> Don't think a regular vacuum cleaner gets anywhere near that vacuum.
> Probably 1-3 psi is more like it for them.
>. . . A shop vac (or house),
> duct tape, and a roll of that cheap plastic drop cloth and one could
> perhaps build up a decent vacuum bag.

1 psi is probably ample. That works out to 144 pounds per square foot. When you consider that people making scarph joints are weighting them with 80 pound bags of sand, which cover about 2 square feet ( equivalent to 40 pounds per square foot), the `weak'' vacuum force you estimate would give a pressure that is over 3 times greater. On the high side of your estimate, at 3 psi (or 454 pounds per square foot) the force from the vacuum would be greater than stacking 11 bags of sand on the joint.

I think I'd rather carry the vacuum cleaner and plastic bag than several hundred pounds of sand. Besides, If I spilled any of the sand, I`d still need to use the vaccuum cleaner to clean the workspace.

Vaccuum pumps used in the graphic arts business regularly draw vacuums of over 8 psi, and those used in the refrigeration industry go to the 12 psi and greater range. These are frequently available at surplus outlets as takeouts from various types of equipment. Look for well-used equipment which is probably no longer suitable for working a 40 hour week, but is much more affordable and should hold up for the occasional use of a hobbyist. I've seen good quality vacuum pumps sold as low volume, low pressure air pumps (compressors) for artist airbrush use.

There are heat sealing tools sold for resealing bags of food ( assuming you consider potato chips and pretzels to be food). You can find these for nominal prices at grocery stores or homeware departments of hardware stores. Some seal a strip 10 inches long at once, others seal only an inch at a time, and are slid slowly along the material to create a long seam.

If you can save some money on the mechanical equipment you can apply those savings to buy the right plastic material used for making the bags, air channels, bleeder valves, etc.

> Good point about the outgassing. Especially of the wood. One might be able
> to use this in reverse. As in vacuum bag the wooden boat for a while, then
> take it out and apply the epoxy for better suck in. I have no idea of the
> time factors for wood to retain vacuum and have no idea if this idea would
> work at all. But it's interesting to think about.

Not sure the use of 1-3 psi vacuum would greatly affect outgassing, either in the resin or the wood. I'm not sure there any `retention` of vacuum in the wood fibers, grain, pores, or cells. I suspect that once the wood is removed from the vacuum it returns to equilibrium with the surrounding air pressure in a matter of seconds, if not faster. It would not suck in resin after that.

As I understand, the refrigeration vacuum pumps get nearly a total vacuum, and have to hold this for 30 minutes to an hour in order to get moisture that may be trapped in the tubing of a refrigerator or airconditioner to evaporate. I expect you would need this much vacuum and that you should maintain it at least this long, in order to get the moisture level in the wood to drop. Trapped moisture, in the form of water vapor, seems to be the likely culprit for `outgassing' problems.

There is a 'solar energy' cure to this problem. It requires no special equipment: leave the boat in bright sunlight for a few hours, then, after it is nice and dry, wheel it into the shade and put on the glass and resin, or just a thin sealing coat of resin, as you prefer. Once out of the sun the wood will cool, and simulate the effect noted when resin is applied late in the day -- the resin soaks in nicely and few, if any, bubbles are formed.

Hope this helps.

Paul Jacobson