irregular pattern when spraying water based poly - Woodworking Talk - Woodworkers Forum
 
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post #1 of 8 Old 05-26-2009, 01:22 PM Thread Starter
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Question irregular pattern when spraying water based poly

Hi all. I've got a maple veneered desktop (made of doubled-up 3/4" appleply) 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):



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/2009/05/2...e-desk-part-1/

Thanks!
Tim
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post #2 of 8 Old 05-26-2009, 01:32 PM Thread Starter
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close up of cool looking triangular panel

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.

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post #3 of 8 Old 05-26-2009, 05:06 PM
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Veneer sanding is tricky, little indents or compressions will remain unsanded or undersanded, even though they feel wonderful and look great until finished with colorant... it looks alot like what you have if I am seeing the pic correctly. I have to sand alot with the coarser grits before going to finer. Does the same thing happen on solid wood or just the veneer part? That might be a clue. I do alot of test samples when using a new finish.
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post #4 of 8 Old 05-27-2009, 01:18 AM Thread Starter
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sanding and dewhiskering veneer

I really don't know what it's like with solid wood bc this piece is all appleply. I did notice that after dewhiskering the veneer (sponging the entire surface with water, drying overnight and sanding the next day with #120, #180, #220) that there were some rough spots in the veneer that I didn't feel right after the sanding.

I think the problem I was having with the spots was related to my spraying technique (not spraying poly thick enough to form a sheet) and lack of sanding between EVERY coat.
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post #5 of 8 Old 06-09-2009, 09:09 PM
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Blotchy finish.

What I can see in the photo, it appears that the blotches are caused by the wood itself. Did you use true Appleply or imported (so called-chinee crap ) Baltic birch? the later will blotch what ever you do. what species is the top ply?
True Birch can be used but the first step is to use a wood conditioner, (I use 3/4 LB cut blond Shellac) Maple can be blotchy or not use wood conditioner for insurance. Go buy your self a good book on finishing. The Best I have found is "Understanding Wood Finishing" by Bob Flexnor. READ THE BOOK
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post #6 of 8 Old 06-10-2009, 02:51 AM Thread Starter
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Appleply has Beautiful Edges

Oh, yeah, it's appleply. Hardwood multiply (15 plies in 3/4") with a maple veneer. Made in the good ole USA. Actually, it's made in this good ole United State of America... Oregon.

The blotch you see in the photo is actually very desirable (to me). It's not a general unevenness - it's just the dye worked deeper into the maple figure and curl deeper than in the areas where the grain runs parallel to the surface. Dye on maple (even veneer) is wonderful - I'm sold on that. It's just my sealcoat and top coats that are my problem. I'm just about done with the top now. It looks something like this (click for fullsize):



More photos here: http://s193.photobucket.com/albums/z...Studio%20Desk/

They aren't great photographs, but they give an idea of the process/sequence. If you're wondering why so many of the edges, it's because I wasn't happy with the dyed edges at first, then sanded it all off, and then ended up just redyeing them.

The idea I had was I wanted to maximize the contrast between plies on the edges bc it's not every day you get plywood you want to show off the edges. And they're beautiful on appleply. Anyhoo, it took me a while to figure out why the dyed edges had a lot of contrast in some areas, but little to no contrast in others. It's not rocket science, and most of you veteran woodworkers probably would intuitively get this, but eventually I figured out that because of the contour and direction of that curved cut in the desktop, in the curved area all plies on the edge are quasi-end-grain, and they both absorb lots of dye. Whereas on the front, back, and side edges, the grain of adjacent plies are perpendicular to one another, i.e. one ply is end-grain and the next is not, so you get the high contrast effect. It all worked out pretty well in the end.

I've read Flexnor, thanks. Great book. This is the first time I really got into wood finishing, and I got in knee deep. There's a lot to learn, and I learned a lot so far, but on a sliver in the grand scheme of things. I think experience teaches more than any book can...
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post #7 of 8 Old 06-10-2009, 11:37 PM
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Sounds like you are ready to invest in a compressor and a real spray gun. Those preval power units are not very good at atomization and that is what is causing the speckles.
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post #8 of 8 Old 06-11-2009, 01:18 AM Thread Starter
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Yep. I am. For this project, I'm hoping I can level and rub out the last coat to eliminate any irregularities... I plan to use #600, #1000, #1500 paper, and then abralon pads #2000 and #4000. The latter are used for polishing bowling balls and I have heard lots of wood finishers use them for polishing poly to high gloss.
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