Mildew on ipe, nothing seems to be working

I've had my 1x6 ipe stickered up under a tarp in my backyard since May, and I am slowly working through the pile. Problem is I am now finding mildew spots on the boards, especially where they touched other boards. Not really surprising, it's been a ridiculously wet summer and even worse fall.

However I've searched here and other forums and nothing I do seems to make even the slightest dent in the mildew stains. Evidnetly straight bleach should dissolve it straight away - didn't touch it. Wolmans deck brightener (says removes mildew stains) - not a dent. Another commercial deck wash (also says removes mildew - smells like bleach) - nothing. Sodium percarbonate - also didn't touch it. I've tried each of these products both before sanding and after just to see if it mattered. It didn't.

What gives? Anything else to try?

I clean and seal exterior lumber and just found this site. I have refinished almost 4 million square feet of exterior lumber the past 23 years including redwood , cedar , Ipe and Mangaris. Do not use bleach. Are you sure its mildew and not tannin bleed?

Pretty sure, it is bluish-black, circular spots. Where a sticker board laid on top of one of the decking boards, it's solid, not small circular spots. FWIW sticker boards were ipe, too, they actually bound up the pallets with ipe scraps.

What would tannin bleed look like, and how would I remove it?

None of the products I used seemed to harm the wood in any way, but it also did nothing for the spots.

Without seeing it ...I say its tannin bleed caused by moister...and yes that is exactly what it looks like. Have you tried sodium hydroxide?

Jim,
I don't think so...just went and looked up the MSDS on the Wolman's Deck Brightener and that's got oxalic acid, so I guess sodium hydroxide is the last chemical I've heard of that I haven't tried. Can you recommend a particular brand or ???

Thanks,
D

Never mind, i just realized sodium hydroxide is caustic. Duh. I work with it every day.

Caustic bead mix it 1/4 cup to a gallon of warm water be careful....test a spot medium bristle brush scrub gently rinse it off...you will have to use a wood brightener afterwards as the caustic darkens the wood slightly....let me know. Should do the trick....

Went to 6 different places and can't find caustic beads. What are the chances sodium hydroxide-based drain cleaner will work?

I am not going to say to use it. I will leave that to you. Look up chemical supply houses in your yellow pages....You should find somebody who sells caustic bead in bulk....

You might try looking for a sodium metasilicate or a sodium percarbonate product..