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trickdhat

New Core...the wrong way I'm told

Rating: 1 votes, 5.00 average.
The first step with replacing the core was identifying justhow much core was rotten. As you canexpect, the affected area was greater than I initially expected.
The void along the edge and between the topskin and balsa created by not spreading the bonding resin allowed any wateringress to propagate through the laminate from the mast to the rear bulkhead ofthe cabin top.This resulted in asection apx. 18” by 8’ along the edge of the cabin top needing to be replaced.For the most part, removing the core waseasy.The rotten areas just fell offwith the bottom skin and the last remaining sections were easy to chisel outback to dry core.Any remaining balsaadhered to the top skin was ground off with an angle grinder equipped with a 60grit paddle wheel type sanding disk (quick work, but one hell of a mess).
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A small detail I hadn’t thought about when removing the core was what I was going to tie the new glass to when it was time to rebuild thebottom core. Along the companion way, the lip only protruded ˝” below the bottom skin.This wasn’t enough to create a good bond, so I decided to stop the core short of the void and wrap the new bottom skin upinto the void.The hope is to stiffen this area by having a vertical section of new glass.I’m planning on filling the void withexpandable foam, replacing the teak trim with a wider section, and glassingover the foam to the back of the teak trim.When it’s time to do the other side, I’ll probably leave 2” of the oldskin so I have a better surface to adhere the new one to. It’s going to be a pain to dig out the oldcore under the 2” overhang, but I think it will be easier and stronger in thelong run.
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The next step was sanding and prepping the bottom of the topskin. I used CSM and epoxy to glass overthe bottom of the old deck penetrations left by the deck organizer, clutches,winch, and cams.I also filled the voidon the underside of the hatch slide with expanding foam and glassed over itwith CSM.I wasn’t sure if it wasnecessary, but I used thickened epoxy to fill in the low spots.This could have been unnecessary as thethickened epoxy I used to bond the new balsa to the top skin probably wouldhave served the same function, but it gave me a little more piece of mind afterseeing the bonding issue that caused a lot of the issues in the first place.

It was finally time to put in the new core. The plan was to use a vacuum pump to ensureadequate pressure, but after a few test bags I realized all the little staplehole weren’t going to allow a complete seal for thevacuum to do its work.I decided to vacuumas much as I could then fill in the gap between the old core and new usingbraces from below.I worked in smallsections and set up as much of the bag as I could before mixing up theepoxy.Each bag encompassed the previoussections to allow a good seal.There werea few small leaks with each layup, but they were easily sealed with the vacuumtape.
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I used West System 205 hardener to wet out the core and prep the bottomof the skin, then switched to 206 with 404 filler to create the bond.
By the time the 205 tacked up, I was readywith the buttered up piece of new core.The thickened epoxy held the core in place while I could seal the other3 sides of the bag.I first tried tapingthe peel ply and breather cloth in place, but after it shifted on the firstsection, I switched to using 3M adhesive tape to temporarily glue them to thebottom of the new core.This workedperfectly and released just as well as the peel ply alone.

Filling in the gaps was a little more challenging than usingthe vacuum. I purchase 2 extendabledrywall sanding sticks that I used to wedge against the sole and the newcore.I backed the balsa with thinsheets of particle board to evenly distribute the pressure and protected themwith peel ply and a sheet of plastic.
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The tricky part was cleaning up the epoxy that oozed out around theedges but was concealed by the plastic and peel ply.The first 2 sections required a lot ofgrinding after the epoxy had cured, but I eventually got the hang of it.The sections applied with the sanding sticksweren’t as consolidated, but I think the gap was adequately filled with theexcess epoxy due to the amount of ooze out I had to clean up.Either way, I’m confident the bond I achievedwas better than the initial bond from the factory.

The final step of replacing the core was creating a filetaround the edge to ensure the glass wouldn’t create a void and had a smoothtransition to the cabin sides.
Next up was replacing the bottom skin of the laminate. I wasn’t looking forward to this part, but Icould finally see the light at the end of the tunnel.

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Comments

  1. 907Juice's Avatar
    That looks like a lot of work but I'm sure it is worth it now instead of putting a foot through. What do you have planned for the headliner? I've seen some pics of people that just painted the fiberglass. Looks interesting.

    Juice
  2. trickdhat's Avatar
    That's the difficult part to swallow. The deck didn't show the typical signs of rotten core. There are a few gelcoat cracks under the winch and at the break in the companion way slide, but it felt solid and didn't flex much. I think this is due to the top skin being so thick and the added structure of the companion way slides. After removing the bottom skin and core, it flexed a little more, but still felt stronger than a racing boat. I probably could have kept it as-is and sailed with no problems, but knowing I had rotten mush in there and seeing the laminate drip from some of the staple holes during intense rain storms didn't give me a worm fuzzy feeling. I know I'm doing the right thing (maybe not the right way), but its tough doing so much work and ending up with only a slightly stiffer cabin top.

    For the headliner, I still have a bit of time because I'm planning on doing the other side this fall/winter and I also have to fit the mast step in there at some point (I think I have to go from the top on that one though). I was thinking about making panels by adhering foamed back headliner to thin sheets and holding them up using strips of teak screwed into firing strips. I'm hoping this will give good access, look OK, and still keep the headroom above my 5'11" head