[Public-list] tar stains

[George Dinwiddie]

brooks.glenn at comcast.net wrote:
> Try a product called Ospho, its a green liquid which chemically
> alters iron oxide into iron phosphate, which is dusty white in color
> and can be somewhat scrubbed off.

According to the manufacturer, "OSPHO causes iron oxide (rust) to 
chemical change to iron phosphate - an inert, hard substance that turns 
the metal black. Where rust is exceedingly heavy, two coats of OSPHO may 
be necessary to thoroughly penetrate and blacken the surface to be 
painted. A dry powdery, grayish - white surface usually develops; this 
is normal - brush off any loose powder before paint application."

I think the loose powder is excess Ospho, and by-products of it giving 
up it's phosphorous to the iron oxide.

I wouldn't recommend it for cleaning rust stains on fiberglass.  The 
usual recommendation for rust stains is oxalic acid.  The cleanser ZUD 
contains this, but is also abrasive.

>  -------------- Original message ----------------------
> From: Villo Marmei <marmei_v at pathcom.com>
>> Now that we are on this subject....
>> How does one remove Iron Rust stains ?? Some one, way back must have ground 
>> some iron inside my lockers and the wall have a fair amount of this orangy 
>> ugly stains.

I'm not convinced these are rust stains.  It's not uncommon for water 
penetration to leach compounds through the fiberglass, whether from 
byproducts of the resin, a rotting core, or the auto-body compound that 
Whitby often used for interior fairing.

  - George

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