Frame sandblasting?

Bill Graham said:

I picked up a beat up Diamondback frame, aluminum, as a refinish
project candidate. Is sandblasting an acceptible method to get rid of
the paint that's left?

Thanks.

Yes, but chemical stripping is probably better.

Bill Graham said:

I picked up a beat up Diamondback frame, aluminum, as a refinish
project candidate. Is sandblasting an acceptible method to get rid of
the paint that's left?

There are always many paths to victory, but bead blasting makes a lot
more work than merely wetsanding the present finish and paying attention
to damaged areas before a primer-surfacer and another wetsanding. Actual
sand blasting on aluminum will increase the surface damage even beyond
bead blasting.

Generally, wash thoroughly with detergent, rinse clean and work with the
manufacturer's substrate as much as possible. Use an aluminum etch on
bare areas before your primer-surfacer.

Try your local library for an auto body textbook before going much further.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
** Posted from http://www.teranews.com **

Bill Graham said:

I picked up a beat up Diamondback frame, aluminum, as a refinish
project candidate. Is sandblasting an acceptible method to get rid of
the paint that's left?

Thanks.

Sandblasting will chew up the aluminum making surface prep be even
more work that chemical stripping would have been. Bead blasting with
glass beads will be more gentle.

But just some sandpaper and elbow grease would probably do the trick.
No reason to get ALL the old paint off.

Joseph

On Fri, 9 May 2008 08:45:14 -0700 (PDT), Bill Graham

may have said:

I picked up a beat up Diamondback frame, aluminum, as a refinish
project candidate. Is sandblasting an acceptible method to get rid of
the paint that's left?

Sandblasting, even done with care, will almost certainly remove any
anodization present, which is inadvisable. Unfortunately, some
chemical strippers will also remove the anodizing, so one must choose
tech with caution when stripping paint from aluminum. There's a type
called "Aircraft Remover" that does a decent job if the coating to be
removed is actually paint, but my experience has been that it
sometimes will do nothing at all to powdercoats. Read and follow the
label instructions if you try it. A Diamondback could have a
powdercoat finish, depending on the year it was made and other
factors, so stripper might not work.

Heat-based removal is a definite no-go with aluminum IMO; the chances
are good that some of the metal will get overheated, changing the
temper.

If the frame is built from thick-walled tubing, then blasting
(preferably with something low-abrasion like nutshell granules) can be
employed, but the choice of blasting agent is pretty important, and
the person doing the job needs to have a very deft hand with the gun
if the surface of the metal is not to be excessively disturbed;
ordinary sand is a poor choice.

An additional caveat: Use ONLY a sealed BB if you blast the frame, as
it is essentially impossible to ensure that all of the grit will be
removed which could end up inside the BB shell later.

Good luck. Sometimes there are no really good alternatives, and you
just have to do the best you can.

(This advice is from someone who has bead-blasted hundreds of engine
parts over the years; the process has its uses, but a bike frame isn't
one that I'd choose it for.)

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Werehatrack said:

On Fri, 9 May 2008 08:45:14 -0700 (PDT), Bill Graham

may have said:

I picked up a beat up Diamondback frame, aluminum, as a refinish project
candidate. Is sandblasting an acceptible method to get rid of the paint
that's left?

Sandblasting, even done with care, will almost certainly remove any
anodization present, which is inadvisable. Unfortunately, some chemical
strippers will also remove the anodizing, so one must choose tech with
caution when stripping paint from aluminum.

Just out of curiosity, is it common to anodize aluminum frames before
painting them? If so, why?

On Fri, 09 May 2008 18:01:11 -0500, Gary Young <[email hidden]>

may have said:

Werehatrack said:

On Fri, 9 May 2008 08:45:14 -0700 (PDT), Bill Graham

may have said:

I picked up a beat up Diamondback frame, aluminum, as a refinish project
candidate. Is sandblasting an acceptible method to get rid of the paint
that's left?

Sandblasting, even done with care, will almost certainly remove any
anodization present, which is inadvisable. Unfortunately, some chemical
strippers will also remove the anodizing, so one must choose tech with
caution when stripping paint from aluminum.

Just out of curiosity, is it common to anodize aluminum frames before
painting them? If so, why?

Not particularly common before painting, but possible; anodizing will
actively interfere with adhesion of some kinds of paint, though, so
it's less likely on a painted frame than on one that's powdercoated.
Either way, it provides some resistance to the kind of insidious
under-the-finish corrosion that occurs with bare aluminum too easily.
The only local powder coat service whose opinions I trusted (in the
days when I had occasional need for such) recommended anodizing
aluminum before powercoating because it didn't make much difference in
the bonding of the coating but it improved the corrosion resistance to
a useful degree in their experience. (They were also the only one
that would mask out bolt flanges and not coat them, and they had
multiple formulas for various working environments. They also stated,
quite bluntly, that there were applications for which paint or some
other non-powder coating was a much better choice. But then, they
catered almost exclusively to the industrial plant equipment market;
they had to be honest if they wanted to stay in business.)

--
My email address is antispammed; pull WEEDS if replying via e-mail.
Typoes are not a bug, they're a feature.
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