Deck core repair - Do I have everything I need?

[minaret]

Originally Posted by boatpoker

I have three close friends who do FRP repair and I also spend a lot of time in the biggest repair shop in Ontario. A good portion of their winter income is derived from rebuilding saturated foam core rudders. Foam is however an acceptable choice for deck/trunk work if (always if) well bonded (I prefer Corecell).

Balsa is an excellent material if installed properly it will last for decades. Wet balsa is universally the fault of sloppy builders.
Don't use plywood .... just ask anyone with a Taiwan Tub.

The foam in rudders is invariably pour foam, a totally different animal than closed cell PVC or polyurethane core material.


I've seen plenty of rotten balsa core result from hairline fractures which were almost invisible and ignored for too long. Not the builders fault.


Couldn't agree more about ply. I usually replace balsa core with foam, and ply core with Coosa. Similar properties, but non organic and proof against rot and saturation.

[boatpoker]

Originally Posted by minaret

The foam in rudders is invariably pour foam, a totally different animal than closed cell PVC or polyurethane core material.

Yet still advertised as closed cell foam.

[minaret]

Originally Posted by boatpoker

Yet still advertised as closed cell foam.

We both know that one is more susceptible to moisture degradation than the other. Can you imagine what would happen if all rudders were built with balsa core?

[Nicholson58]

Originally Posted by boatpoker

I have three close friends who do FRP repair and I also spend a lot of time in the biggest repair shop in Ontario. A good portion of their winter income is derived from rebuilding saturated foam core rudders. Foam is however an acceptable choice for deck/trunk work if (always if) well bonded (I prefer Corecell).

Balsa is an excellent material if installed properly it will last for decades. Wet balsa is universally the fault of sloppy builders.
Don't use plywood .... just ask anyone with a Taiwan Tub.

I dealt with "some guys in Ontario" They refused to use syntactic foam epoxy below water so I have YET ANOTHER fin filled with foam & wood that is destined to become water saturated, frozen and wrecked. I will NEVER EVER use any permiable material, foam, balsa etc. below the water line. I only use microballoons and epoxy because I NEVER want to re-visit any repair. Once is enough. I am so satisfied with this material as fillar that I will use it in preference to anything else all over the boat. US Composites delivers by UPS, its non-hazardous shipping, easier to clean up, used commercially for marine construction. Why anyone would repeat buy the inferior junk sold by the marine stores? 635 thin is 141 dollars for 3 gallons! Beat that - and it works better than any materials I have used form every other source. A 4-gallon pale of 3-M glass balloons is 33.75. The resultant filler is stronger and totally waterproof than anything else you might be considering.

[Ketchgould]

You need vinegar too. It removes dried epoxy from skin

[boatpoker]

completely agree, there is a right job for every material ....

in the OP's case it's balsa and poly

[a64pilot]

I know airplanes aren't boats, but I sold mine without advertising it, and at my asking price. Reason is first my price was reasonable, and my airplane was well know by people that fly the backcountry.
Don't know why a boat would be any different, I think most of the really good ones never get listed.

[a64pilot]

I have no idea how my post got into this thread, ignore it

[colemj]

I have done more work in epoxy than polyester, and am presently doing a large project using both epoxy and polyester, so have much experience with it. I'm not a proponent or naysayer - I just have a lot of experience in both. Trust me, epoxy is less error-tolerant than polyester and more difficult to use in varying environmental conditions and for large non-continuous jobs.

The OP has decided to bond the core with epoxy, but tape the joins with polyester. Since the strength of a cored deck section is more dependent on the continuity of the skin than the bond to the core, how do you feel about this approach?

As for "superior", that is a slippery argument. The project would be even more "superior" using nomex core and carbon fiber with that epoxy. The truth of the matter is that the polyester repair in that deck area will hold through anything that boat will ever experience, so the "superior" argument is meaningless.

There are other parts of the boat and types of repairs that I would not be arguing the merits of epoxy with you. This is not one of those.

Mark

[smj]

Originally Posted by colemj

I have done more work in epoxy than polyester, and am presently doing a large project using both epoxy and polyester, so have much experience with it. I'm not a naysayer - I just have a lot of experience in both. Trust me, epoxy is less error-tolerant than polyester and more difficult to use in varying environmental conditions and for large non-continuous jobs.

The OP has decided to bond the core with epoxy, but tape the joins with polyester. Since the strength of a cored deck section is more dependent on the continuity of the skin than the bond to the core, how do you feel about this approach?

As for "superior", that is a slippery argument. The project would be even more "superior" using nomex core and carbon fiber with that epoxy. The truth of the matter is that the polyester repair in that deck area will hold through anything that boat will ever experience, so the "superior" argument is meaningless.

There are other parts of the boat and types of repairs that I would not be arguing the merits of epoxy with you. This is not one of those.

Mark

In a previous post I said it would probably be ok to use polyester in this case, not that I would. I would use epoxy and a foam core, but that's my preference. My first comment on this thread was that I would use epoxy not polyester. Would polyester work? Most probably. Would epoxy give a stronger bond? Most definitely.
I told you before that I thought your use of epoxy on your stern extensions were it structurally counted made sense. And the use of polyester where you could use gelcoat made sense, as the structural aspect was tabbed in with epoxy.
All resins have their place.


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[redpointist]

UPDATE!


You all probably thought I'd disappeared! The weather didnt cooperate this spring, so I finally dug into this repair over the 4th of July weekend. It was a 3 day weekend with no chance of rain...perfect! What I was most afraid of was cutting into it, running into some delay, and then a thunderstorm popping up. I had tarps handy in case but some water would have inevitably made it to the cut. By this time I have also had some practice working with epoxy through my potting of the handrail holes on the other side of the boat, and having read as much as I could to mentally prepare figured it was time to get the show on the road!



The area was about 5 feet long by 1 foot wide (1 gallon of epoxy ended up being enough, but there wasnt much leftover. I have a gallon of polyester resin I'll be using to glass the seams later.). I used clues from the sound I got tapping the deck, and by digging around in the holes where the handrail was mounted to guess how far the wetness/rot extended. Time to cut it open!



I used a circular saw for a consistant depth. The tyvek suit I got on amazon for $7 was pretty handy. Kept the fiberglass off, and the sun too!



Prying the top panel off war a real chore, but slowly it came up.



Once I got to the very rotten section toward the middle it came right up easy. The edges where it was merely damp was still firmly bonded to the balsa. A thin layer of the fiberglass tore off from the top sheet and wanted to stay with the wood there.



After cleaning off as much wood as I could with the chisel, I used a 4.5 inch angle grinder with a flap disk (something like this thing: Diablo Steel Demon 4-1/2 in. 60 Grit Coarse Grinding and Polishing Flap Disc-DCX045060N01F at The Home Depot) to grind the bottom and the top sheets smooth. It made quick work of it. I also cut my core material to fit the hole at this point. I dug out all the wood that I could reach on the outboard side of the cut since most of the water and rot was on that edge. I got a bit too carried away, probably removed wood 3 inches back and it was hard to fill the gap with core material but I did my best and ended up pumping alot of epoxy down there to fill in the gaps.



I wiped everything down with some acetone that I got from a auto care shop thats clean and made for using with resins. Time to mix up a ton of epoxy! I used a slow hardener to give me plenty of time to work the area. <--Important! I didn't have a good system worked out for mixing larger amounts than I was used to. I only had 20ml syringes and plastic cups and spoons. Should have probably used a larger graduated container of some sort. Luckly my lovely lady was there constantly mixing up cup fulls while I was applying it to the deck.



For the core I used some divinycell foam. It was the only suitable core that the local plastics supplier had available. It was probably twice as thick as it needed to be and was a real pain to sand down to the proper thickness, so invest some effort into finding out exactly how thick your core is so you can buy a matching thickness.



I started at 830am and by 700pm I was finishing up. Still cleaning up while the fireworks start going off!



Try to be careful with the epoxy! Its very hard to not make a mess. I used rocks from shore to weigh down the top sheet after I put it together, and one of them ended up glued to the boat! Luckly it was only touching near the seam. I crowbared it off the next day and it took a bit of gelcoat with it!



I still need to do the beveling and glassing of the seam, but after confirming that the edges were well sealed, decided I could do that later since its waterproof at this point.

Phew, certainly a long day!