SANDING SEALER PRIOR TO NITRO ???

[nick-p]

getting ready to spray my guitar with a nitrocellulose finish but the bare wood requires a sealer first. is it ok to use a sealer that describes itself  [ on ebay ] as "CELLULOSE" and not "nitrocellulose"  ??  ARE THEY ACTUALLY THE SAME THING ?.  getting worried that what ever i use may react badly with the nitro clear coats. thanks

[Frank Ford]

For sealing the bare wood, purfling, binding, etc., I use SHELLAC. I believe shellac is the ideal sealer for any surface and between any coatings of different materials. A quick wipe with shellac can be quick and easy. Spraying shellac is difficult at best.

Wood doesn't "require" sealer, but it is often a good idea to use it to reduce absorption of the lacquer and to make building thickness easier. Sealer needs to be a different material.

Mix your own shellac from flakes and alcohol, or use Zinnser's Bullseye "SEAL COAT." Seal Coat is different from the other contaminated commercial liquid shellacs, so be sure it's the real deal, with age-dating.

Regular liquid shellac doesn't dry hard, and may contain all kinds of nasty things. . .

[Donald A. Fortune]

Hi Nick- I go along with what Mr.Ford said because I use shellac as a base or "sealer" coat on all my builds.
I also do what is known as french polishing on some, love shellac, I think it is fool proof because you can literly
put any kind of top coat on it that you want.. best to you on your project... Peace, Donald

[Russell Vance]

Obviously, Shellac is an option that has stood the test of time and is both versatile and effective.

Practically, as the finish is a critical item and is both time consuming and expensive to do well I would give myself the best chance of success by not taking chances on unknown or poor quality product - take the advice of the pros and use fresh, propriety branded products designed for guitar finishing.

Additionally, you may wish to consider one of the bulked out Nitro sanding sealers for the very grainy (coarse grained) wood often found in electric guitar construction such as Swamp Ash and Mahogany. In this case the lacquer has a suspended translucent solid (sometimes Talc, sometimes a synthetic) in the mix and tends to fill the gaps quickly in preparation for sanding and subsequent coats.

I avoid using Ebay for critical products - it's getting worse as time goes by and the shonks and counterfeiters get more savvy at misrepresenting and ripping people off. Reputable Ebay "Shops" are fine but as for the rest it's a crap shoot these days.

Good luck, Rusty.

[Howard Klepper]

No sealer is necessary under nitro lacquer. It seals and adheres to the wood just fine by itself. So-called "Sanding Sealer" is a product intended to speed production in furniture shops. The key word is 'sanding,' not 'sealer.' It has additives (stearates, which are soaps) that make it sand easily, so it can be sanded back to get a smoother surface, instead of more laborious raising of grain and sanding back the wood. Sanding sealer is actually less transparent than the lacquer, and weakens the adhesion of the lacquer.

Vinyl sealer replaces the stearate with vinyl additive. Better, but still no advantage over either (a) wetting to raise gran and sanding back; or (b) a wash coat of shellac to raise grain and sand back. The main idea of these sealers outside of a production shop is to sell you another product you don't need.

[Ned Knepp]

Sealer is also often used to help even out the color in stained wood. I can see where it might not be needed in a lot of cases and I bow to your greater experience on nitro but I don't know if I would say it has no use in a non-production environment. It can certainly help keep the color even on any stained projects.

Ned

[Russell Vance]

Unfortunately, I disagree with my colleague Howard. Working with porous woods such as Mahogany and Swamp ash requires the use of a sanding sealer and the notion that even multiple grain raising and sanding is going to prepare these timbers for a gloss coat (likewize a shellac wash) of a professional finish standard, is wishful thinking.

Our own high quality sanding sealers and nitro finish coats are made specifically for our guitar finishes by a dedicated paint chemist who would probably raise an eyebrow to the preceding post. Reality is that if we were only making a couple of guitars a year and had all the time in the world to waste gallons of lacquer and time in sanding back and reapplying finish coat after finish until it was flat we probably still wouldn't waste our time - sanding sealer works just fine as a prep thanks.

The reference to sanding sealer being less transparent than lacquer is lost on me relative to the statement that a wash coat of shellac (even pure blond shellac has more color than sanding sealer) should be used in its place.

Sanding sealers are a long established and effective part of most guitar production nitro schedules and have been used since the 50's with no complaints. Some skill is needed to spray these schedules. However, if you don't wish to use it , don't, but it is a product we do need.

[Howard Klepper]

My wishes have come true, I guess. I said goodbye to sanding sealer 40 years ago and do quite well without it.

I believe from your comments about shellac that you are confusing color with a lack of transparency. As you yourself mentioned, sanding sealers contain translucent materials (bulking agents as well as soaps). How could one introduce translucent materials without reducing transparency?

I refer you to Flexner's book if you would like to be further informed about these products. Although I sense that you feel no need for self-education.

[Howard Klepper]

Sorry, this system will not let me edit.

Rusty, I believe you when you say your results are good. But you implied that I am not doing professional standard work and am self-deluded. I hope that was not your intent.

There is no need to waste lacquer when not using sanding sealer. I do not fill surface irregularities with lacquer. The key is good surface prep; shooting the lacquer on a well-leveled surface. Using sanding sealer as your shortcut to surface prep is indeed what it is designed for. It speeds production by allowing shortcuts to be taken in prepping the surface. The price is paid in adhesion and transparency, though. Really, do read Flexner, and I apologize for the remark about self-education.

[Russell Vance]

Howard, thanks for that, and as I said it's a free world and do whatever you want. We'll probably keep doing what we do - the issues about adhesion and translucency are long gone these days. Similarly, modern prep/finishing machinery and techniques coupled with discrete product formulation make yesterdays shortcuts now today's worlds best practices and ensure that a repeatable premium finish can be done at a sustainable and relatively affordable price.

But, we are not a cottage or craft based industry and can see and sincerely accept that devotees to the old ways have a very worthy place in the scheme of things and should be encouraged - the purity and rewarding nature of hand finishing is something that too few get to experience these days and is what I will miss most when I get too old to be on the tools.

I probably won't get to reading Flexner but I'm sure he meant well in the context of my preceding comments. I will also work on my self education when those working constantly on my professional education have finished but thanks for the advice anyway - I probably deserved that one!

[nick-p]

just to add to the mix..... i bought an aerasol can of sanding sealer [ suited i'm told for nitrocellulose top coats ] and applied it to a test piece of flame maple which i had previously stained wine red [ a stain which is miscible with cellulose ] ... now what am i doing wrong ???? when the sealer hits the maple the colour seems to dissolve and streak !!. i'm holding the can at least 10 inches from the work piece . is it possible i"m using an unsuitable stain type ?.. it was described as a "light fast stain", miscible with both cellulose and melamine lacquers.

[Frank Ford]

I presume you mean that for YOU the adhesion issue is long gone. I can tell you for certain that it is still an issue with manufacturers who use vinyl sealer under nitrocellulose. I don't recall ever seeing nitrocellulose simply let go of shellac sealer, but we still get new instruments from major producers with SERIOUS adhesion issues, where the lacquer flakes off in big sheets leaving the vinyl sealer intact and undamaged. Being the warranty shop for a couple of big producers, we see something like this most every month:

[Russell Vance]

No need to yell guys, we don't use vinyl based sealers - and we don't have any problems - whereas cheap Asian instruments (particularly Indonesian/Vietnamese sourced instruments at this time) with mismatched systems,untrained labour and poor schedules and techniques exhibit this sort of problem relatively frequently. I know that.

Whereas, your own premium Fender, Gibson and PRS brands have been using sealer forever and never seem to have any of your frequently seen problems. Ditto, the homily about translucency on figured timber - I suppose PRS and Gibson need some free advice here as their world famous figured tops are compromised, right.

Any fool can do a bad job. So what?

I now have the distinct feeling that I am in the universe where doing a hard job right and learning what it takes to do that is not appreciated, particularly when one is challenging entrenched (rightfully so - the old ways work) values and disposition. Myself and many others in the industry put a lot of time and effort into getting these things right, consistently at the high end of the market and I have shared that with you - just as I have shared our finish schedules and tips, in detail, with this forum in the past.

However, one can see where this is going, and I'm starting to justify rather than explain. I do not need the irritation of being nibbled to death by ducks - use Shellac and nitro and all will be fine.