What Material, Aside From Epoxy, Can I Use to Close Out the Core?

[CarlF]

Your problem is that a thin layer of resin has very little strength or flexibility. It will crack - most likely where the foam meets the inside of the laminate. This can happen just from temperature cycling of the sun on a hot deck.

But for Core-cel ABOVE the waterline and through properly bonded core-cel the water isn't going the spread or damage the core-cel. The worst you get is a drip on your pillow.

You'll get great performance from properly applied caulk (clean the screw, fitting and deck with acetone to assure adhesion). But since you are concerned, you might want to consider butyl. It's pretty amazing. I always use the butyl from MaineSail

https://www.youtube.com/watch?v=3UIFNPKWFzU

https://shop.marinehowto.com/products/bed-it-tape

Balsa is a different matter. For a small screw hole, I'd do a few coats of a penetrating epoxy like CPES. I'd even do this if over-drilling the hole. Then use a good caulk.

For a screw into a deck, properly applied caulk is usually enough. Clean the screw and deck with acetone. Another way to go is wrapping a bit of butyl around the screw

For below the waterline you want to gouge out about 1/2" of core using a bent hex key in a drill. If balsa, for belts and suspenders I'd brush CPES inside. Clean the inside of the laminate well and then fill with epoxy or polyester putty.

[rslifkin]

I wonder... How well would it work to fill the hole with 5200, drill through that, and the install a fastener with sealant? It's flexible and sticky, so it should bond and stay bonded. I've never heard of anyone doing it though, so I'd assume there's a reason for that.

[Scubaseas]

From LBIFiberglass.com whom I have used for years repairing commercial dive boats. Great company, great products. Very knowledgeable and helpful with any kind of technical advice.



VINYLESTER RESIN: LBI-901 & LBI-902

• Stronger and more durable than polyester resin.
• Most professional repairs are done in vinylester.
• Makes strong stiff laminates.
• Excellent bond strength to sanded laminate and core materials.
• Will bond to epoxy resin.
• Higher resistance to chemical, water and UV than polyester resin.
• Higher resistance to vibration and shock loads.
• Due to its higher strengths it has better tensile and flexural characteristics
• Highly resistant to water absorption that causes osmotic blistering that can occur with polyester resins.

[guyrj33]

Originally Posted by rslifkin

I wonder... How well would it work to fill the hole with 5200, drill through that, and the install a fastener with sealant? It's flexible and sticky, so it should bond and stay bonded. I've never heard of anyone doing it though, so I'd assume there's a reason for that.

For a flexible adhesive like 5200, I think you'd also need a compression tube around the bolt.

Could you add filler to polyurethane adhesive a.k.a. Gorilla Glue and get enough compressive strength while maintaining the adhesive properties of the adhesive?

Overall Vinylester resin is probably the best solution for someone who is allergic to epoxy.

[Nicholson58]

My method is drill the top, remove core as far under, around the hole as my specially made tools can reach, fill with MarineTex. I like to make a solid plug between the outside and inside skins that is at least 1/2” larger than the edge of the hole. I know MarineTex is epoxy but it is good and proper for the job. Viscosity is high and the volume is small so you should be able to avoid contact using 9 mill gloves. If the hole is especially large add in glass cloth at the surface. For high stress pull out concerns always use a backer plate. Use a saturated glass mat to ensure there are no gaps between the hull and backer. You could use polyester for this messy bit.

[Joli]

If you're worried about the core becoming wet simply remove the core in those areas. Then you can have anyone do the work in epoxy and whatever mess they make can quickly be cleaned up with a grinder. I wouldn't trust a poly patch on epoxy.

[Flatswing]

If you r worried about polyester adhering to epoxy, take a look at Andy Miller’s (Boatworks today)vid where he bonds various resins together to test the theory. Not really scientific but should give you confidence that (given your severe epoxy allergy) you can safely substitute poly or vinyl to seal the core. Of course all will need to be strengthened with fibers appropriate to the application after meticulous prep.
Most use thickened epoxy to seal the core intrusions in polyester boats, can’t see why you couldn’t do the reverse

[Exctyengr]

I see two issues here. (1) is sealing the hole from the elements and water intrusion and (2) is the structural strength of the fastened hardware. In the case of (1), Butyl tape as previously suggested will work fine. (2) is another story; the deck can be crushed by over tightening and the loads on the fastened hardware can cause local stress cracking. The cored system in common use on fg boats is not designed nor intended to withstand the local loading that bedded fixtures will apply. The recommended approach that I have seen would be to drill the mounting hole, dig out the core material around the hole fill that with epoxy and then re-drill with a mounting plate under the deck. OK so you are allergic to epoxy, time to buy a friend a beer. You can do all of the work up to filling the hole with epoxy, get a friend to do the epoxy work, when it's cured, you can finish it up. To answer your question directly, I know of no adequate substitute for epoxy.

[Chotu]

More different opinions than there are resins. LOL

Thanks you for all of them, however. It’s going to be a very difficult choice.

Regarding the cross sensitivity, thankfully, I’m ok with polyester, but treat all chemicals like nuclear waste at this point. Vinylester, last I read, was a lot more epoxy like in that is used an amine hardener. So, I was thinking I should stay clear of that.

5200: I have to wonder if there is a way of doing the geometry of the plug differently so you have polyester on the extreme outer edge of the hole, then 5200 in the center, just a little bigger than the shank of the fastener. But the head of the fastener hits the polyester. Interesting thought anyway, even if not probably happening.

[rslifkin]

For the 5200 option, you could always over-size the hole, then remove some core. Fill the removed core with 5200 and use the 5200 to hold a stainless steel compression sleeve in place to sleeve the hole back to the desired diameter. That and a good backing plate should avoid any crushing concerns.

[GeneM]

I heard that someone used original gorilla glue because its absorbs moisture. It seems to have worked well.

[thinwater]

Originally Posted by GeneM

I heard that someone used original gorilla glue because its absorbs moisture. It seems to have worked well.

I have actually done this on repairs to older boats. I would not say it is preferred, but if you can't get it completely dry it will give the better bond than polyester. It will also expand into bad core to some extent. particularly if you plug the hole (it expands when curing).



a. Adding a little chopped fiber or small pieces of 6oz cloth to the hole really makes the plug stronger and less prone to cracking.



b. I like a bent roofing nail for removing core. It does a cleaner job, is easy to use, and removes more.

[psk125]

Polyester's ability to stay stuck to wood got demonstrated to me when the fiberglass on the bottom of my cedar strip canoe delaminated. Everywhere. When I peeled off the fiberglass, no wood came with it. Won't make that mistake again.

[Chotu]

Originally Posted by psk125

Polyester's ability to stay stuck to wood got demonstrated to me when the fiberglass on the bottom of my cedar strip canoe delaminated. Everywhere. When I peeled off the fiberglass, no wood came with it. Won't make that mistake again.

Sorry you had that problem. I think that has to do with a wet environment.

I used polyester to tab my wooden cabin soles to the epoxy hull and it’s all just fine. It is also used to completely seal off the wooden soles from the air and whatever humidity is in it.

It’s not the product. It’s the application.

Never use polyester below the waterline on wood.

[Chotu]

Originally Posted by thinwater

I have actually done this on repairs to older boats. I would not say it is preferred, but if you can't get it completely dry it will give the better bond than polyester. It will also expand into bad core to some extent. particularly if you plug the hole (it expands when curing).



a. Adding a little chopped fiber or small pieces of 6oz cloth to the hole really makes the plug stronger and less prone to cracking.



b. I like a bent roofing nail for removing core. It does a cleaner job, is easy to use, and removes more.

Hmmm. This is interesting.

It’s way too foamy but if there were a similar glue that didn’t foam...