Should I reuse the top fiberglass skin

[Drinky Crow]

So how did that work out? Avoiding trapped air I mean. I'm going to do same method about 12" circle of rot but I'll cut square to facilitate dropping in this....

[mlydon]

How about vacuum- bagging the layup. Assuming the lower skin is intact, and airtight, after laying on the old skins, you can put a sheet of heavy plastic over all, and seal it to the surrounding deck with roll-on caulking, in the process sealing a length of vinyl tubing into the ‘inside’ of the ‘bag’ you’ve now made. A ‘wick’ in the form of a length of paper towel along the deck under the plastic, with the end of tube laid over it, and a piece crumbled up around the end of the tube allows the system to draw air from the entire layup. Hook a vacuum pump up to the hose, and draw a good vacuum. A 10” vacuum will compress the skin/core/lower sandwich together smoothly, completely, and TIGHTLY. A 16” x say 70” section, drawn down by say 7” (3.5 psi) = 1050sq inch x 3.5 psi = 3600 pounds of pressure clamping the sandwich together. Let it run for till the epoxy sets.

Vacuum bagging is used in a lot of high-tech layups - very consistent, strong results.

I just did a quck search and found this:
https://youtu.be/AIUq3R-YsQA

He did it cheap with a shop vac - while that will work, it won’t draw that much vacuum, and you really need to run it until the epoxy is fully set. I also didn’t like his tray collector - the pressure on the entire tray is transferred down onto the rim of the tray instead of evenly across the deck piece. The paper towel method is superior. The video does convey the concept, though.

Good luck,

Matt

[jimjimmyjimjim]

Originally Posted by Drinky Crow

So how did that work out? Avoiding trapped air I mean. I'm going to do same method about 12" circle of rot but I'll cut square to facilitate dropping in this....

It worked fine as far as I can tell.

I drilled a 1/2 inch hole every foot or so to let out air and to see that the resin was saturating everywhere. I was careful to weigh down the area from the mid-line outwards to force any air bubbles out. I removed sections of 18"x5' of the top layer of 1/4" fiberglass. This came off easily because the plywood core had delaminated. I removed the plywood completely and undercut the periphery by a 1/4" all around the cut-out. I cut new 1/4" marine grade ply into sections to fit and conform to any curve on the sidedeck. I bedded the ply in epoxy with chopped fibers and cabersol. I then put a thick layer of the same epoxy mix on top of the ply and on the underside of the cut-out fiberglass then put the cut-outs on the ply making sure that I forced out the bubbles and got good sqeeze-out. I weighted it down with sandbags and a clamping system. I haven't cut into the patch job to look for voids but the deck is solid. For the side deck, where there isn't as much stress, I'm not too worried about voids - as long as they don't indicate rot or extensive delamination.

I'm not so sure I saved that much time though. Laying 3 or 4 layers of 18oz fiberglass wouldn't have been that time consuming and I still had to do a fair amount of fairing.

I used sandbags to weigh down the first section but found that very difficult because the area was not very wide. I couldn't watch the squeeze out with the bags in the way. On subsequent sections I used a clamping method that worked much better.

[jimjimmyjimjim]

Originally Posted by mlydon

How about vacuum- bagging the layup.
... Good luck,

Matt

I thought about doing that. I have the equipment and I used bagging a lot making furniture. But in the end I decided to go with a "tried and true" method. I was worried about getting a good seal. Even with the right equipment and ideal conditions I've had seals fail. But when all goes right the results are very good.