Finish Turns White When Applied

A clock-maker learns to fight the milky-white blush that comes from finishing in cool, humid conditions. December 6, 2011

Thirty years ago when we were making clocks, on very hot, humid days when applying finish, it would turn white and the gloss would disappear. The cure was to use a retarder in the finish mix.

Now I have restarted the clock business. I do not have the cash to go with the professional spraying systems I had all those years ago, so am relying on rattle cans for the finish. And actually they do make a pretty nice finish.

But the humid day problem has arisen again. The finish sometimes gets all milky, and loses its high gloss. Is there anything I can do to cure this? Should I make a small area to do the finishing in, and put in a dehumidifier?

Forum Responses
(Finishing Forum)
From contributor R:
Finishing with rattle cans can yield some fine results. But the cost can add up if you use a bunch of them. It's your call to continue to use them but if you do, I suggest you get a couple cans of no-blush.

Something else to consider would be to set your cans in a pot of hot/warm water prior to using them. Once you spray your clock, you could briefly hit it with a hair dryer to coax the drying time.

From Paul Snyder, forum technical advisor:
There are a couple low cost solutions you can use. The first is to get some Mohawk SuperBlush retarder aerosol spray and apply it over the blushed lacquer. The second is to buy some retarder (e.g., MAK) and use a Preval aerosol sprayer from the local home center. The Preval has a bottle you fill with whatever you're spraying and an aerosol canister that screws to it. Apply the retarder very lightly. Once you spray the retarder, do not touch the item for at least a few hours.

From the original questioner:
No-blush... Will look for it. Warm cans... I tried that, and if anything, it seemed to be worse. It seems the finish gets milky when it's hot and humid and the finish dries too quickly. Once I tried outside, and it was worse on a hot humid day and a breeze. It almost looked like white paint.

From contributor I:
How big are these clocks you are making?

You should be able to pick up a decent spray setup used for short money. Then you can mix the finish the way you want/need and certainly save money in the long run buying it in gallon or 5s than all those cans. I can completely identify with money being tight after these last few years. If you watch eBay or even Craig's List you should be able to get a used HVLP for under a hundred that will give you decent service and good results until you can get something better.

Also, don't know if this is related, but one cabinet shop I worked at we sprayed ML Campbell pre-cat lacquer and, especially this time of year, would get the white film a lot on mahogany and other open grained woods. If we let it sit for a day or so it would settle back to clear and would be fine. Have you tried letting the clock sit for a day or so to see if the finish goes back to normal?

From the original questioner:
Yeah, and sometimes it clears, and sometimes it doesn't, but even if it clears, the gloss level is affected. The size is small with many tiny parts and hundreds of nooks and crannies. The clock is 15" wide, 6" deep, and 11" tall.

From contributor I:
For projects that size I would get an airbrush. You can get a decent one of those for about 50 bucks.

From the original questioner:
I always thought of using something like that, but I have never used one. I'd be starting from scratch - no air compressor - so it would be over 100 bucks for something unknown. I know what a full sized gun sprays like, and of course what rattle cans spray like. How does the air brush compare?

From contributor I:
They spray like a touchup gun. You can get up to about a 1-1/2" fan down to a micro pencil line. Easy learning curve.

There are a lot of videos on Youtube. Most will show different techniques, but the principle is the same for what you want to do.

The big benefit is that you can mix your finish the way you need to and then apply it. If you don't have a compressor, you will need one, but you will still come out far lower than buying a full size spray setup. And for the size of your projects that may be overkill.

Search eBay for Paasche - there are some great deals. I would get one that has the different size cups as opposed to the gravity feed. It will give you a little more flexibility.

From contributor T:
I suppose it goes without saying, but.... avoid finishing on a humid day. As I recall, evaporating lacquer thinner drops the finish temp about 15 degrees. If dew point on the day you're finishing is within 20 degrees of the ambient - don't finish. If you do, the cold finish temp will absorb moisture from the air and blush.

No Blush and Mohawk's Super Blush Retarder work well. Another brand calls it Blush Eraser. Remember that these also require a lower dew point in order to be effective.

Airbrush will work too. However, I've found an automotive touchup gun (very cheap) works very well for smaller pieces. Obviously you will need a small compressor.

From contributor J:
The milkiness is moisture trapped in the finish. There are lacquer retarders that will slow down the drying time of the coating, thus allowing the moisture to be released from the finish. Personally I hate adding this as it does tend to tweak the sheen of the finish. I've always had success spraying lacquer thinner out of a cup gun onto the cloudy finish and this works great at releasing the moisture back out of the coating. I've used the heated air assisted sprayers and they work fine but are expensive. Wait for better climate to spray or invest in a little better equipment.

From the original questioner:
I just happened to get lucky, and a dehumidifier the other day appeared on freecycle and I grabbed it. I set it up in a small room and let it run. The dew point out of the room was about only a 10 degree difference from air temp, but in the small room it was able to drop it to 20 degrees below. I tried a control sample out of the room, and got fog. Went inside, and perfect - no trace of milky fog. Thanks for the heads up on the 15 degree drop thing. It works.