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Old 05-19-2014, 01:53 PM   #1
Join Date: Apr 2013
Location: Southeast Louisiana
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How thick to apply exterior oil-base primer

I need to know how thick I should apply exterior oil-based primer.

I am going to install some new 105 drop siding in southern yellow pine on my house in South Louisiana. I plan to prime with Sherwin Williams Exterior Oil-Based Wood Primer. The wood was kiln dried and has been in my garage for a year. It has a few knots but seems to be a high grade of lumber.

The last time I did a little of this I put this same primer on thick enough to completely cover all of the wood grain. The primer took forever to dry and required an excessive amount of sanding. I plan to roll it on and lay it off with a brush.

Do I need to apply this primer so thickly. I have seen others do just one thin coat, which did not obscure the all of the wood grain, and call it primed. I want to do this correctly, but I don't want to make extra work for myself and create longer-than-necessary drying times.

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Old 05-19-2014, 02:18 PM   #2
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How thick to apply exterior oil-base primer

The primer your using is designed to dry slowly. The re coat time is 24-48 hrs under ideal conditions. To get the maximum benefits of this primer, or any coating, it needs to be applied as specified. The recommended wet film thickness for this product is 4mil. That's a fairly thick coat.

If you want to measure the wet film thickness, a mil gauge can usually be obtained for free from SW if you ask for one. It's very simple to use, looks like a credit card with teeth. You can also get a rough idea by keeping track of the spread rate if the primer. On smooth lumber a spread rate of about 350 square feet per gallon should produce close to a 4mil coat.

Putting on a thinner coat to speed drying time is going to decrease the performance of the product.


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Old 05-20-2014, 10:33 AM   #3
Join Date: Apr 2013
Location: Southeast Louisiana
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How thick to apply exterior oil-base primer

Thank you. I appreciate the advice.
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