Metal skins paint preparation, primer or glaze putty ?

Once the metal skins of a tractor have been stripped of paint down to bare metal - if the skins are pitted from rusting - is it better to apply a layer of glaze putty to fill the pits or just several layers of high build primer ?

Guess it depends on the Pits? I was taught to never use filler on bare metal, always on top of primer.

If they are just small pits, give it a whirl with primer, block it flat, then see how big they are. if you still see em, put some putty to em - or just reprimer


then again, thats how I was taught to do it, right or wrong, its my way..

I have a couple of the cheap welders from Harbor Freight (stick and wire feed) and was going to use them for some fill spots and then follow up with a thin layer of Bondo.

Let me clarify - these pits are not holes - maybe 3 - 5 thousandths of an inch deep - classic stuff on the seat pan and where the belt / pto covers join with the floor boards.

Thanks

Chuck
I have heard that epoxy primer is good for filling pits. I have not tried it. I have used the regular primer, sanding and bondo. I have not got the tractor back together and am worried about the bondo holding up. Time will tell.
P.J.

P.J.

that is my concern too - if its better to glaze clean metal or or glaze over primer
or
even glaze at all !!

But that's what we are all here to do .. learn a little as we go along, so maybe I'll let this post cook a little and gather some arguments for and against before proceeding with my own repainting of the skins.

From the paint stripping accomplished so far, I did not see a spec of primer on any panel I have worked with - appears WheelHorse did not use primer on the metal. Maybe applying a primer to the metal now will allow the paint to last a while longer than the original.

thanks to all in advance for your advice.

A couple of things to consider about plastic fillers/putty/high build primer are the heat and vibration they will be subjected to on a Wheel Horse. They don't hold up anywhere near as well as lead/brazing/welding.

That being said though, if your pitting is no more than 3-5 thousandths deep why not just feather the surounding surface down into them and make the pits "disappear". Just filling the pits with primer or putty leaves the sharp edge of the pit which would likely become a starting point for a crack in the finish. Any shinkage of the filler material will also be much more noticable if it takes place against a sharp edge such as the "rim" of a pit. Feathering the edge of the pit spreads this edge out and softens it. A couple coats of primer-surfacer blocked out will then pretty much fill the low spot.

The sheet metal on these machines was not exactly mirror smooth from the factory so a low spot or wave that is feathered out across an inch or more would be hard to detect without a straight edge.

Oh! Primer will not affect the longevity of your top coat. It is used for adhesion (ok, primer-surfacer adds in the ability to level out imperfections). Wheel Horse acomplished adhesion via acid etched surfaces, electrostatic application of the paint, and infrared drying. The infrared lights heated the metal and dried the paint from the inside out. Sort of a precursor to powder coating.

There was a lot of pitting on my Lawn Ranger. There is photo's in this thread:

http://whtractor.15.forumer.com/index.php?showtopic=3240

On the not so severe pitting I used a few heavy coats of "high build primer", sanding with a large block between coats. On the more severe pitting I used a thin smear of filler on the bare metal.

I've never done any lead work, so I dont know what I am talking about, but I would suspect that lead would have adhesion issues to rusty metal as well. I know that bronze (brazing) or lead solder doesnt really want to stick to anything thats not shiny clean, and would guess you would have the same issue with lead.

On the more delicate parts, forr example the grille "spokes" on a roundhood it's pretty tough to sand/grind it to shiny without bending or distorting them.

Also I suspect that the plastic fillers available today are probably much improved over the bondo that was available 20 years ago

On all of my RJ work there were a few areas where pitting was a problem. My body and fender mentor (75 y/o body man) suggested the following;

1. Clean to bare metal, and use a "rust dissolver" to clean any pits and rusted metal.
2. Clean the surface with mineral spirits.
3. "Prime" with rust converter.
4. Block-sand surface to smooth (320 grit).
5. Prime with three high buildup primer coats and sand to 400-600 grit after last coat.
6. Glaze any surface imperfections, spot sand to 320 grit, and lightly prime and sand again to 400-600 grit.
7. Paint and clear coat.

Mike, on your Primer you should be sanding with 120, 220 and 320 dry paper, then on your last coat before paint, wet sand with 400 or 600 whichever you have. If you paint anything with metallic in it, use 600 grit, the rougher grits will align the metallic with the sanding scratches.


1000 and 2000 grit is way to smooth to provide correct grip for the paint layer...1k and 2k and higher papers are used for color sanding and buffing paint and plastic..

There's always powder coating if you have an old oven laying around. Craigslist has a lot of free ones that could be used for that also.

http://www.keystonepowdercoating.com/faq.htm

(from link above)
"6. What If The Parts Are Pitted From Rust or Corrosion?
Powder coat is approximately 2-3 times thicker than standard wet paints. After removing the oxidation, we will give a heavy coat of powder. This feature is great for covering up small pitting, corrosion, rust and revealing a smooth lustrous finish. Please view our Gallery to see an example."

Thanks guys for all the advice.

just wanted to restate my interest here is not so much how to get a mirror finish on the top coat but how to get the topcoat (whatever it looks like) to adhere the best it can to a pitted surface.

I guess the topic I wanted to keep the conversation centered on is :

primer first then putty or

putty to prepared metal then primer

or no putty at all - just primer

(lead is out as I have tried that once, with good results but it would be total overkill on these tractors that are workers and not barn queens).

I was looking for is a logical explanation as to benefits / downfalls of one way over the other - ex. putty adheres to metal than primer or the opposite. Just a little curious about the real world experiences of one over the other .


Anyone have any comments about previous work they did that may not have held up well - or those who have experiences that 5 - 10 years later still show solid adhesion ?

Thanks again.

Great - for free - and I just replaced the light bulb in my Easy Bake oven !!

Point taken, and my previous suggestion corrected. I called and asked the "Old Dude" again just to be sure.

SOI,
To answer your question directly, I have always prepped metal so there is no rust, prime, then putty, prime again then paint. I have numerous jobs of all ages and they are all holding up well over time.

See, this makes the most sense to me - if you prime first - I believe it would be easier for the paint to flow into any surface imperfections in the metal and get a better "bite" into the grain of the metal.

If you tried to force putty onto the bare metal, I believe you might end up with less contact and less "bite" due to the putty NOT flowing into the grain of the metal.

Just my thoughts.

Thanks Mike.

Well, I guess I have to rethink my view on this subject after reading this

http://www.autobodystore.com/filler_&_epoxy.shtml

Think of it this way. When you sand with a more course grit paper, the gouges are deeper but the spacing between is wider. The more fine grit papers leave shallower scratches, but the scratches are closer together. The closer together, and the more of them in a given area. creates the greatest surface area. The point is, you are trying to create the greatest surface area over a given physical area of metal, so the paint has a greater surface area to adhere to. As the test clearly demonstrates, but is not well explained, is that the 180 grit sanding leaves more surface area due to closeness of scratches combined with depth of scratch.

The three biggest mistakes I have made in the past are;
1) Not preparing the metal so that all rust (or moisture) is abated. I.E. Leaving microscopic rust on the metal which will eventually rust-through the painted coatings.
2) Putting primer on too dry, too wet, or too thick, all cause adhesion problems.
3) Re-Coating outside the re-coat window. I.E. Putting a coat of paint on, and not allowing 1/2 hour or so of flash-time before re-coating, or re-coating inside the 48 hour cure window.

Lessons Learned: Surface prep and material application is everything!

These four articles give a lot of good information for those restoring the finish on a tractor. The articles are directed at cars but are the same process for any metal refinishing, whether doing a show finish or simply a paint refresh. The final result depends on how meticulously you perform each step.

1) Vintage Project, Part II: http://www.scottgrundfor.com/ideas/iproject2.html
2) Getting the Old Paint Off: http://www.scottgrundfor.com/ideas/paintoff.html
3) Preparing for Paint: http://www.scottgrundfor.com/ideas/paint2.html
4) Applying Paint: http://www.scottgrundfor.com/ideas/paint3.html

If you're looking more towards adhesion and not really concerned with a mirror finish why not just bead blast at low pressure, prime, and paint?

If you're looking more towards adhesion and not really concerned with a mirror finish why not just bead blast at low pressure, prime, and paint?

Media (sic, bead) blasting is a paint removal technique, not a surface preparation. Bead blasting doesn't remove all of the primers and fillers sufficiently enough to get a good surface for adhesion (RE: the articles I posted).

In order to get the best adhesion surface, the metal itself needs to have its surface area increased by sanding. It's the scratches in the metal, or in the underlying surface preparations, which hold the primer/paint to the metals surface.

Just to add to the myriad of suggestions there's also some high temp fillers like
http://www.alvinproducts.com/Products/Prod...id=2#Durability (and many others) that are designed to deal with higher temps
You may want to consider High Temp paint also.

I guess I should have included the word GLASS in my description of bead blasting.

Abrasive (glass bead) blasting will blow holes through steel if the gun is held in one spot. It's been used as a rust removal technique for decades and will get the rust out of the very deepest pits more quickly than almost any other method. It has less of a work hardening effect than sand and is less likely to warp thinner panels. It takes a bit longer than sand but the results are worth it.

It WILL etch a metal surface in a very uniform manner and if attention to detail is used it works great on irregular surfaces without knocking down high crowns like sandpaper can. The degree of etching is dependent upon the coarsness and hardness of the media, the force with which it is applied, and the amount of time it is allowed to stay in contact with a given area of the surface.

Ah, that's a horse of a different color! When you said "media" I assumed you meant the cob or walnut types and not the silica/soda-lime types of media. I don't necessarily like any kind of blasting on sheet metal, as it's almost impossible not to get a peen action from any of the medias. I agree it would take off the finish, but it also tends to em-brittle the metal to some extent. Just my personal preference.

I didn't say "media" Mike. I said "Bead". As in glass. The imbrittlement/surface work hardening/stretching/etc. usually is caused by trying to rush the job by using too aggresive a media (uh-oh..there's "that" word. In this case media is all inclusive of anything that can be run through a blast gun.)/ too much pressure/ generally not paying attention to detail.

Lower pressure blasting with an abrasive that is just slightly harder than steel and working slowly gives great results.

It has no more work hardening effect than the vibrations of a mechanical sander.

Jim, Mike,

just curious on your opinion of using coal "slag" ( and I don't know / care if its media or whatever) to blast the skins for paint prep. I am new to the blasting process - just picked up a HF cabinet listed at 300$ - on sale for 219$ and with 20% coupon got it for less than 175$ - so let the madness begin.

The only question I had was that coal slag is available in this area for 12$ per 100 lb bag while oxides are 3 and 4 times that cost. Are the aluminum oxides longer lasting and slag that inferior of a blasting media that I should consider the use of oxides to remove paint from steel skins ??

I don't recall having ever used any coal slag so I can't give a definitive answer. I would compare it's hardness and sharpness to the oxides and go from there.

If you're referring to Black Diamond, ect blasting media that stuff is way too aggressive for any sheetmetal under 1/8". It will deeply etch nearly any metal in a big hurry and is mainly used for heavily painted/rusted thick items. Aluminum oxide or glass bead in the lighter grades works about the best for most media cabinets. The amount of dust, air pressure and evacuation system all are factors in determining what media to use in your cabinet. The cabinet should come with a list of what media is recommended for it in the manual.

I prefer the lighter grades of glass bead myself, takes a bit longer but a lot less surface filling/prep on the thinner metals and won't destroy cast aluminum.
Sarge

Senior Moment, I said "media" not you, my bad!

Couldn't say, I've never used it. I only resort to any kind of blasting when there isn't another less aggressive way.

So officially,

no one can say "media" "glass", " bead" or "beads" in this thread.



only "primer", "glaze" or "metal prep" are acceptable



Thank you

Come Again


Don't make me go CAPS LOCK on you guys

Sarge,

since I've outlawed the word "m$d$A" from this thread,

the "black stuff" I bought appears to be coal slag marked "Fine 3060".

does that make any sense ?

to me, coal slag could easily be renamed black diamond.

having lived in Scranton Penna for most of my childhood, I remember my grandfather coming home with similar material in his pants cuffs when he worked in the coal mines.

i loaded some up in a spot blaster and it did do very quick work of making a muffler rust and scale free.

can't say it did much damage at 75 psi.

thanks

At 75 psi I'm surprised the nozzle even works. Unless it's a pressure pot system you either have to use above 100psi or a very high cfm flow rate to move your media. And btw-media is the correct word for any material used in blasting.

Coal Slag, Black Beauty, Black Diamond are all basically the same thing, just depends upon region. Since we're not in the Belt, they charge around $7/50lb bag for the stuff around here. Useful for pot systems (with the correct nozzle/gun system) but only when doing heavy work, like a large semi-trailer. At work we used that material for blasting the coating off the local 36" gas pipeline. With the high-volume rotary air systems and large nozzles the blasters could clean a 24" wide pattern all the way around the weld joints in less than 2min. It also left some serious scars on the high alloy pipe for the joint coating to bite. Rough enough that one wouldn't want to run your knuckles across..

Just fyi- "3060" is one of the many combination grits available. Using two different grits like this (30/60) allows the material to blast off heavy rust scale and very thick paint and yet still retain a smoother finish overall. In my media cabinet most times it is filled with 170/400 glass beads. This is for two reasons - mostly allowing me to work with light cast aluminum alloys and leaving a smoother finish on steel for painting. If you run into the common "kid with a paint brush" on a tractor the glass is not up to the task without a lot of time.

Good general purpose medium grade aluminum oxide will last longer and produce more cutting efficiency for most of the work folks use a blasting cabinet to do.
Sarge

Sarge,

I have a run of the mill 5hp 50 gal compressor and have not setup the blasting cabinet yet.

Your feedback makes me think this media is useful for such items as hubs, mule drive, and the outside of wheel rims (probably not the bead area)

crap, I said bead and media on my own post !!.

So thanks, I'll check out the alternate medias and learn a few new things this weekend.

Honestly, read the manual that came with the equipment. Many make the mistake of running the wrong media and destroy new tools . Air pressure, gun orifice size/nozzle all must be considered when picking media grades/types . For example, my current gun on the pressure pot I use outdoors will not work with Black Diamond, no matter what grit/size , it just eats the tip . The gun head is designed for use with Slicon Carbide or Aluminum Oxide only. I have run some washed types of silica through it and that works just fine .
BTW-I am fully liscened and trained for Hazmat work, and own a full array of protective equipment . I do not recommend anyone using silica-based media of any sort .

Back to your original question-
For deeply pitted metal , I thoroughly blast the parts clean, degrease and even sometimes use the DA sander to finish the surface off . The parts are either coated with epoxy primer, red oxide primer or polyester filler to take care of the pitting . The Polyester I use directly reads to apply it to bare metal, never on top of any primer . There are many types of fillers out there, each one has it's unique recommendations from the manufacturer. At any rate, whether to bare metal or over primer the whole thing must be properly sealed before final top coating. If not, the rust will come right back through.
Sarge

Thanks Sarge,

I finally hooked up the blast cabinet yesterday and the results were excellent on the thicker metal parts such as hubs, seat springs and the mule drive parts.
The coal slag definitely "frosts" the metal but nothing that 2 coats of primer and a sanding can't cover up.

My next question would be how to determine if the coal slag will damage the body skins. I heard conversation about "warping" and "distortion" happening from using media which is too aggressive.
Is this warping pronounced enough to see or do I need a straight edge to tell ?

Thanks for all the advise so far.
.

Most warping issues on sheetmetal are from heat and very coarse media will do just that, makes the surface very hot. I know from experience you have to really focus on one area to create a problem, but it can happen. More likely is damage from the stress of heavy blasting which can lead to brittleness and cracking. I'd much rather put a few extra hours on the compressor than spend half a day repairing a hood that was overblasted. As a plus, the coal slag will be much quicker removing paint runs and thick spots that most grades of ground glass or glass beads will hardly touch.
Just a note-some folks' definition of distortion is in fact "frosting", nothing more than the surface of the metal being somewhat pitted from blasting . It all depends on velocity of the media, crank things way up and you can literally blow holes even in heavier metals.
Sarge

A few more comments and questions on this topic.

First is the life of the coal slag media.
I have blasted 4 hubs, 4 rims, 2 seat housings, 4 seat springs, 3 hitches, 2 belt guards and 4 tachmatic brackets and 4 floor boards. All this on 10lbs of slag and its still going strong. Is slag this long lived ?? Does it regenerate its sharp edges as it blasts apart ? I'm truly amazed on how little media I have had to use to accomplish all this work.

The setup I'm using is a HF cabinet - 5 mm nozzle with 50 gal / 10cfm compressor at 90 psi at the compressor. Media is 30/60 coal slag. After all this work, the nozzle is still intact and never a gun clog !

From a standpoint of warping the sheet metal, I purposefully tried to overheat the sheet metal by keeping the gun in one spot. Maybe my setup is not that powerful, but I did not see any evidence of heating the metal. I have not yet tried a larger or smaller nozzle. What difference in performance would I expect to see on a larger or smaller nozzle?

Thanks

Wow... I got lucky on my "media blaster". My father-in-law had an old gravity fed one that I was able to replace the hose on and use. Went to the local farm store got some aluminum oxide and used it ran out and next trip got the glass bead, been using it ever since. I have had no problems with it. I think if I had read this before hand I would have been worried about PSI, proper tips, and so on.

Sometimes ignorance is bliss.

I have looked in to buying a cabinet but they seem to small or to much $$. Before my E-Tank was made I was using a plastic 55 gal container and capturing my media. Now all I have to do is the hood and fenders witch wont fit in the 55 gal container so my driveway will be getting a new coat of glass bead.

I have no experience doing body work and really no one to show me. I have read a lot and have had to redo some things but so far I'm real glad with the outcome. I do want the best looking finish I can give but as off now it wont be going into a museum. I do seem to be taking along time to complete this project and am not sure if my process is right or wrong. I'm sure I'm taking extra steps that are not necessary but in till I know the difference this is how I will do it. It seems like there are as many ways to do the clean, prep, paint and finish as there are people doing it.

Live and learn. When I quit learning hopefully it will be my last day on earth.

The slag should last a long time, and yes it does regenerate it's cutting edges a bit as it degrades. At 90psi and only 10cfm, better leave it alone if it's working well for you. Bigger nozzles equal much more cfm required- my compressor here is 80 gal/27cfm. Using a 4mm air jet with a 5-7mm tip taxes the pump pretty hard but I'm also running 150psi . In comparison, if I used coal slag in this cabinet the glass lense and possibly the cabinet wouldn't last long at that pressure. If yours hasn't started cutting the nozzle a bit it may be a carbide or hardened steel head. Ceramics are ok but don't last very long unless you use a less aggressive media.

It sounds like your current setup is working ok, better off leaving it as-is if the tip isn't wearing out quickly. If nothing else, post up a sunlight pic of some fresh blasted sheetmetal- it will show if it's getting deeply pitted. A smaller nozzle will probably just clog , larger one would kill the compressor trying to keep up or run low on pressure . I just prefer a smoother finish and work with a lot of delicate cast materials-mostly carbs. The smaller media is also easier to rinse out of passages where larger types can literally jam themselves in tight.

To heat the metal, it takes a pretty aggressive media, a very high volume of air and a lot of pressure. Mine will heat thinner metals above 20ga if I concentrate on a spot for very long-hot enough to be easily felt through the cabinet gloves.
Sarge

Sarge,

thanks for the explanation of tip sizes and materials.

I'll try to post a sunlight picture of a sheet-metal piece, maybe half blasted to show a bare metal pre and post blasting divide line for comparison.

Ditto on the Plexiglas viewing port and the replaceable vinyl protectors. The replaceable vinyl covers work well ,but if you don't get all the adhesive areas perfectly flat , media can start collecting between the lense and the protector and cause more visibility issues.

Replacement of the plexi with tempered glass will be the first modification I will try to make on the cabinet.
Just don't hold your breath for any quick updates !

Again, thanks for benefit of your experiences. All starting to make sense now.