I have been a professional house painter for many years and finally shut down my painting business last august to pursue designing gardening web site and producing garden videos full time. My personal prefrence would be to use a solid color stain to paint a fence. This only requires two coats, and will normally outlast paint since it penetrates the wood, where paint is only covers the surface and will peel.
If you have a dark stain on a storage building, then you need to use a primer/stain hider. If the current stain is oil based then I would prime with Zinnser BIN (tinted toward the color of the top coat), if the current stain is latex then I would use the Zinnser 1-2-3. Sometimes these dark stains do require 2 coats to cover them enough so that when you appley two top coats you get the color you want without the bleedthrough..Then I would paint the buidling with Sherwin-Williams Supepaint latex. Paint the siding with a satin finish and the trim with a gloss or semi-gloss.
A lot of these storage buildings have T111 siding that will suck up paint in a big way. You will definately save a bunch of money by priming first since primer is much less expensive than quality top finish paint. The primer will seal the wood so that the paint goes on easier and not require as much.
Bobby Baxter Happy Moose Garden
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