On Sun, 30 Aug 2009 14:29:57 -0700, "Steve Lusardi"
wrote:

Your question is far too vague, but painting steel is not rocket science. However, here are some rules. Don't paint over mill
scale or rust. If the steel has not been shot blasted, it still has mill scale on it and that will lift on its own, so it must be
removed. Wire brushing and grinding is slow and ineffective for this. Sand and shot blasting to white metal is much better.
Purpose rusting helps to lift the mill scale and makes blasting faster. If rust exists and cannot be removed. The use of muratic
acid works well. If that cannot be used, then it can be converted with converters. In the case of chemical use, the chemicals need
to be washed away with water and neutralized with a soda and then washed again. After all of these processes, you have a short
window of time to get the first coat of etching primer applied before corrosion sets in. Depending on prevailing conditions, that
window is between 20 minutes and 2 hours.

Use of a passivating metal treatment will extend the window
considerably and will also aid wetting and adhesion significantly.

On Aug 30, 4:51*pm, Don Foreman wrote:

.. After all of these processes, you have a short
window of time to get the first coat of etching primer applied before corrosion sets in. Depending on prevailing conditions, that
window is between 20 minutes and 2 hours.
Use of a passivating metal treatment will extend the window
considerably and will also aid wetting and adhesion significantly.

Whether you just neutralize the acid and wash, or whether you use
phosphoric acid, you should apply the primer as soon as the surface is
really dry. Tests done on aluminum treated with fpl *pretreatment,
found that the bond strength was highest with immediate application of
the paint. Just sitting around for a couple of hours produced lower
bond strengths. No corrosion involved. Just airborne contaminates.

Dan

On Sun, 30 Aug 2009 21:25:29 -0700, "Steve Lusardi"
wrote:

Don,
Are you referring to phosphoric acid compounds as passivating treatment? I often use one as cheap insurance even on white metal.
Steve

Uh...yes.

I use a couple of PPG/Ditzler products. DX579 metal cleaner contains
phosphoric acid and a detergent. DX520 metal conditioner (used after
DX579 if at all) contains phosphoric acid, zinc oxide, nickle nitrate
and nitrobenzenesulfonic acid sodium salt. The cleaner (DX579)
removes oils, waxes and light rust. The conditioner (DX520) leaves a
passivating coating of zinc phosphate.

http://www.tcpglobal.com/autobodydepot/rustremove.aspx


"Don Foreman" wrote in message ...
On Sun, 30 Aug 2009 14:29:57 -0700, "Steve Lusardi"
wrote:

Your question is far too vague, but painting steel is not rocket science. However, here are some rules. Don't paint over mill
scale or rust. If the steel has not been shot blasted, it still has mill scale on it and that will lift on its own, so it must
be
removed. Wire brushing and grinding is slow and ineffective for this. Sand and shot blasting to white metal is much better.
Purpose rusting helps to lift the mill scale and makes blasting faster. If rust exists and cannot be removed. The use of muratic
acid works well. If that cannot be used, then it can be converted with converters. In the case of chemical use, the chemicals
need
to be washed away with water and neutralized with a soda and then washed again. After all of these processes, you have a short
window of time to get the first coat of etching primer applied before corrosion sets in. Depending on prevailing conditions,
that
window is between 20 minutes and 2 hours.

Use of a passivating metal treatment will extend the window
considerably and will also aid wetting and adhesion significantly.

Don,
Are you referring to phosphoric acid compounds as passivating treatment? I often use one as cheap insurance even on white metal.
Steve

"Don Foreman" wrote in message ...
On Sun, 30 Aug 2009 14:29:57 -0700, "Steve Lusardi"
wrote:

Your question is far too vague, but painting steel is not rocket science. However, here are some rules. Don't paint over mill
scale or rust. If the steel has not been shot blasted, it still has mill scale on it and that will lift on its own, so it must
be
removed. Wire brushing and grinding is slow and ineffective for this. Sand and shot blasting to white metal is much better.
Purpose rusting helps to lift the mill scale and makes blasting faster. If rust exists and cannot be removed. The use of muratic
acid works well. If that cannot be used, then it can be converted with converters. In the case of chemical use, the chemicals
need
to be washed away with water and neutralized with a soda and then washed again. After all of these processes, you have a short
window of time to get the first coat of etching primer applied before corrosion sets in. Depending on prevailing conditions,
that
window is between 20 minutes and 2 hours.

Use of a passivating metal treatment will extend the window
considerably and will also aid wetting and adhesion significantly.