Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Tim Shoppa
 
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Default Etch/primer/paint for aluminum panel?

I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.

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Peter DiVergilio
 
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Default

Normally, if you're down to bare metal, an Acetone wash should suffice for
pre paint on aluminum.

--
Peter DiVergilio
Most of the money I've wasted was mostly spent trying to impress people who
were never going to like me anyway!


  #3   Report Post  
Wild Bill
 
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If you sandblast there's not much need to etch, because both processes are
intended for adhesion. Sandblasting can distort metal panels.

If you fine sand it, you might want to etch with a diluted phosphoric
etching solution. There are numerous names for it, but it's widely referred
to in the U.S. as metal-prep, and is available at most autobody shop
suppliers. Make sure you get the instructions for diluting it (normally on
the product label), because it's used in different strengths (water ratio)
for different metals.

If you don't want to do either of the above, you can strip the panel,
carefully clean it with acetone or lacquer thinner, and use an etching
primer which is available in spray cans.

Another primer for aluminum and galvanized metals is zinc chromate primer.
If you get this product in a spray can, you won't need to use the metal-prep
etch, or the etching primer, since it's also intended to applied directly to
clean bare metal.

Depending upon which particular primer you use, you'll need to select a
finish coat that's compatible with the primer you choose. Generally, all the
enamels are compatible as finish coats. Some of the so-called epoxy paints
in spray cans might not be, and some lacquer paints might not.

WB
.............

"Tim Shoppa" wrote in message
ups.com...
I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.





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Wayne
 
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I've been using a spray can of "SELF ETCHING PRIMER" from NAPA.
Number on the can is 7220. I let it dry for a while, then use Krylon.
No sanding in between.
It has worked well for me.

Wayne D.

I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.




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yourname
 
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Tim Shoppa wrote:
I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.


sand clean [acetone alcohol etc] prime within 15 minutes. Aluminum
oxidizes that fast

I found rustoleum baked is harder than krylon
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Don Foreman
 
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On 12 Jun 2005 03:57:07 -0700, "Tim Shoppa"
wrote:

I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?


PPG/Ditzler "Alumaprep". It's a phosphoric acid-based aqueous
solution, found at auto paint suppliers. It cleans the metal and
significantly improves wetting, levelling and adhesion of paint.
  #8   Report Post  
Dave August
 
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Years ago when I was taught to do anodizing on aluminum we used lye as the
final surface prep. Unfortunatly I can't remember the solution percentage
but IIRC it was pretty week. You might try googeling and see if you can't
get a good number.

--.- Dave

"Tim Shoppa" wrote in message
ups.com...
I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.



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john
 
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Tim Shoppa wrote:

I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.



A good acid etch after a thorugh cleaning and sanding will give good
adhesion for the paint. Oil is your enemy so make sure you have clean
paper towels rather than rags to apply the solvent cleaner. Also make
sure the bottle of solvent, acetone, mek or such has not been
contaminated by someone holding a rag over the opening and turning the
bottle upside down to wet the rag, Many paint jobs have come out second
best doing this little trick by someone with an oilly rag.

I dont know if you can still get it but zinc chromate is the one i
always used. The trick is to put on a real light mist coat and let it
dry for at least three or four days before you put your paint on. For
magniesium we would let it dry for a week before we painted it.




John

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Jon Elson
 
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Tim Shoppa wrote:
I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

I've got some stuff I bought 20 years ago, and you probably can't get
exactly that stuff anymore. There is a 2-part concoction that seems
to be a mixture of contact cement and Zinc Chromate. It has a totally
noxious solvent odor. And, I know about the cement part because I
always get it on my hands, and it peels off just like contact cement.

I sand the aluminum with 240 grit wet or dri sandpaper, but do it wet
to prolong the life of the sandpaper. I then wash with water, and then
wipe down with rubbing alcohol.

The label on the primer reads "zinc chromate wash primer". The zinc
chromate is an anti-corrosion treatment, and probably isn't necessary
in my use.

After the primer, I use a "baking enamel" that is only slightly less
noxious smelling than the primer. I let the parts dry for a day
or so, and then sometimes pre-heat them with a heat gun while still
in the fume hood to drive off the last of the solvents before a
200 F bake in the kitchen oven.

This produces a pretty tough coating, but it is not as rugged as a good
appliance finish.

Jon



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tomcas
 
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Tim Shoppa wrote:
I've got an aluminum panel (front of a very fancy instrument) that I
want to re-paint. Current paint is pretty shabby, but then again it's
from 40 years ago. I'm sure I can get the old paint off (between
strippers and sanding) but what's the next step?

What's a good pre-painting etch for aluminum? I've used
phosphate-based etches before but something tells me that this isn't
the best thing for aluminum.

And after the etch, I'm probably limited to cans of spray paint.
Although going to an automotive paint shop and asking them to load a
paint can for me is a possibility, I don't walk in without a clue as to
what I want to buy. OTOH if I can buy it off the shelf then that's
great too.

I can bake the panel after painting, in my past experience (with
discount-store brands of spray paint) this makes a big difference in
durability.

So any advice before I walk in the paint store and make a fool of
myself?

Tim.

Degrease, irridite (alodine), prime, paint.
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