Blushing or Spray-Can Touch-Up Pre-Cat

      Working in hot conditions, a finisher reports that spray-can touch-up lacquer started to show blushing as the space warmed up. Pros advise on corrective measures. August 26, 2006

Question
Iím doing touchup work in Las Vegas in a high rise tower under construction. Todayís temperature is low 87, high 98 with humidity 15%. HVAC is not running yet, no open windows! Iím not sure what the inside temperature is, but the glass clad 33 story building is a pretty fair green house. We are using Mohawk pre-cat (spray can) to seal repairs, etc. Early in the morning, we have no problems. Still early, but when warmer, the pre-cat began to blush. This is a new problem for me. Please advise with the correct material and methods. I don't use or have a spray gun for this work. I noticed there are three different types of spray cans -no blush - in my Mohawk catalog. My dealer was out of it. Not sure how to use it, or if that is what I need?

Forum Responses
(Finishing Forum)
From contributor A:
Two suggestions - First is to see if your supplier has any of the retarders, and if not then see if he has "Blender Flo Out" in an aerosol, I think the number is 103-0419.

Now, here is one that you may have never heard of, but you won't be the only one. Give it a try, but first test it with extra care. Ask your wife for a can of hair spray, or buy one. Shake it up good, and then spray it on the blushing. It may take a few applications to pull out the moisture. There is no guarantee, as there is blushing, and then there is BLUSHING. Let us know if it worked for you.



From contributor B:
If you're going to be working there all summer order the no-blush from Mohawk. They have plenty of it in their warehouse. I call it the finisherís friend. I don't go on a touch-up job without it. It will take care of your blushing problem. Just fog a little on your wet lacquer and it won't blush. On areas that have already blushed, spray it on heavier (wet coat) and the blush will go away. I also use it when I do shading with aerosols - wet the area first with no-blush and shade over the wet area. The wet no-blush allows the speckles from the spray can to flow out to give a much more even look.


From contributor A:
That's exactly what "Blender Flow Out" is intended to do. BFO also contains some solids plus the slower retarder.


From contributor C:
With 15% humidity I wouldn't expect blush either. Is it really 15% inside or more like a hot, humid green house? Behlens Blush Eraser is the same as Mohawks No Blush and is usually more available over the counter. I think both Rockler and Woodcraft carry it if they exist where you are. I've gotten blush when I didn't give stain enough time to dry or when the surface is contaminated with wax or oil. Be sure your surface is clean and dry. Mac's hair spray will probably work (it's a little lacquer with a lot of solvent and propellant) but I would lightly abrade the surface first. Iíd suggest unscented or you may find friends you'd rather not have. And if all else fails, abrade the surface lightly and wipe the area with a lacquer thinner dampened cloth; let it flash and repeat until the blush is gone.


From contributor A:
I would be very careful with trying to wipe lacquer thinner or denatured alcohol to remove the blush. Itís very possible you may do more harm than good. Whenever you are doing your aerosol repairs, you must only make one pass, and then wait for the coating to flash dry. Do not use multiple repeated passes, because this will retard the exiting late solvents and actual cause the moisture to be trapped.

If the hair spray doesn't work, you just might be better off waiting to get some aerosol retarder. You might want to try some other options, like padding the damages. Maybe padding lacquers would be better for you. Another option is Pour and Wipe. This is an oil base wipe on finish. A third option is to try Finish Up, another wipe on finish that is a waterbased polyurethane.



From the original questioner:
Thanks to all of you for the good advice. I found some aerosol No Blush at another store. Just what I needed.


The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor K:
Blushing as I've always understood it is a moisture issue. The problem you're having is likely caused by the material drying between the can and the work. One way to combat this is with Mohawk or Behlens no-blush.

To avoid burning through $6 cans try this: Spray your touch-up, and then immediately spray the outer perimeter with NB. In areas with wide overspray or heavy touch-up coat I sweep from the center outward with the NB starting far away and sweeping in toward the work. This keeps from over-wetting the repair, causing runs, while providing enough to flow out the dry droplets on the perimeter.



Comment from contributor D:
A method to deal with blush is to heat the blush with a heat gun and the blush disappears shortly. Itís safer than a solvent, and faster. The heat allows the moisture to evaporate. My encounter was at 80 degrees in the shop and 90% humidity. The second coat of wax free shellac sealer (isopropyl alcohol base) and blush showed up within ten minutes. A redo was almost certain so I had nothing to lose with the heat gun (or hair dryer) and it worked.



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