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irregular pattern when spraying water based poly

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Forum topic by masrapido posted 05-26-2009 07:20 PM 3950 views 0 times favorited 22 replies Add to Favorites Watch
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masrapido

15 posts in 2755 days


05-26-2009 07:20 PM

Topic tags/keywords: maple veneer dye turquoise preval

Hi all. I’ve got a maple veneered desktop that I’m finishing using the following schedule:
0. sanded up to #220
1. transtint/transfast dyes, rubbed
2. 50% thinned zinsser sealcoat, sprayed via preval portable sprayer
3. 10% thinned GF high performance water based poly, sprayed via preval portable sprayer

The top coats of poly were so thin and dried so fast that I ended up spraying 3 coats, then sanding with #400, spraying 3 coats, then sanding with #400, spraying a final coat and then sanding with #600. It feels wonderfully smooth, but has kind of a spotted look. you can see the dots in the finish here if you look closely (ignore the triangular panel):

Sample maple veneer panel on backside of desktop. Love the glistening turquoise color but what about the spotted look of the topcoat?!

Any ideas what I’m doing wrong? Am I just not sanding frequently enough/fine enough?

FYI, the line in the middle is where I applied Tried & True danish oil (100% BLO) in between the dye and the sealcoat. Note that the spottedness encompasses the entire panel, however.

More photos and a more complete description of what I’m doing here:
http://timblack.homeip.net/2009/05/24/finishing-the-desk-part-1/

Thanks!
Tim


22 replies so far

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masrapido

15 posts in 2755 days


#1 posted 05-26-2009 07:32 PM

By the way, here’s a close up of that triangular panel. I (accidentally) got sort of an iridescent mother of pearl effect by:

0. sanding to #220
1. applying 2 thin coats of danish oil
2. before oil fully cures, deciding I didn’t want danish oil on there, and sanding using #120 – #180 – #220
3. working transfast turquoise dye into it
4. shellac sealcoat

I apologize for the not-so-great photo. It looks much cooler in person in natural light. It really has a holographic iridescent appearance remeniscent of abalone or mother of pearl. The dye pattern was of course dictated by the application of oil underneath. The (water-based) dye doesn’t penetrate where the oil got in deep. So you end up with essentially a blotchy appearance, but IMO it is a pleasant blotchiness bc it follows the grain and figure of the wood. You also get the amber effects (from the BLO) under the dye which makes it unique.

Mother of Pearly Panel

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CharlieM1958

16244 posts in 3686 days


#2 posted 05-26-2009 07:41 PM

Did the spots not appear until you applied the poly? It almost looks like something (sealcoat or poly) was interacting with the dye.

-- Charlie M. "Woodworking - patience = firewood"

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masrapido

15 posts in 2755 days


#3 posted 05-26-2009 07:48 PM

I didn’t notice them until I got a few coats of poly on. And it looks like the spots are on the surface. Come to think of it I saw the spots appear when I lightly sanded some of those last coats of poly. So maybe I didn’t let it cure long enough? I didn’t wait long before sanding (30 minutes or so) but it seemed smooth and hard.

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CharlieM1958

16244 posts in 3686 days


#4 posted 05-26-2009 08:03 PM

The dye might be tricking my eye a bit, but… when you sand a coat of water-based poly, you tend to see little rings like that everywhere there was a dust nib or where the surface was not perfectly smooth. If you didn’t see the spots until you sanded, that might be the problem. I find that if I lightly rub the last coat with a 320 sponge, I won’t get this. You can also eliminate it by rubbing out the finish with pumice and rottenstone.

If you want to test this out, spray on another coat and I’ll bet the spots disappear. (until you sand again)

-- Charlie M. "Woodworking - patience = firewood"

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masrapido

15 posts in 2755 days


#5 posted 05-26-2009 08:11 PM

Thanks, Charlie. Yeah, the spots definitely look like dust nibs when you get up close in the light. Plus, knowing that they appeared when I started sanding tells me that it probably wasn’t perfectly level when I got around to sanding. I’m hoping that it was just caused by my spraying multiple (albeit thin) coats in between sandings, as opposed to sanding every layer. My spraying skills and tools are not very advanced, so it’s entirely possible that it was a little bumpy before I sanded.

I am learning that the water-based poly levels quite well, as long as you get enough sprayed onto the surface. It’s possible that my spray was too thin, so the droplets didn’t mix together enough to form a layer on the panel.

has anyone out there sprayed water based poly with a preval for small jobs before?

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poroskywood

618 posts in 2832 days


#6 posted 05-26-2009 09:00 PM

I spray water based poly a lot. You may be experiencing “Fish Eyes” do to water or condensation in your air lines or in your tank. Do you have a water catcher on the out of your compressor? I don’t but I always drain my tank and blow out my air hose before use. That fine drop of water hits the surface like a meteor and disperses the poly on a minute scale creating a “Fish Eye”. You would not notice this until after it dried. I may also completely not know what I am talking about so….

-- There's many a slip betwixt a cup and a lip.--Scott

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masrapido

15 posts in 2755 days


#7 posted 05-26-2009 09:45 PM

I’m using a portable cup-type sprayer called a preval, which uses a compressed butane mixture as propellant. see http://www.prevalspraygun.com/

The cans get cold and condensation builds up after a long spray, but I am now careful to only spray for short durations. Then I stop, and switch to another warm can. I rotate cans this way in and out of a warm water bath. I dry them off meticulously before hovering back over my work. So I’m pretty sure it’s not fish eye.

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poroskywood

618 posts in 2832 days


#8 posted 05-26-2009 10:49 PM

Sorry, amateur giving a professional advice. I would do better actually working while I’m at work. no offense or none taken. I use a Husky HVLP Sprayer where fish eye can be a problem. I didn’t know what a Preval was. Got my 50th post in anyway I’m comin for ya Charlie and Jim. ;) It’s comments like that, that will probably get me in trouble eventually. Sometimes I type as I am thinking, Diarrhea of the brain.

-- There's many a slip betwixt a cup and a lip.--Scott

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masrapido

15 posts in 2755 days


#9 posted 05-26-2009 10:55 PM

I’d say I’m the amateur here! Almost by definition anyone using a preval is amateur. Or, in my case, at least just too cheap to buy a real HVLP system!

Let me ask you this: how do you tell if you’re spraying the correct amount of water based poly? Do you just eye it or do you use a wet mil gauge? If you eye it, can you describe what it looks like?

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a1Jim

115206 posts in 3044 days


#10 posted 05-26-2009 10:57 PM

Just a thought you could be sanding though your first coat and getting different penitration, It also could be some form of contaminate also maybe from your preval.

-- http://artisticwoodstudio.com Custom furniture

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poroskywood

618 posts in 2832 days


#11 posted 05-26-2009 11:08 PM

Sorry man. It does not matter we are just trying to help each other out. I eye it. I have florescent lights in my shop, so I put down a nice coat, get down eye level with the piece, and look for a smooth water like reflection, like trees being reflected on the lake. This will definitely show thin areas they will be cloudy, no reflection. It sounds like you may be worried about putting on to much. My thought there is you can always sand it heavier. I found for nice thin coats of poly, wipe on is the way to go, because you are not building up a thick glassy layer, which is easy to do with a sprayer. I’m such an amateur I don’t even own a Hand Plane or a set of parallel clamps much less a wet mil. dohicki

-- There's many a slip betwixt a cup and a lip.--Scott

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poroskywood

618 posts in 2832 days


#12 posted 05-26-2009 11:41 PM

Ok, I just saw your web page, and the desk is awesome. The color blending and the process is super cool. I didn’t think you could do that to wood. You are living on the edge. Hope It all works out. This may be my last post, I have seen the future an it contains Blood orange and turquoise Sun Bursts.

-- There's many a slip betwixt a cup and a lip.--Scott

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masrapido

15 posts in 2755 days


#13 posted 06-06-2009 06:18 PM

How do you rub out the final coat of water-based poly? I have been sanding lightly between each coat with #400 or #600 paper. In the light, even with this fine paper, I can see the gouges in the coat from my very light sanding. These go away when I put a new coat over it, but so far, every coat I have applied has not been perfect, and is splotchy in some way. So I anticipate I will want to rub out the last coat somehow. But I’m worried that using #600 paper is going to leave these visible gouges in the light. I would be surprised if I really need to go finer than #600.

The other thing is sanding orientation. I have been sanding only with the grain. So the gouges I refer to above are essentially parallel lines. When you rub out the final coat, are you doing more of a circular motion?

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kolwdwrkr

2821 posts in 3058 days


#14 posted 06-06-2009 06:26 PM

Maybe your preasure was to low. If the preasure is to low but your out put is high you will get “clumps” of spray. Turn the preasure up and lower the amount of finish coming out. It’s got to balance between air and finish.
Sorry that was my answer to the original question. Sanding out water based finishes is a pain because the finish is softer then Lacquer. The harder the finish the easier it is to sand out. I don’t know what product you are using but Varathane makes a waterbased poly called something like Diamond something or another. It is very hard when dry and easy to sand out. Maybe you can try a coat or two of a different waterbased poly and see if that works. The scratching you are getting could be a result of clogged paper. You’ll notice that the dust from the finish “gums” up into small hard balls that scratch the surface. Wet sanding eliviates this to a point. You need to get some “wet/dry” sanding paper. You can’t just use whatever. You also need to know if the paper has silocone in it. You don’t want that. I would actually spray a coat and let it dry, then wet sand with 2000 and then pumice or rottenstone. Starting low and working high gives you more work. The project is basically complete so why sand with different grits?

-- ~ Inspiring those who inspire me ~

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CharlieM1958

16244 posts in 3686 days


#15 posted 06-06-2009 06:33 PM

Try wet sanding all the way to 1200, or rubbing out with rottenstone. I used rottenstone for the first time on tis project, andI was really pleased with the results.

Click for details

-- Charlie M. "Woodworking - patience = firewood"

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