Sticky latex finish

[Doug_H]

Hello

I find that objects tend to stick to the surface of shelves that I painted with water-based interior paint long after the paint has dried -- a year and more. (I much prefer oil-based enamel but I use water-based when the MS fumes would be offensive.) I don't remember whether the products I used were labeled "acrylic" or "latex", but they were from freshly-opened cans. The finish feels hard but acts "sticky".

I'm a long-experienced finisher and always prepare the surface properly.

Do you recognize this problem? How can I avoid it? Is it latex vs acrylic?

I notice that clear water-based acrylic finishes like Polycrylic dry hard and do not have that problem, although on furniture tops, drawers, etc I always apply paste wax as the final step.

Doug

[fredhargis]

I believe you have been using wall paint, at least that's what will happen if you do.. Switch to a 100% acrylic paint...they do have that property, known as "blocking".

[Howard Acheson]

Yes, it's called "blocking'. It can happen with most types of finish but, waterborne exterior finish is particularly problematic.

If you want to use a waterbased finish, be sure it is on that contains "acrylic" on the label. You can apply a waterborne acrylic or shellac finis on top of the "latex" and it should take care of the problem.

[Doug_H]

OK. Thanks very much. I doubt that I used exterior wall paint because the surfaces are gloss or semi-gloss. BTW I "never" buy cheap paint, but I see that my problem was probably choice of paint. But I'll make sure to look for acrylic in the future.

Good to learn something every day.

Doug

Doug

[jteneyck]

Yes, there is paint and there is paint. Some people will tell you not to use latex paint, to only use an acrylic water borne paint. Well, they are both latex. Latex is a generic description for water emulsion of a polymer resin. Polycrylic is a latex. Acrylic water borne paints (or clear coats) are latex. So, you need to know what you are looking for and, as was mentioned, you want a product that is anti blocking. Most trim and enamel paints are anti blocking. Sherwin Williams Pro Classic Latex is one such paint. Too thick to spray w/o an airless, but it goes on great with a brush and flows out very well and dries to a nice, hard film that doesn't block. Benjamin Moore's Satin Impervo is another. Keep in mind that all of these products take about 7 days to fully cure and may block if you put stuff on them before that.

A slightly different approach is to use a water borne lacquer type product. The one I've used is General Finishes White Poly. It can be tinted with UTC's but I've only used it as it came. It sprays beautifully with a pressure assisted HVLP gun and cures to a very hard coating. ML Campbell's Pigmented Aqualente has a viscosity about the same as many clear coats and you could spray that product with a typical gravity feed HVLP gun.

John

[Doug_H]

All,

I have used Impervo to refinish kitchen cabinets. Excellent stuff. I wish I had remembered to consider it. I'll put SW Classic on my "list".

For my latest shelving projects I am using up old latex that probably will block, but I'm cheap and old paint is inconvenient to dispose of in a responsible manner. On the last one, I sprayed a light coat of blond dewaxed shellac on the top surface. It added a very slight yellow tinge, but the top surface of the shelf won't show. For the one I am finishing as I write this, I will finish with a coat of Polycrylic, which I know will dry hard. Maybe I'll add a few tablespoonfuls of the white gloss latex.

I appreciate the advice

Doug

[JR1]

Latex is a marketing term not really a technical description anymore. One problem with waterborne finishes is that it says nothing about the finish chemistry and properties. I have run across one waterborne that requires a catalyst and appears to be an epoxy and GF makes a catalyzed conversion varnish. For all I know there is a waterborne UV catalyzed or Polyester. Another problem is for unknown reasons "Poly" got to be a marketing buzzword and many waterborne finishes have poly in the name but not the chemistry.

Doug please let us know how the shellac over latex works. I would expect it to crack over time if much weight is applied.

BTW paint once dried is no longer a hazzmat. You can pour it out on a painter's cloth let it dry and then vacuum it off or just use old news papers (do news papers still exist?).

[Alan S]

JR1 said:

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"Poly" got to be a marketing buzzword and many waterborne finishes have poly in the name but not the chemistry.

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Actually, it's the other way around. Almost all finishes are polymers and should have "poly" in the name, but for some reason some people believe that only polyurethanes should be labelled poly. That's sort of like people insisting that the only person who can be called "Jim" is the first person they happen to have met of that name.

Polyurethanes were developed in the 1930's, the word "polymer" is about 100 years older, and the prefix "poly" meaning "many" derives from Greek and is much older than that.

As pointed out earlier in this thread, the technical meaning of "latex" is a dispersion of a polymer in water, so it fits almost any water based finish regardless of which polymer that happens to be. Properties of the finish depend on the polymer, so I'm just being pedantic while agreeing with the point you're making.

[JR1]

I was inexact. Poly==polyurethane for most purposes. e.g.Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion. There are polyesters as well. I've no idea why polyurethane got it's reputation for a high quality finish. So long as we take Latex to be an emulsion of a coating in water it is almost useless.

[Woodenfish]

Try using a alkyd latex hybrid paint. They have the resins of a oil base paint but are a latex. They dry very hard which prevents blocking and is perfect for cabinets, doors, drawers, furniture and trim.