Woodworker's Journal 2002-26-3, страница 5

LETTERS

Defoamer — or Bug Food?

gently — don't beat air into theiji. Overmixing can decrease the efficacy of the defoamer. Second, micro-foam is a difficult problem to remove. Even some silicone-based defoamers have problems with this: 1 doubt the cream would completely eliminate the problem.

If the finish is for interior use, it will not contain a mildewcide. Putting the cream in your finish is putting food for fungus, mildew and algae into your coating. Over time, this may produce black or green splotches where the bugs are growing. Exterior coatings do contain a mildewcide, but all mildewcides used in clear coatings will eventually leech out of the film. It is best not to have any "bug food" in your finish.

To get rid of microfoam, I'd suggest the following: Tap the can on your bench. Lift it up an inch or so and let it drop. This will help coalesce the bubble. If you can, let the finish sit for a day or two to allow the bubbles to rise on their own. If you must add anything to the coating, try ONE of the following: a drop of mineral oil, a couple of drops of mineral spirits (probably the safest bet), or try spraying a small bit ofWD-40 on the end of a paint stirrer, wipe it off, and use the stick to gently stir the finish.

The defoamer used in urethane and acrylic clear finishes is a careful choice made by the formulators. They take into account the defoamer's effect on gloss, surface tension and clarity.

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A Paint Guy's Thoughts

I just received my first subscription issue of Woodworker's Journal and enjoyed it very much. I did have one bit of criticism regarding the water-based finishes article (Finishing Thoughts, February 2002), however. While I cannot hold a candle to Michael Dresdner in finishing technique, I do know a little about formulating paint.

Mr. Dresdner recommends adding some half and half cream to a water-based polyurethane to get rid of microfoam. He is correct in that the half and half will act as a defoamer (due to the homogenized fat globules in the cream), but it may introduce other problems.

But first, I want to point out that it is much easier to prevent foam than remove it. Always stir clear finishes

In my experience, home remedies are rarely the answer for a long-term solution.

As for my qualifications, I have been in the paint and coatings industry for 16 years, formulating paint for several companies, including Benjamin Moore. I also held the position of senior research chemist for Ashland Chemical in their coatings lab, where my principal job was formulating defoamers for the paint industry. And, I sold biocides for Arch Chemical, which supplied mildewcides to the paint industry.

I have several friends who work hard inventing and tweaking these types of formulations, and they would groan to know that someone is recommending putting cream into their formulas!

Phil Peterson Crown Point, Indiana

He's an Ian Fan

I am a novice woodworker. Really new. Still shiny. Still no finger scars. OK, a little one. 1 read many, many articles looking for a tutor in basic woodworking skills with hand tools. I saw Ian Kirby's instructive articles

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June 2002 Woodworker's Journal