Keep getting dust and specs in sprayed finish

[Ian Scofield]

Been practicing on a scrap piece of plywood to get a hang of spraying a finish before spraying my project.

In preparation, I spent a weekend building a paint booth in the garage using plastic sheeting and PVC pipe (all sides + top + floor) I have a hanging air cleaner that I have coming through the top and taped off. I also have a box fan with a filter on it within the booth. I bought one of those jumpsuit things to spray in to prevent any thing coming off my clothes. I've shop-vac'd the whole area, walked around using my air compressor to blow the everything to stir it up and let the air cleaner run for a few hours. Cleaned the gun numerous times. I've tried with the air completely still, with just the box fan, with just the air cleaner, with both the box fan and air cleaner. I've tried just about every combination/variable I know to mess with.

Through all of this, I'm still getting dust/nibs in the finish. I am completely at a loss and getting quite frustrated as I see them in the finish before I even finish spraying the piece (2' x 2' square). I'm spraying GF enduro white with a fuji q5. When the finish dries, it looks fantastic and is nice and level....except for the dust specs and other debris in the finish here and there. I'd love to stop wasting paint and time and actually move onto my project, but don't want to risk it until I know how to do this without having dust in the finish.

Am I missing something? Does anyone have any recommendations?

[Scott Holmes]

It is nearly impossible to get a perfect finish off the gun... Dust, etc. !!! You should be able to rub out the imperfections once the finish a been applied to to the proper thickness; 2-6 spray coats, depending on the final dry mil thickness of your finish.

[Ian Scofield]

Scott, I'm starting with BIN primer -> GF Enduro white -> GF Enduro clear poly. Currently on the GF enduro step. So your suggestion is to do light sanding to get rid of the dust specs, then move onto the clear poly? Wasn't sure if they would still be visible after the clear poly (which I feel will have specs as well).

I just figured that there were people out there that have conquered this and have some secret to get the dust free finish. Maybe I'm trying to chase perfection.

Additionally, since the coats are 2 hours apart, I've read that I can leave finish in the gun. Is there anything special on top of this that I need to be doing? I'm literally just putting it back in the gravity stand. Before I spray the piece, I do a brief spray on a piece of cardboard to ensure nothing dried on the nozzle gets shot onto the piece. Is this correct?

[Wayne Lomman]

Ian, unfortunately I have to disagree with Scott - it is routinely expected that a sprayed finish should be good off the gun. That being said, here are some things to check.

Air velocity through your booth. You need a gentle movement, not a howling gale.

Gaps. Is air leaking in where it shouldn't?

Spray position. It's easier to get good finish on an angled or vertical surface than a horizontal one. Gravity is the one to beat here.

Paint cleanliness. Strain your paint through a cone filter before use. Buy them where you would buy auto paint.

Correct solvent. Use the manufacturer's recommended solvent. Theirs has to work and sometimes cheaper alternatives can react and cause graininess.

Coating thickness. Make sure you put enough on. If your coat is too thin it won't bury the solids properly. This is incorrect film formation. Get hold of a comb type wet film gauge and practice getting the correct film thickness.

Don't expect too much from the first coat. Problems reduce with succeeding coats.

Sand between coats using the correct grader the coating. The data sheet will tell you what grades to use. This varies with the coating. For example I regularly use Interthane 990 which will cover 180 grit sanding no problems but you will more likely need to sand with 400 or finer.

Try these. I will probably think of more things to suggest but have to keep driving now although I wonder why use a clear over white. Good whites are best stand alone. Cheers

[Ian Scofield]

Wayne, thanks for all the pointers/suggestions.

Everything appears to be sealed correctly, but I'll have to double check this.

I am spraying on a horizontal surface which makes it certainly easier for dust and other debris to settle on the surface which makes sense. I was hoping to be able to spray horizontally as I know I won't always be able to hang everything so was hoping to use this as a learning experience to figure it out. I'll have to give it a try vertically, which brings other challenges of runs and not leveling as nicely.

I have strained the paint through a strainer and didn't see any clumps or anything in the strainer either, so that's good.

No solvents necessary yet, as I haven't had to thin the BIN or the GF enduro white thankfully, but thanks for the note!

I've tried using the wet film gauge and I'm putting down the 3-4 mil thickness and the finish is leveling nicely. I really like this stuff, it looks fantastic when it levels out.

I don't think it's an imperfections thing that I need to cover up, as I'm going on 7 or 8 coats on this board (just going to keep spraying/sanding till I get the hang of it). These imperfections are things that are landing in the finish, new each time.

I've been sanding with 320 in between coats which takes the imperfections out, shop-vac'ing it, then wiping down with a tack cloth to get the remaining dust specs.

I did just try spraying all the walls/floor/table I'm spraying on with water to keep the dust settled in place which seemed to help some....except for a hair that landed in the piece. So I can't see to win. :/

[John TenEyck]

I pretty much agree with Wayne. I have sprayed several gallons of Enduro White Poly over BIN pigmented shellac primer. It is no different than clear finishes in that I can get a smooth off the gun finish that requires no further work. Where you are getting stuff into your finish is a bit of a mystery, but I can tell you that I don't go to near the extremes that you have. I use a temporary spray booth; nothing more than plastic sheeting hung from nails in the floor joists with brown paper on the floor. It's about 8' wide and 10' deep, not sealed in any way. One end is open. The other end has a 5" exhaust duct drawing about 1200 cfm of air through the booth, which is not nearly enough if you look at face velocities but it works fine to draw away over spray and keep it from falling onto the freshly sprayed work. Make up air comes from an open, unfiltered, window about 30 ft away. Any large particles coming in drop out before they make it to the spray booth. When I get dust nibs it's almost always caused by stuff falling from the ceiling or off me with the latter being the more frequent problem. As long as I clean up me before spraying I almost never have problems. I spray within an hour of putting up the booth and vacuuming up the shop.

I have had issues with stuff coming off the spray booth plastic sheeting and falling on the fresh finish. It's over spray from prior uses that peels off over time. It happens when I'm too cheap to throw it away and try to squeeze in another few runs. Every time it happens I throw it out and swear I'll throw it out as soon as I see appreciable build up or signs of peeling, and then I don't do it. Make sure your spray booth isn't the source of your problems.

Personally, I would not have a box fan circulating air within the booth. I would run air into and out of the booth, period. You can do that by sucking out air like I do, or making a sealed booth and blowing in filtered air that flows out a second opening. Either works; neither circulates air within the booth. That's just asking for trouble. I have a friend who gets great results with no booth and no moving air proving even the simplest approach can work.

John

[Wayne Lomman]

Ian, I missed the fact John pointed out that you have an extra fan circulating air. Don't use it. As John said, linear flow is the best. Cheers

[Andy Giddings]

Ian, I've sprayed the same materials as you with no issues. My set up is a knock down spray booth made from rigid 2 inch foam insulation and a single large fan behind the booth extracting air through a furnace filter out the window. I spray in a double garage that is also used as my workshop. While I clean the floor with a shop vac before starting I don't do anything else and don't have an air cleaner.

Couple of questions - after each coat I assume you are sanding the surface as recommended? What are you using to remove the sanding dust? I would avoid blowing any dust around with compressed air as it takes ages for this to settle even with an air cleaner. Do you wipe the end of the nozzle after you've finished spraying as there is typically a small amount of dried material there? Is your Q5 exhausting into a clean area and not blowing dust around? Is it really dust you are seeing or dried overspray which would indicate not enough flow to take the excess away from your work? Are you spraying toward the air flow as often as you can?

[Scott Holmes]

I agree with the others that think you have too much air flow in the spray area.
I would lose the tack cloth; wipe it with a damp lint-free cloth. Getting a perfect off the gun finish is possible; but can be difficult in a home shop... Especially if you used a vacuum the same day! I too have gotten flawless finishes off the gun; not every-time. Dust sounds like your problem

[Don Kondra]

I'd suggest you need an exhaust fan with a minimum of 500 cfm although something smaller may still work.

After you have "cleaned up" the shop, run the fan for ten minutes or so. Then use an air hose to clean the booth area, blowing towards the exhaust.

Let the fan run for another ten minutes or so. By this time your ambient air should be relatively dust free.

When spraying the trick is to have the overspray moving out..

I do my sanding in the booth and use the air hose, NOT a rag to remove the sanding dust. Anything large enough to be a problem will be blown away and either fall to the floor or go out the exhaust. Any fine dust will melt into the next coat.

Cheers, Don

[Evan Stewart]

Ian, I have a 4 stage fuji that I switched to a few months ago from a airless. I had the same issue early on. For me it was too much overspray in the air that was not exhausting fast enough. I upgraded my exhaust system and got my spraying technique down to reduce over spray. The other key was like Andy mentioned, being sure to spray toward the exhaust. I did this by making a 2' x 7' bench on wheels so I can rotate it as needed without moving the piece.

I generally had the issue when I had multiple pieces in the booth at the same time. If I had say 4-5 cabinets in there by the time I started spraying the last couple units, some of the over spray would fall on the first units causing the gritty finish.

I was able to fix the finish with 800 grit wet/dry sand paper and then 1500 and buffing.

Getting the piece as close as possible to the exhaust and always spraying toward it helped more than anything. This was the advice both Andy and Wayne gave me.

[John TenEyck]

Ian, what sheen are you using? I have a similar problem right now with Target Coatings EM-9300. First time ever using a TC's product - may be my last. I'm using the satin sheen and it sprays great, levels very well, and dries to a nice rough finish! That's right, hundreds of little bumps every square foot. I got out my jeweler's glasses and looked closely and they are perfectly round spheres of glass. I put some of the finish directly from the can onto a clean piece of glass using a brand new foam brush. There they are. I'm using a 3M PPS cup system which has an integral filter, but they are getting through it.

I've never had a problem like this with Enduro White Poly, but just thought I'd pass along my experience with the TC product. Have you looked really closely at the specs. you are getting under enough magnification to see what they are?

I'll be calling TC tomorrow. Ugh.

John

[Steve Jenkins]

One more in favor of using only an exhaust fan in your booth. For the occasional dust nib after its dry rub out with a piece of brown kraft paper . Think paper bag. It won't affect the looks of a satin or dull finish at all but will take down the nibs

[Ian Scofield]

Thanks everyone for the replies and help. Turns out my problem was ventilation. There really wasn't any moving air so everything was just falling into the workpiece. I ended up getting three more box fans and installing all four into one of my walls and now the ventilation is much better and the pieces are coming out great.

[John TenEyck]

Just a follow-up on the EM-9300. It turns out that most of the "particles" I was seeing were air bubbles. There were some angular looking agglomerates, too, as well as some other trash like colored fibers, but the big offensive stuff was caused by air bubbles. I'll create a new thread after I get to the end of the story with Target Coatings. At this point, I can say that Jeff Weiss called me back in 45 minutes after I left a message with their answering service, and has promised to call me by mid day tomorrow with an update and, hopefully, a course of action.

John