Another epoxy question

Despite my efforts to attain that flawless finish from poured epoxy, I still can't seem to be able to do it (I always need to sand out some imperfections). I used to have problems with flecks of dust and such getting trapped in the finish, but I managed to solve that buy having the epoxy cure in a relatively air tight container. My biggest problem now is that I'm ending up with (for lack of a better term) voids in the finish.

I'll thoroughly coat the scales in epoxy, making absolutely sure I don't miss a spot, then set them aside to cure. But after the epoxy has set, I always seem to end up with little voids in the finish, usually no more than a few sq millimetres. It can't be a problem with lack of epoxy, because I always have to deal with drips of excess forming on the undersides of the scales as well. And I spend several minutes mixing the epoxy before I pour it, so I doubt that's it either. My best guess is it's caused because I usually shape my scales to be smoothly curved down the edge. Being as such, the epoxy gets pulled down towards the edges (and then drips off) and epoxy on the top part of the scales thins out so much that it's surface tension pulls it apart to cause the voids.

Anyway, if anyone knows a solution, I'd be very appriciative to have it.

Here's a few pix to show you what I mean.

I do not have a lot of experience with using epoxy as a coating but I do work with a multitude of finishes. The voids look like a surface tension issue caused by some sort of contamination. I would try wiping the scales with a solvent then coating with epoxy. I would use mineral spirits or naphtha then acetone. Wipe with a clean paper towel using each section of the paper towel once so that the contamination is just not moved around.

Charlie

Alcohol might be another solvent to use to get a good, even distribution of the epoxy. My late uncle who was a machinist talked me through bushing a rear axle housing on an old car so I could get a proper interference fit for some new bearings. I turned the bushings and hogged out the journals in the axle housing so I could epoxy in the new bushings. I also turned some locating plugs to align and center the bushings. With evereything in place in the housing, I now had to get epoxy into the narrow space between the bushing and housing. My uncle said to fill that void with alcohol and with a thin blade work the epoxy into and through the alcohol. It worked! - I drove that old Plymouth for another 2 years.
The original problem was that the bearing journals were too big and allowed the differential oil to migrate past the bearings and into my rear brakes. New bearings with their internal seals (thought to be the problem) were a slip fit into the axle housing - not a good thing especially since a junk yard replacement housing was even sloppier. So it was greasy brakes or figure out a way to fix it. Some relatives can be a real blessing, hmmm? :rock:

I realize this tale is non-shaving related, but the technique may bear some looking into for helping distribute epoxy evenly on some new scales.

good luck

Mine are cured in a vacuum chamber ,I also cure at 67 degrees farenheit.Cures above 73 will cause bubble inclusions.If you cannot vacumm degass put the scales in a small flat pan approx 2 inches high,and pass a propane flame over the top,(you dont have to heat much)the carbon dioxide will cause the included air bubbles to collapse.This is the way a lot of small shops,that cant afford a vac chamber degass.I find I get much better results with as slow(cool)cure rates as possible.Makes the resin much clearer(less anamine blush)..............Lots of trial and error.Best Regards Gary

Hmmm, looks almost like fisheyes. Are you by chance using stearated sanding paper? That's about the most likely cause of your problem, unless you've gotten some wax or silicon contamination going on. If you are using stearated papers (often called no-clog), switch to non stearated paper, a plain garnet paper would be fine, it's cheap and you're not sanding a lot of area so the clogging issue should be bearable. Washing the scales down with a liberal amount of mineral spirits might work if it's not the stearated paper that's causing the problem, but do let the scales dry very well before attempting to coat with epoxy.

Regards

Christian

OK :OT

Are there pin holes drilled in there someplace that I am missing?????

Traveller,

Thanks for the epoxy curing recommendations. It's always a great benefit to hear from someone who knows what works.

And Merry Christmas,

thanks toxik for bringing this up. i am having some of the same issues.

thank you all for the suggestions. as gary said, LOTS of trial and error.

vgod

Thanks for the tips guys. I'm guessing that's it's probably a contamination issue, or the surface tension issue.

The coat in the pix was actually a second coat on top of a fully cured coat of epoxy. So it wouldn't be air bubbles drawn up out of the wood. I also doubt it's air bubbles left in the epoxy as I go over the scales rather thoroughly after a pour to release the air bubbles and make sure the scales are completely coated. There's also no pin holes in the scales yet; with epoxy finish I usually drill the pin holes after.

I'm going to try wiping with mineral spirits and then putting on another coat, hopefully that'll work. I'll post the results when I'm done.

Don’t use alcohol or mineral spirits. Alcohol can cause grain lift (the grin that you worked so hard to sand smooth suddenly ripples up) and mineral spirits takes too long to dry and can leave a residue behind. Use as acetone. I give my scales a wipe with it before I start measuring out my resin.

What about if the coat is on another coat of epoxy, not the wood? Is it then safe to use alcohol or mineral spirits?

Uh... if you are coating epoxy with more epoxy, you ARE scuff sanding the first coat, right? Otherwise you WILL have issues. And I'll second the use of a faster evaporating solvent such as acetone as mentioned above... I suggested mineral spirits with a longer drying period as it tends to flush contaminants out of raw wood better, but nothing is perfect. I actually keep a can of R/C modeling "dope thinner" around for when I need to degrease quickly. Lacquer thinner works the same.

Christian

Quote:

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Originally Posted by kaptain_zero

Uh... if you are coating epoxy with more epoxy, you ARE scuff sanding the first coat, right?

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Yup. I learned a long time ago to rough up the surface before applying anything like an adhesive.

If you are using a finish that is thermosetting like epoxy, CA, or varnish it is important to scuff between coats. With finishes like that, there is a mechanical bond between the coats and scuffing the surface increases the surface area and promotes better bonding. Scuffing is not always necessary if the prior coats are not fully cured. They do not melt into each other like a lacquer or shellac would do.

The reasoning for the two solvents (like mineral spirits and acetone) is that they have different solubility parameters. Between the two of them, they will get the most common contaminants. Odorless mineral spirits can be slow to dry but regular mineral spirits and especially naptha evaporate quicker.

Alcohol will absorb some water out of the air and cause some grain raising, but in my experience this is mostly theoretical and does not happen to a great degree.

Charlie

Just wanna say thanks to everyone who helped here. I started wiping down the scales with mineral spirits before a pour and that seemed to work. I guess it was a contaimination issue that caused the voids. Now I can finally get those damn near flawless epoxy pours :D

If you're cleaning up epoxy, denatured alcohol is a good choice, as well as acetone. Just don't soak it too much in the acetone.

If you can't vacuum the scales while it cures (which is going to be the best way), you can also vacuum the resin. Just mix it up properly, put it in a proper container, and set a vacuum to it. You can suck excess air out that way, then use an acid brush to brush the resin on. Finish sand it with a high grit paper and you're good to go!

I tried to find the vacuum pumps, but to no avail. They're affectionately called "pucks" by composite guys, but they're small disks of metal that connect straight to an air compressor and provide good vacuum pressure (45 psi if I remember right). You get that, some non-stick vacuum bagging, and you're on your way to easy vacuums and high pressure.