Last year I had a deck built in my backyard of Garapa Gold, a beautiful golden toned tropical hardwood. We put 2 coats of Penofin for hardwoods on it (the lumber yeard's recommendation)- first on the boards before the deck was built (May), then another coat in September. Now the deck is a mess- it's covered with what appears to be a dark mixture of grime and mold, which is uneven and flaking off in some places. From doing web reading it seems as if I should powerwash/clean, possibly brighten, then reseal. But I do not want to use the Penofin again; with the mold problem (there's a mixture of sun and shade, and there was tons of snow this year) I should not use an oil based sealer again, correct? One contractor wants to charge me a ton to resand the whole thing...another says use a deck cleaner and scrub adn then evaluate, another says just try powerwashing first. What exact procedure and products do you recommend? My long term goal is to be able to do as little maintenace as possible- one suggestion has been made to NOT use any sealer, and just let it turn to silver naturally, although the wood is so lovely that would be a shame...maybe for down the road if the yearly maintenance becomes too much for me to handle on my own.
Thanks so much,
mhg

Very good questions.

Problem with Hardwoods such as Garapa is that it is extremely dense. This wood will require a annual coating. To fix your scenario I would suggest:

1. Strip off the Penofin using a biodegradeble stripper. This softens the Penofin so that a "low" pressure wash will remove the coating, blackness, and mold
2. Use a wood brightener to neutralize the strippe
3. Apply a water based sealer that is designed to penetrate hardwoods.
Defy Stain for Hardwoods

This stain will drastically reduce any issue of turning black from mold and mildew. The Defy can be cleaned and recoated easily.

Do not sand the wood as this is a waste of time.

Do not powerwash without a stripper