Old Trimboards with Grey Coating

Tried alt.building.construction with no luck.
What is it and what was it for?
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House is 28 yrs old. I have found on the trimboards that there is a grey paperlike (?) coating under the paint. It appears to be factory installed. When exposed material gets wet it gets soft and mushy. If it has been wet for a few minutes, a pressure washer will just melt & blow away leaving the bare wood.
Backside 1:
    Backside of board. Grey paper all on front. Wraps over one edge to back. The paper has a thickness and you can slide a razor blade from the bare wood to the paper and get under the paper.
Backside 2: nother backside pic Backside 3: and another.
Frontside:
    Painted side. Although this was found on the exterior trimboards it was also found on some of the old boards indoors. This is from a closet rod bracket which has always been painted around. Grey paper (?) under layers of paint.
Thanks, Al...
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Al Bundy wrote:

Can't say for sure but glued on paper = smooth surface for paint...wood grain/pattern doesn't telegraph through. They used to sell particle board pre-covered with same.
--

dadiOH
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