Starting on the Moulds

I worked out that I would need 5 sheets of material (2.4 x 1.2 metres) to make the temporary moulds that the boat will be built over. Looking around for inexpensive ply I found some smoke damaged 7mm thick plywood and bought 10 sheets for $30. At 7mm these sheets of ply are too thin so I glued them together in pairs to make sheets 14mm thick.

To do this I laid a sheet on the floor of the shed, spread a thin layer of glue on it with a rubber squeegee and then laid the second sheet on top. To apply pressure while the glue set I laid a sheet of polythene over the plywood sandwich sealing all around with some cheap gap filling goo and then sucked all the air out with a vacuum pump. This gave me close to 15 pounds per square inch over the whole surface of the sheet. This is approximately the same as putting a 30 ton weight on top of the sandwich!

Here are a couple of photos. First the whole setup. The vacuum pump (at the top left of the black sheet) was home made using a 1 HP electric motor (blue) and a very old compressor (pinkish).

Below is a corner of the sheets where the vacuum tube enters. It was a bit tricky getting a seal where the tube went under the sheet but I succeeded by adding more of the gap filler. The sharp fold over the edge of the ply and the very small radius where the sheet hits the floor give some idea of the vacuum achieved.

I used a glue called Purbond which has a drying time of 2 hours at 20 degrees C and ran the pump for about 5 hours for each pair of sheets.