- 14 August 2006 -
Painting Problem Solver: Compliance with Specifications
By Ron Joseph, Organic Coatings Editor

Q: On Fed. Spec. 1952b we meet volume by solids but come up short on volume by weight. Is there a problem with this or does this do anything to the quality of the paint?

A: Unfortunately, I do not have a copy of the specification with me and, therefore, my answer is generic.

For the most part, the performance of the coating might be unaffected if the percentage by weight is off spec. Since your volume solids are within the spec, you seem to be pretty close, and perhaps you are using lighter-weight pigments or extenders for which the formulation was originally designed.

From a contractual perspective you do not meet the spec, and if you were involved in litigation the other party might find you liable for noncompliance. You might want to contact the custodian of the specification, whose contact name and address should appear somewhere on the specification itself. It is possible that the custodian will give you a waiver for being under the weight requirement. Alternatively, you might want to have your paint tested for all the physical and chemical properties listed in the spec and verify that you do, in fact, meet the specification performance requirements. At least you will cover yourself in that respect. In any case, you might need to get permission to sell the "out-of-spec" product.

REPAINTING AN ALUMINUM PONTOON BOAT
Q: I have read several articles about prepping and painting aluminum, but the more I read the more I am confused.

I recently purchased an older pontoon boat that was painted with automotive paint, and the paint is chipping off. I would like to remove all the old paint by sandblasting then repainting it. Where I’m confused is after sandblasting the aluminum. Do I use a wash primer, like Alodine™ or Chemfilm™, then a self etching primer, then an epoxy primer, finishing it off with automotive or marine paint? Or, can I use a self-etching primer, epoxy primer, automotive, or marine paint. What is the correct method or are there several different methods? Which method is better? I would like a simple, but durable method that will hold up to the elements. Do you have any idea what prepping and painting methods pontoon manufacturers use?

A: Alodine™ and Chemfilm™ are multi-stage conversion coating processes made by Henkel and Chemetall Oakite, respectively. A vinyl butyral wash primer is not similar to either of the former; however, Plaforization (Carpenter Chemicals) and X-It Prekote (Pantheon Chemicals) are apparently single-stage processes that, in my opinion, are expected to outperform a vinyl butyral wash primer. I have not seen results of tests on aluminum boats for either of these two products, and you would need to get more information on each.

If you apply a conversion coating, such as Alodine, Chemfilm, (multi-stage) or Plaforization or X-It Prekote (single stage), do not apply the wash primer, as it will have nothing with which to react.  Instead, apply the epoxy primer and topcoats. On the other hand, if you do not wish to apply the conversion coatings, then you can apply the wash primer followed by the epoxy. However, you must read the instructions for the wash primer and ensure that it has been formulated for application to aluminum. Too much excess acid in the wash primer can cause the epoxy primer to blister. Application parameters of the wash primer are critical.

PAINT COATING FOR LABORATORY BENCH TOP
Q: We are renovating a lab to study insects. The question of what type of paint is best for our purposes is being debated. The criteria are:

• It must be non-porous, easily cleaned, and must withstand periodically being wiped down with commonly used bleach-type agents;
• it must be very durable;
• and its VOCs must be non-toxic to insects. The insects will reside in cages, and the ventilation rate in the space is fairly high with no recirculation of the air.

A: Either of the two coatings you suggested might work. I would probably lean toward a waterborne polyurethane, which might be more durable. My hesitation in giving you a recommendation is that I have absolutely no idea how sensitive the insects are to any organic vapors. Frankly, before you commence the project, you might expose some insects to the vapors of each of the three coatings and determine if any are affected. If none of the coatings harm the insects then, in my opinion, the polyurethane will be the best choice.

PAINTING VERSUS POWDER COATING
Q: I am planning to have wrought iron fencing installed. It's a large project and one that I would not want to paint frequently (every five years). All bids have specified powder coating versus painting, except one company, which believes that its method, which is to dip into paint, is just as good. According to the company, this will seal all areas, such as welded joints, whereas the powder coat won't. The company guaranteed the paint would last at least 15 years.

How much of this should I believe, and should I request that it powder coat? The company provided that as an option but said even though I could save money, "It's not worth it."

A: The job is only as good as the surface preparation. Regardless of whether liquid or powder coatings are used, you must ensure that the contractor has a well-controlled pretreatment process. The liquid paint might be okay, but will the contractor apply a primer over the pretreatment? What type of coating resin will he use as the topcoat? Have the contractors (liquid and powder) specified the film thickness that they will achieve? Have they specified the resin type? Have they told you how they will prepare the welds to prevent early onset of corrosion? Will they inspect the coated welds for holidays (small voids) to ensure that moisture and oxygen won't migrate to the weld surface? Have they been in business long enough to be able to stand by a warranty of 15 years? In summary, both liquid and powder coatings can do a great job if the coatings are properly applied.

I assume that the coating will be applied in a shop, but if the contractor intends to apply it on site, powder coatings must be eliminated.

The selected topcoat resin must have proven long-term exterior durability, and I strongly suggest that you confirm this by reading the online literature for the coating systems that your contractor recommends.

Ron Joseph is an independent coating consultant in San Jose, Calif. You can e-mail questions to drrojo@aol.com.