On 3/17/2020 1:01 PM, Robert11 wrote:
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How really "necessary" is pressure washing ?

Absolute.

Wouldn't the new paint just cover up any dirt on the existing clapboards ?
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So you're going to waste the paint to put it on the dirt as a substrate.

If it's been very long since it was painted and has therefore oxidized,
not only should it be pressure washed but to have much hope of lasting,
use triphosphate or the like. Weathered wood, even if clean, will not
take paint.

There are some specialty products for the purpose but they ain't cheap.

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