In theory this is a good idea. That is precisely how refrigeration systems that are adversely affected by small amounts of moisture get the unwanted moisture out of the pipes. When a certain vacuum reading is reached, the moisture is gone. The problem with any system that is being evacuated in order to remove moisture, or air or any gas, is the tightness of the system. I would think that this would be a matter of trial and error to determine if a given volume in a deck core could be made sufficiently tight to decrease the pressure in the core to hasten the evaporation of moisture. This is probably different for each deck situation. The success also depends on the capacity of the vacuum pump. If the pump capacity can stay ahead of the leaks it will be more effective than a smaller pump that cannot stay ahead. How practical is the idea? Are vacuum pumps available to rent at a reasonable price? In summary, I think this might be worth a try. I have a small soft area in my deck. I could take off the top layer of fiberglass and remove the wet core, replace the core, and fiberglass to solve the problem. It would be a lot easier to drill holes, dry out the core and inject epoxy to cure the problem if there was a good easy way to dryout the core. If a vacuum system could do it in 24 hours it would certainly be worth the trouble to determine if it is indeed a solution. Where is Capt. Wil (to test this idea) when we need him? Herb Hoffman My Tyme Prairie 29 <snip> >I'd like to pass on a tip that a marine surveyor gave me last year....<snip> >The theory is to use a vacuum pump to reduce the air pressure in between >the two fibreglass layers to the point where the water will boil. The >water vapour would then be removed by the vacuum pump. <snip> >1. Drill a grid of 1/4 inch holes into a small wet area of the coring. > >2. Lay the end of the suction hose flat on deck near the centre of the >section you are working on. > >3. Cover the entire section with burlap to allow unimpeded migration of >air and vapour. > >4. Cover the burlap with a heavy guage poly and tape all edges to the >deck to create an air-tight seal. > >5. Run the vacuum pump for about 24 hours. > >6. When a moisture meter indicates the coring is dry, inject epoxy into >the holes to fill all voids. > >This should be done in small sections at a time (I can't recall if it >was 2 or 4 square foot sections). <snip>