AR15.Com Archives
 to sandblast, or not to sandblast
TRIGGERFIN  [Team Member]
3/30/2005 10:13:02 PM
I'm going to do a moly job on a 6920 that's in very good shape, but has the typical crappy colt millwork and finishing. What are the pros and cons associated w/ sandblasting to prep? I see the Norrels instructions say to sandblast first w/ fine grit media, but most people on the board doing it seem to recommend against this. If its going to smooth out the service a bit and improve adhesion, why wouldn't you? Why do I care about losing the anodizing if I'm going to moly it? I've got sandblast equipment/cabinet and would just as soon do it, but of course don't want to muck up a perfectly good colt.

Also have a new armalite that was just poorly finished as well - pretty bad pitting on the upper and the lower is almost perfect so they look like they don't match. I'm tempted to blast the hell out of it too.
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mongo001  [Team Member]
3/30/2005 10:29:41 PM
Your standard hard coat anodize and parkerizing finishes are some of the best surfaces for adhesion. That is why most would recommend against sandblasting them off to coat over them. If, in your case, you want to smooth out some blemishes, it might work, but keep in mind that you may remove some of the hard coat anodizing in the process, leaving you with relatively soft bare aluminum underneath, which would be susceptable to dings and scratches that you just worked so hard to remove.
neilfj  [Member]
3/30/2005 10:36:36 PM
The anodized coating is only 0.001" -0.002" thick. Anything that will even out the surface, will remove the coating.
Stickman  [Member]
3/30/2005 11:16:28 PM
Don't blast it, you are only looking to cause problems.
donovan007007  [Member]
3/30/2005 11:39:14 PM
if you are looking at just taking off the finish completly, go to a autoparts store and get some chem-tool, dip it in there over night and voila, no more finish at all. it will be completly bare and clean for refinishing. hey maybe you can chrome it................bling-bling.........just kidding.
james4208  [Member]
3/31/2005 1:39:01 AM
Chroming it would be cool, but I would suggest reanodizing it. Google home anodizing or check out a few paintball sites and you should find instructions on how to do it at home. I used to have them but the disk it was on got corupted. The process was simple and only required a car battery charger some weak acid and some plain ol Rit dye.

NevadaARshooter  [Member]
3/31/2005 6:31:33 AM
Like others have said, don't strip the anodizing and simply paint over it. If you strip it, re-anodize. If you plan to paint it, you don't have to dye the anodizing.
cmjohnson  [Team Member]
3/31/2005 7:09:49 AM
DO NOT SANDBLAST ALUMINUM, EVER.

The likelihood of causing it to warp or change substantially in dimension is far too high,
plus it's likely to rip up the surface way too much.

Stripping of anodizing is done chemically using a lye bath. It's best to have a pro anodizer do
the stripping and later refinishing.

To restore the finish on the aluminum part after stripping, it is acceptable to LIGHTLY beadblast
the part, but not SANDblast. It gives a nicer finish anyway.



CJ
rockytherotty  [Team Member]
3/31/2005 8:12:46 AM

Originally Posted By Stickman:
Don't blast it, you are only looking to cause problems.


+1
torstin  [Member]
3/31/2005 9:03:03 AM
also, the silica tends to imbed itself in the aluminum and can cause refinishing probelms later. glass bead is often used, but you may be able to get away with walnut shells, but i dont know how this might effect anodizing process though.
NevadaARshooter  [Member]
3/31/2005 10:30:04 AM

Originally Posted By cmjohnson:
DO NOT SANDBLAST ALUMINUM, EVER.

The likelihood of causing it to warp or change substantially in dimension is far too high,
plus it's likely to rip up the surface way too much.

Stripping of anodizing is done chemically using a lye bath. It's best to have a pro anodizer do
the stripping and later refinishing.

To restore the finish on the aluminum part after stripping, it is acceptable to LIGHTLY beadblast
the part, but not SANDblast. It gives a nicer finish anyway.

CJ



This is not true. The work piece is not going to warp or change substantially with sand blasting (most of us use aluminum oxide not silica sand). I have done it a couple dozen times with no problems.

The receivers I finish after blasting with 90 grit aluminum oxide @ 85 psi match very closely to my commercial receivers (Bushmaster, Oly, and Armalite).
NevadaARshooter  [Member]
3/31/2005 10:31:40 AM

Originally Posted By torstin:
also, the silica tends to imbed itself in the aluminum and can cause refinishing probelms later. glass bead is often used, but you may be able to get away with walnut shells, but i dont know how this might effect anodizing process though.



This isn't true either, at least with al-ox. You should not sand blast with silica sand anyway, for health reasons (use al-ox).
torstin  [Member]
3/31/2005 4:33:06 PM

Originally Posted By NevadaARshooter:

Originally Posted By torstin:
also, the silica tends to imbed itself in the aluminum and can cause refinishing probelms later. glass bead is often used, but you may be able to get away with walnut shells, but i dont know how this might effect anodizing process though.



This isn't true either, at least with al-ox. You should not sand blast with silica sand anyway, for health reasons (use al-ox).



what do you feel is incorrect? silica will imbed in alumium...and if you use high enough pressure and hold long enough you could probably get it to warp as well. totally agree with you on avoiding silica for all blasting though. silicosis is nasty and i personally don't risk the possibility. glass or plastic beads will work on aluminum...as will walnut shells. however, i really do not know how they relate to anodizing, as its not somethign i've done.

as for al-ox, i didnt mention anything about it.
Stickman  [Member]
3/31/2005 9:31:16 PM

Originally Posted By cmjohnson:
DO NOT SANDBLAST ALUMINUM, EVER.

To restore the finish on the aluminum part after stripping, it is acceptable to LIGHTLY beadblast
the part, but not SANDblast. It gives a nicer finish anyway.

CJ



Don't bead blast if you are going to use Norrells, it makes the surface a little too smooth for decent adhesion.
Model_One  [Team Member]
4/12/2005 12:19:52 AM
I have done a number of 80% lowers and finished with the Norrell products.

A light blasting with 100-grit sand preps the aluminum for maximum adhesion of the molycoat.

I've had no problems after finishing my lowers according to the Norrells instruction sheet.

PS, their Colt Gray is a dead-on match for the original finish.
Knight_Shadow  [Member]
4/12/2005 12:27:49 AM
i was a grit blaster and blasted all kinds of metal and aluminum. unless you have blasted aluminum before i would say never blast a receiver! if you have the psi to high and heavy a grit you can screw it up big time! i have taken a 1lb block of aluminum and turned it to bust in just a few mins.
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