prepping siding for paint

Hi Folks,
We have scraped and sanded loose paint from our cedar siding, primed exposed wood and are ready to begin painting. Problem is our siding is covered in a thin layer of dust that refuses to come off when using a high pressure garden hose. Is our only option to take a damp sponge to each piece of siding? This seems pretty labor intensive, but we want the paint to adhere well so we may have to go this route.
Thoughts?
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Maybe it's dry wood, not dust. Does it really come off with a sponge?

exposed
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adhere
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If the siding is sound wood, meaning if you use a wire brush and remove the oxidation, washing with a hose is enough. A little dust is normal. Use oil primer and latex paint, or consider stain
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I have always washed chalked paint off with a sponge and detergent (that's what the dust is). But if you have pressurewashed everything, the new paint will probaby bond ok.

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Mitch A wrote:

Can it be oxidized primer - primer been on a while? Try some kind of detergent, like TSP? Scrub with brush on extension, rinse.
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Cedar always has dust, I will bet your previous finish was stain , you washed , now stain or prime , with oil not latex and paint
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