Grrr...

Finishing the ends of sandwich panel

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I need to fabricate some hatch boards.  I've come down to two options - white acrylic, or self-made fiberglass laminate.

I don't have a vacuum bagging system, so I'm going to fall back on an old method.  I'm going to lay it up on a sheet of waxed glass (not fiberglass, actual glass), and then lay another piece of waxed glass on top with a couple weights.  You end up with a very flat finish that's easy to sand a paint, and it squeezes most of the air out.

My problems comes with the ends where there will be essentially raw foam.  What's a good method of finishing before painting?  Dig out some foam and put coloidal silica all the way around?  Maybe just wrap the bottom layer of glass up and onto the top before I set the glass on it?

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I asked basketcase about how he finished his panels, and his recommendation was to make the panels, fit them, and then laminate the edges with about 30mm of overlap.

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I use a router bit in a drill to cut away the foam between the glass 3/8” and fill with thickened resin, with some micro balloons so that I don’t want to die when sanding it flush. 

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It's time consuming but remove core and backfill with thickened resin.

Russell Brown's e-book on epoxy (a gem) also has a technique for glassing sharp 90 deg corners like a flat panel.

Acrylic is heavy but lot less labour in just cutting out 2 or 3 panels than fabricating glass/foam panels.

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Okay, ignore whatever I said in my previous posts in this thread - just noticed the OP wants to make hatch boards.  I was thinking hatch covers.   That post is hidden now anyway.

Agree with Zonker.  Unless you are totally weight obsessed - go with acrylic.  Only thing I can add is to flame treat the edges for a smooth finish.

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We use regular melamine board and sand it smooth with 240grit and wax it.  You can use it to build edges for a real mold. Make the edges 2”(50mm) tall. Inside dimensions are final. The first layer is large enough to wrap the edges and a bit beyond. Throw that in the mold. Add as much glass as you want. Place the foam. It should be sized to give you enough room for resin & glass to wrap the edge. Add the next layers. Wrap the bottom over the top. Place another sheet of melamine over the top. Add some heavy objects to crush the laminate. You can unscrew the melamine edges to remove your part.

It’s like using a piece of Tupperware as a mold. 

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Another alternative is to edge the foam before you laminate it. The pic is a centreboarder's foredeck before laminating, the ply bits are inserts where hardware gets mounted, the yellow cedar is where there will be exposed edges, mast gate and c/board. For a robust hatch cover / washboard i'd get say 50mm x 6mm timber of your choice, run thru thicknesser if you can to same thickness as the foam, something tough, and glue this , edge on, to the foam, just 'tacked', doesn't have to be super well done as all gets consolidated in the laminate.  Place it so its centreline is somewhere in line with where the edges will be, bit like a picture frame,, ie you're making the panel oversize, with timber all around,  Laminate it up, vacuum bag best,  or your preferred work around if you can't, then trim down to size.  Can round / bevel / sand to your heart's content afterwards. 

20201020_195350.jpg

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 because it is a washboard/hatch board, and you are taking it in and out a bunch, and there is a chance the edge could get damaged, i would shy away from back filling and cap the edge with laminate. its a lot more durable.  just a 30mm lap on each face would be fine.

board.jpg

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8 hours ago, basketcase said:

 because it is a washboard/hatch board, and you are taking it in and out a bunch, and there is a chance the edge could get damaged, i would shy away from back filling and cap the edge with laminate. its a lot more durable.  just a 30mm lap on each face would be fine.

board.jpg

+1, lightly used floorboards can be edge-filled, but wash boards (hatch boards) and frequently used floorboards (primary bilge access) should be taped.

 

Remember that tape will add thickness, so build the primary board accordingly.

 

Basket, what are you using to cut out the C&C logo in that cloth? Finish is really nice.

 

HW

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6 hours ago, Haligonian Winterr said:

+

Basket, what are you using to cut out the C&C logo in that cloth? Finish is really nice.

 

HW

thanks. i use a box cutter, a 150mm rule and a roll of tape for the curves.

 

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3 hours ago, Will1073 said:

Hmm my 4 year old edge filled drop boards that get tossed into the cabin have held up perfectly...

congrats. seriously.

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1 hour ago, basketcase said:

thanks. i use a box cutter, a 150mm rule and a roll of tape for the curves.

 

Your inbox is full FYI, or you've got messages turned off.

 

Pre-preg? Or other magic to keep fibres together during cutting and working?

 

HW

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28 minutes ago, Haligonian Winterr said:

Your inbox is full FYI, or you've got messages turned off.

 

Pre-preg? Or other magic to keep fibres together during cutting and working?

 

HW

Will fix inbox.

Other magic learned over years.

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Cut your outer skins a half inch or so larger in each dimension, then add one inch teak or mahogany around the inside of the edges before laying the foam inside that wood perimeter. Then cut the boards down to fit after it all cures. The wood around the edges should take the beating from repeatedly removing the boards and there's less chance of gaps or failing bonds as would be the case of routing and back filling the edges. 

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