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Unfinished spruce clapboards over rainscreen system

Kyle Arve | Posted in General Questions on

Hi, looking for thoughts and opinions on using unfinished spruce clapboards over a rain screen system. Durability? Weathering? Mildew?

Will sealing with a waterproofer extend the life of siding or is air gap enough to do that? 

Furthermore, does anyone have experience with Vermont Natural Coatings penetrating waterproofer with juniper on exterior siding?

Thanks a lot.

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  1. Expert Member
    Malcolm Taylor | | #1


    Where are you building?

    1. Kyle Arve | | #3


      1. Expert Member
        Malcolm Taylor | | #4

        I'll let the New England contingent weigh -in. Out here in the PNW it wouldn't be an option, but perhaps your climate is more forgiving.

  2. Keith Gustafson | | #2

    unfinished spruce is probably not the best bet for longevity. I would think they are primarily intended to be painted, but I could be wrong.

    VG cedar would last forever........

  3. Expert Member
    Michael Maines | | #5

    I've installed spruce clapboards, from the Ward clapboard mill. Spruce has essentially no rot resistance without a finish. Even if installed on a rain screen they won't last long--maybe ten years before they start failing. I use spruce leftover framing lumber for outdoor projects regularly, and even above grade where the wood can dry readily it does not last long. That's fine for my projects, which are intended to be temporary, but you want siding to last more than a few years.

    Clear "waterproofing" sealants don't last long. You would either need to recoat regularly or use a finish with a pigment that protects the wood from UV exposure.

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