Cold Weather Flowout Issues

      Troubleshooting a pinhole problem when spraying in a cold shop during winter. May 17, 2010

Question
I am getting tiny pinholes in pigmented material on vertical surfaces. I feel the material is not blending together and leveling well (all clears on verticals are fine, just paints). My coat thickness is fine and if any thicker, sags and runs begin. On horizontal surfaces such as frames or doors, I probably mask this problem by piling material on enough to where it flows. Before winter, this was not a problem without thinning. Yes, my shop is cold, as well as my wood, buy why do all my clears spray fine with this same setup? Clears are thinner in nature, so should I thin my paints as a quick fix?

I currently spray with a Graco AAA FinishPro 395 and ML Campbell material. The gun rep stated "no thinning" as a selling feature - this was one reason for my purchase. I use the High Performance Pre-Cat line for all my clears and paints, which is referred to as the new baby MagnaMax.

The only thing I use is space heaters. I do heat my products after I spray to speed up drying, but that's it. I run the heaters before spray, but this does only so much. I use power blankets pail heaters to heat my fluid and if I had to guess, my fluids are close to 80 degrees before the line and to the tip. As winter begins, using these heaters became a big help, but paints have become more of a challenge.

So what gives? It's impossible for my shop to be heated and sustained to 70 degrees for spraying, so would thinning alone help level and hide my problem? Again, my clears are fine horizontal and vertical, as well as paints horizontal. I may buy a 130 degree heater as opposed to my 90 to account for loss of heat when the paint reaches the wood.

Forum Responses
(Finishing Forum)
From contributor C:
When a sales person states "no thin necessary," that is based on using the material at the temp/humidity/etc. that was tested at their labs. When those parameters change, you do what they tell you to do - so contact them or wait till someone who is spraying in the exact same circumstances using the same setup as you responds.

Just so you know - the temp of the air/sprayed work/material should not be more than 10 degrees in difference for best results. This is before/during/after.



From contributor L:
Thin it. It is winter and if you don't have a temp controlled area to spray in, it is likely cold. The other reason may be air flow in the drying area. If the product is skinning over, you may be getting solvent pop. If you have any fans in the drying area, make sure they are not blowing on your drying product.


From contributor R:
If the bubbles are caused by drying too quick or a draft, then a little lacquer retarder should slow dry time, allowing trapped air to escape. I had that problem one time or ten, and that worked for me.


From contributor C:
Talk to your supplier. Retarder can work, and so can thinner. In warmer weather I use retarder; in colder weather I use fast thinner high in alcohol solvent. Butyl cellosolve or other slow evaporative solvents in cold weather can cause more problems than they solve.

From the original questioner:
As far as solvent pop, I know for sure it's not that. In the summer I battled this on oak and cherry, which was another headache. If you take a pencil and push in the finish after it's dried, this resembles what my finish looks like. On flat surfaces when I see these, I just shoot another coat or spot hit to force the coat to level. On vertical surfaces I just can't do this. I have spoken with my ML rep and he said thinning should help, and for my material I should be in the 26-32 seconds for Zahn 2 cup. I don't have a viscosity cup yet, but after I purchase one, the thinning will begin.


From contributor C:
Did you tell your rep how cold your space is? Is your product recommended to be sprayed at that temp? Most pre-cats I've used from SW and others state not to apply under 70 degrees for proper catalyzation.


From contributor O:
I've had the same problem a time or two. One thing you may look at is air entrapment; if you have air in the material hose you can actually spray tiny bubbles out. This usually happens when you are low on material. Make sure you flush out your line completely, then start over and see if that stops the problem. I'd agree on thinning the material some as well with your temps.


From contributor N:
After finishing for 17 years I don't know everything, but after living in Fargo, North Dakota for 40 years, I have learned a little about finishing in cold shops.

Since you said there was no problem before winter, there may be no problem with your products. I'm a long time ML Campbell fan and MagnaMax is a great topcoat. I have never had any problems with their Resistance or Stealth pigmented products.

I have found heating lacquer to 80 degrees may be a little high. In the summer lacquer at 70 degrees works just fine. Warm lacquer makes for great gun flow and fan control, but when that very thin coat of lacquer hits that cold wood, it cools fast, and flow can almost stop if cold enough.

That's when thinning comes in, but be careful with the balance between heat and thinning - too much of both and you will have uncontrollable runs. I favor a little heat and a well managed recipe of retarder and thinner. A mix of each for each situation will vary.

A red flag did pop up when you mentioned heating with a space heater. Up north we live with these heaters and learned quick about the oily fuel film left behind. Some fuels burned in these things are worse than others, but all can contaminate your finish.

I grew tired of compensating for the cold instead of actually finishing. I'm now finishing in Nashville, TN.

One other thing - I have never run across a situation where the gun I'm finishing with dictates if I thin my product or not. At best, I may have to change the tip. Try not to believe everything that comes from a salesman's mouth and I think you'll be better off.



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