing, buy a good boat, not a fixer-upper. The fixer will get in the way of your goal. If your pleasure in life is fixing boats instead, more power to you (buy the fixer)!
Thank you for taking the time to talk with me. The information you have supplied has boosted my confidence in getting this done.
Downloaded the "book" as suggested.
Plenty of other great information on this thread.
Now if the weather will cooperate for next weekend, I will tackle my repair.
So much great information.
Thanks. Best regards,