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Paint spray technique?
Paint spray technique?
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Old 20th January 2018, 01:57 AM   #11
phase is offline phase  United States
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Join Date: Oct 2004
With a metallic, I have made the last coat almost all thinner to get all the metallic particles to lay down in the same direction or evenly.
Another trick to keep the paint from running or puddling is to spray a light tack coat at first. This can sit for about 5-10 minutes before putting on about three full wet coats. The paint should be just about the same viscosity of milk.
Test first or do some less critical parts before the important parts. The urethanes will flow out a bit after spraying for some time, so absolute gloss isnít required.
I am still sensitized to a certain version of a Sherwinn Williams product, even after thirty years of not using it. Toxic is putting it mildly.
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Old 20th January 2018, 07:35 AM   #12
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by phase View Post
With a metallic, I have made the last coat almost all thinner to ...lay down in the same direction evenly...
Thanks, this confirms my idea that lower paint viscosity is the key.
Made it hard for myself with the worst possible combination, a small fan and metallic.
Still haven't done the last coat yet, partly because it's too hot, ~40 C, and partly in case there was further advice.
But there seems to be reasonable consistency of recommendations so I will do it soon.

Also just realized additional reasons polyurethane is perfect for speakers, it has the qualities that Nelson Pass identified for mythic audio components, it's both expensive and toxic

Best wishes
David
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Old 27th January 2018, 12:36 AM   #13
dangus is offline dangus  Canada
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Paint spray technique?
Do you have a viscosity cup to test your thinned paint? I got mine from Sears, but any decent tool place that sells spray guns ought to have them.

Last edited by dangus; 27th January 2018 at 12:42 AM.
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Old 27th January 2018, 01:07 AM   #14
jplesset is offline jplesset  United States
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There are paint additives to slow evaporation and drying, that will make flow-out better. Floetrol is one I have used. Must be more careful not to spray too heavily, or it'll run/sag on you.

I like to spray horizontal surfaces, and let it dry, roll the cabinet, and spray more. Can't run then. Just be careful of overspray on the sprayed side.
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Old 27th January 2018, 01:33 AM   #15
phase is offline phase  United States
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If leaving a day or two in between coats, I have found it to be beneficial to very lightly sand the surface with 400, and use a bucket of water for lubricant with a couple drops of dish soap. A light wipe with an alcohol dampened rag, followed by a tack cloth will help the next layer flow out.

I wouldn’t do this before the clear coat however, just put that on right after the base has set up a bit.

Materials are so costly, I usually try and do a sample panel before the intended surfaces.
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Old 27th January 2018, 03:54 AM   #16
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by dangus View Post
Do you have a viscosity cup to test your thinned paint?...
Yes I do.
It is a little tricky with 2 pack paint because, of course, it thickens even as it sits in the cup.
Because the 2k is expensive I first did a few tests with an enamel then tried to thin the 2k to the same viscosity.
I have seen it recommended to wait a while after the 2 components are mixed, perhaps there is an initial reaction that settles down, with only a slow increase in viscosity after that, or so it seemed.

Best wishes
David
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Old 27th January 2018, 04:35 AM   #17
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by jplesset View Post
There are paint additives... Floetrol is one I have used.
I know of these for conventional paints, I don't know how they would behave with a 2k polyurethane, they may even mess with the chemistry and I am reluctant to risk this.

Quote:
I like to spray horizontal surfaces, and let it dry, roll the cabinet, and spray more. Can't run then. Just be careful of overspray on the sprayed side.
I tried to spray as much as possible horizontal but it's not just a simple box, it's a sort of tray stand with projections in the middle.
So it's mostly horizontal but when I spray the vertical bits I am stuck with some overspray. This didn't mess up the finish as much as I feared.

Quote:
Originally Posted by phase View Post
...I have found it to be beneficial to very lightly sand the surface with 400, and use a bucket of water for lubricant with a couple drops of dish soap...
I don't understand what you mean helps the next layer flow out, the fact that the surface is sanded or the dish soap or the alcohol?
I have to sand between coats to fix minor problems anyway, even it wasn't required to improve the adhesion of the next coat.
But I try to keep the surface perfectly clean, also to improve the bond.

Quote:
Materials are so costly, I usually try and do a sample panel before the intended surfaces.
Materials are so costly that I can't afford to paint a sample panel
I try to do a sample on the bottom or back where the paint isn't wasted but the finish is less critical.

Thanks to everyone for the continued recommendations (previous post too, should have included both replies into one tidy post but ran out of time)
I think I may buy another spray gun for panels.
Can't decide between HVLP and conventional.
Despite all the claims, I have seen very little actual data to compare.
What are the actual structural differences? air cap hole sizes?

Best wishes
David

Last edited by Dave Zan; 27th January 2018 at 04:44 AM.
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Old 27th January 2018, 01:39 PM   #18
phase is offline phase  United States
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The sanding is pretty much as you are already doing by just cleaning up the surface before the next coat. The tiny bit of soap helps with any potential tearing of the soft paint, and the alcohol removes any residue prior to painting.
Another trick is to cut a small radius on the sandpaper corners to prevent them from digging in while doing this.
Just keep that respirator on!
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Old 27th January 2018, 04:42 PM   #19
jplesset is offline jplesset  United States
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Comparing HVLP vs conventional, the advantages that were used when HVLP was first introduced were mostly better control of overspray. Over the many years I've been spraying, I've never found a good reason to shift from my conventional equipment.
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Old 28th January 2018, 05:58 PM   #20
phase is offline phase  United States
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^^I remember when the HVLP guns were coming out, some made it sound like you were incompetent if you didnít use one...
The Chinese copies of the popular DeVilbiss guns do work pretty nice I have found.
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