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I finished pore filling with zpoxy on the my test board (which is a side from an EIR set for a future build.....plenty thick to sand the finish off when thicknessing before bending). Todd's vidow was a big help here and he also gace me some good advice while I was trying to figure out how to pore fill with zpoxy. It took me 3 coat/sanding cycles to get the pores filled, then I finished off with a very light coat of zpoxy for consistent color. On this final coat, I used a tiny amount of zpoxy, spread it across the entire surface, then used a squegee to remove every bit of zpoxy I could.......so this coat is very thin.

I'm tempted to try the KTM-sv right on top of the zpoxy; however, after reading Randy Muth's caution that oils in rosewood can affect adhesion of KTM-SV that seems inprudent. So I'm thinking of adding a couple coats of Zinnser SealCoat shellac (all I have on-hand without ordering shellac flakes).

So question one. Seems I should scuff the zpoxy before applying the shellac but I don't want to go through the final, thin coat of zpoxy. Todd and others use a Scotchbrite pad but it appeared Todd used the grey pad in the video (best I could determine). All I have on-hand is the maroon colored pads. Are the maroon Scothcbrite pads too course to use at this point? I also have P400, P800, and P1,000 Carborundrum Premiere Red Dri Lube sandpaper if one of those would suffice. thoughts?

Second question. Any benefit to spraying the shellac over applying with a cotton cloth wrapped in a ball? I have a new spray gun and compressor now......just haven't yet used it. Either the shellac or the KTM-SV will be my first attempt at spraying.

And last question. The top doesn't need pore filling........but seems something should be applied before spraying finish. Shellac would likely work fine......are there other options? The SealCoat I have on-hand adds an amber tint so if I want to use shellac and not have an amber tinted soundboard, I will need to order Super Blond shellac flakes I guess. I like both the aged, amber look and the clean, white look. The top on my guitar is Carpathian spruce and it's not super white as it has some darker flecks you see in some old growth spruce. It also has nice silking which the amber tinted shellac may make more pronounced. Any suggestions on what to apply between the KTM-SV and the top?.........or comments about the tint of the shellac?

Thanks!

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Formerly known as Adaboy.......

I used seal coat on epoxy on a few builds, worked fine. I don't know how rough the maroon pads are so can't help there, but I'd guess that if you use a light touch you'd be ok, just don't press hard. I would definitely hit the spruce with a few coats of shellac before the SV. I like the amber tint. On my last two I used the yellow capped Zinsser stuff, not 100% dewaxed but it seems to have worked. One thing I found troubling though. When removing the finish to fit the bridge I was able to peel off the x-actoed section like a sticker. The shellac had to be scraped. This happened consistantly with six guitars using both 100% dewaxed shellac and the other stuff. I worry about dings causing the finish to de-lam. Also, really really be wary of heat when buffing SV. Buffing this stuff out is real easy except for that. I've had a lot of troubles. Mahogany buffed out great but on a recent pao ferro effort all the black lines sunk deeply, even after several attempts to level sand and rebuff. It happened a bit on rosewood too. But I'm using a setup designed for UV poly so the trouble may lie therein.

Thanks for that info!

The de-laminating you are describing sounds scary. Am I understanding correctly that the SV is pulling loose from the shellac with little effort? I'm leaning toward using the Seal Cote on the top,

Would sure like to hear other opinions on sanding the last thin coat of zpoxy before applying shellac. Better to use fine sandpaper or maroon Scotchbrite?

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Formerly known as Adaboy.......

Oh, thanks for the tip on buffing KTM-SV. If you don't mind my asking, what RPM and diameter wheel are you using on your buffer? What buffing compound?

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Formerly known as Adaboy.......

Having finished two guitars with KTM-SV, I must say I have some reservations where adhesion is concerned. Given that Randy Muth and others are so enthusiastic about this finish, I’m hopeful that it’s a matter of improving my application techniques rather than it being an issue with the product itself.

I’ve used de-waxed white shellac as a sealer and tie-coat under my top coats in an effort to improve adhesion, but I suspect I need to scuff sand the shellac coats more thoroughly to provide a better mechanical key before I spray the first of the top coats; when I removed the finish on the soundboard in readiness for gluing the bridge I was a little alarmed at how easy it was to remove the finish from the spruce.

I hope those with more experience can weigh in on this subject.

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Cheers
Pete

OK, the first thing I'd like to address is the buffing problem. I think what you are seeing on the rosewood when buffing is a result of insufficient sealing. Your experience on the mahogany seems to bear this out. The problem with KTM-SV is that it never gets fully hard on certain woods if they are not completely sealed. I don't sand my sealer coat for this reason. This problem shows up when you buff. I am pretty aggressive on the buffer and I don't have a problem, so I think the warning is misplaced. I have never used shellac as a sealer under KTM-SV so I have no personal experience. However, Rolfe Gerhardt has and has reported this problem as well at times.

Concerning adhesion. I use the two part sealer sold by Ilva, which I believe is comparable to McFadden's rosewood sealer. There is an application window for this stuff. It is suppose to be reapplied or top coated after 2 hours but before 4 hours. After 4 hours, it has to be scuffed for adhesion. I use two coats and spray KTM-SV within those windows. Both KTM-SV and the sealer are urethane based. I believe with this system I am getting good adhesion between my sealer coat and the KTM-SV. Again, I can't speak to shellac. I also use this sealer on my soundboard. I have glued bridges to the finish in the manner that Rick Turner does and have never had a problem. CA sticks tenaciously to KTM-SV, so the weak link would be the bonding of the KTM-SV to the sealer coat. With this system it works.

One time I was able to peal the finish of a section of ebony. I believe I may have waited too long to spray my first top coat. How fast the sealer completely cures will depend on a number of factors including amount of hardener (there is an acceptable range), temperature, pore filler, perhaps the pH of the wood being sealed, etc. This winter I want to set up some experiments to study these factors.

In sum with KTM-SV, the sealer seems to the critical factor.

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Randy Muth
RS Muth Guitars Website
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Well, this is a test board so I guess I'll see how the shellac works. I wanted to use a sealer other than shellac. I checked on the Ilva isolante sealer but the smallest quantity you can buy is 1 gallon. Add hazardous shipping charges and it's expensive for a hobby builder like myself (not an issue for a professional using larger quantities). I can't find McFaddens rosewood sealer anywhere. I'm guessing it is no longer made. Not sure what other options are out there but my searches on "isolante sealer" have turned up few options. I've wondered if a vinyl sealer would work ok as a barrier coat. Would love to hear suggestions.

For this test piece, I will lightly scuff the zpoxy with something (the maroon Scotchbrite or fine sandpaper) and apply 2-3 coats of shellac. Then I won't sand the shellac before spraying. Any thoughts on spreading the shellac with a cotton rag vs spraying? I'll then be able to see how well the SV adheres and can look for other sealer options if there are issues.

I also have a 2'x2' piece of Luan plywood that I've used to practice applying zpoxy. Maybe I should test using a couple thin coats of zpoxy as the "sealer" and test spraying SV directly on the zpoxy. If the test piece is flat and you spread a minimum amount of zpoxy over the entire surface.........then use a good quality squegee to remove all the zpoxy you can pick up, it leaves a very thin coat.

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Formerly known as Adaboy.......

Doing some Google searches I came across this article on "HowStuffWorks.com". Interesting that they don't recommend using shellac as a sealer for polyurethane varnish. Here is a clip from the article and the end of the first paragraph states not to use shellac under a polyurethane varnish. No wif I just knew what a "penetrating resin sealer" is....<smile>.

http://tlc.howstuffworks.com/home/how-to-seal-wooden-furniture.htm

Choosing a Sealer

The traditional sealer for shellac, lacquer, and natural varnish finishes is thinned white shellac. This basic sealer is simply a mixture of 1 part white shellac (4-pound cut) and 3 to 4 parts denatured alcohol. Shellac is suitable for most refinishing jobs, but it cannot be used with polyurethane varnish or with water or NGR (non-grain-raising) stains.

Where shellac cannot be used, the easiest sealer is a commercial sanding sealer. Sanding sealer dries quickly and provides a very good sanding base; it can be used with varnish, shellac, or lacquer. If you plan to finish the piece with polyurethane varnish, read the label carefully; sanding sealer may not be compatible with polyurethane. Sealing is not necessary before finishing with a penetrating resin sealer.

Under natural varnish or lacquer finishes, some professionals prefer to seal the wood with a thinned mixture of the same finish. To make a natural varnish sealer, thin the varnish with turpentine or mineral spirits to make a 50-50 mixture. To make lacquer sealer, mix lacquer and lacquer thinner in equal parts. These sealers cannot be used with shellac or with polyurethane varnish.

Polyurethane varnish demands special treatment. Read the labels carefully when you buy. Some polyurethanes can be thinned with a specific thinner; with these varnishes, the manufacturer may recommend thin varnish coats as sealers. Some polyurethanes do not require sealers. If you must seal stain or filler before polyurethane is applied, make sure the sealer is compatible with the varnish. Otherwise, use a penetrating resin sealer. This finishes the wood completely, but you can apply polyurethane over it if you want a smoother finish.

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Formerly known as Adaboy.......

Darryl, those are good ideas. If you can spray shellac, I think that would be the way to go. McFadden's rosewood sealer was only available in 5 gallons and now I think the company was bought out. The only supplier of Ilva that I'm aware of in the US, at least for gallon quantities, is Camger. You may be able to avoid the hazmat fee by having them ship the components separately, as I believe 1 gallon is the cutoff for the fee. I know Rolfe Gerhardt at Phoenix Mandolins uses shellac as a sealer, so you may want to pick his brain. He's a real nice guy and was the past editor for ASIA's Guitarmaker magazine. He posted his finishing schedule online, but he may have improved or modified it since then. Definitely worth a call. He doesn't wet sand, but unlike with other waterbornes, there is no problem doing so with this stuff.

This really is a nice finish once you figure it out. It is a varnish type finish so it has a more natural look than polyester. Of course, poly does have that "pop". For what it's worth, the sales rep for Menzerna told me my guitars had the nicest finish at the Woodstock show. That was before he asked me if I used Menzerna buffing compounds. I felt pretty good about that even if I'm not sure I totally agree.

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Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

Darryl, just saw your latest post. I would not use sanding sealer, since I believe most of them contain stearates. Stearates and waterbornes don't get along. You could try thinned nitrocellulose lacquer. Don't know if it will work, just a suggestion.

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Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

One more thing, I would never use shellac with wax in it. Dewaxed only. I believe the Zinsser SealCoat is good stuff, no need to go to flakes.

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Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

FWIW....
I have used both dewaxed and regular shellac and encountered similar results re adhesion.
Randy, I would love to hear about your buffing setup. Several other builders looked at my problem areas and instantly said 'heat!' but that of course doesn't 't mean any of us are right. One thing that speaks against heat is that the tops all buffed out wonderfully. But any time I 'hung' or tried to spot buff little blisters appeared, and on a cutaway the first time I was going around the horn it just peeled off in sheets and I had to respray. But I am not very experienced with spraying so there could have been a lot of factors as work. It's encouraging go hear that you're getting such good results as apart from the issues I'm having I really like it.
One thing I was thinking about is whether or not shellac needs a longer cure time before topcoating. It may be dry to the touch in a hour, but possibly not cured and then not able to do so under the topcoat? I'm going to use the stuff Grafted coatings sells next time in the assumption that compatibilty will not be an issue.

Again, I can't really speak to the proper way to use shellac as a sealer or your adhesion problems, since I don't use it. Rolfe Gerhardt is probably the guy to speak to.

Your results on the top and on the mahogany is the answer to your question. On certain woods, i.e. rosewood, ebony, KTM-SV stays soft if it is not completely sealed. When you buff I think you are just abrading the finish away. You can take your fingernail and press on those spots very easily. This happened to me when I scuff sanded my sealer before spraying. No matter how gentle I buffed I still saw it. The only answer is to make sure it is completely sealed first. Again, I use the Ilva sealer with confidence, as long as I don't sand it.

I have 14" buffs spinning at 860 rpm. I use a cotton bias buff with medium Menzerna compound, followed by a domet flannel buff with fine Menzerna compound. The cotton bias buff is much more aggressive than the flannel buff and things do heat up. That's why I don't think it's the heat per say.

One more thought. Both nitrocellulose and shellac can melt with too much heat. Thus people with experience buffing nitro would naturally come to the conclusion that too much heat is the problem. I don't know if too much heat is a problem with a shellac seal coat. But again, in this particular case, I'm very very confident the problem is that the finish is not curing all the way due to an interaction with the wood. By the way when this happens, it never seems to get hard no matter how long you wait.

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Randy Muth
RS Muth Guitars Website
RS Muth Guitars Blog
Facebook Fan Page

I've got no experience with KTM-SV but if it's anything like other polyurethane finishes I wouldn't use shellac, especially on Rosewood, or other oily woods. Thinned Nitro wouldn't be a good sealer either. Nitro off gasses for a really long time. This, along with (probably) different expansion and contraction rates would cause adhesion problems. You can put Nitro on top of a bunch of different finishes, but Nitro under other finishes doesn't usually work. A catalyzed barrier coat like Randy uses is probably the best practice on oily woods. I can't speak for compatibilty, but there's several similar products available. I use ML Campbell Exotic woods sealer ocassionally. I'm not sure if it's available in quarts. I buy it locally. Again, I have no experience with KTM-SV. Google "barrier coat" and see it any products are available locally for you.........and test on scrap. There is no such thing as a "universal sealer". Different woods, and different finishes require different products and procedures.

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

What stores typically carry ML Campbell products?

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Formerly known as Adaboy.......

I use ML Campbell Post Cat Duravar and Resistant exclusively in my cabinet/furniture work.

http://www.mlcampbell.com/locator/

Anyone have an opinion if a couple of light coats of zpoxy will suffice to seal the oils in the rosewood so they don't come into contact with the KTM-SV preventing it from curing? That would sure be easy and cheap compared to obtaining an isolante sealer (must buy a gallon and only need a couple ounces per guitar, hazmat charges, etc.).

I guess I could try it on my EIR test piece and see if the SV cures properly and has good adhesion. What is a good way to test adhesion?

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Formerly known as Adaboy.......

Finish a test piece. Take a knife and score the finish. I usually cut an "X" into it. Stick a piece of tape on it, and then yank the tape off. You can also flex it, and bang it against stuff.

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

I did as Randy Muth suggested and emailed Rolfe Gerhardt. He tells me he's had adhesion problems with Zinsser shellac, but since switching to Zinsser Sealcoat, he's had no problems.

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Cheers
Pete

Well the Zinnser shellac is likely not wax free but the SealCoat is. Pete, you apparently used de-waxed shellac on your top and still had adhesion issues. Do you now have an idea what caused the adhesion issue? Are you planning on using the same shellac and just scuffing the surface of the shellac next time for a better mechanical bond? that may work fine on a spruce top, but doesn't seem the ideal solution for a back and side wood with oils (like rosewood). My fear would be that you could easily scratch through a couple thin coats of shellac while sanding and then the SV may not cure properly in that area.

I'll probably add a couple coats of shellac on half my test piece (EIR) and try the KTM-SV directly over zpoxy on the other half and see what kind of adhesion I have. In both cases, I hesitate to sand the last coat of zpoxy or shellac so I guess it will essentially test how much of a chemical bond forms between SV/Shellac and SV/Zpoxy. Some folks spray finish over seal coats (like vinyl sealer) before the seal coat completely dries and it improves adhesion. I wonder if it would help if the SV was sprayed over the shellac or zpoxy before it completely cures?

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Formerly known as Adaboy.......

I noticed no difference in adhesion between the Universal Seal Coat from Zinsser and their regular aerosol shellac with the yellow cap. Sv peeled quite easy off of both.
Darryl, let us know about the direct over epoxy test...

BTW, I called the good folks at Grafted Coatings today. They weren't aware of any issues spraying KTM-SV over shellac. He had samples (I think that were sent to him by Rolf Gerhardt if I understood correctly) of SV over SealCoat that have very good adhesion. They seem willing to test applying SV over Zinnser SealCoat and reporting the results. I asked about a recommendation for a sealer between exotic woods and SV to prevent the oil contamination issue causing the SV not to cure properly and it appears they want to look into this also. Sounds like they will be consulting with LMI (SV available through LMI) on oily, exotic woods for testing a barrier coat. I will sure post anything I hear back from them. Overall, they seemed very interested in addressing any issues luthiers might be having.....which is nice.

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Formerly known as Adaboy.......

Darryl, I guess you're our "crash test dummy" at this point. Looks like I'm back in my all-too-familiar holding pattern so I'll be interested to hear how your test panel turns out, and what Grafted Coatings are able to tell us. In the meantime, I'll scour Australia for the Ilva product Randy uses.

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Cheers
Pete

I started out with a Luan plywood test panel that was EXTREMALLY rough and porus. It has had a 1/3 of a bottle of zpoxy put on and sanded off at one time or other before I gave up and switched to an EIR test board (and it sure was much easier to get the EIR level).

Anyhow, is there any reason it wouldn't be a good test specimen for testing adhesion of KTM-SV to Zpoxy? If not, I'll put a thin coat of zpoxy on it tonight (just like I put the final, thin coat of zpozy on the EIR test piece for consistent color) and maybe I can spray it tomorrow if the weather cooperates. Since I'm not going through the leveling process, any reason to put more than 3 or 4 coats of SV? I may cut the 2'x2' test panel in half and put another thin coat of zpoxy on one half 1 hour or so before spraying and see if the KTM-SV adheres better to the partially cured zpoxy than it does to fully cured zpoxy.

I'm not planning to sand the zpoxy at all before spraying the SV so there will be little to no mechanical bond. Seems this would be more realistic to how it would need to be done on an oily wood to ensure no sand through allowing oils in contact with the SV.

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Formerly known as Adaboy.......

I wonder how often Rolfe uses oily woods like rosewood in mandolin constuction? Isn't maple used quite a bit for mandolin backs, sides, and necks? Possibly this issue has never came up with Rolf due to not using exotic woods.

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Formerly known as Adaboy.......