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Help with a Spraying problem - dimples.
http://luthiersforum.com/forum/viewtopic.php?f=10101&t=47408		 Page 1 of 1
Author:  Colin North [ Mon Mar 07, 2016 2:29 pm ]
Post subject:  Help with a Spraying problem - dimples.
I'm assuming this is some kind of contamination, but can't for the life of me think what.
I try to be very careful about wax, polishes, silicons, oils etc in the shop.
I thought the gun might have been contaminated so I stripped it, cleaned everything, sprayed lots of soapy water though it followed by clean water (I'm spraying Enduro Var Gloss, new tin)
Still getting the same - dimples, some 1/16" wide and I can see the unwetted surface at the bottom - not cute!
Just doing test panels at the moment, one with Art Epoxy, one with shellac (1lb cut sanded back) both prepped originally to 180 with Abranet , then 320 Abranet between coats - both have had the same dimples.
Any suggestions, or perhaps I have missing something??
Author:  Alex Kleon [ Mon Mar 07, 2016 3:11 pm ]
Post subject:  Re: Help with a Spraying problem - dimples.
What kind of spraying rig are you using, Colin. If you're spraying with a compressor, the hose might be contaminated with oil and/or moisture from the tank. Adding an inline moisture trap and a dedicated air hose might help, in this instance.

Alex
Author:  Colin North [ Mon Mar 07, 2016 3:25 pm ]
Post subject:  Re: Help with a Spraying problem - dimples.
Alex Kleon wrote:
What kind of spraying rig are you using, Colin. If you're spraying with a compressor, the hose might be contaminated with oil and/or moisture from the tank. Adding an inline moisture trap and a dedicated air hose might help, in this instance.

Alex

Sorry forgot to mention , Fuji turbine, mini-mite 3 HVLP, XPLC gun, so it shouldn't be anything coming down the line.
Used it before with no problem like this.
I've sanded back another panel with my drum sander (I have 2) and will try again tomorrow using a different abrasive to prep the wood. Wondering if it could be stearate on the abrasive (Abranet)
Author:  Tom West [ Mon Mar 07, 2016 4:56 pm ]
Post subject:  Re: Help with a Spraying problem - dimples.
Colin North wrote:
Wondering if it could be stearate on the abrasive (Abranet)

:idea:
Tom
Author:  kencierp [ Mon Mar 07, 2016 5:35 pm ]
Post subject:  Re: Help with a Spraying problem - dimples.
Not sure if General Finishes has a similar product -- non-silicone fish eye remover.

http://www.highlandwoodworking.com/hydr ... 2pint.aspx
Author:  B. Howard [ Tue Mar 08, 2016 7:30 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
Looks like solvent pop. could simply be spraying coats to heavy, not enough dry time between coats or a draft in the drying area. basically the surface is drying quicker than the body of the coating and when the solvent escapes it leaves behind craters.

Here is a link to a handy finish problem solving chart I put together.
http://howardguitars.blogspot.com/2015/ ... rt_18.html
Author:  kencierp [ Tue Mar 08, 2016 7:46 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
Solvent pop?

This (Enduro varnish) is a water borne coating --- still can happen?

Thanks
Author:  Colin North [ Tue Mar 08, 2016 8:35 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
Don't think so Ken.
Author:  Pwoolson [ Tue Mar 08, 2016 8:54 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
To my eye, that has the tell-tale signs of silicone contamination. Any lube get sprayed in the area?
Author:  Colin North [ Tue Mar 08, 2016 9:21 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
Yes, that or oil is what I suspected myself.
So, stripped all 4 panels to bare wood, sanded one pair with Abranet, another with my old abrasive, 3M (no problems before)
Sprayed one set of each with EV Gloss, same problem.
Sprayed the other pair with EV Silk, no problem.
So I suspect the tin of Gloss - is that reasonable? Unopened tin?
Author:  Barry Daniels [ Tue Mar 08, 2016 10:01 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
I dealt with a very similar issue a few years ago that looked exactly like this. It was caused by oil contamination in my compressed air system. Even a turbine compressor can put small droplets of oil into the air stream. You definitely need a filter and you can assume that your existing air hose and spray gun are contaminated.
Author:  Woodie G [ Tue Mar 08, 2016 10:16 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
I am not sure where oil would come from in a turbine sprayer. We've had an old Apollo apart (same turbine unit as Turbinaire, Fuji, etc., says the boss) and there are no lubrication points or other oil sources in that sealed turbine unit. Other than a source of misting oil near the filtered intake, there does not appear to be a way to introduce oil into the air path. Perhaps the gun was incorrectly cleaned or lubricated, which introduced oil or silicone into the fluid path?

We've been playing with EnduroVar as part of what the boss calls the "...necessary but usually disappointing business of assessing what passes for the state-of-the-art in waterborne finishes." When applied on a flat surface, I did see some issues when we allowed the film thickness to get to truly ridiculous levels, and when sprayed on unsealed, porous woods like mahogany, we saw similar 'dimple' effects for the first few coats, but the pores eventually filled and we were able to build enough to allow sanding and buffing per usual practice. On epoxy, TimberTech, and on well-dried pastewood fillers, we saw minimal issues with pore-sucks (I did not coin that term, thank-you) or bleeds which might result in serious film thickness variations.

According to my notes and General's technical data sheets, EnduroVar has about 75g/l of VOCs, or about 1/10 of what standard instrument lacquers have per unit volume. Very thick coats and elevated temperatures would encourage these VOCs to migrate to the surface just as it does for higher VOC finishes, but from looking at the vapor pressure numbers for the solvents used, I doubt this is what you are seeing unless your film thicknesses are very, very thick and surface temperatures elevated well outside the acceptable range. HVLP systems tend to both heat and dry the finish with the blast of warm, dry air air from the turbine, and we use a heat exchanger hose in line during warmer periods of the year to avoid really hot air temperatures. It seems unlikely that there is much in the way of VOCs which could be cooked off in any reasonable wet film thickness.

The suggestions here seem to be to see if dialing back the air to minimum for atomization and reducing material flow to just get a wet coat on a vertical surface might be worth looking at. A former student is building in John Greven's shop - a waterborne enthusiast in general and an EnduroVar user in particular, so I will ask the boss to touch base with him for more information.
Author:  Colin North [ Tue Mar 08, 2016 11:19 am ]
Post subject:  Re: Help with a Spraying problem - dimples.
:oops:
Shot myself in the foot, just went back to look at my stirring stick.
Old piece of maple I had lying about which was used to support a wall hanging from an era when I normally finished stuff like that with a couple of wipes of wax paste polish....... hang my head in shame.
duh
New tin on the way (would you believe about $65 a quart in UK) - will not forget this in a hurry.
Author:  SteveSmith [ Tue Mar 08, 2016 1:30 pm ]
Post subject:  Re: Help with a Spraying problem - dimples.
I wish I could say I've never done anything like that idunno

Good that you found it [:Y:]
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