Replies

1. 
   piffin_ | Dec 07, 2001 04:15am | #1

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   Thirty days is standard. Get an alkyd paint and read the label.

1. 
   Jeff_Clarke_ | Dec 07, 2001 07:10am | #2

   *I agree with the 30 days (minimum) but not the alkyd recommendation (no offense Piffin). IMO this is a typical situation for a high-build primer-sealer and an acrylic top coat, not alkyd.Click here for Sherwin-Williams product selection for this, and any other material condition.Jeff

1. 
   Wayne_Law | Dec 08, 2001 12:53am | #3

   *As an engineer, I researched this topic before painting my cement siding. You should not use oil based paint on cement. There are two reasons not to. 1. When fats and oils come into contact with alkali, a chemical reaction takes place turning them into soap. That's how they make soap -- lye and fat. Cement and paint oils will do the same thing, and the result is peeling. Quoting fromi Paint in Americapublished by the National Trust for Historic Preservation: "Oil paints are attacked (saponified) by alkali. ... Today the recommended practice in painting fresh plaster or masonry is the application of an acrylic 'latex' primer or some other type of alkali-reisitant primer." 2. Latex paints are more durable than oil based paints. Quoting again from the book, "Resins used in [latex] generally have much higher molecular weights than resins used [in oil]. ... Because of the inherent chamical stability of good acrylic resins and because of the high molecular weight of emulsion resins, acrylic emulsion (acrylic latex) paints offer by far the highest degree of weather resistance of any type of paint in common use today on American buildings." He goes on to say this is not true when going over old, chalky paints. Of the three kinds of "latex" paints, he says that the 100% acrylic is the best: "The principal synthetic polymers that have been used in emulsion paints are of the acrylic, poly vinyl acetate, and styrene-butadiene classes (and combinations of these). The molecular structure of good acrylic resins renders them more resistant to oxidative degradation than styrene-butadiene and more resistant to water than poly vinyl acetates. They [acrylic] are generally considered the best class of emulsion paints for general architectural use." The label requirements about not painting when the surface or air temperature is too cold should be followed. Below a certain temperature, the water from the paint will still evaporate, but the emulsified latex particles will not come together and form a film. The result is paint that looks dry but will not stick.I recommend waiting till spring if it's an outdoor job.

1. 
   jurassicjockey | Dec 09, 2001 06:09pm | #4

   *Thanks for the answers.

2. 
   jurassicjockey | Dec 09, 2001 06:09pm | #5

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   I just parged the inside of a stone wall and now it needs to be painted. How long do you recommend I wait before I paint

   Thanks