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Adhesion testing with UV cured finishes
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Author:  bcombs510 [ Sat Apr 08, 2023 11:18 am ]
Post subject:  Adhesion testing with UV cured finishes
Sharing here results from doing some adhesion tests. Nothing surprising really. I wanted to test topcoat on bare wood because Cardinal recommends isolante on any wood, including spruce. That’s just another 1mil of “stuff” on the top that may not be needed.

Interestingly, Simtec says that the adhesion promoter is only needed on oily woods. So I figured while I was at it testing bare wood adhesion I would test over isolante in three scenarios - no scuff, scuffed with 220 paper, scuffed with maroon scotchbrite.

Here is the setup:

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Testing with Cardinal polyurethane over Isolante different scuff levels:

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Testing on bare wood:

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Note: The polyester is Simtec. I didn’t have any Cardinal to test.

Interpreting the results is a little tough, anyone have experience with this in a more professional setting and can confirm my ratings? :)

Brad


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Author:  Toonces [ Tue Apr 11, 2023 3:36 pm ]
Post subject:  Re: Adhesion testing with UV cured finishes
You don't need isolante on the top ... or probably even for woods like Mahogany but it is just good practice to apply a thin coat of the isolante on everything before spraying your clear. It doesn't need to be a heavy application. The SimTec sealer I use is extremely thin and I imagine the coat is easily less than 1 mil. I don't like polyester and stay away from it. If using it as a pore-filler, then I would want to sand back to wood. Currently, I'm spraying a SimTec isolante sealer first ... then epoxy for pore-filling ... then sanding all the way back to sealer/wood. Then a very quick sealer coat which I let dry for 24 hours. Scuff sand with scotchbrite and then shoot my SimTec urethane base clear coat. Wait 3 days and sand back as much as I dare ... hoping to leave around 1 mil. Then come back and spray around 3 mils of additional urethane clear. The sanding takes around 1 to 1.5 mils and that leaves me with a flawless finish at around 3 mils.

As regards adhesion, always maroon scotchbrite everything. It ensures good adhesion and is better than sanding, IMO. I don't think there is much need to test this stuff yourself ... all these mfgs supply test results themselves and the settings are rigorous and consistent.

For any of these modern finishes that rely on adhesion ... the biggest component of a good finish, IMO, is to get everything level before the final coats and also get that 1st base layer consistently thin. For me, the best way to do that is to rely on Frisket tape and to sand the finish evenly. I don't mind sanding through to the sealer and in fact, if I could do that with precision then that is what I would aim for but that walks too close to the knife's edge between success and failure for me.
Author:  bcombs510 [ Tue Apr 11, 2023 3:58 pm ]
Post subject:  Re: Adhesion testing with UV cured finishes
Thanks, Simon. Good info as always!

I’ve spent more time than I care to admit with test panels of polyurethane & polyester over the last 6 months. My personal experience has been that polyurethane, while it might be more desirable for that last bit of 0.05% tone, it’s a total PITA to work with compared to polyester. How polyester sprays, how it hangs, how it levels, how it sands, all way easier and more forgiving.

I don’t sell my instruments for many thousands of dollars and I’m not going for ultra thin, just reasonable in the 3-4 mils range.

I’ve almost talked myself into just going back to polyester, at least for now. :) I’ve done a few instruments with the Cardinal polyurethane and when I started back doing test panels I was reminded how forgiving the polyester is!


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Author:  joshnothing [ Wed Apr 12, 2023 5:57 am ]
Post subject:  Re: Adhesion testing with UV cured finishes
What UV finish does Taylor use? I see plenty of them with adhesion issues, especially their gloss finishes.
Author:  bcombs510 [ Wed Apr 12, 2023 6:18 am ]
Post subject:  Re: Adhesion testing with UV cured finishes
joshnothing wrote:
What UV finish does Taylor use? I see plenty of them with adhesion issues, especially their gloss finishes.

I don’t know if they still do, but I was told by the guy at Simtec back in 2017 that they were using their polyester.

I was also told some early issues were from trying to wetstack too many coats in order to just cure one time. Take that for what it’s worth. :)

I’m curious if you’re seeing this on newer Taylor’s as well?


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Author:  joshnothing [ Wed Apr 12, 2023 3:30 pm ]
Post subject:  Re: Adhesion testing with UV cured finishes
bcombs510 wrote:
joshnothing wrote:
What UV finish does Taylor use? I see plenty of them with adhesion issues, especially their gloss finishes.

I don’t know if they still do, but I was told by the guy at Simtec back in 2017 that they were using their polyester.

I was also told some early issues were from trying to wetstack too many coats in order to just cure one time. Take that for what it’s worth. :)

I’m curious if you’re seeing this on newer Taylor’s as well?


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Yes, had a newish 814ce last month that had lost adhesion on a palm-size area of the sides in the cutaway and numerous other spots, particularly around the edge of the back. Also, any Taylor I see that’s had the neck shims changed seems to commonly have small areas around the heel where adhesion has been lost.


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Author:  bcombs510 [ Wed Apr 12, 2023 6:00 pm ]
Post subject:  Adhesion testing with UV cured finishes
Good to know. I’m a little surprised there are still these issues with adhesion in the factory setting. Maybe it’s being applied too thick? I’ve done 12 with UV cured finish, if I follow the proper procedure, no adhesion issues. ;)


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