Our redwood house has been oiled with shingle oil for 40 years and is turning black. We can rub the boards with a dry cloth and the black comes off. What can we finish it with that will not turn dark? Can this house ever be painted?
The black is most likely mildew. A mild solution of bleach and water applied should remove the mildew, temporarily.
As for painting, if you have allowed at least 5 years to pas since oiling the surface, a normal application of an alkyd primer followed by 2 – 3 coats of exterior acrylic house paint should be fine.
I am not certain alkyd primers are available in California, so visit your local paint dealer and ask for suggestions.