I painted a front wrap around porch that my husband put on made up of treated lumber decking and post and spindles,against my husbands advice, he wanted my to wait till the next season and age it, I simple couldnt wait any more than the 5 yrs it took to put on the porch, anyhow--a black mold spoting that is very dry but doesn't come off is coming thru the white posts and picketts. This was a latex white stain we used. We tried stainkill but its not working, I also wiped with a mixture of bleach and soap 2 years ago,but now is thru more than ever. I plan on cleaning and repainting all picketts and posts but need to kill this black coming thru first. Any suggestions?