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I have some fiber cement board that I need to paint on the side of my building. Painters and manufacturers recommend 100% acrylic paint but I need to use solvent based paint to match the rest of the concrete building that's not covered by fiber cement board. I live right next to the ocean so I'm using solvent based paint to prevent mildew and stains from the ocean spray salty mud around my home.

I read here on cement.org (very authoritative site) that you can use a water based primer on cement board and then apply oil paint onto it. I also read here that you can use water based/acrylic primer and then topcoat it with oil paint.

These are my only two sources so far telling me I can do this but I've also read people say not to use water based primer with oil based topcoat many times. I do know that the GOLDEN RULE is to never use oil based paint over latex paint. Some "water based primers" are actually just self priming latex paint, thus that's why you can't you oil paint over that and I'm thinking that's why most people just say "don't use water based primers with top coat oil paint."

Can I have input from some people?

Additional Note: I already bought the Solvent Paint and can't return it. So I will test it in a small section but I'm not sure what to "look for" when trying to identify if this will be a NO GO. So, what to I look for to make sure I can proceed?
 

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Hmm everyone suggested not using it, any cement based siding company I've ever installed also suggest 100% latex paint only.
Just makes no since to me to use oil based paint.
Oil over a latex primer is just not going to work.
As long as the color and sheen matches what difference does it make if it's oil or latex?
 

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What makes you think mildew wont be present on oil? Mildew will grow on any surface that doesn't get sunlight and stays damp for most of the day. Use an acrylic and wash it once a year.
 

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Hey Foxman...

Part of your problem is you're getting advice from the wrong people...To begin, there is nothing wrong with using an acrylic latex primer beneath an oil topcoat for the type of structure you've described. Every manufacturer in the nation (and beyond) states that their latex primers may be topcoated with any conventional, architectural coating - including oils. ...and that is what you're using, right? You've mentioned "solvent-based" and "oil paints" - and they're not necessarily synonymous terms.

For cement board, you really need to use an acrylic, or latex primer - especially in the environment you've described. An oil primer application could lead to disastrous results... But you have chosen an "oil" finish to fend off mildew and salt staining? As Red Dog said "what makes you think mildew won't be present on oil?" - and it will be. The truth is mildew is far more likely to grow on an oil surface than an acrylic surface, because of the organic make up of the oil products...Oil base paints actually provide a food source for mildew, where acrylics do not. That's not to say mildew can't grow on an acrylic surface, that's just saying that an acrylic will not contribute to mildew growth as an oil based film will.

Also, acrylic products will perform fine in a salt air environment - actually better than oils will. Oils soften in caustic environments way moreso than acrylics will - and, as far as exterior paints go, there are few environments more caustic than a salt air environment.

Finally, regarding the "Golden Rule" of painting....um - not so true these days...and not for the structure you're painting. That rule pertains more to wood surfaces than concrete, due to wood's annoying expansion and contraction issues...If after everything we've discussed, you still opt to finish with an oil, you'll be fine with an acrylic, or latex primer (as long as we're talking "oil base" paints, that may be different with "solvent base" paints - depending on resin types and solvent structures). ...And, as already mentioned, virtually every manufacturer in the known universe sells their acrylic (or latex) "universal bonding primers" as an appropriate coating for beneath oils, latex, acrylics etc.
 

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Hey Foxman...

Part of your problem is you're getting advice from the wrong people...To begin, there is nothing wrong with using an acrylic latex primer beneath an oil topcoat for the type of structure you've described. Every manufacturer in the nation (and beyond) states that their latex primers may be topcoated with any conventional, architectural coating - including oils. ...and that is what you're using, right? You've mentioned "solvent-based" and "oil paints" - and they're not necessarily synonymous terms.

For cement board, you really need to use an acrylic, or latex primer - especially in the environment you've described. An oil primer application could lead to disastrous results... But you have chosen an "oil" finish to fend off mildew and salt staining? As Red Dog said "what makes you think mildew won't be present on oil?" - and it will be. The truth is mildew is far more likely to grow on an oil surface than an acrylic surface, because of the organic make up of the oil products...Oil base paints actually provide a food source for mildew, where acrylics do not. That's not to say mildew can't grow on an acrylic surface, that's just saying that an acrylic will not contribute to mildew growth as an oil based film will.

Also, acrylic products will perform fine in a salt air environment - actually better than oils will. Oils soften in caustic environments way moreso than acrylics will - and, as far as exterior paints go, there are few environments more caustic than a salt air environment.

Finally, regarding the "Golden Rule" of painting....um - not so true these days...and not for the structure you're painting. That rule pertains more to wood surfaces than concrete, due to wood's annoying expansion and contraction issues...If after everything we've discussed, you still opt to finish with an oil, you'll be fine with an acrylic, or latex primer (as long as we're talking "oil base" paints, that may be different with "solvent base" paints - depending on resin types and solvent structures). ...And, as already mentioned, virtually every manufacturer in the known universe sells their acrylic (or latex) "universal bonding primers" as an appropriate coating for beneath oils, latex, acrylics etc.
Alkyd or "oil based" paints are the caviar of the paint world to mildew. Years ago alkyd paints were used in areas of high mildew because they would hold up to much more scrubbing and bleaching than the older generation acrylics (water based) paints. That is no longer the case, in fact most premium exterior acrylics have mildewcides in them, and none of the alkyd paints do. At least none that I have ever seen. Add to that the fact that premium acrylics are much more color stable and much more chalk resistant than alkyds, and there is no reason whatsoever to use an alkyd in this situation. Listen to people who have actually been in the paint business in the last twenty years and not people who haven't touched a paint brush or sold a gallon of paint in over thirty years.
 
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