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Necessity of using a sanding sealer
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Author:  jac68984 [ Wed Jan 26, 2011 11:41 am ]
Post subject:  Necessity of using a sanding sealer
I believe I remember reading here where some believe sanding sealer is unnecessary and might cause unwanted witness lines if the top coat is sanded through. I am trying to get things rounded up for my first sprayed finish, and I thought I would pick your brain. How many use a sanding sealer to build the majority of your finish? If you don't use sanding sealer, does it take significantly longer to build the finish? Thanks.

Aaron

Edit: For what it's worth, I plan to use a waterborne (Colortone, Target something, etc.).
Author:  woody b [ Wed Jan 26, 2011 12:34 pm ]
Post subject:  Re: Necessity of using a sanding sealer
IMHO sanding sealer has no place on a guitar. Some finishers use vinyl sealer under lacquer, but I'm not a fan of that either.

I don't use waterborne finishes. I suspect you may need some kind of sealer. I recommend zinsser seal coat if a sealer is needed, for any type finish, except catalyzed finishes. You should'nt use any sealer for "build" reguardless of what finish you use. Stew Mac is great, with alot of good products, and excellent customer service, but they're dead wrong in saying to use sealer to "build the majority of your finish thickness."
Author:  klooker [ Wed Jan 26, 2011 1:29 pm ]
Post subject:  Re: Necessity of using a sanding sealer
I submitted a post about using rattle cans of Deft with their sanding sealer.

I sanded through the laqcuer & sealer. When I applied more coats of lacquer to the area, the lacquer seemed to soak into the bare wood too much and also had severe orange peel. gaah The areas that still had lacquer on them were fine.

I don't think Deft in rattle cans likes going over bare wood. Don't know how the StewMac lacquer behaves.

I'm going to use my buddy's HVLP system on the next one.

Kevin Looker
Author:  jac68984 [ Wed Jan 26, 2011 2:00 pm ]
Post subject:  Re: Necessity of using a sanding sealer
Thanks for the replies. I plan to use Z-poxy for the first time on this one. I will seal that with some Zinsser (love this stuff) and just shoot regular lacquer for the enter finish.

Will one quart be sufficient to finish one guitar? I might use TruOil on the neck (I like the feel of the TruOil rubbed with 0000), but haven't fully decided.
Author:  David Newton [ Wed Jan 26, 2011 2:28 pm ]
Post subject:  Re: Necessity of using a sanding sealer
You know, a lot of pros use thinned lacquer as a sealer, and lacquer on top of that, just saying...
Author:  Corky Long [ Fri Jan 28, 2011 5:22 pm ]
Post subject:  Re: Necessity of using a sanding sealer
[quote="Todd Stock"]I don't use sanding sealer, but vinyl sealer or shellac provides a very good tie coat between lacquer top coats and either unfinished wood or pore-filled wood. As for sand throughs...if you manage to go through to the sealer, you'd have hit the wood anyway...if sealer, just shoot a new coat of lacquer; if wood, it can be interesting to matc things up again and topcoat.[/quote

Ditto -

I havent' used vinyl sealer before, but I just loooooove shellac. The stuff is just magic. Goes on easy, repairable, non - toxic (well, except for the denatured alcohol that it's dissolved in, and I don't generally drink the stuff- and wear nitrile gloves, so I'm feeling pretty safe.)

I just finished french polishing an old parlor guitar, and I've re-fallen in love with shellac. It's so forgiving, and as far as I can tell from previous experience, other finishes love to stick to it.
Author:  CharlieT [ Fri Jan 28, 2011 6:14 pm ]
Post subject:  Re: Necessity of using a sanding sealer
woody b wrote:
...but they're dead wrong in saying to use sealer to "build the majority of your finish thickness."


Hi Woody - I'm interested in your thoughts behind the above comment. I know StewMac's waterborne lacquer is a Target product and Target recommends the same thing (building the majority of the finish thickness with the sealer product). I have just assumed that the "sealer" is just a high solids/build version of the lacquer and that the lacquer used as the final gloss coat (e.g., EM6000) is formulated to flow better and provide a high-gloss final coat. Is that not the case?

It sounds like if using EM6000 you would forgo the high-solids sealer coats and just use the EM6000. Is that right? I'm just interested in you thinking here as I'm about to begin my first finish job and am using EM6000. Any wisdom you could share would sure be appreciated. :D

Thanks,
Charlie
Author:  woody b [ Fri Jan 28, 2011 8:39 pm ]
Post subject:  Re: Necessity of using a sanding sealer
Waterborne finishes are constantly changing, or evolving. (one of the reasons I don't use them) Think about what we're trying to do with a musical instrument finish. We want to protect it and make it look good with a minimal impact on tone. Sanding sealers are designed to be easy to sand. They're kinda soft. They're also relatively heavy for a finish. On a ~5 mil finish, according the Stew Mac you should have ~3 mils of "sanding sealer". What is the sanding sealer doing? It doesn't take 3 mils to "seal". (According to Target Coatings EM6000 is "self sealing") 3 mils of sanding sealer is just.....sitting there, adding weight, without adding much protection. If you have a 2 mil scratch, dent or ding you're into the softer sealer, instead of just scratched, dented, or dinged finish.
I believe Stew Mac's instructions are based on older products. Maybe someone from Stew Mac, or Target will see this and correct me. Again, I've done alot of wood finishing, but not with waterborne finishes.
As stated earlier, according to Targets website EM6000 is "self sealing", meaning no sealer is required. I would recommend sealing with Zinsser Seal Coat, but only one or two thin coats. Just enough to seal[i]. This [i]isn't based on actual experience, but I know for a fact some people are having success using it. EM6000 is ~29% solids, the EM1000 "sanding sealer" they have listed is ~23% solids, so it would actually build a little slower. I doubt you could tell the difference in build though.

Again, waterborne finishes aren't my thing. There may be some differences between them and solvent based finishes I'm missing.
When spraying any finish, even waterborne it's important to wear a respirator.
Author:  CharlieT [ Fri Jan 28, 2011 9:28 pm ]
Post subject:  Re: Necessity of using a sanding sealer
Woody - thank you for that information! You make some excellent points. I hope you know I wasn't disagreeing with your earlier post...I was just intrigued and wanted to understand it better as I had not even considered forgoing the sealer step recommended by the manufacturer. It seems to make good sense though, especially when I throw out my bad assumptions. :lol:

Thanks again!

Charlie
Author:  woody b [ Fri Jan 28, 2011 10:12 pm ]
Post subject:  Re: Necessity of using a sanding sealer
Everyone is welcome to disagree with me. The world of guitar making is big enough for different views, methods, and opinions.
Author:  Tai Fu [ Sat Jan 29, 2011 2:43 am ]
Post subject:  Re: Necessity of using a sanding sealer
For lacquers, I believe a sanding sealer is simply regular lacquer with stuff added to it to make it easier to sand. That stuff also makes the finish look murky and imparts a different color to the wood that it soaks into. For example clear lacquer will bring out more figuring in the wood, while sanding sealer will not do so as much due to the filler added to it. I also think the sealer causes adhesion problem later on. I had lacquer chip off of sanding sealers before.

The first few coats of lacquer will always be a bit rough because the finish soaks in and raises the grain slightly. What I do is first spray on a coat of lacquer (it is always thinned, because lacquer must be thinned to spray properly), if the wood is open pore like ash, mahogany, rosewood, etc. I fill them with a pore filler which consists of wall putty that has been thinned a bit and colored to match the wood (since I cannot find oil based wood filler here). Once the filler dries, I sand it down to bare wood, and spray on another coat. Repeat the filling process until the pore is almost filled. It doesn't have to be completely flat (because it won't be with lacquer... the finish will shrink later on) but should be reasonably filled. Three coats of lacquer after that, sand with 400 until all gloss is gone (but not down to the wood), then three more coats, let stand for a month, sand with 1200 and buff.

After that, I get a finish that is nearly indistinguishable from factory guitars. I've seen polyester finished guitars with visible grain... it's just the nature of the beast.

I don't mess with waterbased finish because I never had good result with them. They would be good for average furniture or whatever but I've found that if you let a drop of water sit too long on the cured finish, white spots will develop where the water drop was. This never happens with solvent based finish except maybe shellac. The only water based products I have been happy with was a product called "UV Smooth Prime" which was a primer developed for filling weave holes on fiberglass parts. Non-toxic, sands like a dream too. However I would not use them on a guitar because that is opaque white. The other downside to this product is that it's a bit expensive...
Author:  Kim [ Sat Jan 29, 2011 3:03 am ]
Post subject:  Re: Necessity of using a sanding sealer
woody b wrote:
IMHO sanding sealer has no place on a guitar. Some finishers use vinyl sealer under lacquer, but I'm not a fan of that either.

I don't use waterborne finishes. I suspect you may need some kind of sealer. I recommend zinsser seal coat if a sealer is needed, for any type finish, except catalyzed finishes. You should'nt use any sealer for "build" reguardless of what finish you use. Stew Mac is great, with alot of good products, and excellent customer service, but they're dead wrong in saying to use sealer to "build the majority of your finish thickness."


+1 [:Y:]
Author:  bluescreek [ Sat Jan 29, 2011 7:12 am ]
Post subject:  Re: Necessity of using a sanding sealer
A sealer of some sort needs to be used . To get that perfect finish ,there is much more involved than spraying lacquer. The sealer helps to keep things from bleeding into the finish and sealing the filler. Shellac can work but it can also have adhesion problems. Working to high in sanding can burnish the wood or sealer coats not letting things burn into the lower coats or biting into the wood . 220 is what I use .
I use Nitro and that is different than varnish and water borne . Find what works for you . Finishing is as much about technique as it is about product used.
Author:  Andy Birko [ Sat Jan 29, 2011 8:01 am ]
Post subject:  Re: Necessity of using a sanding sealer
I've used the Stew Mac branded USL following their directions where it's 2/3 sealer and 1/3 top coat and also with 100% top coat. Visually, there's little to no difference between the two. I found that the sealer didn't leave as good a finish as the topcoat though - I had some pebbling type of thing going on that needed serious leveling before the top coats went on.

When using water borne lacquers, it is essential to seal the wood from the water to keep from raising the grain. I've always used a coat or two of home mixed shellac. I've also read about troubles with the pre-mixed styles of shellac, something about the solvents in the lacquer.

As to whether you need to do the 2/3 - 1/3 thing? I don't bother any more. My last two or three instruments have been 100% topcoat and they've worked out just fine, better than the one I did per stew mac's instructions. No need to have two cans of stuff sitting in the shop.
Author:  Howard Klepper [ Sat Jan 29, 2011 1:18 pm ]
Post subject:  Re: Necessity of using a sanding sealer
I gather that for using a water borne over oily woods such as rosewoods, some barrier coat is needed. But I'm sure that it doesn't need to be stearated "sanding" sealer.

I never use water borne. I never use "sanding sealer." I do use shellac in the role of a sanding sealer, but I sand it back to wood. Nitro lacquer needs nothing to make it adhere to wood.

To say that the bulk of a finish should be sanding sealer misunderstands what "sanding sealer" means. It means stuff you put on that sands well, so you can level out scratches you didn't sand out of the wood, or not bother raising wood grain and sanding it back. This is useful in furniture production shops since it saves time and covers up for sloppy surface prep. The role of "sanding sealer" is not to be a barrier/sealer coat, although it may incidentally do that for those finish and wood combinations that need a barrier. If you are not in need of the stearates because you did good prep, you are better off with either nothing (in the case of nitro) or either dewaxed shellac or a proprietary sealer (in the case of water borne and UV/cat finishes). Stearates are not fully transparent, and stearated finish is softer than the topcoat (bad, you are putting lean over fat). It also weakens adhesion, contrary to popular belief. Again, it is not intended as a tie coat or the main finish body if it says "sanding" sealer. It is an aid to surface prep in a production setting.
Author:  nickton [ Sun Jan 30, 2011 3:11 am ]
Post subject:  Re: Necessity of using a sanding sealer
Aha. Great thread.

Never really thought about that burnishing effect before when using high level sandpapers before sealing. Just wondering too do people usually seal before grain filling or after? Must be before. just thinking after the numbness ensuing gluing my first cutaway bindings. Quite an ordeal. bliss
Author:  Mike_P [ Sun Jan 30, 2011 10:20 am ]
Post subject:  Re: Necessity of using a sanding sealer
please take note that certain people are advocating the use of VINYL SANDING SEALER...its a great product...I agree though that normal sanding sealer has issues that negatively affect things...
Author:  Tai Fu [ Sun Jan 30, 2011 11:20 am ]
Post subject:  Re: Necessity of using a sanding sealer
Mike_P wrote:
please take note that certain people are advocating the use of VINYL SANDING SEALER...its a great product...I agree though that normal sanding sealer has issues that negatively affect things...


I just wish that such things are available in Taiwan. I can get nitro clear coats, sanding sealer, but not vinyl sealer.
Author:  Howard Klepper [ Sun Jan 30, 2011 1:24 pm ]
Post subject:  Re: Necessity of using a sanding sealer
Vinyl sealer doesn't improve adhesion. It can hurt it. According to Michael Dresdner, you must spray your first lacquer topcoat about 45 minutes after the vinyl sealer because it will not adhere well or burn into fully cured vinyl (this, BTW, explains some issues I had several years ago using nitro lacquer over some vinyl bindings). Martin had some peeling nitro finishes a few years back; according to Frank Ford, the problem was traced to vinyl sealer. Someone may have gotten better results with it than without, but there are too many variables to an individual's finishing to draw much of a conclusion from that.

The adhesion of nitro to wood is not something that needs improvement, and certainly doesn't need the risk of a product that can cause that very problem.

Dresdner says the benefit of vinyl sealer is to prevent color bleeding of some woods into the lacquer.

Bob Flexner says vinyl sealer can be used as a first coat to improve pore filling, because vinyl will bridge pores rather than sink into them, making the pores shallower for the filler. Sounds risky to me.

There appear to be vinyl sealers and vinyl sanding sealers. The latter have stearates added. But who knows if the manufacturers are using terms consistently.
Author:  AlexanderLou3 [ Sun Jan 30, 2011 11:41 pm ]
Post subject:  Re: Necessity of using a sanding sealer
I use a vinyl sealer for the first coat on a guitar, and then build with nitro the rest of the way. The sealer seems very important to adhere.

My main job is spraying vinyl sealer and topcoat on cabinets and doors, always sherwin williams brand so I'm not sure about properties of any one elses product. I spray 2 coats of vinyl sealer, sand with a 220 pad and top once (semi gloss) and get a nice finish (for cabinets that is). 2 coats of sealer is nice because less chance of sand through. Touching up stain can be near impossible, depending on stain and wood type.

Building cabinets, we ran out of sealer once and had to use topcoat only. What a joke. All sorts of weird things going on. The finish pulled off and peeled in places when the masking tape was pulled up. Also, the first couple coats had to be much lighter than I'd normally spray top. It seems the sealer gives it something to grab onto. Otherwise it just ran on me. It should also be mentioned that deft is no replacement for sealer. Tried that too and it caused some sort of reaction in the sherwin williams top.

I've sealed on a Friday and sprayed a top on Monday plenty of times and have never noticed a problem caused by the laquer drying so long that the next coat wouldn't stick. Finish on 3 year old doors and drawer fronts in for repair can easily be dissolved again with laquer thinner, so it seems no matter how long the wait in between coats, it would always melt a little bit of the last layer and bond well.

And yeah, sanding back into the sealer after having to sand topcoat for some reason (since we normally shouldn't have to for a cabinet grade finish) is when problems start! you can almost always see the separation if you top over it again. Sometimes its best to just strip the whole panel and tape the rest off than try to repair runs, insects, hair or other contaminates ...

I'm not a pro though, just my observations, mainly with cabinet spraying.
Author:  Tai Fu [ Mon Jan 31, 2011 12:05 am ]
Post subject:  Re: Necessity of using a sanding sealer
Perhaps the difference with cabinets is that since an oil based stain was used, a barrier coat is needed...

With guitars most of us clear over bare wood, or if we used any dye it would be water or alcohol based aniline dye. We never use oil based stains because it just looks weird on guitar woods. I don't know, it must be different products. Perhaps some who have clear coated over a tru-oil finish can comment?
Author:  Howard Klepper [ Mon Jan 31, 2011 12:45 am ]
Post subject:  Re: Necessity of using a sanding sealer
AlexanderLou: If you sanded the vinyl with 220 you got a mechanical bond to the topcoat. Dresdner says you can do that if you have left it to dry too long.
Author:  jac68984 [ Mon Jan 31, 2011 11:26 am ]
Post subject:  Re: Necessity of using a sanding sealer
Just wanted to say thanks for everyone's participation and ideas. My spray gun outfit should be arriving on my doorstep from Homestead today or tomorrow. You have given me much to mull over. I will try a few different products and combos while practicing my spray/finishing techniques. Thanks again.

Aaron
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