My 3d printers Sylgard 184 vat floor coating had fogged and needed to be replaced. I believe it fogged due to having made some long base layer exposures. When I originally coated the vat floor I needed to let the Sylgard cure for 48 hours before I could use the vat. I didn’t need to wait that long this time. Sylgard 184 can be heat cured in as little as 2 hours at temperatures that do not damage the plastic parts of the vat. Sylgard 184 is a 2 part mixture the base material and a curing agent. Mixing the 2 parts of the Sylgard produces so many bubbles that the liquid almost becomes a foam, if the vat floor was coated with the mixture and heat cured the bubbles would be frozen into the coating and it would be useless. To get around the problem the bubbles in the mixture can be removed by “vacuum degassing” the Sylgard before heat curing the coating.
Knowing that I would need to replace the vat floor eventually I had gathered the parts needed to make a diy vacuum chamber. I already had a vacuum pump ($100), tubing, ball valves and brass fittings ($20). I needed something to use as the vacuum chamber and after doing some looking around on google found that others had used a good quality thick walled cooking pot for the purpose, I obtained a very good teflon coated pot from an estate sale for $10 (thick walled cooking pots can be very expensive if purchased new), also a sheet of 1/2″ lexan for the vacuum chamber top from a plastics supplier ($15), a vacuum gauge from american science and surplus ($4), the vacuum gasket was made from non slip shelf liner. It took all of an hour to assemble the parts into a working vacuum chamber. When I tested the vacuum chamber it rapidly pumped down to -29″ hg and held there.
Note: The brass fitting and vacuum gauge both have 1/4″ npt fittings. If you drill a 1/2″ hole in the plastic top, using a flat or spiral drill bit, you can screw the fitting into the plastic without needing to tap threads (it’s a tapered thread). I put a dab of silicone on the threads of the fittings before screwing them in just to be sure of a vacuum tight seal.
To replace the Sylgard coating in the vat I cut the coating around the edges after which it easily peeled off of the glass bottom of the vat (Sylgard does not adhere to the glass). I mixed 27.5 ml of Sylgard (25 ml of base, 2.5 ml of hardener) poured it into the vat and placed the vat in the vacuum chamber. I turned on the vacuum pump and slowly the Sylgard began to foam then the bubbles began to burst. It took about 20 minutes for all of the bubbles to disappear. After all of the bubbles had disappeared I turned off the pump and slowly released the vacuum through the bleed valve (without a bleed valve you are going to wait a long time before being able to remove the lid). I took the vat and set it on the griddle side of my George Forman Lean Mean Grilling Machine (which i had previously leveled) covered it with a sheet of glass and let it sit for a half hour with the heat turned off to make sure the Sylgard was perfectly flat and level in the vat. After the half hour was up I turned the heat on to the lowest setting and slowly increased the temperature to roughly 170 F over about 10 or 15 minutes using a non contact thermometer to determine the temperature of the griddle surface (this lets the temperature of the glass equalize across it’s surface and thickness so it won’t crack). I let the vat “cook” for 2 hours after which the Sylgard was fully cured and perfectly clear (much better than the original coating).
Note: This method is for glass floor vats, if your vat has a plastic floor you will ruin it.