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mzuch
08-15-2012, 03:37 PM
Does anyone have experience using KTM-SV (waterborne spar varnish available from LMI) as a top coat? Iím spraying it for the first time and having a problem with orange peel. Iíve thinned the varnish with distilled water (1 oz. of H2O per 8 oz. of varnish) and added lacquer retarder (3/4 oz. per 8 oz). Any more thinning makes the finish too runny, so I think I found the right mix. Iím spraying with an Earlex 5500 turbine with a 1.5mm nozzle on the gun, keeping the nozzle about 4Ē from the workpiece. Iíve had to level sand after every coat but the pebbly texture shows through unless I sand almost all the finish off. The clear coat is on top of a wash coat of shellac over Z-Poxy pore filler. Any suggestions on how to get a smooth coat will be greatly appreciated.

weerpool
08-15-2012, 04:51 PM
4" is too close IMO. i use a palm length distance when i spray and i also use sanding sealer in between the grain fill and first coat
Does anyone have experience using KTM-SV (waterborne spar varnish available from LMI) as a top coat? Iím spraying it for the first time and having a problem with orange peel. Iíve thinned the varnish with distilled water (1 oz. of H2O per 8 oz. of varnish) and added lacquer retarder (3/4 oz. per 8 oz). Any more thinning makes the finish too runny, so I think I found the right mix. Iím spraying with an Earlex 5500 turbine with a 1.5mm nozzle on the gun, keeping the nozzle about 4Ē from the workpiece. Iíve had to level sand after every coat but the pebbly texture shows through unless I sand almost all the finish off. The clear coat is on top of a wash coat of shellac over Z-Poxy pore filler. Any suggestions on how to get a smooth coat will be greatly appreciated.

Rick Turner
08-15-2012, 05:02 PM
If you want flat and smooth use a different finish...

ksgjlg
08-16-2012, 12:36 AM
Rick, I've used the em6000 with very good results on my "yes another first uke". I'm on my second one. What would you recommend for a high gloss finish?

mzuch
08-16-2012, 03:56 AM
If you want flat and smooth use a different finish...

I suppose I should add that I have a guitar finished in KTM-SV, and its has a wonderfully smooth, flat and clear finish. Unlike acrylic waterbornes such as Target EM6000, KTM-SV has no bluish tint. It also is used by Maine-based mandolin maker Rolfe Gerhardt, who wrote this article (http://www.newenglandluthiers.org/contents/Articles/Tips_Techniques_Tools/ktm-sv_an_overlooked_finish.html) about it. However, I found that Gerhardt's thinning ratio was too low for my setup. Note that he says to keep the gun tip 4 to 6 inches from the workpiece to prevent the finish from drying before it hits the wood.

Chris_H
08-16-2012, 06:30 AM
Are you getting a 'fully wet' 'glass' film that dries orange peely, or does it never lay out flat. The distance from the tip to the sprayed piece depends on the amount of finish coming from the tip, and how the fan is working. For most of my spraying, 4" happens when things are moving very fast. Sometimes it can go closer even, but that leaves little room for error, very fast (or occasionally very fine like an airbrush fan for small areas, not like an uke. I like it when things are fast, surfaces are covered quickly with minimal drying between the gun and the film surface. If you are spraying slowly, and 4" seems right, that may be a sign of the problem. Is your spray rig pressure assist at all? i.e. an air pressure line down from the air chamber to the cup? Is it solely siphon feed? Siphon feed works best with very thin finishes, and can work very well with nitrocellulose. The waterbornes I have worked with have been higher viscosity than nitro. Waterborne finishes are wierd, I do not care for them, though for years I used one particular waterborne, as I found a system that worked.

Make sure that your gun is absolutely clean, all of the fluid and air parts. Careful about metal cleaning devices in the small precision openings. Small, almost indetectable dirty orifices can make it a nightmare to get a good spray pattern. Waterborne makes it that much more difficult.

Big smooth orange peel happens when the film is too thick, or the finish is poor at laying out due to various possible reasons. Fine textured finish 'orange peel' mostly happens when there is not enough finish to flow correctly, or something else is affecting the flow.

Finishes can be picky about spray equipment. I have had many guns over the years, and for particular finishes, there is always a preferred gun/ setup.

Nitro is so much easier than waterborne.

Dan Uke
08-16-2012, 06:46 AM
I suppose I should add that I have a guitar finished in KTM-SV, and its has a wonderfully smooth, flat and clear finish. Unlike acrylic waterbornes such as Target EM6000, KTM-SV has no bluish tint. It also is used by Maine-based mandolin maker Rolfe Gerhardt, who wrote this article (http://www.newenglandluthiers.org/contents/Articles/Tips_Techniques_Tools/ktm-sv_an_overlooked_finish.html) about it. However, I found that Gerhardt's thinning ratio was too low for my setup. Note that he says to keep the gun tip 4 to 6 inches from the workpiece to prevent the finish from drying before it hits the wood.

I have a uke with Target waterbased and I don't see a bluish tint. However, I've read some reviews on Stewmac that some people get it.

mzuch
08-16-2012, 07:54 AM
Are you getting a 'fully wet' 'glass' film that dries orange peely, or does it never lay out flat.

Thanks for the input, Chris. This is exactly what I was looking for. To answer your questions, the finish never lays out flat, the Earlex 5500 has a pressurized suction cup and I clean the nozzle and needle after every coat. Interestingly, the orange peel seems to diminish as each coat dries, especially if left overnight. Based on a viscosity test of the thinned finish, the needle/nozzle I'm using may be a bit too large. I've ordered a 1.0mm set which should arrive tomorrow, so we'll see if that helps matters at all.

I wish I could spray nitro, but I'm not spending $600 on an explosion-proof fan.

Beau Hannam Ukuleles
08-16-2012, 09:05 AM
A friend of mine used some kind of water based finish (there seem to be only 2 or 3 brands) and he said that after sanding/cutting back, the powder left had to be fully removed as the next coat didn't dissolve the sanded finish particles. It left his finish with white powder dots so ill never use water based finish although i'd love to for health and environmental reasons.

Is this non-disolve thing a common known element in all water based finishes??

Chris_H
08-16-2012, 12:31 PM
watercolor paints will dissolve and blend with previous coats, most all other waterbase coatings do not dissolve. Especially clearcoats. This can cause a problem with polishing if you go through a layer, depending on how the coats were applied, and the product.

jedejo
08-16-2012, 12:44 PM
I've tried using the KTM-SV and found it to have all of the usual problems of waterborne finishes. It's too thick; it has the hazy, bluish hue of a waterborne; and was too soft to buff out to a nice, smooth, flat, sheen. I eventually just sanded it all off and decided to use another, more conventional, product.

I should also add that the finish was used on a flat-top acoustic guitar.

ksgjlg
08-16-2012, 04:55 PM
wMy uke was done with em6000. I dry sanded with 320 between coats and wiped off with a dry rag. All residual dust melted into the next coat. No blue tint once dry. It is very blue when wet. I kind of like that. its an indicator for a wet even coat. It drys fast and can be sanded in an hour or two. Of course I'm in Texas where its 104 or so in my shop. I did have a problem with witness lines when I sanded back and from what I found, you should put each sucsessive coat with in 2 hours, if not the witness lines appear. I just sprayed two more coats of laquer and was able to sand and polish without the lines returning. I'm pretty pleased with the stuff.