"Lew Hodgett" wrote in message
b.com...

"John Grossbohlin" wrote:

A pressure washer or perhaps a media blaster (e.g., think sandblaster)
that uses something gentle like baking soda for media. In either case the
risks of blasting water or media into the building need to be assessed.

You might also be able to scrub it off with a long handled scrub brush
and a mixture of warm water, TSP or other strong detergent, and bleach.
Warm water and Simple Green works pretty well too. I've used this method
to clean old pressure treated wood that was covered in dirt, moss, mold,
bird excrement, UV damage, etc. and ended up with wood that looked like
new. Spray the solution on with a garden sprayer, brush it a bit to
loosen the heavy accumulation, spray it again and let it soak for a while
before giving it another brushing--do not let dry out during this
process. The detergent and bleach do the bulk of the cleaning if you let
them work. Then hose it off with water and examine it for any areas that
need further attention. Generally work from the bottom up to limit the
effects of streaking... wear long gloves and safety glasses!
-------------------------------------------------------
Real teak doesn't like the above.

P/T lumber is a whole different game.

The usual practice to clean teak is salt water and a soft bristle brush,
if you want your teak to last.

At $16-$18/bd'ft, I try to get the longest life possible from my teak.

Lew

I agree that generally you'd want to take a gentler approach. However, the
surface conditions the OP articulated call for a relatively aggressive
cleaning approach--though probably not as aggressive as the sanders or
planers they have been using or might try... A "crust" of weathered decayed
wood full of micro organisms is pretty tough to remove...

I wonder if using something like vinegar first and then soda water combined
with a stiff brush might work for cleaning off the crust... The acid to kill
organisms and the baking soda to neutralize the acid followed by a water
rinse.