Any natural oil based preservative will mold, as mold thinks it is food. It
is.
Go with Cabot, and get either the acrylic formulation (no oil) or one with a
fast-evaporating solvent. Also you can get cabot with both UV resistance
and mildewcide in it.
You may first have to remove as much of the old finish as possible, with a
pressure spray or deck finish remover/prep solution.
Roger
"Thomas G. Marshall" . com
wrote in message news:GlT9i.7066$UD4.5690@trndny07...

My composite deck has cedar rails, for esthetic reasons. I know, I know,
don't bust on me.

I've treated the rails with Austrailian Timber Oil, which did a wonderful
job at keeping a red hue while showing all of the grain.

Problem is, mold has grown on it like crazy.

Could I add fungicide to it? ATO is an odd beast and supposedly cannot
even take a tint added to it.

Or should I just punt ATO entirely and go with Cabbot, like everyone else
in the world seems to like for outdoor stuff ?