Prepping and painting aluminum???

[David_L6]

I need to re-paint my trailer's motor box. It's aluminum and has been painted several times already. Now the paint is about 1/8" thick and is flaking off.

What's the best process to use so that new paint will adhere?

Should I have the trailer sand blasted to get all the old paint off??? If so, are there any special steps to get the new paint to stick to the bare aluminum?

[Andrew 4CE]

One thing I learned the hard way is be careful how powerful the dude's sand blaster is... It can warp the panels if it's thin aluminum/sheet metal if it's the kind of blaster used for sand blasting car frames and he says "Well, never sand blasted one of these before!" just before he starts.

[Andrew 4CE]

Oh and there are special primers for alum... don't even bother if you don't use them. I forget off hand what they are called. But yup, not ordinary primer.

[jneises]

Special primers for painting on aluminum???? Maybe not so true. The facts are that any metal surface needs to be properly prepared prior to the application of prime and top coat paints. Some primers are available with an etching additive that assists the primer to adhere to the base metal all in a one step process. These primers can be used for steel or aluminum. You can also use any primer that is compatible with a certain top coat if the metal is properly etched prior to priming. This material is generally mixed with water and applied to the base material via a sprayer or some equal application method, then rinsed clean and allowed to dry. Expensive paint and primers do not necessarily mean good adhesion. Good prep work does. FYI.

[Tomtall]

Aluliniummmmmm painting

Been there,Done that.Step #1 - Strip old paint.Body grinder with 80 grit pads.Don't bear down to hard!Take you 1 - 2 hours tops. Step #2 - Wash box with soapy water then rinse.Let air dry overnite.Step #3- Wash surface with mineral spirits.Let air dry.Tack off metal with tack cloth.Step #4 - Paint first coat with Zinc Chromate Primer (this will help primer to adhere and also help with corrosion of the alum.) Step #5 - Apply base primer.(gray for liter top coat color,brown for darker ones.) Step #6 - Scuff primer after it's dry,with scotch brite pad.Blow off box with air and tack off.Step#7 - Apply top color within 48 hours of primering box.Step # 8 - Invite all your buds over to drink beer and admire the **** fine job you did painting your trailer box! Good Luck!

[Bill Huson]

coating Al is problematic . . .

Bare aluminum oxidizes very rapidly, but it isn't like rust - you can't see it. An auto paint shop will have a two-step treatment. #1 is an acid wash, rinse with loads of water, and then apply #2 which is a conversion chemical. Then you can paint.

Of course that method is overkill and I rarely do all that anymore, and only on small parts. Paint will stick mechanically to a rough surface, although 80 grit is way to rough. I use 80 to strip paint, but then go 180 and 220 on the metal to smooth it out some. BEWARE of zinc chromate primer! Zinc chromate is poisonous, very poisonous. Use a mask with the proper filters, or hold your breath :-) Cover the bod too, lest you develop a real nasty reaction rash. Check the substrate requirements for whatever topcoat you use. Lacquer likes a 400 grit finish under it, but enamels can handle 220. DO NOT sand the zinc chromate if you use it - dang ZC dust is worse than the wet paint, Coat it with sandable primer, light gray or dark gray is a fav with me. Forget sealer unless you're going for show quality finish and then you'll need FeatherFill on top of the base primer. FeatherFill kicks butt, no more sand scratchs in the finish!

[Jakeroub]

As perviously mentioned...

Aluminum will always have a thin layer of Aluminum Oxide on the surface. You need a self-etching primer (such as Zinc-Chromate) to get rid of the aluminum oxide.

Thats how stainless steel works too, but I think its a layer of chromium or something. Learned this stuff in my material science class last year...

Jake

[Andrew 4CE]

Yeah Zinc Chomate is the special primer I was thinking of and what I used... I thought this was required when painting aluminum.

[David_L6]

Thanks for all the replies.

Been there,Done that.Step #1 - Strip old paint.Body grinder with 80 grit pads.Don't bear down to hard!Take you 1 - 2 hours tops. Step #2 - Wash box with soapy water then rinse.Let air dry overnite.Step #3- Wash surface with mineral spirits.Let air dry.Tack off metal with tack cloth.Step #4 - Paint first coat with Zinc Chromate Primer (this will help primer to adhere and also help with corrosion of the alum.) Step #5 - Apply base primer.(gray for liter top coat color,brown for darker ones.) Step #6 - Scuff primer after it's dry,with scotch brite pad.Blow off box with air and tack off.Step#7 - Apply top color within 48 hours of primering box.Step # 8 - Invite all your buds over to drink beer and admire the **** fine job you did painting your trailer box! Good Luck!

OR

Drill out all the pop rivets holding the aluminum sheets on and replace with wood!

Tom,

What do you mean by "Tack off metal with tack cloth."? What is tack cloth?

[Dave_E71]

...

What do you mean by "Tack off metal with tack cloth."? What is tack cloth?

Tack cloth is a gauze material coated with rosin or something else that will stay tacky that you wipe over the surface before you paint to remove any dust....although, I think there's a design feature in tack cloth that leaves crap on the largest flattest surface you're painting so that it immeadiately draws your eye to it

http://www.acehardware.com/sm-paint-...g-1267579.html

[Bill Huson]

tack cloth secret . . .

Gently brush the tack cloth over the surface - DO NOT RUB! If you rub like you're polishing the surface the varnish scubs off and puts your soon-to-be-applied paint job inna world of ugly hurt.

[nbranews]

Heck David you always pit between Burt and Ralph anyway. With Ralphs big trailer on one side and Burts old war relic on the other combined with the speed of your equiptment and the show you always put on who's gonna notice a few chips in your trailer. Doug Schultz

[David_L6]

Doug,

I'm going to have to quit putting on those shows! That last one took too long to get over.