A company I worked for in Hawaii uses an oil primer on the ext. of houses and follows with latex paint, because the oil primer “seals everything up better”. Im building my own house now in a fairly wet and cool (for Hawaii) area, and I’m hearing that oil is more likely to mildew. Should I stick with the oil primer, latex paint formula that my former employers used, or go latex all the way? Also, I need to consider that I’m using borate treated wood, which Ive been told, must be covered with something that is not water based to avoid leaching of the borates over time from exposed areas like the soffit and deck railings etc…
Thanks for any experienced input
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I don't know about borates--maybe to seal them you should use something like Kilz or even pigmented shellac--don't know how the latter would hold up outside though. In most cases though, I've read that latex "breathes" better than oil-based, so water vapor would go in and out better through latex and not bubble the paint--and if it does, the paint will flatten out again when the walls dry out--latex is more flexible than oil and will not crack and flake off.
Several years ago here at BT we had a long and excellent disccussion of this topic as latex was becomming more prevalent.
to sum it up - many of us agreed with the pratice of your employer.
Here is why - The oil cures slower so it can somewhat penetrate and bind with bare wood especially for a primer coat. it is also a waterproof coat once cured. Latex will allow moisture to pass throguh over time and/or pressure.
Latex has proven to be better at resisting UV now that oil paints have had all th egoodness legislated out of them and the laatex paints have improved immeasurably since I first saw them thirty years ago, so they have come to be accepted for exterior use where they were once rejected by the quality conscious builder.
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Forgot the borate thing.
I don't think that is a concern either way unless you left it natural with no finish. Water will leach borates, but you will not have much water moving through the wood under any painted finish.
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