Author Topic: Preperation for Tank Paint  (Read 5315 times)

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Offline JonathanJoy

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Preperation for Tank Paint
« on: 25 Nov 2011 at 18:16 »
Hi, I'm about to start to paint the tinware on my Douglas.
There is surface rust plus some pitting . When I restored my Scott I used Finnigans rust treatment followed by grey primer. This has caused problems with the final coats some lifting etc.

If I used etch primer do I need rust treatment first ?

Could any one recommend the complete steps/system to get a reasonably good job. I read somewhere on the forum about POR15 but I can't find the article now.

Kind regards Jonathan


Offline Dirt Track

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Re: Preperation for Tank Paint
« Reply #1 on: 26 Nov 2011 at 03:35 »
G'day Jonathon
Vehicle painter by trade.
Any sort of "rust treatment" in my book is a waist of time, why bother converting the stuff....get rid of it!
If your cycle parts are in reasonably good condition consider bead blasting them to get back to bare metal, try low pressure blasting for the tank so as not to warp it in any way. Quickly apply your 2 pack primer after blasting.
Bead blasting gives you the best substrate condition for your new paint finish to adhere to.
Choose a quality paint and be willing to pay good money for it.
Howard.
PS make sure your tank is not leaking before you paint not after.

Offline JonathanJoy

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Re: Preperation for Tank Paint
« Reply #2 on: 26 Nov 2011 at 06:50 »
Thanks for the reply Howard,
I've a grit blasting gun is there any grade of bead that you would recommend, how about deeper pitting, I presumably fill with epoxy filler after blasting. 
With the colour coat is it best to use base - coat clear coat and can I apply decals between ( is it petrol resistant). 
Or should I use gloss followed by lacquer.

ps I was thinking of investing in a mini spray gun.  Are they worth it and what size nozzle should I choose

Thanks for the advice
Kind regards
 
« Last Edit: 26 Nov 2011 at 07:10 by JonathanJoy »

Offline Dirt Track

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Re: Preperation for Tank Paint
« Reply #3 on: 26 Nov 2011 at 10:18 »
G'day Jonathan
If you intend to blast your items yourself please practise on something before attempting it on your good parts.
Your local blasting supplier will best advise on grit grades, take your bits into them so they can see exactly what sort of job is to be done.....maybe they will do it for you.
Any filler should be used after blasting of course.
There are so many different paint finishes nowadays, again have a chat to your local automotive paint supplier and buy good quality products.
Small spray guns..touch up guns and the like have their place but you can buy a full size spray gun quite cheaply and as long as you have a suitable air supply they will be good enough for your job.
Whilst I always encourage "amateur's" to have a go I have seen some expensive disasters that have needed to be taken to a professional to fix, think about it....paint is not cheap and if you want a 100% professional job..............
Howard.

Offline JonathanJoy

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Re: Preperation for Tank Paint
« Reply #4 on: 26 Nov 2011 at 10:37 »
Thanks again for the prompt reply,

i know from attempting to spray my Scott tank, that it is not easy and is expensive ( I'm on my third attempt now !! ), but I quite enjoy the challenge.  Another guy was advising etch primer followed by coach enamel. Whats your thoughts on this pros, and cons.. Hope you don't mind me picking your brains

Kind Regards Jonathan

Offline Doug

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Re: Preperation for Tank Paint
« Reply #5 on: 27 Nov 2011 at 00:27 »
Jonathan,

My 2-cents worth. I'm not a professional painter, but I do all my own painting on my bikes and cars (for better or worse!) :)

The etching primers are more to acquire a good adhesion to the base metal. They do not 'etch out' the rust, and the etching process is very subtle. If fact, they really are only good to paint over clean, bare, fresh metal. They are not intended to compensate for poor surface preparation.

Bead blasting is the gentlest of the 'hard' media that will remove old paint and rust. As mentioned, with sufficient pressure it is possible to warp sheet metal, as you are in effect shot peening one side of the sheet and imparting a surface stress. Start out with too low a pressure, not too close to the nozzle, and with a glancing blast. Then work your way up with the pressure until sufficient to do the job. Several light passes is best, if you are striping it clean in one pass you are probably using too much pressure. Curved areas will tolerate higher pressure than large flat areas as the former will be more resistant to changing shape.

Glass beads or fine sand still will not remove rust at the bottom of the deepest, small pits. Two options. Encapsulate it so that moisture and oxygen can not continue to fuel the rusting process; or convert the rust into something more inert. Actually I suggest doing both. There are pre-rinsing solutions to purchase that help 'etch' the rust out and convert the remainder from iron oxide to a more inert iron phosphate. This is the route I use. Then cover with a impermeable epoxy or moisture cure urethane primer (depending on you preference) to keep the air and moisture at bay. 

Regards,
-Doug

Offline JonathanJoy

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Re: Preperation for Tank Paint
« Reply #6 on: 27 Nov 2011 at 20:20 »
Thanks Doug what paint do you use, enamal , 2k , cellulose . Do you finish with lacquer.

regards Jonathan

Offline Doug

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Re: Preperation for Tank Paint
« Reply #7 on: 27 Nov 2011 at 23:00 »
Jonathan,

For primers, I use DuPont Corlar (epoxy) or Por15 (urethane.) If I expect to lay it on heavy and cut back, I use the epoxy, as I know it will cure in 24 hours regardless of thickness of application. If I do not expect to much of any sanding, I will use the Por15, which gives a very hard and durable surface. Too hard to readily sand, as it quickly blunts silicon carbide paper! This can be an advantage, as if there is minor pitting you can primer with a light coat of Por15 and then go over it with a rapid fill primer made for sanding back. It is then easy to sand back to the Por15, at which point the sandpaper stops and you need not fear so much cutting through the primer. The a second coat of Por15 to cap it off. If I expect to do a lot of sanding, cutting back the primer too, then I will use the Corlar. It does not sand very well, but it can be sanded.

The rapid spray fillers are usually a polyester.

For top coats, I have been using standard automotive acrylic enamel. Generally DuPont Centari, mainly because it is readily available more so than I think it is the best around. To this I usually add some of the optional gloss hardener component. This tends to counteract a tendency of Centari to orange peel, and as the name suggest accelerates the cure and makes it possible to compound the surface as traditionally done with lacquer. This is particularly handy with larger surfaces where orange peel would be more offensive. Beware, too much of the gloss hardener alters the surface tension of the paint, causing it to pull back from sharp edges, reveling the primer below. On petrol tanks I will also add a clear coat of the same acrylic enamel after lining and transfers. I usually give it a dry dusting over the transfers and let that dry before giving it the proper wet coat, and so far have not had problems with the paint attacking varnish or water slide transfers.

I did one frame early one in lacquer primer; never again! It is too brittle. Between bolting the bike together and stone chips, you will be hard pressed to keep the top coat intact. I also did one frame with DuPont Imron (Polyurethane) top coat as I was lead to believe it was tougher than the standard acrylic enamel. It was not, it is just as prone to stone chipping as anything else. It just cost even more and is more trouble to spray. What it is excellent for are large surfaces left out in the weather. A friend had a small airplane painted in Imron, and while it chalked out in the sun just like a acrylic enamel, it took far, far less time to buff it back into a high gloss. However you will probably not be leaving you cherished motorcycle out in the weather, so I do not see any advantage to using Polyurethane as a top coat. 

By the way, besides the general health hazards of spraying paint and volatile organics floating about, any of the two-part paints and the hardener/accelerators for the acrylic enamel are carcinogenic. So carbon filter pack respirators or better yet a positive pressure fresh air supply to the mask is to be preferred.

Powder coating is o.k. for small items like wheel stands, but is generally too thick and soft for the frame. It will extrude out from any fastener/component clamped onto it.

Regards,
-Doug

Offline aggettd

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Re: Preperation for Tank Paint
« Reply #8 on: 01 Dec 2011 at 15:49 »
Just to add to the previous posts regarding preparing metal prior to primer, I have had good results with two products. These cleaners and conditioners contain mixtures of phosphoric, chromic and other acids plus a variety of equally unpronounceable and hazardous chemicals, so respirators, eye protection and gloves are NECESSARY.

For pretreating aluminum I use PPG's DX533 Aluminum Cleaner, followed by their DX501 Aluminum Conditioner.

For steel, I use Sherwin Williams Dual-Etch W4K263. I haven't found anything particularly good for cast iron, but the Dual-Etch is probably better than nothing.

Please do yourself a favour and get the Material Data Safety Sheets and manufacturer's user instructions for the products. They should be available from the vendor or on the web. Having said that, this stuff is very easy to use and makes a huge difference to the longevity of your coating system. Good luck.

One final word, when Dupont Imron ( a two part polyurethane) first came out, I can recall being warned that the standard cartridge respirators were ineffective in protecting users from the vapours released by product, and that supplied air was the only safe PPE for its use. I don't know if the formulation has changed, but you might want to check that out first if you do go that route. I can vouch for Doug's use of the POR15. It's dead easy to use, hard as bullets and much less toxic than some other options. They also make a tank liner system that doesn't gum up with ethanol or other solvents.

 

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