Why Wont My Filler Stick

mvernon · Jul 15, 2019

I have been working on repainting my bridgeport. I seem to be having problems with my 3M Platinum Filler not adhering to the bare cast iron. The process i have used so far is -
1. Purple power degreaser
2. Wire Wheel all paint and bondo off
3. Purple Power Degreaser
4. EastWood After Blast to prevent flash rust
5. Acetone to remove After blast and clean for Filler
6. Apply Filler

I was concerned about adhesion so I did some test spots. When scratched it seems to flake off. I know that everyone says put epoxy primer on first. But the filler should still be sticking to cast iron even if it isn't ideal. Does 3m not adhere to cast iron? Do I need to switch to a different filler? I still have practically a whole gallon as it was bought just for the bridgeport.

mvernon · Jul 15, 2019

Items 3 through 6 were all done with in a 3 hour period.

72bwhite · Jul 15, 2019

epoxy primer ......

atomarc · Jul 16, 2019

Lots of Purple Power Degreaser...I wonder if it's soluble with Acetone, or if it's leaving a residue that doesn't allow the filler to grab the substrate. I would try an area sprayed with something like 409, skip the Eastwood junk, wipe with Acetone and give it a go. If you try to scrape the stuff off you'll probably do just that. Let it dry for a day and see if that helps.

Buzzing it with that wire wheel could also be smearing a mixture of paint and Bondo over the metal that simply won't come off with your next cleaner and that's interfering with the bond betwixt filler and base.

Stuart

thermite · Jul 16, 2019

72bwhite said:
epoxy primer ......

Prolly WORK.."POR" tribe especially. But IMNSHO, it's treating the symptom, not the disease, may be bridging, reliant on its own film strength easily as much as good adhesion?

My prep ends with dilute Naval jelly, small jobs, ignorant Phosphoric acid out of a jug, larger ones.

Last application is left to "dry" - eg: go frosty grey-white, leave the tooth of Iron phosphate, similar to "bonderizing" of galvanized sheet steel... but without the Zinc.

If one does not GET that, then the surface was contaminated.

See "wire brush"? Power-driven? May as well have TURTLE WAXED the f****r.

Back up a step or three. FIX that.

Mought try TSP instead of Purple-wotever AKA "lye"?

Cheap, Iyam.

Cheap but also effective. On Iron & steel, anyway.

2CW

TheOldCar · Jul 16, 2019

Maybe cast iron is different, but wire wheelin' steel almost polishes it. I never paint over wire wheeled steel without sanding, etching, or sandblasting the steel afterwards. When using filler before primer, I make sure the area is scratched up.

Epoxy doesn't have to go on first; there are good arguments for both ways. But as far as adhesion, I'm a big fan of always mechanically abrading the surface. You get both benefits when using an etching primer or DTM epoxy when the steel is scuffed/scratched.

thermite · Jul 16, 2019

TheOldCar said:
Maybe cast iron is different, but wire wheelin' steel almost polishes it.

Used, not just-cast CI is way worse. Has its own graphite cousins, plus age-old hydrocarbons trapped in itty-bitty structures and bacterial corpses and their manure from its prior service life.

That actually can be very similar to a wax coating as to how it affects paints.

HAND wire-brush, stiff and still sharpish, not soggy, OTOH, not a big problem. Scratches a tad rather than smears and burnishes as powered ones are wont to do.

Caustics (the "Purple" tribe, but not-only..) "saponify" old oils. Turn them into soaps. Greases are special-use case of soaps. Both leave soap films. Nature of the beast.

Acids are more aggressive, and brand-new nano-flash rust not really a big deal to a decent primer, a mere REDOX partner for Phosphoric acid.

That's why we use it at all. It JFW.

CAVEAT: Acids "active ingredients" - Hydrogenish s**t - also travel widely in ignorant air near and far. Not a welcome approach for any machine-tool that is NOT stripped to basic castings, nor innocent bystanders, same space. Hard on fine mechanisms, etc.

That's why we use it with care, and "elsewhere".

jrmach · Jul 16, 2019

Think the Purple crap was a no no.
Just like citris cleaner is a big no before paint
Now you wired wheeled the purple crap in there but good.
Try good ol laquer thinner

cranium · Jul 16, 2019

Dow oven cleaner.
Scrub it off with running water.
Let it dry thoroughly.
Apply filler.
Sand.
Damp wipe.
Dry.
Primer.
Sand.
Damp wipe.
Paint.

gustafson · Jul 16, 2019

Really Dow oven cleaner but no solvent after?

DMF_TomB · Jul 16, 2019

i would use
.
mineral spirits
.
then alcohol wiping
.
then sand 50 grit sandpaper
.
then alcohol wipe til wiper tissues come off clean. til the dirt is off it aint clean yet. might take 10 wipings
.
also if epoxy or filler is old it dries out and doesnt work as normal. usually check expiration date and i dont use anything expired
.
when i want tape to stick i have used rubber contact cement and let dry. it provides a sticky surface for sticky tape to stick too.

Pathogen · Jul 16, 2019

The cast iron has absorbed the oils used in its work life. Should have just left it alone and enjoyed the patina. If you must paint it, disassemble completely and deep soak in mineral spirits for about 3 months. Remove and used oil based paint before it dries out from soak.

Alternative method would be to place in the ocean underwater about 30 feet for at least 2 weeks, then thermocycle for another week. In this method you will have to use water base paint. Be sure to get off all the salt.

Dan from Oakland · Jul 16, 2019

Get some Dupont Metal Prep or equivalent and follow the instructions. It has phosphoric acid in it and will etch the surface so primer and filler will adhere.

thermite · Jul 16, 2019

gustafson said:
Really Dow oven cleaner but no solvent after?

Folks should read the data sheets. Oven cleaner is just a fancy way to package ignorant lye so as to get paid more for it.

Purple <wotever> - also the "basic" caustic should have worked just fine, too. As it has for hundreds of others.

The killer seems to have been three-fold;

A) he had "pockets" of gradoo left, probably in corners, around bosses for bolts and such.

B) power wire brushing smeared that crap around and forced it into "the usual" CI surface imperfections; also burnishing whatever the other areas of the casting held to add to the problem.

C) MORE goes at it with the caustic, AND THEN ALSO serious-good RINSE was not done thoroughly enough. HOT water, and plenty of it before any solvent rinse or wipe.

No need to get overly fussed about "flash" rust, BTW.

It is actually a good indicator that one HAS gotten clean clear to truly bare Iron. If it does NOT show up uniformly? There may still be contaminated areas as need more cleaning.

Don't fight that. Put it to your advantage.

Richard King · Jul 19, 2019

So many guesses. Have you checked the expiration date on the filler? What is the humidity in the area where you are dong the project? 3M has a help line you can call or write: Help Center | Contact 3M United States Call Monday - Friday 8AM to 5PM Central Time 1-888-3M-HELPS (1-888-364-3577) Have the product info off the package when you call.

M.B. Naegle · Jul 19, 2019

I'd add heat lamps to the mix to warm and help dry out the surface before the bondo. Also how much Acetone are you using? We use Lacquer Thinner for surface prep, but when you are working with porous rough surfaces like cast iron, It's not enough to just "wipe it off." You almost have to sop it on and let it dry. It'll get deeper into the texture and help leach any oils out of the material. If the troubled area is one that may have had a lot of oil exposure in the past, you might first need to take a propane torch to it and bake the oil out.

DMF_TomB · Jul 19, 2019

yes old epoxy dries out, literally not suppose to use if expired for good reasons.
.
epoxy anchors for concrete the capsules are clear and you tilt and see if liquid flows inside. old ones liquid gets thick and or does flow as it is dried out. basically old epoxy is no good
.
spray on scrubbing bubbles tub and tile cleaner is not regular caustic as it will cause rust. concentrated caustic doesnt cause rust, its when you wash it off with water and do not immediately dry it that you get rust.
.
usually i use mineral spirits if there is soaked in oil. it works better than alcohol on heavy oils.
.
plenty of primers that are oil based and have acetone or mineral spirits or MEK or other powerful solvents will tolerate some oil. many times alcohol shellac is used to provide a primer base that other paints will stick to better.
.
rubber cement solvent based is another that i have applied and let dry where i need masking tape to stick. sticky sticks better to other sticky things

Demon69 · Jul 19, 2019

M.B. Naegle said:
I'd add heat lamps to the mix to warm and help dry out the surface before the bondo. Also how much Acetone are you using? We use Lacquer Thinner for surface prep, but when you are working with porous rough surfaces like cast iron, It's not enough to just "wipe it off." You almost have to sop it on and let it dry. It'll get deeper into the texture and help leach any oils out of the material. If the troubled area is one that may have had a lot of oil exposure in the past, you might first need to take a propane torch to it and bake the oil out.

^^
Polyester body fillers stick pretty well to most materials, surface prep doesnt have to be too fussy, no amount of sanding or wiping will remove soaked in oil which is the likely problem here. Oil literally runs away from a torch, I remember getting ready to braze some CI, watching the oil come out the moment the torch got near was an eye opener.

DMF_TomB · Jul 19, 2019

some cast iron is porous. literally it will not pass pressure test cause air goes through micro cracks you cannot see. oil can be soaked in like a oilite bronze bushing has oil in the metal

M.B. Naegle · Jul 19, 2019

Iron of course isn't very consitent either. You find voids and slag, but sometimes some other oddities too. When I was cutting on my Hendey's saddle, I found one spot, not the whole casting, but one spot that had become saturated with oil to the point that I would clean it, and then come back in the morning to find a puddle in the same spot. Did this multiple times as It just kept oozing out once I cut away the surface layer of iron.

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