Body Filler Over PPG MP182 Question

[Cockbird_Hunter]

I just completed surface preparation/priming of a tractor nose cone with the following procedure:

A. Applied 2 coats of PPG MP170 epoxy primer over bare metal.

B. Applied 4 coats PPB MP182 2K surfacer over the epoxy primer.

After priming, I noticed a couple of small dings I missed in my initial surface prep. of body filler on the bare metal. I have done no sanding to the MP182 yet....

My question is can I apply body filler (fiberglass + resin mix) onto the MP182....possibly scuffing first with 80 grit sandpaper and get good adhesion of the body filler? Typically in the past I have only applied body filler directly onto bare metal scuffed w/ 80 grit & have had good results.

I"m assuming the next step after applying the body filler (if recommended) would to be sand 220, followed by 400 grit the entire surface & reapply 3-4 coats MP182 then sand 220/400 grit again. I am planning to topcoat w/ PPG MTK single stage urethane.

Thanks

 

[GordoSD]

I'd treat the dents just like a new dent. Use the pick and dolly, sand with the board and 80 grit down to metal, filler, and right to 182 again.

 

[thebigyellowtruck]

regular body filler can not be applied over primer even after sanding, however, you can put glaze coat over top of the primer if you scuff it first. its called glaze coat, metal glaze, or finish glaze. only good for minor imperfections though. a small ding should be fine for this though. We used it quite a bit in the body shop that i used to work in.

napa carries it so should any body shop supplier. Oreilly auto parts even carries it.
Metal glaze

 

[CNKS]

What the others say. Just go to bare metal and sand with 80, followed by 100-150. You will then apply epoxy to the bare metal, then apply 182. Finish the 182 with 400 grit, being sure it is blends in with the previous 182.

 

[RandyB(MI)]

I might get some flak for this but I've made my living since 1972 in the body/paint trades so I will stand by what I know works. That being said , body filler should never be applied to bare metal. There is virtually no corrosian protection this way. Body filler has zero corrosian resistance and actually absorbs moisture. As far as adhesion , body filler doesn't know (or care) whether it's substrate is sand scratches in bare metal , bare metal w/epoxy over it or a sound cured substrate of any kind. Yes you should use the finer textured "glaze" or finish coat type filler as it will penetrate in and bind better than course regular fillers. Apply a thin coat of "glaze" to the dents (after bumping out best you can) and let it set up completely and then rough that up with 80 grit and then use the heavy filler for filling deep spots. In your case I would have no problem roughing up the 182 with 80 grit and using regular filler , just work the first layer in hard and different directions and then lay on the "build" layer. When I repair small door dings etc I lay the 80 grit DA flat over it and sand until the outline shows and hand rough the low spot and never go through to metal and then fill. NO corrosian or adhesion problems ever. The "grind to steel w/36 grit" is old school and probably was needed back when filler was "black majic" or other such junk. Smear a thin coat of filler on a chrome bumper sometime and let it cure and see if or how long it takes you to get it off. Will surprise you.

 

[GordoSD]

When I said "sand down to metal" I meant sand down until you JUST SEE A METAL SPECK near the what used to be dent. That's your high spot and you want to build up to that.

 

[SWMO]

B-maniac, you are absolutely dead on in your reply to Cockbird_Hunter . I-CAR and ASE as best I recall recommends them same procedures in their certification tests.

 

[CNKS]

B--I won't argue with your experience because you have much more than I do. But as far as body filler not being waterproof, I usually go to bare metal if I have already applied 182 then apply the body filler. It is never around moisture, and my climate is so dry that the air in the building is dry also. As to putting it on sheet metal that I have just begun working on, I just put it on bare metal. It may get painted within a week, maybe 6 months. I get no rust on anything because of the climate. Yes it can be 100% relative humidity in the morning, it may even rain (all of 7 inches this year). Perhaps I should move to a wetter climate, then I would know the wet peoples problems, but I do not get rust, ever. Also not disputing what happens where you live. Only another opinion. As to sanding, I usually use 80 grit. On small repairs, I have used 100 occasionally. It has never cracked or fallen out in the 10 years I have been doing this -- probably because I never go more than 1/8 inch deep, I try to keep it to 1/16. I have filled some small depressions that I missed that the surfacer did not cover, with single part glazing putty when I got lazy, probably not a good idea, though.

 

[CNKS]

Yes, the Evercoat products work fine. As to regular body filler, the hardest one to use, IMO, is the original one, Bondo.

 

[RandyB(MI)]

CNKS , you are fortunate to have low humidity. Here in MI there are times a tractor/car will sweat like a cold beer just sitting in a garage. The other thing I didn't mention was that most all my methods originated from daily driven ,out in the weather , cars/trucks. That being said , an original 1940-50,s tractor , painted at factory without primer by minimum paid painters with old school paint , if kept inside like most restored tractors are now-a-days , would probably still look pretty good. Most all the approved procedures and products of today are real overkill for a pampered restored antique tractor. Body and paint has always been a "judgement call" profession and probably always will be. Every situation and climate is different. Every new job has it's "unknowns" and as such , there is no "book" on it. Some persevere and most drop out. The rewards are great but so is the heartbreak. You have done enough , you know exactly what I mean. I and a lot of my "old timer" comrads in auto body are about to call it quits and it's sad when you offer to give a young one 30 - 40 yrs of experience and they want no part of it. They want the quick results. There aren't any. So they move on to something easy. They would rather take out a 2yr loan to pay me to do it than to learn it themselves. In 1970 I paid a body shop $100 (paint inc) to paint my '65 Mustang and I vowed to learn it one way or another because I would never pay someone $100 to paint my car again. That's where it all started. I can't stand to pay someone to do something for me that I can learn to do myself. Farm raisin' probably had something to do with that. My praises go out to all you people on here that make a living , do it as a hobby or are trying to learn the body/paint/restoration profession. RB

 

[CNKS]

B, good post -- As to humidity, it was pretty bad where I grew up in south Texas. Maybe 150-180 miles to the east was the Gulf of Mexico. In less than 2 years a new car near the gulf would begin to have rust eating through. Sort of like even the newer cars in Minnesota, etc that suffer salt damage from salt applied to the roads. I certainly have no negative comments on the problems in your area.

 

[Red Ford]

The following is first hand experience learned from using primer and filler in highly demanding situations.

Some prefer one way and have no problems. Others do the opposite and also don"t have problems. No matter what you do it"s a trade-off because:
- Primer adheres to metal better than filler.
- Filler adheres to roughened metal better than primer.

I have had better results with filler on metal, but as I said, that"s when adhesion and strength are pushed beyond what a normal paint job needs to withstand.

It is true that filler is damaged by moisture. Unless it has a hole in it, body sheet metal isn"t porous. So, whether that filler is applied to bare metal, or over primer, so long as it is sealed from moisture it"s ok.

For pin holes and detail repairs a product like Evercoat Polyester Glazing Putty is better. Although it"s harder to sand, it doesn"t flake and crumble as spot repairs done with ordinary filled sometimes do. It"s also stronger than ordinary filler, but like ordinary filler, can only tolerate limited flexing.