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mark faultersac 09-28-2011 04:49 PM

mold on the bottom side of the roof deck overhang
Looking for anyone that can explain why mold occurred on the bottom side of the roof deck overhang, between the rafter tails.
It is an open overhang, so no soffit. Black roof. The mold is on the back side of 3/4" exterior plywood which replaced original 80 year old deck 11 years ago. This playwood was painted with oil based Sikkens Rubbol DEK. This mold is occurring on all orientations of the house. It is a gambrel roof, dutch colonial style. A detached garage with the same style overhang has the original wood deck and has no mold. I originally thought that the sun was driving water vapor slowly through the shingles, wood deck and it condensed on the back side.

jsheridan 09-28-2011 05:55 PM

Hey Marc, is the original decking overhang on the garage painted with the same Rubbol DEK as that on the house?

TimAllen37 09-28-2011 06:24 PM

i would try cleaning it off yourself the best way possible, and maybe put some type of abrasive cleaner

mark faultersac 09-30-2011 10:31 AM

No it is not. It probably has about 5 coats of paint over 80 years, the last of which I know is latex

jsheridan 09-30-2011 12:52 PM

Then I'm venturing to say that the Rubbol of eleven years ago had linseed oil or some other oil that is a favorite food of mildew. Been there, experienced that. Hit it with some bleach/water, rinse and kill it off.

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