I've looked on the net and called suppliers and can't get a clear answer. This is not the epoxy vs filler which is first debate so let's not go there. My question is: Have you applied filler directly to clean sandblasted metal? TDS sheets say sand. However most primers do better with sandblasted metal. Sand blasting creates a better profile than sanding.
My blasted profile is more rough than than a 36 grit finish. If I sand after blasting it smooths the surface. I could understand it if I was using glass or soda....
I am OLD SKOOL More bite the better, I always grind the area to throw down that Light Weight polyester auto body filler
What do you mean? I understand feather edging but how does that correspond to a blasted vs ground surface?
Rough and clean, PERIOD. Scaler, grinder, sandblast, acid etch (but totally neutralized), and clean, Clean, CLEAN. There can't be even a remote trace of abrasive in the surface or it won't feather at all (as mentioned above) and simply flake away. Another method like hardcore wire brushing can leave carbon deposits and also inhibit adhesion even if it looks clean and rough. Power wire brushing should be slow and thorough so as not to overheat the tips of the wires which then slightly melt and get stuck on the surface. So the simple answer is yes, but be certain to use a lot of clean and dry compressed air and even a stiff brush to be sure no traces of sand are left in the now somewhat porous surface. I've said it before, other than some very slight surface corrections I won't put fillers over epoxy. Every product has it's own solvents within, and that includes not only polyester fillers but their catalysts (hardeners) as well. Since most of those fillers create their own heat as they cure that temporary increase in surface temperature can slightly soften the epoxy below. Once cured it traps the softened epoxy substrate for months at a time. A slight whisp of fill over epoxy is no problem, but if anything over about an eighth thick is used I'm going to metal. Once that slick flat finish gets sunbaked a time or 20 those thicker repairs will shrivel up and ghost themselves making all that hard work look like backyard hack shit. No thanks. So yes, clean blasted metal can take filler without issue. Did I say clean? Cuz yeah, it has to be CLEAN. Good luck...
Yea I have applied primer and mud both to sand blasted metal. it works for me but I am not a professional body man so I am not sure that it will not work.
Ive seen all kinds of finishes left from blasting. Gotta make a call if you need to give it some tooth or not. I always went with 36 grit, took the time to hand sand the area. Been years since I applied filler to bare metal - heavy fill, my metal work has gotten better, been skim coating over primer if needed. @theHIGHLANDER makes very good points above and has me thinking.
Listen to the guy from the rust capital . the highlander should know . When I lived in Michigan we sit around and listen our cars rusting away. Clean your metal and work the metal as smooth as you can . Less filler the better. My painter and I got in a big argument over putting filler over bare metal. It makes sense to prime before filler. It makes sense to put filler over properly prepped bare metal. your car ,your choice. Done it both ways with no issues.
That is a good repair. I live in a very corrosive environment like you. I take it a step further. I metal prep the surface I use my own urethane primer 2 coats then comes the filler another coat of my primer which will seal the crap out of it then a surfacer either a urethane or epoxy. My 20-year-old Van still looks presentable. In a industrial coatings environment where corrosion is most severe they put 2 coats of the aluminum pigmented moisture cured primer followed by an epoxy intermediate coat and then the finish coat. In a recent inspection at a coal-fired generating plant along Atlantic Ocean this system after 20 years showed very little signs of corrosion anywhere.
In my mind, on the surface and temporarily ignoring the details - the filler on fresh blasted metal makes good sense. Now looking at the details, every little high and low in that blasted profile is a potential dirt pocket. Fresh blasted metal is really filthy. That profile has little hoods and roofs that partially cover the divots and pockets holding the dirt. It’s so bad that even welding on blasted metal that’s been cleaned is not good. Filler on clean metal, yep. So what’s the process for cleaning blasted metal? That’s what we should be talking about really. I think it’s going to boil down to sanding those high hoods and roofs off of the divots. It Don’t take much usually.
I'm with Highlander on the solvent theory, Also you should Always knock down any Sandblasted surface that's not getting worked/mud with a DA grit depending on the media used to blast...
Good point 'vic, didn't consider the deep details but right on. Someone mentioned etch primer. Be careful there. Some etching primers WILL NOT TAKE POLYESTER. Not poly primers, fillers, etc. It can act like mold release and the stuff can come off in sheets. I'm not sure which etch prime formulations are safe so I avoid them all if I'm filling or poly priming. Your results may vary but this work basically sucks to begin with. The only thing worse is have to do it over
The below was copied from the Rage filler tech sheet. It does not recommend any primer first, but does stress cleaning any substrate well. IMO, sandblasted and cleaned as described would be fine. I hope so, 'cause I've done it and will again. There is a board at autobodystore.com with a bunch of pros. they did a test years ago using epoxy first and direct to metal. After curing the test pieces were bent, sharply to try to separate the filler. Direct to metal fared much better. I haven't seen any recommendations for primer first from filler makers only from primer makers.. There may be some, but I haven't encountered them. Advanced formula with ZNX-7™ provides superior to galvanized steel, aluminum, SMC and sanded OEM finishes. Part of the METALWORKS® System. Blue cream hardener includedAPPROVEDSUBSTRATES:SteelAluminumFiberglassGalvanized Steel.PREPARATION: Clean and degrease the entire panel to be repaired with soap and water, followed by a mild cleaning solvent. Thoroughly dry the surface before repairing. Keep the repair area small. Use 80 grit to remove the paint andfeatheredge.MIXING:
Since every mudslinger in the HAMB family is probably looking in, as well as those who wish to use the stuff, it's ok to use a mild layer on any properly roughed surface of an auto body. Yes, that includes painted surfaces too. Now you can't sculpt a car rendition of the Venus D'milo with it like that but a drag out to the painted or primed surface for nice easy fethering to a repair will not only work but last for decades. Is the A-#1-Best ever approach? No, but when you're doing something that can use that surfacing aid, that slight drag and pretty feather edge, don't lose any sleep over it. Much like primers, a heavy coat can bite too deep. But then too this is where the really dense fillers like Evercoat MetalGlaze can really help get the work to the finish line without going back to square 1. As long as the use isn't abused it's all good. Did I mention a clean blasted metal surface above? I think I did...
A helpful tip to guy's that are unaware of a product called icing, I highly recommend it, especially in the final stages, a skim of this is the equivalent of the slather it on red oxide putty.... Except it hardens In 5 minutes solid, an sand's/feathers at a quicker rate than standard mud, it ain't cheap but well worth the loot...
I have used 2 part glazing putty over blasted for small stuff with no issues this was for cleaning up a chassis I never trusted heavy fillers directly over it. Not on sheet metal. Usually by the time the sheet metal is straight and all the rust repaired there is very little sand blast left. I would rather skip a step at the end of a paint job than at the beginning, its cheaper to fix
Love my icing, couldn't live without it. Bout $23 a tube but well worth it. Makes for a better and easier job. I go through about 5 tubes a month.
Before I had to quit paint and body work because of COPD I used Icing with great results. I quit sand blasting and started using Dustless blasting.
I'm pretty sure PPG still recommends DP on metal first, then filler. I think they specify " cleaned, sanded bare metal" and for increased adhesion use metal etch.
The Jalopy Journal
