Official Luthiers Forum!

Should I at least scuff the zpoxy with something before spraying to knock off any dust nibs? I just put the third and final coat of zpoxy on the neck. It looked really good before putting the 3rd coat on but the color wasn't consistent......and they always say put one more coat after you think all pores are filled. I put a very, very light coat. Mixed only 2 grams of zpoxy for the whole neck and didn't use all of it. Put it on with a nitrile glove and spread it as thin as I could get it. It sure looks nice!

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Formerly known as Adaboy.......

Darryl,

As you know I am not an expert but here was my rational for sanding the zpoxy before I put on a couple of coats of shellac to seal before KTM-SV

The zpoxy even thinned is much thicker than a couple of coats of shellac. It is hard to see level on unsanded shinning zpoxy. So my fear was that the first time I had to level sand that if the zpoxy was not completely level there was a good chance of sanding through the shellac in the high places. Since I was using the shellac to assure the KTM-SV adhered well and to provide a slight warmer color, I though it important to make sure that I applied it on a level base. (Sanded zpoxy until there was no gloss)

John

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http://www.Harvestmoonguitars.com

Thanks for that feedback John.

At lunch, I tried a white 3M pad on the zpoxy and it just didn't have enough "cut" to it to do anything. I then tried a purple, P400 3M rubber "cloth" like pad that is thin, flexible, and has holes throughout the pad. I used it with light pressure and this seemed to work great.......smoothed out the zpoxy very nice but removed very little so the color is consistent. The feel of the neck is great......extremely smooth. The texture of the unsanded zpoxy just didn't feel right for spraying a finish coat without this sanding.

I found one a thick, run spot in the zpoxy on the back of the headstock and a thin spot on the EIR veneer on the front of the headstock so I sanded those down and will recoat those two areas with zpoxy. I want to make sure the zpoxy coat is thin yet perfect on the headstock since it will be my sealer between the oily rosewood and the KTM-SV.

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Formerly known as Adaboy.......

Receive my boards of rosewood, ebony and cocobola. Next week testing begins.

Happy Thanksgiving to all.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

Any updates?

I'm close to ready to spray but the weather is not cooperating.........too cold. Just put what I hope is the last coat of zpoxy on the back of the guitar (3rd coat). I used zpoxy thinned 10% (by weight) hoping for a light coat that needs little to no sanding as I don't want to sand through since this coat will be my barrier coat between the rosewood and the KTM-SV. I wish I had more time to experiment but I would sure like to finish this guitar by the end of the year.......be nice if I could spray this weekend.

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Formerly known as Adaboy.......

I hope it turns out well for you Darryl - let us know how it goes.

I'm looking forward to spraying a body and a couple of necks soon, but I'll be using the Ilva sealer between the epoxy and the top coats. I'll report back when they're done, hopefully, with a generous smattering of these when I do!

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Cheers
Pete

Formulated one of the test wood sealers, trialed 2 coats per rosewood, ebony and cocobolo and all 3 feel good as a sealer. No sanding of the wood before 1st coat. Dried under heat, some grain raise, scuff sanded down, applied 2nd coat and dried. Nice smooth coat, feels hard, and ready for...topcoat tomorrow.

When testing shellac or epoxy over oily woods, how do you really know that it sticks to oily woods? How do you test for adhesion before saying that the topcoat failed?

If sealer applied over oily wood is brushed, then you are moving the oils around on the brush throughout the sealer coat. This alone doesn’t help the situation. If it happens with both brush and spray, then intercoat adhesion could be true. If only via brush, then the oils are being transferred to the top of the sealer causing intercoat adhesion failure. Many ways to look at it.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

Hi Matt, Since this is a new formulation for a sealer how long will it be before it is available to purchase?

Thanks
Richard

Everything I am discussing is experimental at this time. I am making it an open discussion in hope of feedback in regards to the need for a waterbased sealer for oily woods.

By early next week I will have more results to:

A) Does this product so-called 'block' oily wood problems?

B) Does KTM-SV and KTM-9 stick to it?

Since this was coated today, I will wait overnight and finish with SV/9 tomorrow; allow sitting over the weekend and testing Monday.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

Matt,
I can't speak to SV on epoxy as I haven't tried that, only on shellac. I sprayed every time no brushing, using Zinsser traditional shellac premixed in an aerosol can, and the Universal Seal Coat premixed in a can and sprayed with a Preval sprayer. Each time I was able to peel off the finish from the bridge area as if it were a sticker, but I still had to scrape off the shellac with a razor to get down to raw wood. As this happened on non oily spruce it leads me to believe that there is intercoat adhesion issues between the SV and shellac. The shellac was lightly scuffed. I never tried to peel any off the sides so I don't know about that, though I did have trouble with a burn through while buffing turning into a big mess, but there are a few factors in play in that scenario that would foil trying to isolate any one factor. Another issue I had was having the SV lift off around the washers of the tuners on rosewood. On that guitar I sanded through the epoxy porefill so I sanded back to bare wood, shellaced it then SV. I look forward to hearing more about your test results. Are you spraying your test shots onto bare wood? If so, what grit have you sanded to?

Heres a quick picture of what it does to the grain. Like I said, experimental coating that will take a few days to determine where I go with it.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

One simple test for adhesion is to cross hatch the finish with an exacto knife and see if you can pull up the finish with some sticky tape. I saw that on some video recently.

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http://www.Harvestmoonguitars.com

One of the first tests we do is a cross-hatch adhesion test. Basically its a tool that has 4-5 knives that you create the cross with. along with the astm std tape, you have an offical test.

Any other ways luthiers determine adhesion from wood to the sealer and sealer to the topcoat...

Tomorrow I will topcoat with 1-2 coat of sv and ktm-9, allow to dry until monday and perform a cross-hatch.

http://www.defelsko.com/technotes/adhesion-testing-wood.pdf for example.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

Temperature. That test looks good, with the exception of temperature changes (unless I missed it). One thing that can cause problems is if the sealer expands and contracts at a different rate than the top coat. If a finish passes my knife and tape test, I repeat the same test at 40 degrees F, then at 100 degrees F.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

I just finished a ukulele with SealCoat and KTM-SV. Douglas fir top and curly cherry for the rest. I was unable to get the SV to peel off the SealCoat after a ten day cure, so I had to work under all the finish to get the bare spot for the bridge. SealCoat has additives that straight shellac does not, and they seem to improve adhesion.

Small update.

Cross-hatch test on the KTM-SV over trial sealer passed
Note: Even though it passed, feels good, small picking possible of topcoat. Will re-do this trial - need to repeat issue or if works, trial again for accuracy.


Cross-hatch test on the KTM-9 over trial sealer pass
Note: Picking of the topcoat not possible at this time. Feels very hard and durable.

Tried another coating we use for exterior products (urethane/acrylic) yesterday, not as hard as above trial sealer over exotic wood, but sticking quite well. Will topcoat with KTM-9 and KTM-SV today and see how it looks in a few days.

Thanks for the patience. Looking forward to the results like some of you.

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Matt Lawrence
Formulator/Tech Guy
www.graftedcoatings.com

I have had poor results with waterbornes containing acrylic. The acrylic gives a bluish cast to the finish which makes the whole instrument look cheap. When I started having problems with my previous finish, I searched for a good waterborne that did not contain acrylic and ended up with KTM-SV.

My trouble with ktm 9 was having it blister under hand sweat. I am scared to try any acrylic finish now. Good thing there's SV!