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

[Chotu]

Since boat design . net has been an utter failure lately (see link for example), I’ll keep asking questions about building here.

https://www.boatdesign.net/threads/a...9/#post-884960

My boat is epoxy/corecell for the most part and epoxy/balsa in a few areas.

I need to finish off the boat’s interior and place deck hardware and things like that.

This involves drilling (and cutting) into the laminate, exposing the core.

What can I use to properly seal off the core in these cases that isn’t epoxy?


Example pic showing how to do it with epoxy:

[Wotname]

Polyester or vinylester ???????

[Chotu]

Originally Posted by Wotname

Polyester or vinylester ???????

I was thinking polyester would be fine. They always say it won’t bond to epoxy well (and it doesn’t if you peel it off) but it should keep the water out of the balsa, right?

The doubts the internet or Gougeon Bros marketing puts in your head sometimes can be quite loud.

Imagine this is for a deck cleat or a winch and there is a balsa core.

There will be a lot of cyclical loading. Will the polyester stay bonded to the skins, keeping all water out?

[rslifkin]

I'd probably remove a bit more core and make a bigger plug, just to be sure. But it should bond well enough to keep it from leaking given good load spreading on the top and bottom. Don't be afraid to use a base plate on the cleat in addition to a backing plate to minimize any deck flex around the penetrations.

[Chotu]

Originally Posted by rslifkin

I'd probably remove a bit more core and make a bigger plug, just to be sure. But it should bond well enough to keep it from leaking given good load spreading on the top and bottom. Don't be afraid to use a base plate on the cleat in addition to a backing plate to minimize any deck flex around the penetrations.

Thanks! I was thinking the same about enlarging the plug area.

Good ideas about keeping the flex to a minimum. Fortunately, I have 1” core to help with that and plates on either side would probably virtually eliminate any flex at all.

Where do I send your ticket for a free day of sailing on this high performance catamaran when she’s done? Seriously, thank you for all of your responses to questions on this project.

[rslifkin]

Originally Posted by Chotu

Thanks! I was thinking the same about enlarging the plug area.

Good ideas about keeping the flex to a minimum. Fortunately, I have 1” core to help with that and plates on either side would probably virtually eliminate any flex at all.

Where do I send your ticket for a free day of sailing on this high performance catamaran when she’s done? Seriously, thank you for all of your responses to questions on this project.

No problem! And if you end up sailing it up towards the great lakes area at some point, let me know! Unfortunately due to work constraints, I doubt we'll be coming south any time soon, at least not further than we can get in 4 - 5 days.

[coopec43]

Originally Posted by Chotu

I was thinking polyester would be fine. They always say it won’t bond to epoxy well (and it doesn’t if you peel it off) but it should keep the water out of the balsa, right?

The doubts the internet or Gougeon Bros marketing puts in your head sometimes can be quite loud.

Imagine this is for a deck cleat or a winch and there is a balsa core.

There will be a lot of cyclical loading. Will the polyester stay bonded to the skins, keeping all water out?

There are several ways you can do it but (if I understand it) I don't think what you are doing is correct at all.

Did you have a look at this thread?

https://www.cruisersforum.com/forums...le-238113.html

https://www.soundingsonline.com/feat...on-cored-decks

[Chotu]

Originally Posted by rslifkin

No problem! And if you end up sailing it up towards the great lakes area at some point, let me know! Unfortunately due to work constraints, I doubt we'll be coming south any time soon, at least not further than we can get in 4 - 5 days.

The boat will, without a doubt, be in NY State within the next couple years.

[Chotu]

Originally Posted by coopec43

There are several ways you can do it but (if I understand it) I don't think what you are doing is correct at all.

Did you have a look at this thread?

https://www.cruisersforum.com/forums...le-238113.html

https://www.soundingsonline.com/feat...on-cored-decks

I’m one of the people giving the advice in that Cruisers Forum thread. Ha ha.

Yes, the Soundings article is the way I’d be doing it. Drill and fill.

[Bill O]

I like the drill, remove core material and fill senario. I'd stick w/epoxy though.

I know you have the severe allergy to epoxy, but again possibly hire a competent helper to do the stuff you can't do.

Once you show them what you want done it's not that hard to drill a hole, ream out the core, tape off and refill w/epoxy. Could have them place a camera on the work spot to supervise from a far if needed.

[Chotu]

Originally Posted by Bill O

I like the drill, remove core material and fill senario. I'd stick w/epoxy though.

I know you have the severe allergy to epoxy, but again possibly hire a competent helper to do the stuff you can't do.

Once you show them what you want done it's not that hard to drill a hole, ream out the core, tape off and refill w/epoxy. Could have them place a camera on the work spot to supervise from a far if needed.

This is one of those things I have to do myself to be sure. Competent is such a relative term. Ha ha. Lots of “that’s good enough “ going on with this task that I can’t really trust to anyone.

I’d prefer to hire the help for the laminations that are in plain sight and the interior sanding. Good god, the interior sanding....

[Bill O]

Yes I chose "competent" as a relative term and they need to be up to your standards. My standards are also high and why typically have done all my own work. Also owners have more skin in the game and they want the best possible job done, where some workers cut corners just to get the job done.

Eventually, for a variety of reasons, we need to let the jobs go if we can no longer do them. As I get older, reality sets in and time to farm things out.

Finding the right person to help that your trust to do a good job will be another chore, but once you've found that person your boat will get completed much faster.

[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 hot sun alternately heating and cooling the 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 from a thrubolt.

You'll get great performance from properly applied caulk (countersink the hole 1/8" by using a slightly larger drill bit, clean the screw, fitting and deck with acetone for adhesion).

But since you are concerned, you might want to consider butyl. It's pretty amazing. I always use the butyl from MaineSail. (hint, when using butyl go back the next day and give each screw another 1/8th turn of tightening. And as shown in the video, countersink the hole with a drill)

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

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

For interior screws you don't have to do anything unless there is a risk of water regularly running along the surface - in which case caulk or butyl.

Balsa decks are a different matter. If you weren't allergic to epoxy, I'd do a few coats of a penetrating epoxy like CPES with a q-tip or tiny brush but for you regular varnish would be better than nothing. I'd even do this if over-drilling the hole. Then caulk or use butyl.

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 by sanding and with acetone - then fill with epoxy putty. Given your allergy and the potential problem of below waterline leaks - I'd have someone else do the epoxy part.

[Jammer]

There are two facts to consider:


* Allergic cross reactions are common among various sensitizers, so if you have a reaction to epoxy, you are more likely to develop a reaction to other resins and catalysts


* Epoxy is the only recommended product for this application because of problems with adhesion with other products. You could use polyester or vinylester resins, or alternative epoxy formulations like G/flex, who knows


Sadly, the safe alternative if your reaction is serious is to avoid composite work completely

[mikereed100]

The problem with using polyester for plugs is that it can be very brittle (don't ask how I know this). If you go that route I would use milled fibers to thicken the resin.
Fillers
That should go a long way towards preventing cracking and will give you better compression strength. Vinylester, while a bit more expensive, would be my choice in this application as it is less prone to cracking, has better water resistance and bonds better to core materials.
https://www.thoughtco.com/vinyl-este...-resins-820376