Rust & Residue from PT Lumber

[Brett Bobo]

When working on an outdoor project, I stacked the pressure treated material on the surface of my table saw for about two days before finishing the milling process. When I moved the material, the table saw surface was severly discolored and rusted and shear panic set in. My typical maintenance plan is either WD-40 or PB Blaster with a Scotch-Brite pad, followed my mineral spirits to clean the surface, and then paste wax. I think I managed to get almost all of the rust out but there's still a black discoloration in several spots that I'm having trouble removing. I"m not sure if this is still rust or one of the chemicals in the pressure treated lumber that has soaked into the cast iron.

What products would you recommend for the discoloration and rust? Would an automotive rust remover from an auto parts store work better and be more of an "industrial" product?

Thanks for the help,
Brett

[Joe Chritz]

PT lumber will rust cast iron in a few hours.

I have never tried to get the discoloration off, I'm not even sure it is possible short of a complete re-grind.

Joe

[John Pratt]

One of the guys I have working in the shop left some PT lumber on the TS over the weekend one time. Same result. I used naval jelly and steel wool with some success. It did leave some discoloration from the naval jelly but after repeated cleanings with mineral spirits, Boesheild T9, and paste wax. it is hardly noticable any more.

[Lee Schierer]

PT lumber contains two things that are bad for cast iron. Moisture and chemicals.

The black spots are in the pores of the cast iron and nothing will get them out that I know of.

Conventional framing lumber can also cause rusting if left on a TS for very long depending upon how well it has been dried.

[David Thompson 27577]

Since about 5 years ago, most treated lumber has been quite caustic. It rusts through fasteners in less than six months, unless they are stainless or galvanized.

And when I say "rusts through", I mean that the fasteners are no longer effective after only six months.

If you leave the stuff siting on you tablesaw, you should expect rust which will be permanent.

[Jacob Reverb]

Since about 5 years ago, most treated lumber has been quite caustic. It rusts through fasteners in less than six months, unless they are stainless or galvanized.

And when I say "rusts through", I mean that the fasteners are no longer effective after only six months.

Yep, the EPA or someone banned whatever they used to use in PT lumber to keep bugs and rot out (arsenic?) and now some compound(s) of copper are used instead.

It's a BIG problem if you want to use PT lumber for the mud sills on a house and you want to put aluminum sheet metal under the PT mud sill as a termite shield. In the presence of moisture, copper will eat through aluminum like you wouldn't believe, through galvanic corrosion. The aluminum becomes the (sacrificial) anode, and the copper in the PT lumber becomes the (more noble, and this protected) cathode.

Bottom line: Goodbye aluminum.