Rotten core repair

[gkmoore]

I've been potting the holes for hardware and when I removed the electrical connector found a significant rotted area- could pass a wire forward about 8 inches through the hull. It sounded quite hollow on most of that area so I have cut out the deck and cleaned out most of the rotted wood (see pictures).

I plan to replace the wood, epoxy etc as discussed on many threads. I had planned to replace the deck panel I cut out, so I would have very small areas visible and would maintain the non-skid and the tan color.

A few questions: Is reusing the cut our portion reasonable thing to do? Do I need to bevel the edges of the fiberglass and have a larger 'joint' between the cut out piece and the other deck?

I appreciate all your help, I'm moving along slowly rehabilitating this old sailboat that has had many modifications (aka holes in the boat) in the past.

 

[shemandr]

Usually those who do a deck repair from above re glass the deck over the core repair. I've wondered why not replace the existing skin over the new core? One reason I can think of is that it's not the usual case that the skin can be removed from the old rotted or wet core cleanly. So by the time you get the old deck off it's too beat up to be replaced. DianaofBurlington has given us the warning that without bonding of the new core to the inner laminate there isn't enough strength in the system. But if the core is bonded to the inner skin, and the old deck is intact, then I would think that you can bond the old deck to the new core and finish it off to a good result. Why not?

 

[Gene Neill]

I'm not an expert, so stand by for someone more knowledgeable to elaborate. But yes, you can reuse the skin. There have been threads here recently detailing it (Hawk232?) So don't throw it away.

 

[CloudDiver]

Typically you would re-use the top laminate you sliced out... primarily because it has a slight curve to it. Laying down new glass flat would be difficult to regain that shape. Also, if I were you I'd go ahead and check the rest of the boat for any further core damage and repair it now. The mess you have to deal with at this point trying to fix the non-skid pattern just isn't worth it, so plan on doing something like kiwi-grip. Go ahead and pull all of your deck hardware and check all of the surfaces and do soundings for damaged core. Once you have everything repaired also go ahead and drill out and epoxy pot all the mounting holes. Wet sand and polish all of your white gelcoat (do minor repairs if needed with spectrum gel-paste, otherwise paint if you have to), then go ahead and sand down all of the old nonskid pattern, wipe with acetone to delay, and roll Kiwi-Grip. Finally re-bed all your deck hardware with butyl tape or 4200.
I know it sounds crazy to do all that work, but once you have cut into that non-skid pattern there really is no going back. Might as well repair all damage at once, brighten up the white gloss, and lay new non-skid. Your decks and hardware will be good for a decade or more.

 

[25yearslater]

Been there; done that: http://forums.sailboatowners.com/index.php?threads/and-so-it-begins.123244/ Season 4 coming up and no problems. Regularly sail in Small Craft Warnings just to see how well things hold up. Bulletproof so far. Pushed this boat over ten knots last year which isn't bad considering theoretical hull is only 6.4K. Remolding nonskid is reasonably easy using Flexmold once you get the technique down. Why waste time trying to bond the cut out section when the new biaxials and epoxy add a staggering amount of strength to the composite. At least 60% stronger than cloth and polyester. If you only use tape you still need the 12 to 1 bevel around all the edges including the cut out to achieve the proper surface area. West Systems has a tech article on replacing rotted core in their how to articles. Good luck.

 

[njlarry]

Whilst I agree with the above points I would also consider the KISS school of thought. For such a small area, use the deck skin over again, do not bevel it. There will be a thin line seen around the repair but the color and texture will match the rest of the original deck. I think that small area could have simply been filled with West G Flex through two small holes. ( call West System first )
Depends on the amount of time, work and effort you want to invest. Sometimes I think a museum quality restoration is called for. Sometimes I go for a simple functional fix.

 

[gkmoore]

Thanks for the thoughts and advice. I usually try to improve things as I repair them, but given my timeline, budget (especially time) I think I will try to reuse the skin. Although I don't know what this area under the skin looks like from the factory, it appears someone may have tried the approach of forcing epoxy through the holes. In one area with little plywood left, there is a hard epoxy irregularly shaped mass.

CloudDiver, I'm in the process of potting all hardware holes, which is what led me to this problem.

25 yrs later: I looked over your thread yesterday and am amazed at all the work you did and how nice it turned out. Looking at your thread made me question whether or not to reuse the skin. I'll see how it goes, and if I have to re-do it in a year or two then I'll let everyone know that reusing the skin did not work.

 

[njlarry]

Sounds like a good plan. Please post a picture of the completed repair. Good luck.

 

[CloudDiver]

Been there; done that: http://forums.sailboatowners.com/index.php?threads/and-so-it-begins.123244/ Season 4 coming up and no problems. Regularly sail in Small Craft Warnings just to see how well things hold up. Bulletproof so far. Pushed this boat over ten knots last year which isn't bad considering theoretical hull is only 6.4K. Remolding nonskid is reasonably easy using Flexmold once you get the technique down. Why waste time trying to bond the cut out section when the new biaxials and epoxy add a staggering amount of strength to the composite. At least 60% stronger than cloth and polyester. If you only use tape you still need the 12 to 1 bevel around all the edges including the cut out to achieve the proper surface area. West Systems has a tech article on replacing rotted core in their how to articles. Good luck.

I went through this entire thread, really great work and a good example of how something like a re-core can lead to a pretty extensive re-fit (since you started with one thing, might as well get everything while you are at it). My big question is the use of gel-coat non-skid over epoxy repairs and laminate. The rule of thumb I have always followed is that epoxy will stick to polyester resin, but polyester resin (gel coat) does not adhere well to epoxy. So when I do a repair that requires the top coat be repaired with new gelcoat or gelcoat based nonskid I would have to do the repair using polyester resin. I do favor epoxy for its superior secondary bonding and strength and would go that way for any structural repair.... So, I take it after an 80 grit sanding you've no issues with the newly applied gelcoat nonskid sticking to the new epoxy laminate decks? No de-lam or cracking over these last few years?
Funny, 'Rules of Thumb' sometimes get de-bunked. I wish they would come up with an epoxy resin based gelcoat. In general, I don't care for gel-coat molded non-skid. I like Kiwi Grip, Interlux Interdeck, and similar roll on products for ease of repair and future color matching, but that's just a preference.

 

[25yearslater]

I checked on the poly - epoxy thing also CD. Here is the article; http://www.westsystem.com/ss/polyester-over-epoxy/ Personally I haven't had any problems and I live in an area where the boat is exposed to over 100 degree temperature changes from winter to summer. -20 to 95 or so F.

 

[CloudDiver]

I checked on the poly - epoxy thing also CD. Here is the article; http://www.westsystem.com/ss/polyester-over-epoxy/ Personally I haven't had any problems and I live in an area where the boat is exposed to over 100 degree temperature changes from winter to summer. -20 to 95 or so F.

Thanks for that link... this makes me re-think how I have done repairs in the past and different ways I can do them in the future. Best thing is, I can pretty much quit buying polyester resin! I can't believe I missed this article, I thought I had digested just about everything on the West System website... you learn new things every day!

 

[25yearslater]

Glad I could be of assistance CD. I was bugging out about this since I had a very distinct idea of what I wanted to accomplish. It would be nice if Gibco the makers of Flexmold had colored products that could be cut and glued down. It would be so much easier. Of course the cost would probably skyrocket. The Flexmold sheets at 4' X 11' cost $1100 each. That's why I bought the half sheet in the male pattern and made the urethane female molds. Still have the Flexmold in the basement for future need should it arise.

 

[Slartibartfass]

This test might be helpful:

 

[gkmoore]

An update on my repair- it didn't turn out as good as I hoped. I epoxied in new plywood but did not quite get the level correct. I initially mixed two batches of epoxy, one with thickener. The neat epoxy batch "went exothermic" on me about 5 to 10min into the project and I got spooked and rushed through the project. I'm sure you can tell that I am relatively new to the epoxy repair- did my sliding hatch before and that is my experience. In any event the result is not horrible, but not to my liking in that some areas of the replaced skin are 1/16" or so below the surrounding deck.

I would like input on why this batch of epoxy 'went exothermic' or whatever the term is. I had 90ml (about 3oz) of epoxy in an old butter dish appx 3.5 in in diameter, the depth of epoxy was about 1/4 inch and ambient temp of 70 deg. My other batch of epoxy did not do this. Any thoughts??