It truly pains me to have to ask this after being absent for so long, but I have a bit of a problem, and hope that you kind people will help with a good solution. Rebuilt a fairly large deck last summer for a good customer, using pressure treated 2 x 6 for the deck material. The homeowner coated it after about two months in the mostly dry heat, using Thompsons tinted deck sealer. Two pretty thick coats I think. Now we have black spots showing up almost every where. The questions that I have are related, is the black under the stain, or on top? If under, what is the best way to remove Thompsons, or are we going to end up painting over it to hide it? If on top of the stain, how hard can I clean before I end up restaining to hide the damage? Will any of the Good Finishes go over the existing mess, or are we stuck? Help please, these folks deserve a good result, and I am feeling guilty over letting them finish it in the first place.
Dan Olson
PS We are located in Hawaii, where warm and humid is the common condition.
Replies
It has been said in some reviews of deck sealers that some use a chemical (mineral oil?) that promotes mold growth.
I suspect that the black spots are probably a form of mold and are probably on top of or in the sealer, but that's just a guess.
I would be careful about using the word mold, though, and with devising your plan of action, until you have considered all of the ramifications of the use of that word: emotional, physical and liability-wise.
If you don't get expert answers here, first read the pages at http://www.epa.gov/iaq/molds/moldresources.html , keeping in mind though that those pages address issues of Indoor Air Quality, not Air Quality on Decks, then break out the TSP, gloves and goggles and elbow grease and experiment.
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It lindseed oil, Bob
And call it fungus or mildew rather than mold, that is it is not sap/dirt.
If it is surface fungus then bleach should clean it. Soap and water if it is surface sap/dirt.
If it is in/under the finish then uses some Deck Refinsisher/Cleaner to remove it and the Thompsons.
By next year the Thompsons will be gone anyway.
Thanks to you all for the reply's, and hopefully good suggestions. No trees within striking distance. Probably some dust from area construction, but these a re definitely black spots of some sort. I am hoping against reason that it is on top of the finish, so as to escape the removal process for the Thompsons. I think that it may have trapped mosture into the lumber and caused mold/mildew/crud to grow. I will keep listening for a miracle cure if you happen to know of any.
Dan
"I will keep listening for a miracle cure if you happen to know of any."
Yes,
The deck finish remover comes in a concentrate. Mix it with water from Loures.
how big are the spots?
the construction dust.... could it be small fragments of steel that got trapped between the finish and the PT wood?
with the steel dust trapped and a little bit of water causing the steel to blacken the wood?
dan, is this deck out in the open or are there any overhanging trees?
Remodeling Contractor just outside the Glass City.
Quittin' Time
Bob and Calvin bring up two logical points. Try a bleach sloution (staring in a small, inconspicuous area) to see if it kills possible mildew growth, and look for sources of sap and such from trees. I built a nice deck this summer with expensive composite decking that was promptly spotted with sap from the white pines over head.
Al Mollitor, Sharon MA