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Old 01-27-2015, 06:51 PM   #1
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Swim platform with wet core

The core of the fiberglass swim platform on my newly aquired 36' Marine Trader is completely saturated and rotted. I've removed it and am ready to tackle the repair. The top of the platform is in good shape and the non skid pattern is good.

My tentative plan is to carefully cut off the bottom layer (how?) of fiberglass and remove the rotted core material. I would then fill the core with one of the synthetic core materials, epoxy the bottom layer back on top of the core. Then sand and paint.

I've never completed a core repair of this scale and would really appreciate everyone's comments and experience.
P
Thanks!
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Old 01-27-2015, 06:56 PM   #2
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Why epoxy? You can use polyester with most of the core materials.
Unless you are using plywood, no need for epoxy. The top and sides that you are going to be marrying the laminate to are polyester.
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Old 01-27-2015, 07:18 PM   #3
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A secondary bond of polyester will be much weaker than the mechanical and chemical bond of epoxy. This is ok in some applications but for something that close to or sometimes in the water I'd go with epoxy. You don't hear of anyone getting a "polyester" bottom job.

Cut the skin with a multi-tool. The chances of getting it off in reusable condition are slim.
Dig out the rotten core and replace it with Corecell or the like and laminate a new skin. It's dirty work but not difficult.
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Old 01-27-2015, 08:20 PM   #4
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Greetings,
Mr. mn1. You can use a multi tool but IF you have access to a good air supply, I would suggest one of these. 3 in. High Speed Air Cut-Off Tool
Or the electric alternative... 3 in. Heavy Duty Electric Cut-Off Tool
Add 3 in. 40 Grit Metal Cut-off Wheel 10 Pc
...and you're off to the races. I would use epoxy myself.
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Old 01-27-2015, 08:37 PM   #5
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Hi Mike-
Depending on woodworking skills, if I was in your shoes, I'd scrap the fiberglass swim step all together and make a new one out of Teak
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Old 01-27-2015, 08:43 PM   #6
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Quote:
Originally Posted by Max Simmons View Post
Hi Mike-
Depending on woodworking skills, if I was in your shoes, I'd scrap the fiberglass swim step all together and make a new one out of Teak
Have you priced teak lately ?
I don't think they'll even let us buy it anymore with Canadian dollarettes
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Old 01-27-2015, 09:38 PM   #7
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Quote:
Originally Posted by mike_nickens1 View Post
...My tentative plan is to carefully cut off the bottom layer (how?) of fiberglass and remove the rotted core material. I would then fill the core with one of the synthetic core materials, epoxy the bottom layer back on top of the core. Then sand and paint...
What a great set up. You have a mold already. Cut the bad out and build up with new core. SOF and BP suggestions will both work but cut the new core material so you aren't using lots of resin to fill voids. Resins aren't made to bride gaps.
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Old 01-28-2015, 07:45 AM   #8
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When I do core repair I cut the skin using a circular saw and fine tooth blades. Make the depth to just barely cut thru the skin. Then peel it back. If you don't get to the edge that's ok, actually probably better as you'll have something to bond the new layer to.
I've used both epoxy and polyester, my personal preference is the polyester.
Have fun.
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Old 01-28-2015, 11:50 AM   #9
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Thanks for everyone's comments. Here's an update. I used jleonard's advice and cut out one section of the bottom skin. Came off fairly easy (thanks for the tip).

Surprise! What I found was not plywood, but an open cell foam, saturated with water. See pics below. The foam looks like I can remove it fairly easy. My plan is to epoxy or fiberglass in new core panels, Then mix a batch off epoxy or fiberglass with some filler, spread the mixture out and re-install the cut out panels. Then fair, sand and paint.

Does this seem like a good plan? Anything I'm missing?
Thanks!
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Old 01-28-2015, 12:37 PM   #10
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Why not fill with a 2-part expanding foam? You would probably need to drill a series of injection/expansion holes, but those would be easily repaired, and if you put them all on the bottom side they won't be visible anyway. By using foam, you get the benefit of more complete coverage and better adhesion to the fiberglass, which will greatly improve strength. You just have to be careful not to put too much foam in or it will blow apart the swim platform when it expands.
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Old 01-28-2015, 01:42 PM   #11
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I would not try to re-use the cut out panels. Just glass it up using 1 1/2 ounce mat or whatever material and build it up to the proper level, then gelcoat if polyester or paint if epoxy.
Well, that's how I would do it anyway.
And I'd probably use exterior plywood for core, only because I know how to work with it and it's relatively cheap.
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Old 01-30-2015, 11:44 AM   #12
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Mike
I've done exactly as you planned on a Carver platform and it worked well for me. I did the cut w/ a router & carbide bit from a Rotozip tool - cut F'glass nicely easy to guide by hand. I skipped the core in any place where I had attachments and just built it up solid w/ mat & resin. Other places I sawed end grain pine instead of balsa and set the blocks in resin as I placed them. After replacing the old skin I filled kerf w/ thickened resin and did put one layer of matt & resin over the filled seam. Slightly thicker in those areas but it's the bottom of the platform - who cares.
Good luck
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Old 01-30-2015, 12:24 PM   #13
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was everything well to remove salt water residue, mold etc.


The idea of the proper coring is to create a box structure that will be much stronger than just a filler.
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Old 01-30-2015, 01:52 PM   #14
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Why did the core get wet in the first place? In my experience with rebuilding my swim platform it was through the leaking fittings that attach the platform to the boat. To prevent this from happening again make sure that all fittings like bolt holes are through solid epoxy/FRP. Relying on just caulking to keep water out of the core means that it will eventually fail again.
To do this I drilled all bolt holes over size in diameter, then epoxied an FRP backing plate under the over size hole, filled the hole with epoxy, then redrilled the hole.
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