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EM 6000 first coats over epoxy
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=40581		 Page 1 of 1
Author:  Mike OMelia [ Wed Jun 05, 2013 11:57 pm ]
Post subject:  EM 6000 first coats over epoxy
I have noticed that EM 6000 first coats over an epoxy prepared surface is a horrible beading mess. I'm guessing this is a surface tension problem. What I do is apply 5-6 coats without regards to this mess, let dry, then sand and start full regimen. Which works fine. Once a good substrate is established, subsequent coats go in with no issues. Anybody else notice this?
Author:  B. Howard [ Thu Jun 06, 2013 4:32 am ]
Post subject:  Re: EM 6000 first coats over epoxy
That" beaded mess" is telling you that the products are not compatible and you are risking de-lamination and finish failure. You may be getting enough material to lay on and cover but it its not bonding to the substrate.
Author:  Colin North [ Thu Jun 06, 2013 5:04 am ]
Post subject:  Re: EM 6000 first coats over epoxy
Ive been using Shellac between Z-poxy and water based finishes, first coats seems to go on fine.
but I can't say for 6000, not used it
Author:  Burton LeGeyt [ Thu Jun 06, 2013 8:40 am ]
Post subject:  Re: EM 6000 first coats over epoxy
I would agree, that is a bad sign. a simple coat of shellac as the barrier would solve it very quickly.
Author:  johnparchem [ Thu Jun 06, 2013 9:16 am ]
Post subject:  Re: EM 6000 first coats over epoxy
I use zpoxy and EM6000 with shellac in between. My first coat flows out without any beading.
Author:  Pat Foster [ Thu Jun 06, 2013 10:47 am ]
Post subject:  Re: EM 6000 first coats over epoxy
Could be a problem with the Z-poxy itself. If it was bought long ago, amine production from curing might be higher. I had beading problems with putting Z-poxy over Z-poxy. After hearing from Stuart (Zlurgh), I dumped those bottles and bought new ones. That fixed it. This was Z-poxy over Z-poxy, not EM6000, however.

Now, after each coat of Z-poxy, I wipe with damp paper towels to get rid of amines, before any sanding. I do this no matter what finish goes on afterwards.

Pat
Author:  Ken C [ Thu Jun 06, 2013 11:43 am ]
Post subject:  Re: EM 6000 first coats over epoxy
Don't have that issue, and I use ZPoxy as my primary pore filler. How long do you let the zpoxy cure? Mine usually sits for a couple of days. I don't sand back the last coat, but I do swab lightly with DNA prior to shooting my first coats of EM6000. I shoot shellac on the top to keep the grain rising to a minimum, but not on anything else.

Ken
Author:  Mike OMelia [ Thu Jun 06, 2013 11:45 am ]
Post subject:  Re: EM 6000 first coats over epoxy
I disagree that there is some kind of chemical adhesion problem. I think it is related to the smothness of the expoxy substrate. I have never had problems with adhesion to epoxy. Just this initial "beading" that resolves itself after 3-4 coats and a light sanding. It's like there is a surface tension issue. Once the beaded surface has dried, it is completely attached. I would agree that a shelac coat would be a good idea. I've never seen shelac bead up on epoxy. Of course, this is for the hardwood components only. There is no epoxy on the top and no issues with beading there.

To me, this is an interesting problem that has no real consequences, only interested in not having to go through the beading stage. If shellac solves it, then I'm good. BTW, the epoxy (Z-Poxy) is new.

Mike
Author:  Mike OMelia [ Thu Jun 06, 2013 11:47 am ]
Post subject:  Re: EM 6000 first coats over epoxy
Ken C wrote:
Don't have that issue, and I use ZPoxy as my primary pore filler. How long do you let the zpoxy cure? Mine usually sits for a couple of days. I don't sand back the last coat, but I do swab lightly with DNA prior to shooting my first coats of EM6000. I shoot shellac on the top to keep the grain rising to a minimum, but not on anything else.

Ken


I wonder what DNA would do to cured epoxy? DNA is a solvent for uncured epoxy. Does it affect cured epoxy? Even a little? If so, that would make sense.
Author:  Ken C [ Thu Jun 06, 2013 12:21 pm ]
Post subject:  Re: EM 6000 first coats over epoxy
Hi Mike,

Yeah, it does soften the cured epoxy, but flashes off quickly. When I swab, I quickly run a damp cotton cloth over the entire surface. I don't scrub and I don't dwell in any give area. A guitar handled right afterwards can have a bit of a tacky feel to it. EM6000 goes on at this point without a hiccup, and I have never seen it separate from the ZPoxy. I usually swab then hang the guitar back up while I get my spray gear setup and lacquer in the gun. Then shoot. The first coats of lacquer cure as if they were your 6th or 7th coats. No issues.

Worth trying. I'm sure the shellac would work to. Finisher's choice ;)

Ken
Author:  B. Howard [ Thu Jun 06, 2013 3:19 pm ]
Post subject:  Re: EM 6000 first coats over epoxy
Mike O'Melia wrote:
I disagree that there is some kind of chemical adhesion problem. I think it is related to the smothness of the expoxy substrate.


If it will not wet out and flow, it is not adhering properly. That is the long and the short of it. Could be the epoxy was sanded out too smooth, could be the products are incompatible, maybe contamination or numerous other issues but something bad is going on. It may appear to be fine now, film failures can take quite a while to manifest. Sometimes a few years but when they go it is not pretty. A barrier/bond coat as others have suggested is a good idea and cheap insurance.
Author:  Mike_P [ Thu Jun 06, 2013 7:33 pm ]
Post subject:  Re: EM 6000 first coats over epoxy
do this:

take a scrap of decent size and do your regimen...make sure the problems you describe occur...

let test piece cure appropriately....

then do 2 tests:

finger(thumb)nail scratching test and an impact test...

if there are indeed adhesion problems you will most likely be able to scrape the finish to the epoxy pretty easily (been there, done that, failed that test before)...

impact test may or may not indicate problems...if big flakes come off then there are issues...

my first truck would scratch very easily and in front of the service adviser I took the paint off to the primer with my thumbnail...got it stripped and repainted under warranty...

got stuck once, when I had a period of lack of 'normal' work, making panels for a body shop's entrance desk and they wanted it to match the furniture they just bought...yuck...cherry wood stained coffee brown...ended up having to do a 3 stage dye/staining process to match...looked great...problem???? oh yeah...I ended up leaving a very light film of stain on the wood to get it dark enough...look at it this way, the layer of stain wasn't really bonded to the wood...hence the lacquer bonded to the layer of stain (pigment) which wasn't bonded to the wood...let's just leave that ugly mess at that....I will never again (OK, if I'm starving like I was then I will) stain something that dark again and will most likely tell the customer to stuff it...thing is the work passed the impact test fairly nicely...made a nice dent with a hammer and while a little flaking was observed most of it flowed nicely with the dent...live and learn (the typical hard way we humans usually actually learn from)

either way, I wholeheartedly agree with B. Howard's sentiments...

also take the time to do the above tests without using ZPoxy to get a fair comparison of what's up
Author:  Mike OMelia [ Thu Jun 06, 2013 10:36 pm ]
Post subject:  Re: EM 6000 first coats over epoxy
Thanks for all the advice. I will take it to heart. I do think I sanded this last one too finely. Heck, it was shiny! Guess I got carried away with Todd's epoxy technique (not that he recommended sanding to a sheen!)

Mike
Author:  Mike OMelia [ Sun Jun 09, 2013 10:35 pm ]
Post subject:  Re: EM 6000 first coats over epoxy
I found out what the problem was. My gun had gotten out of adjustment. I was not anywhere near the pressure (at gun) I needed to be at. I think one of my kids was messing with the gun.

Mike
Author:  SteveSmith [ Mon Jun 10, 2013 9:49 am ]
Post subject:  Re: EM 6000 first coats over epoxy
I don't have any longer term experience over epoxy but I always seal with shellac before spraying water based. I've sprayed EM6000 directly over wood for a neck repair and after 3 years that area of the neck has lost a lot of the finish while areas directly adjacent (sprayed over shellac) are ok.
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