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Removing Bubbles in Epoxy Fill Using a Vacuum Chamber

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Blog entry by Rich posted 02-06-2018 05:21 PM 341 reads 0 times favorited 6 comments Add to Favorites Watch

I’m working a lot with mesquite lately. It often requires a significant amount of epoxy to fill cracks and voids. I was having a real problem with bubbles that, after planing, were a nightmare to deal with. Initially, I tried to work on filling them with different hard fills, and had excellent results, that is until I applied the finish. There was a distinct difference in the way the Arm-R-Seal cured on the board and epoxy versus the fill. This was true with a variety of fill options.

Ultimately it became obvious that I had to find a way to eliminate the bubbles in the first place. I tried methods folks had mentioned on here, like using a heat gun. While that did bring some bubbles to the surface, it didn’t go deep enough for fills in 4/4 and thicker wood.

There is a lot of information available on pouring the epoxy while the wood is cooling. Again, on a thick board a heat gun is going to do a marginal job, and other methods of warming a large slab of mesquite aren’t practical.

I finally stumbled onto a method that’s been working great for me — a vacuum system to pull out the bubbles before I pour. I have a VacMaster chamber vacuum I use for food storage that can pull a 99%-plus vacuum, but any number of systems would work. Even a Food Saver with the mason jar attachment would be very inexpensive and should pull a strong enough vacuum, although I haven’t tried it.

By switching off the power a couple of seconds before the full vacuum cycle ends, I can leave the container of epoxy in the chamber for two or three minutes, which is enough to pull out all of the bubbles. My pours have been flawless since I started doing it this way.

I did learn the hard way that it’s necessary to stabilize the mixing cup, since the release of the vacuum causes a strong rush of air that will blow it over and cause a nasty spill.

-- No matter how much you push the envelope, it'll still be stationery.



6 comments so far

View CaptainSkully's profile

CaptainSkully

1565 posts in 3461 days


#1 posted 02-06-2018 05:32 PM

That’s great info that I haven’t seen covered anywhere else they’re filling voids. Thanks for sharing!

-- You can't control the wind, but you can trim your sails

View MrRon's profile

MrRon

4627 posts in 3146 days


#2 posted 02-06-2018 05:50 PM

I made some epoxy castings and the method for removing bubbles that was recommended to me was to PRESSURIZE, not vacuum; which I did and the castings came out perfectly. I was using a paint pressure pot, but the physical size of your project may not allow for a pressure setup.

View johnstoneb's profile (online now)

johnstoneb

2781 posts in 2075 days


#3 posted 02-06-2018 06:31 PM

To get the bubbles out of epoxy you need to reduce the surface pressure the vacuum would work great.

-- Bruce, Boise, ID

View CaptainKlutz's profile

CaptainKlutz

114 posts in 1397 days


#4 posted 02-06-2018 07:19 PM

Glad you found something that works for you!

FWIW to others looking for more information:

MIL SPEC 276A list methods for resin de-gas. Although they are very generic.
There are thousands of internet references concerning de-gassing of resins to make fiber reinforced parts. :)

One method for removing bubbles/voids from military epoxy casting resins I used:
1. Place container in vacuum chamber and pump down to below 29 inHg pressure and hold for 2 min.
(expect volume to grow 2-3x, so use a large enough container, this removes the gross level of bubbles)
2. Release vacuum and return to ambient pressure for 5 seconds.
3. Apply vacuum and return to greater than 29.5 inHg pressure and hold for 5 minutes.
(mixture will almost double in volume, then begin to “boil” as air releases)
4. Repeat step 2.
5. Apply vacuum and return to 29.5+ inHg pressure and hold for 10 minutes.
(at end of 10 min or when properly de-gassed, minimal bubbles should form and rise to surface)

Industrial de-gassing chambers make use of supplemental vacuum storage tank to reduce time required to pump down chamber volume which will shorten actual working time for epoxy application.

The purpose for multiple cycles, using more vacuum each time is to reduce the frothing that happens during de-gas process, which will allow air to remain trapped in resin when it is returned to ambient pressure.

It is generally not recommended to use pressure below 29.9 inHg as this may create boiling point that is below the boiling point of light weight diluents in the epoxy system.

The time at vacuum and level of vacuum are subject to modification based on level of air entrapment that is tolerable. The process times are frequently adjusted to accommodate ambient temp and cure time of resin.

There are other Mil-SPEC resin de-gas protocols:
Pressure only for forcing resin into voids of metal castings, and one that involves alternating high pressure and vacuum cycles. The high pressure/vacuum protocol is used for certain resin systems (mostly silicone) that can not tolerate vacuum below 29 inHg without boiling out some key ingredients required to complete cure, or when need to de-gas and infuse resin inside an object without voids.

For a hobby wood project you likely do not need the same level of air removal as a resin going into a military electronics box or composite aerospace hardware, but hopefully this provides some insight. :)

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View Rich's profile (online now)

Rich

2265 posts in 492 days


#5 posted 02-06-2018 07:59 PM


1. Place container in vacuum chamber and pump down to below 29 inHg pressure and hold for 2 min.

- CaptainKlutz

That’s good to know, thanks. I hadn’t seen the vacuum needed before. I can boil water at 40ºF in my chamber vac, which indicates greater than 29.6 inHg of vacuum.

-- No matter how much you push the envelope, it'll still be stationery.

View woodbutcherbynight's profile

woodbutcherbynight

3929 posts in 2311 days


#6 posted 02-07-2018 02:37 AM

For what it is worth we routinely vacuum down Automotive A/C systems to 29-30 inches of vacuum for 15 minutes. The purpose being to remove the moisture from the system. Water boils out and is evacuated through the pump. Leaving a clean moisture free environment for the fresh R-134a. The aluminum lines used would corrode with the moisture causing all sorts of issues, never mind the mess water and R-134a make when mixed.

Once under vacuum the dye and oil are easily sucked up into the system.

-- Live to tell the stories, they sound better that way.

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