Last year I completed a 3 meter dory out of epoxy, glass and foam in Thailand. My intention was to learn by making mistakes and I was extremely successful in that.
My shop was a concrete slab with a roof but no walls – in the US we would call it a carport. The slab was smoothed fairly well, but not more carefully than normal for such a use.
I began by cutting the foam to the shape required for the bottom and sides, which led to unnecessary difficulty in cutting the glass as it moved quite a lot during cutting and infusion. It would have been much easier to cut it oversize for infusion and trim with a jigsaw later. There were also some areas of the foam on the edge that wound up with no glass at all.
I did the infusion one side at a time using a large heavy clingfilm (1.4m wide) that I get from Central (which is a major department store in Thailand). The procedure was
1. roll out the clingfilm to the length required
2. put the foam on the clingfilm followed by glass, hoses and nylon peel ply
3. roll the clingfilm on top to form a bag
4. hook up the shopvac for suction and check for leaks
5. connect epoxy and apply suction
The epoxy spread very evenly with no problems. After the epoxy had set, flip the panel and repeat. I never found a leak in the clingfilm and never needed to use tape as the clingfilm always formed a perfect seal with itself and around the shopvac and other hoses.
After a few panels the shopvac got too hot and melted its plastic bucket, which ruined the suction, so I did the remaining panels by hand. I don't think the shopvac would be strong enough for larger panels so I need to find a better suction source for the next project. I think the main reason the shopvac overheated is because I started with epoxy that was too thick and set too quickly for the weather here, it worked much better when I got the correct epoxy, but the shopvac died shortly after that.
Based on this experience I don't see the point in building a table or infusing both sides at once. Granted my panels were relatively small – the largest was about .6m x 3m. However, even a very large panel – say 10m x 5m – would weigh less than 100 kg after the first infusion and could be turned with a few willing hands. I am not sure how to turn it if it is significantly wider than the height of the ceiling, but the weight wouldn't be a problem.
Infusing on the floor saves all the hassle of building and cleaning a table, which would be significant for a large panel. Also, the infused side is very smooth as the foam provides a smoothing buffer against minor imperfections in the floor. These imperfections would probably prevent a smooth double sided infusion. It also saves the hassle of drilling holes through the foam to allow resin to flow to both sides.
The second side can eliminate the use of clingfilm all across the bottom. Only a strip around the edge is needed as the infused side provides an air tight surface. Breeze created some minor annoyance by causing the clingfilm to fold over and cling to itself, but that was adequately handled by beer bottles (I found beer Chang the most effective:).
In Thailand use of benches, sawhorses, etc. is unknown as everyone is comfortable squatting (except for obese westerners like me). After a little adaptation even I find it relatively easy to squat for some time. Work is usually held by 1 bare foot when cutting or sanding, which works very well. The temperature is almost always between 25 and 35 here (similar to Florida or California) so the normal clothing is shorts and flipflops. This habit also makes infusing on the floor seem the obviously correct way to do it, just as using a table seems obviously correct in the west.
Best regards
Herb