Sanding Sealer- Between Coats

Vic D

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Using stewmac colortone waterbase sanding sealer and lacquer. I'm about to shoot sanding sealer and I don't have a clue as to what I'm doing. If I spray a coat every 2 or 3 hours or so I don't need to sand I suppose. But tommorow after say 12 hours of drying time I'll need to sand before I start with more coats of sanding sealer... correct?
Pffft, I'm so confused.
 
Thanks guys, but those instructions are vague and don't answer my question. I have the book and what I understand from it is 12 to 16 coats of sanding sealer at 3 to 4 coats a day 2 to 3 hours apart. There is a mention of sanding after the first couple of coats in another chapter but in the next sentence it has a reference to nitro (scratches will melt away). I have another reference that says you need to sand if the sealer has dried longer than like 6 to 8 hours. There's a void in the information. An anomoly in the spray sand continium.

I read the book the other night pretty quick... there may be clearer instructions somewhere but this book bounces around like a top. They could have spent more time on step by step procedures for each type of finish and less eye candy and flash splashed throughout the book. Rereading it now.
 
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I would sand after I felt the sealer has set up...I've only used their sanding sealer twice--Maybe give them a call?
 
Ok I've gone back over the sections in the book dealing with sanding sealer and I still don't have a definite answer. I'm going to just start shooting it and scuff sand tommorow then level sand when I think it's thick enough.
 
Thanks Flyfish... I was debating whether I should call them or not. Might have to.
 
The instructions of the website say to sand between coats if more than 48 hours have elapsed or you risk adhesion problems.

Water base is out of my league. Tried it once but I didn't like the process or the finished result. That was ten years ago so I'm sure technology has changed.
BUT...........12 to 16 coats of sanding sealer??????? Sure sounds like overkill to me. And with up to 12 topcoats that's a possible total of 28 coats without even mentioning grain filler!!!!!!

Just as a comparison, with nitro, I apply a total of eight coats. One vinyl sealer and seven top coats with one sanding session in between and further sanding and buffing afterward.

Keep us posted. I know you will :)
 
Chuck, when I tried the stewMac stuff the sanding sealer was already reduced and super thin. When I did my guitars, I used Belhens(sp) and it did a better job filling what the grain filler didn't...I had a very hard time buffing the waterbased clear too. Hopefully Vic will have a better time than I did.
 
The instructions of the website say to sand between coats if more than 48 hours have elapsed or you risk adhesion problems.

Water base is out of my league. Tried it once but I didn't like the process or the finished result. That was ten years ago so I'm sure technology has changed.
BUT...........12 to 16 coats of sanding sealer??????? Sure sounds like overkill to me. And with up to 12 topcoats that's a possible total of 28 coats without even mentioning grain filler!!!!!!

Just as a comparison, with nitro, I apply a total of eight coats. One vinyl sealer and seven top coats with one sanding session in between and further sanding and buffing afterward.

Keep us posted. I know you will :)


Thanks Chuck! Yep the 12 coats of sealer blew my mind too. I'll see what I have after tommorow. This is nothing like painting a car.
 
Yeah, the Stew-Mac finishing book is more confusing than it is helpful. Lots of contradictions within the book and with what's posted online. I'd go with the online instructions. I think the 12 to 18 coats is for the top coat, not the sanding sealer.
 
Yeah, the Stew-Mac finishing book is more confusing than it is helpful. Lots of contradictions within the book and with what's posted online. I'd go with the online instructions. I think the 12 to 18 coats is for the top coat, not the sanding sealer.

Again, from their online instructions:
http://www.stewmac.com/shop/Finishi...terbase_Lacquer.html?tab=Instructions#details
12 to 16 coats sanding sealer foolowed by 9-12 top coats. Add them up and it's a lot!
BTW, does it still have a bluish cast to it?
 
I read awhile ago in Mya-moe’s website ( I think they were blogging) that they were using the StewMac water based stuff and were having good results. I just checked their site for the info but it’s not there. They say they’re using UV cured polyurethane now ( which cuts the cure time down to something like 7 minutes). Maybe PM them to see what they did/do.

I look at spraying ukes just like I'm spraying a car!

Good Luck and happy adhesion!
Stephen
 
12 tp 16 coats of "sanding sealer"?

Nobody in the professional world of guitar, uke, etc. finishing does that. Nobody. That's some crazy sh...

Stay away from lacquer sanding sealers. They just cloud your results. Literally.
 
Waterbased lacquers do not cross-link. In other words you are putting one layer on top of another hence the need to coat within a given time frame and then sand between 'cured' coats. Cellulose lacquers 'burn in'. In other words each successive layer bonds to the one beneath by integrating into it - slightly disolving that bottom layer. In this regard you get a 'homogenous' finish. The big difference is: if you do not meet the critical coat and recoat timings of a waterbased finish, when you come to buff and polish the final coat you will almost certainly cut through the layers and produce 'witness' lines, visible when held to the light. Waterbased finishes are therefore fine if you can finsih from the gun and you have a perfect spray set-up. Cellulose, despite its bad environmental rep is ideal for the beginner who is using cans...

If your decision to use water based was due to conservation issues and your impact on the planet the way I deal with this issue is that these substances are, in general, natural (although xylene is a straight chemical) and belong in the environment and the over-spray and fumes from spraying the 4 - 6 instruments I build a month is not going to kill the local habitat at the back of my workshop. Simplistic I know. However as a one man shop this type of finish is fine.

If you need a detailed account go to Kathy Matsushitas site - she has a complete section of wrestling with this type of lacquer and makes it work for her.
 
Call Stew mac they are very helpful and for the most part can answer your question right on the phone. Tech support calls you back for the most part.
Right on Pete. For me I got an air scrubbing system that cleans the air while I'm spraying. The fumes go through 3 filters one being activated carbon.
Seems work very well.
 
Here's the MyaMoe finishing info from their builder's blog.

http://myamoeukuleles.com/blog2/

"Water-based lacquer notes
Thursday, April 16th, 2009

We just started our 100th instrument, and I finally feel like I’m starting to master the application of the water-based lacquer. It’s not as good as nitro, but that is the nature of the product. It’s harder to apply, a bit more finicky, and it doesn’t give you as “wet” a finished look. But, given all the positive impacts to your health and the environment, the water-based lacquer is excellent. So, here’s my process:

* I use Stewart-MacDonald’s water-based laquer product line. I tried KTM-9 (from LMI), but it is more finicky. The big negative is that when you use shellac as a sealer and don’t need a pore filler (such as on spruce), the KTM-9 easily blisters during buffing. The StewMac products are really solid, and the folks at StewMac have done a lot of testing. They are a great help.

* I sand to 180, then mask, then put on one coat of shellac as a sealer.

* After a quick sanding, I put on StewMac’s water-based (clear) pore filler. I mix some micro-beads into the pore filler to thicken it a bit. This is a really important step–it reduces the number of times you need to pore fill and results in a much better surface.

* One day later, I put on another coat of pore filler thickened with micro-beads

* One day later, I sand it flat with 320. I put on 5 coats of the StewMac sanding sealer at 45 minute intervals. I’m using a Walcom STM HVLP gun and I put on relatively light coats. I never get any runs or sags, and I overlap each pass of the gun by 50%. I leave the product in the cup of the gun during the day and clean it out after the last shooting. I keep the room at about 70 degrees and the humidy fluctuates during the year from about 35% to 45%.

* The next day I sand everything flat with 320. This is the biggest sanding day. I don’t want to sand through the finish and expose new pores, but I want to get it as flat as possible. Some pores still show up after this sanding. I think put on another 5 coats of the sanding sealer.

* The next day everything gets sanded flat, and you shouldn’t see any pores. I then put on 5 coats of the StewMac water-based lacquer at 45 minute intervals. Again, the coats are relatively light. If you get runs or sags, or you see any milky look to the finish, then it’s going on too thick.

* I wait about 7 days before sanding & buffing.

* I go right to 1500 grit wet-sanding. Surprisingly, the surface right off the gun is so good that I can sand with 1500. This sanding goes pretty fast.

* Then I go to the buffer and buff with the Menzerna medium, then extra-fine.

With this process, I get a great gloss finish. StewMac notes that to get as transparent a finish as possible, keep each coat of finish light.

Gordon"
 
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