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Monday, April 19, 2010

Advice from the Pros:

Why, oh why, did the paint not dry?

Wet paint sign 

There is more to paint than application. To make the point, here is a very short lesson about a very long cure time that could help you next time you paint your basement floor or other enclosed area with an alkyd paint.

The project was inside a large six-story apartment building--one which the painter estimated to take approximately four weeks to complete. In assessing the scope of the job, the seasoned contractor decided to use an alkyd gloss enamel to recoat the high-traffic hallways, stairwells, doors and trim, specifically Moore's Super Spec® HP P22 Urethane for the metal doors and framing.

In this case, the painter followed the first rule of the "SEE" principles for sizing up a project: S for Substrate. He analyzed the type of surface being painted (i.e. wood, metal, drywall, plaster, etc.). The second consideration (E for Environment) calls for looking at whether the space is an interior or exterior, a confined area or an open one, etc. The other E refers to Exposure. In other words, what are the conditions that the coating must endure in terms of temperature fluctuations, moisture levels, abrasion, traffic and/or chemical exposure?

As the project progressed all went according to plan--or at least appeared so until the "Wet Paint" signs came down some time after the finish's requisite drying time. Although the paint film had been dry to the touch for several days, it remained a little soft and was easily marred upon impact. Small dings and dents appeared around doorknobs and along door frames where keys, bags and briefcases contacted the finish.

Here's where paint chemistry comes in: The reason for the soft film had to do with the building's narrow hallways and poor ventilation (ie the Environment). Because it dries by oxidation, this alkyd enamel coating requires interaction with oxygen molecules to properly dry--and cure. (Other types of finishes dry by evaporation, coalescence, chemical cure, etc. See product specs on the MSDS of paints you use.) Since the film's initial drying phase was impaired by inadequate ventilation, its curing process had been stunted. To fix the situation, the contractor still had to repair and repaint the damaged areas but this time he made sure the work area got additional ventilation--something to bear in mind when using alkyd paint in an enclosed area, like a boiler room or a basement.


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