Deck products, especially the ones with linseed oil are a perfect food choice for mold. Though the Cabot's offers a decent mildewcide, it is not iron like in it's resistance to growth.

Make a fine solution of household bleach and water. Try two cups of household bleach to one gallon of water. Let it sit on there for twenty minutes..Rinse well..then rinse again

Thanks pressurepro...does it make any difference whether it is an oxygen based or chlorine based bleach....?

oxygen based would normally be preferable, but it will be more time consuming and you need to be careful as it may strip a bit of the ATO off ipe when mixed strong enough to kill mold. This is one rare case where I would say used regular sodium hypochlorite.

This makes me very nervous. Is the mold a common problem with the ATO?

It's a common problem with all oil based sealers ATO, TWP, Sikkens, Superdeck etc.. But yes, the type of oil needed to penetrate hardwoods is more susceptible to growth. You have to remember, we are talking about outside. If you look at areas of your concrete, you will find mold. Wherever moisture can gather, you find some form of it.

This is why I tell people, do NOT seal the underside of your deck before (or after) installation unless it is high off the ground.

I didn't think TWP was likely to grow mold because it was formulated to resist mold growth in the hot and humid environment of Southern Florida. Plus, isn't it a resin based product?

From what I understand, the oil-based sealers discussed here are made of the same basic ingredients, mostly linseed oil with resins to form the binder, along with pigments, solvents, and mildewcides. Alkyd seems to be popular for the resin component. One of the key ingredients in these is the mildewcide. I don't know if they use different chemicals for this purpose or if they all use the same. If the manufacturers listed what they used, and how much, maybe we could start making sense of all this, but I have not seen that published anywhere. I also wonder if these mildewcides last as long as the finish, or if they leach out before the finish is gone. I also wonder if they settle out in the can - if so, stirring would become very important. But I really have no idea.
Regarding TWP being resin-based, it comes in different series. The 100 series is an oil finish, with resins in it. The words "positive drying" and "no free oils" in the 300 sereis description lead me to think it is a varnish. Several conversations w/ Amteco mostly confirmed this, although they weren't too easy-going about talking about chemistry. They also didn't think it was a good idea to use on a deck, mainly becasuse it would be very difficult to remove. A varnish is a combination of oils and resins that is then reacted under heat to form a product that is neither resin nor oil, but varnish. This can then be mixed (by the manufacturer) with raw oil to form oil-varnish blends.
If you want to understand wood finishes, the best reference I have seen is a book called Understanding Wood Finishes by Bob Flexner. It strips a lot of the mystery away. Unfortunately, it does not adress the specifics of outdoor wood finishes, being geared more to the furniture finishes. Also useful is the Forestry Products website. They are a department of the US Government that does a lot of research into wood products and finishes.

pressurepros,

Our deck is a full floor above ground. Just dirt underneath, with lattice around. Does this change sealing advice? Or just stick to on top? Thanks.

I have just purchased a 3 year old hoause that has IPE (e-pay) decking. The handrails are a beautiful color still, but the floor boards have grayed...can I restore the color with the Timber Oil...what other maintenance should be done to restore the color and continue to preserve it over time. Thanks SO mcuh!

I havent had any problems using twp 116 rustic, the 516 works the same for me its a little darker and has some oil mixed in probley to fawn to the green mafia. I also talk to the twp folks,they have a major office 20 miles from my house, many of the things I have done with twp finish for many years they do not recomend but they put up with me. I have put down 6 layers of twp 116 on S Americal wood that is now a simi gloss 5 years old with no prep,lifting,pealing you can see the refelction of your hand on it.

Far as what is is made of I dont even read the can, I already know what it will do.If there was a better outdoor finish I would be using it. Mold and mildew will grow on anything thats not kept clean with my ipe/twp projects this stuff grows on top of a deck that has had 0 care when I go back for a restain after cleaning/oxalic acid wash the finish is still there ready for another coat.

All the problems I have seen on this board far as pealing,lifting,mold coming up thru the finish,sticky overcoat,fading with in reason, striping before a recoat I just dont have with twp.

I got word from the DeckExpo get together that twp sales have gone up in a big way the last few years,bout the same # of years I have been saying the above, do they even take me out for a 7/11 microwave bean wrap????? Nooooooooooooo. J