I've sanded the body of my 'A' to bare metal. I understand that you want to apply bondo/filler to a rough metal surface. But, I believe that this old bare, pitted metal needs to be coated with some type of rust preventative. I was thinking of getting some Ospho and treating all of the surfaces with that, but then I got to thinking, will the fillers properly adhere to it? Please correct me if I'm wrong, but is not the order of proper proceedures as follows? 1. Bare metal with rough surface 2. Acid etch with ??? 3. Apply bondo/fillers 4. Sand to shape 5. Primer surfaces 6. Finish sand 7. Primer again 8. Apply Topcoat Your help is greatly appreciated.
There are several way to do it. I like this process. 1. Clean freshly ground metal. 36 or 40 grit where your going to apply filler. No etch primer under filler! Some guys like epoxy under the filler, (I dont. Find and read oversprays post in the tech section and read it) 2 After all the filler work is done and finished to 120 grit, sand the rest of the bare metal with 120 on a DA. 3 clean with wax and grease remover. 4 Etch prime the bare metal, avoid the filler areas. It can soak in the acid if you get it wet too on the filler. 5 then prime with a two part filler primer, you can put down an epoxy first, but make sure it's compatible with the etch primer you used. 6 Block sand your filler primer. You'll need to repeat the filler primer, and blocking cycle til the surface is straight, and the scratches are filled. Each time you block sand lightly etch prime any bare metal you sand thru to before more filler primer (primer surfacer) Stay with one brand of materials all the way thru to job. Ask for P sheets(proceedure pages) for every product you use. Read and FOLLOW the instructions. The P sheets will tell you what is compatible with what, how much to put on, mixing, dry times, flash times etc.
If the whole car is in bare metal (pretty much everything I do is. Gotta get naked to come in my shop) First thing after media blasting I like to put on a "shop coat" That's a light prime that is removed as I do the body work. I use all PPG stuff so I spray a light coat of DX1791 etch prime. It mixes 1 to 1 with 1792 You can see thru it, it's easy to get off when you prep for filler, and it's compatable with DPLF epoxy. You can then prep and prime each panel after the body work, or wait and prep and prime the whole body when your done, It depends on how long your going to take with the body work stage. Most every thing I do is bare inside too. I spray inside and out with 1791, it's good till I'm ready to coat the inside with whatever I'm going to finish it with. Just sand, re-coat with 1791 on go on from there. Just keep in mind that etch prime should shot light. It's for adheasion, & rust protection not build or filling.
What about the manufacturer's recomendations? I don't think PPG or DuPont formulate that stuff in a vacuum. I know PPG has a website that provides all of their product info and how to use it. My understanding is that you don't apply polyester filler to bare metal since is hydroscopic and encourages corrosion whre it contacts bare metal.
The P-sheets are the manufactures recomendations. Epoxy under filler is an option. The corrosion issue that your refering to is caused by tempature and humidity extreams outside the windows recomended by manufactures. I've never seen corrosion failure of filler without obivious preperation mistakes, or other paths that water and oxy can get to the surface..
Polyester resin based primers--Evercoat's Featherfill, Morton Eliminator, etc. These primers are based on the same resin in bondo/body filler. They work well over filler and it usually is a good high build system. I like Tinbender's system. I didn't think many were using the 1791/1792 etch primer system. These products have changed somewhat over the years, but that used to be the best automotive etch primer 30 years ago. I'm betting it still is a very good system if used following the tech instructions. overspray
I thought that's what he ment (Featherfill) I haven't used it in years. How stable is it Overspray? Or anyone that has used it on something they have been able to keep track of for a few years. I've got a 63 impala with aftermarket quarters and some serious issues with the roof. Ive been thinking of using it on that.
There are 2 types of bonding in this type of work...mechanical and chemical. Mechanical is best for fillers. Even poly types like Slick Sand and Featherfill. Mechanical requires a rough surface, chemical requires an "open" surface. To open a surface requires sanding. There's also a combination involved of mech and chem. One instance would be if the basecoat sat too long before a clearcoat. That's what a re-coat "window" is about. Sanding that surface allows for both. As far as fillers go, they like a rough surface. not too many fillers like to be over fresh primers and such. The finer you can sand the surface for the filler and still maintain adhesion (mechanical) the better the final outcome. I recommend no more than 80 grit for run-of-the-mill fillers. In most EVERY case, 36 and 40 grit grinding marks show up at the end due to shrinkage and solvent penetration. It's also hard to feather. Don't mix the filler too fast or "hot" and 80 grit is just about perfect. The better you apply the filler, nice fine almost ready to use surface, the better the final outcome and the easier it is to work out. The rest of the above advice is right on. Etch primers have their place. Under fillers is never one of them. Good luck with it.
As far as spray Poly goes ive been useing Raderal from Spies for about 8 years. I like it, and havent seen any issues with it. But then again, Ive never needed to seriously abuse it iether.
BRAVO!! to "theHighlander". That info is the reason I prefer mechanical adhesion of filler to bare metal. There are "schools of thought" with a large following, for putting filler over epoxy primer, even while the epoxy still is releasing solvents and not fully cured. That makes me nervous about possible adhesion loss between the two from solvents, and some shrinkage later as trapped solvents finally leave the substrate. All epoxies are NOT created equal. There are different formulas of resins and different solids added in different quantities. Some of the tech sheet reading I have done lately on some epoxies shows some for use under filler and some not. Also, in reading tech on epoxies, make sure to read ALL the tech to see how the manufacturer reccommends the surface, metal or coating, be prepared-and what flash, dry or cure times are needed before applying any materials or coatings on top of the epoxy. Tinbender: Polyester resins have changed with resin technology changes in the last 15 years. Mostly, they are more flexible and have even better adhesion. Featherfill is not the same as 20 years ago. It should be better, I hope. These primers are highly reccommended on fiberglass bodies because of comparable flexability. They work well on metal, but again not with etch primer underneath. The acid in etch primers will slow down the cure of polyester resin. This could be hard to see or feel and could give the false assumption the primer was cured completely but was actualy only dry of solvents and not totally "resin cured". Polyester resin primers usually have very good solvent holdout and do not let solvents from topcoats penetrate through. I've used Featherfill on old cracked and crazed factory GM lacquer paint to seal off the old finish. I know it's not the best, but to save the customer the cost of stripping, it did the job. I did a Featherfill job on a 1964 Chevy in 1977 over crazed original lacquer followed with an Acrylic enamel paint job. I saw the car about 5 years later, and it still looked great, no shrinking or crazing telegraphing through. TomH used polyester primer on his Track T, after using metal conditioner to prep the steel (rinsed off of course). Check the tech post we did "Shootin' a Track T". That is a "low-buck" job that turned outvery well for a "garage paint". I still prefer to etch prime, after sandblasting and DA sanding the sandblast texture, followed with a high quality 2 part hibuild urethane primer surfacer. I also like to etch prime long term projects and grind off the areas to bare metal that I do filler work on. Spridle: that's good to know about the Spies Hecker product. There are so many good products and systems available. AHotRod: Glenn, I hope your head doesn't explode with all the information you need to acquire about these products and techniques, but it will definately be worth the effort of learning before you actually purchase and use these products. A good job and some time and money saved are the results of preparation and research. overspray
Thanks Overspray, and others that added. I'm still nat sure if I'll go with the "featherfill" on this chevy. We'll see how bad the roof looks when done. One more question. The Feather fill I used 25 years ago could not be wet sanded. Is this still the case?
I think that may have changed. There are several versions of polyester primers from Evercoat. Let's both check the website and tech info to be sure. overspray
Well it is definately a better product (Featherfill G2) than the stuff from 20-30 years ago (according to the tech sheet). Sands wet or dry, and OK to use under 1K or 2K etch primer (which extends the dry/cure to sand time). It comes in Buff, Gray, and Black and is tintable (10%). That seems good enough to me to try it again. I know it used to be very reasonable in price for the performance and fill quality it provides. I'll think I'll have to spend some more time reading some updated product tech. You gotta keep up learning the product. overspray
Thanks O.S. Keeping up with all the developments in our products in gettng tuffer all the time. It's one of the reasons I'm not painting much anymore, and concentrating on metal work. I won't be painting this Impala, but I'll still do the prep. It's hard to let go and trust someone else to paint over your work. It's getting hard to do it all. And still do it right! Good thread, Good info. Well, I gotta go hit the shop. Need to finish rubbing a black paint job I've been working on for what seems like forever. We'll have to talk cutting & buffing systems some time!
Get rid of all of the rust first, otherwise it will still spread. You can epoxy the car before the filler, if you use newer filler like evercoat rage. This is actually recommended by some car manufactures(Toyota as well as aluminum cars) for repairs in some of the more humid regions of the country. You can also apply filler straight to the bare metal as long as it is primed before it gets wet, because it will hold in water as will surfacer. For the record if you are using filler on painted surfaces I usually grind the area and then sand it with 80 grit and feather edge it with 150. Do not use a grinder or anything coarser than 80 on hoods, roofs,deck lids, or aluminum cars because the heat can distort the metal and you will spend too much time on the panel and use too much bondo(If you have high spots use a file or a hammer).On aluminum don't use a file, or a hammer that has been used on a steel car. Also use a clean spreader and apply evenly.
Well, Glenn, you see that even with lots of experience us "old" guys still have to keep up with tech info. Part of "improving" products has to do with environment (EPA) and hazzards to health. A lot of primers and paints used to contain lead and (zinc) chromates. Those addatives were extremely beneficial for the performance of the coating, helping with durability and corrosion protection, but sadly hard on health and the environment. A lot of the "improved" products won't measure up to the old stuff due to the lack of these addatives. We just have to rely on the tech info available and the experience of others who have used something (correctly) to make good choices in selecting fillers, primers, and paints to get good value for the cash outlay. Sometimes the "cheap shit" is just that, and other times it's a very good value. Always consider the foundation products-fillers and primers-to be the most important step to good protection and durability of the whole refinish job. overspray
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