Metal skins paint preparation

[Save Old Iron 1,571]

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 ?

:scratchead:

[KyBlue 655]

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..

[pbradley68 1]

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.

[Save Old Iron 1,571]

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

[bitten 134]

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.

[Save Old Iron 1,571]

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.

[linen beige 15]

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.

[sorekiwi 761]

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

http://www.wheelhorseforum.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

[MikesRJ 558]

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.

[KyBlue 655]

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..

[linen beige 15]

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..

:ychain:

[pbradley68 1]

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."

[Save Old Iron 1,571]

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.

[Save Old Iron 1,571]

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.

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

[MikesRJ 558]

Mike, on your Primer you should be sanding with 120, 220 and 320 dry paper, then on your last coat before

[Save Old Iron 1,571]

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.

[Save Old Iron 1,571]

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

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

:scratchead:

[MikesRJ 558]

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

[linen beige 15]

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.

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?

[MikesRJ 558]

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.

[pbradley68 1]

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.

[linen beige 15]

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).

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.

[MikesRJ 558]

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.

[linen beige 15]

When you said "media"

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.

[Save Old Iron 1,571]

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 ??