after staining my co. spruce logs, twice the last 6 years, it is turning black in areas not covered, steaks are terrible. it looks like mold but a simple bleach soloution doesnt touch it. the product was cuprinol. ive seen this on other spruce cabins in this area. hot,wicked sun, and very high hummidity. ive done plenty of sanding in my life, please no more. youre help would very appreciated. thanks scott