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Sanding Epoxy Glassed Models

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Old 11-05-2017, 11:03 AM
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redtail
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Default Sanding Epoxy Glassed Models

Hey guys - here is a tip to put into your shop bag. I am currently sanding on my West Systems Epoxy glassed TBF Avenger prior to primering it. Was talking to a close modeling friend Rick Moreland this morning and told him how badly the sandpaper was being gummed up by the wax coming off the epoxy. He told me no problem. An old controlline guy gave him this tip and he uses it regularly. Sprinkle some CORN STARCH on the area you are sanding and sit back and be amazed. I am using 220 dry and could not believe how easy and smoothly the 220 cut through the epoxy and very, very seldomly did the sandpaper gum up. What a breeze the sanding went. Cut the hand sanding time down to a few minutes. All I can say is WOW. He said when finished - wipe the model down with a cloth sprayed with something like Windex, let dry, and shot your primer. Chic.

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Old 11-05-2017, 11:22 AM
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A great tip indeed, if I ever have issues with epoxy gumming up the sandpaper I will give it a try. However, the situation you are describing has nothing to do with wax. Epoxies contain no wax. What you are describing is called " Amine blush ". The cause is an incomplete crosslink in your resin system. The solvents or volatiles as they are commonly referred to did not flash off correctly. Causes for this range from not mixing throughly enough, poor product quality or ambient temp too low during cure. It is nice to know of a solution on the occasion when it does happen.
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Old 11-05-2017, 04:55 PM
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Thanks for the teaching lesson. Now I know what I'm talking about "Amine Blush". I do believe I added a bit tooooooo much hardner when I mixed the epoxy. Gotta luv this website for its knowledge. Chic
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Old 11-05-2017, 05:09 PM
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That would do it as well, I didn't think of that when I replied. When I replied your post I was leaning towards low ambient temp as that is what I had discovered with West systems. I found it did much better when cured at 75 degrees or better.
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Old 11-05-2017, 05:15 PM
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I will take the temp in the workshop before I mix up another batch of West. I usually keep the lights on in the shop night/day to prevent dropping temps. Will check right now to see what the temp is since it is night 8pm here. Chic
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Old 11-05-2017, 08:36 PM
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Moreland is one of us older guys who has a wealth of knowledge. Now if we could just help him regain his flying skill from 30 years ago! All kidding aside, Rick's probably forgotten more model building tips then most of today's so called experts will ever know. A great example of a super individual who is always willing to share all of his knowledge with anyone.
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Old 11-06-2017, 04:39 AM
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Hello Greg, he talks good stuff about you all the time. He is a good guy but his pylon skills do need honed a bit. I told him at our age - Practice, Practice, Practice. Smile. Thanks Greg. Chic

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Old 11-06-2017, 06:50 AM
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Never heard of the corn starch solution. Will have to try it.
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Old 11-06-2017, 06:58 PM
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Chic, Let me guess: The initials of the control-line friend who gave Rick this suggestion are J.E.A.
And that's what I keep telling myself; Practice, Practice and more Practice, just might compensate
for all that birthday cake. Don't stop smiling. It makes everyone wonder what you're hiding.
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Old 11-06-2017, 07:42 PM
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Your Good "GREG". J.E.A is correct. Hey 'dpetsel', is that Vette being run off of corn grown in Iowa? Smile. Looks good, I have an 82' Collector Edition myself. Chic
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Old 11-07-2017, 04:24 AM
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Chic,
It has been my experience that the "Amine Blush" is usually caused by incorrect mix of the resin/hardener and/or a low temperature. The "Blush" is water soluble and can been removed with a dampened Scotch Brite pad and a paper towel cleanup. I mix my West Systems epoxy using their pumps and select the appropriate hardener according to the ambient temperature. For smaller batches I measure by weight and use a gram scale. Each component is weighed separately, in a mixing cup, then blended together, at least twice- from one cup to another. I'll have to try the cornstarch method also and it proves that you're never old enough to learn something new. BTW, the other contributors on this thread are true experts in their fields and "good guys" also.
Regards,
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Old 11-07-2017, 04:44 AM
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Thanks Art, I too use the West System pumps, but I have noticed that sometimes, the pumps are not fully primed. Now I know that is when I am in trouble. The pump will spit out a measure of glue or hardener then it will catch a full prime. Either the epoxy or the hardener will not be balanced. Don't know how to correct that problem. Thanks Art. Chic
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Old 11-07-2017, 10:24 AM
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I've had several sets of pumps, and I've given all of them away. I pour from the can into mixing cups on a gram scales that has accuracy to tenths. I use a small paddle (like a propeller) on the end of a rod, in a drill, to mix. I use 206 hardener.
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Old 11-08-2017, 03:31 PM
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Quote:
Originally Posted by redtail View Post
Thanks Art, I too use the West System pumps, but I have noticed that sometimes, the pumps are not fully primed. Now I know that is when I am in trouble. The pump will spit out a measure of glue or hardener then it will catch a full prime. Either the epoxy or the hardener will not be balanced. Don't know how to correct that problem. Thanks Art. Chic
I've found this to be an issue, an incomplete prime, with pumps that have sat a while. If I have a question about the pump's output, I'll pump a couple of shots into a mixing cup before actually mixing anything in a second cup. If, after a third pump, I still don't like what I'm seeing, I'll replace the pump and start over. I've only had an issue with a resin pump once but, with hardener, it's a much bigger issue

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Old 11-08-2017, 05:22 PM
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I would never trust a pump to give me the correct ratios. I always find out the mix ratio by weight and use a gram scale. I transfer the components into bottles much like the old school diner Ketchup squeeze bottles for easy dispensing. I discovered a couple years ago just how critical mixing is as well. I discovered I did not mix well enough. For this reason we have mechanical mixers at work and no longer mix anything by hand. Over mixing can be just as bad as under mixing and will lead to a much reduced pot life. I have been told that overmixing introduces more oxygen and speeds up the crosslink. Adding fillers like micro balloons or cabosil introduce oxygen as well leading to less pot life. Now when mixing a batch of laminating resin, I will mix for a minimum of a full minute for batches up to 4 oz and a little longer for larger batches. Since adopting this practice and weighing the components I have not had a case of gummy resin. I am usually sanding on glass about 24 hours after application and have it powder up really nicely.
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Old 11-08-2017, 09:11 PM
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I've never had a problem with mix ratios using the pumps, that is as long as the pumps haven't gotten caked with dried hardener. If you don't feel you can trust a pump, that's fine too
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Old 11-09-2017, 06:09 AM
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Two things.

First. To get reliable ratios when mixing small quantities of epoxy use electronic scales with those small medicine cups. West System for one is sensitive to the correct mix.

Second. I would strongly recommend that you DO NOT DRY SAND EPOXY. There is a significant risk that you may become sensitized to epoxy and develop very unpleasant allergic reactions to epoxy products. Such reactions can result in hospitalization. Wet sand with an extractor fan and be careful to dispose of any residue before it dries out. A simple face mask is not enough. I am one such person and I now have to be careful not to have any contact with epoxy dust.
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Old 11-09-2017, 07:17 AM
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Thanks Guys, I think I will begin using a gram scale and mixing cups to mix my West Systems epoxy. Good idea. I always sand with a mask. My wife insists. Chic
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Old 11-09-2017, 11:29 AM
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Quote:
Originally Posted by redtail View Post
Thanks Guys, I think I will begin using a gram scale and mixing cups to mix my West Systems epoxy. Good idea. I always sand with a mask. My wife insists. Chic
A mask is not enough unless it is fed from an external source of clean filtered air.
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Old 11-09-2017, 05:45 PM
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I think that may be a bit overkill. I personally use just a dust mask but I also do my fiberglass sanding outside. IMO doing your layup indoors subjects you to more harmful vapors then what the dust is. Neither of the large aerospace companies that I have worked for have required us to use anything more then a dust mask when sandeing fiberglass. No activities at either facility required an SCBA.
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Old 11-10-2017, 06:25 AM
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Quote:
Originally Posted by speedracerntrixie View Post
I think that may be a bit overkill. I personally use just a dust mask but I also do my fiberglass sanding outside. IMO doing your layup indoors subjects you to more harmful vapors then what the dust is. Neither of the large aerospace companies that I have worked for have required us to use anything more then a dust mask when sandeing fiberglass. No activities at either facility required an SCBA.
Fiberglass which is usually polyester based and epoxy are totally different animals when it comes to triggering allergic reactions. I am fine with dry sanding polyester resins but thirty seconds after a bit of epoxy dust hits me my lips *****le my nose runs and my tongue and throat swells to the point where my breathing is affected. I will be nauseous for hours.
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Old 11-11-2017, 04:27 PM
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Fiberglass is NOT polyester based. It is glass based,
thus the name fiberGLASS. When sanded it makes
very small sharp shards that can be easily made
airborne and breathed in.


Jenny
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Old 11-11-2017, 05:20 PM
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I used to make hot rod bodies, model fuselages, and propellers and they were polyester resin / glass fibre. I did not use epoxy resin because of the cost, and the fact that I had a 5 gallon pail of polyester. I wonder if the corn starch would work with the polyester clogging the sandpaper. The casting and finishing resins were different I believe. One of them would have a wax on the surface. The two types I used always did, and plugged up the sandpaper. Yes it was itchy, I did not have a reaction, but some people do. Maybe the reaction is just whining? I whine about the itching. I use a barrier creme now and it isn't so bad.
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Old 11-11-2017, 05:22 PM
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True however fiberglass parts can be made from either using Epoxy or Polyester resins as the substrate. It's not the fabric that he has issues with but the epoxy resin chemical makeup. Usually people have issues with Polyester. Neither should be absorbed into the skin and I personally always wear gloves no matter what my batch size is. That being said, most people do not have allergic reactions to epoxies. For almost 10 years now I have worked in a composites shop and work with epoxies every day and have no issues related to exposure to epoxy.
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Old 11-11-2017, 08:01 PM
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Usually it is the glass fibres that bug me, I suppose the resin, whichever type aggravates the itching. You would not want any of the stuff in your lungs. I just recall the guy where I bought my supplies walking out of the room with the chopper gun with his work boots on. The soles were sticky of course, and the glass fibres were stuck on. They looked like big snowshoes. When trimming, diamond wheels on a circular saw or angle grinder would get an inch thick on your clothes. It was only in the last 20 years that they used tyvek suits and masks. Third generation there now.
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