what comes first primer or body filler

retro48/52 · #1 (**permalink**) 04-16-2009, 08:08 PM

Boy I might have made a mistake !!!! I am patching all the metal on my 48/52 ford f1 and read all the READ FIRST stuff on the Forum but stillgot over zellous and right after the metal patch panels were weldedin the fenders and ground down to perfection, I used ALL METAL to start the first coat of filler in the patched areas..... I know what I read but now I am wondering if I should have primered the fender first....Oh well.... Now I was wondering, can I continue my restoration this way or should I sand it all out and primer the pieces first??? If I don't, what will I be in for later down the line? Can anyone shed some light on if I can get away with what I have doen so far?Thanks in advance.........

Chaosracing · #2 (**permalink**) 04-16-2009, 11:26 PM

Put your fiberglass or body filler on bare metal first, work it to near perfect, then prime on top and do your spot putty. The reason for this is the body filler wont stick to paint or primer.

dman2008 · #3 (**permalink**) 04-17-2009, 12:09 AM

You know I used to work in an autobody shop when I was younger, and never apprenticed or anything but I would always see them grind the paint off and then put the filler on and then prime.

But I am at the same stage I have sandblasted my metal and now I am actually priming with a primer that actually is a Direct to Metal Primer - Does not require a self-etching primer, eliminating extra labor, time, and gun clean-up costs! Primer Filler - As a high build filler this product is capable of 2.5-3.0 mils per coat requiring less coats per application. Combined with easy sanding, this product will reduce repair time and increase shop productivity! Primer Sealer - The addition of urethane reducer or acetone makes
#5425 an excellent primer sealer. Highly versatile, #5425 is the
perfect alternative to replace three products with one! It is 5 star.(courtesy of 5 star website)

Now from what I understand filler itself is a complex mixture of goop that contains, among other things, fiberglass (polyester) resin and talc. The resin allows adhesion as good as most epoxy adhesives and the talc (yes, as in talcum powder) makes the material flow smoothly. Talc is hygroscopic (that is, it absorbs moisture) unfortunately, and that's the reason fillers absorb water. The main solvent in the filler is styrene, which vaporizes as the mixture cures. Bubbles in the filler occur when the mixture cures too fast, trapping the styrene gas.(courtesy of second chance garage website)

So with all that being said I have heard that filler is essentially dirt, and will absorb moisture so that is why i have chosen to prime first to protect the metal and eliminate moisture on bare metal. But the big question is if you are building a sunday driver and it is not on the road when it rains then you may never have any issues but if water some gets in it may cause it to bubble. (IMHO)

But I am no expert and in fact just don't want my hard work having to be redone. I am told that the reason most body shops grind down to metal and then apply filler is to save time could you image priming let it dry and then applying filler? Most body shop I have seen you have Bodymen and preppers but really bodymen should do replacement of metal frame work and welding jobs really, and the prepper should actually apply the body fillers and puttys but that is my opinion.

Hope this helps

D

dbuck50 · #4 (**permalink**) 04-17-2009, 12:45 PM

epoxy primer and then filler...

Action4478 · #5 (**permalink**) 04-17-2009, 05:22 PM

Quote:

Originally Posted by dbuck50

epoxy primer and then filler...

I doubt that is from a tech sheet ,from any filler manufacturer...

grumpy46 · #6 (**permalink**) 04-17-2009, 08:00 PM

i have seen it both ways. i do bare metal then filler. there is a shop in ventura that does $20 thousand body and paint jobs that does it the sam way. must be ok

tbm3fan · #7 (**permalink**) 04-19-2009, 02:04 AM

I do it bare metal first and it seems that Len on Autobody forum does it the same way. They had a test over there, informal, to see which way had greater bonding. The filler on metal or filler on primer. Filler on metal was stronger.

retro48/52 · #8 (**permalink**) 04-19-2009, 07:57 AM

Thanks, so with all that said I think I will be ok the way I am doing it.
Thanks for the statement Mike, Filler on metal was stronger - did not know this
but this puts me in a better frame of mind. The thought of taking all my work
off the bare metal made my head ache.

E30tdf · #9 (**permalink**) 10-09-2009, 07:12 AM

Just a bigginer here as to body work,. I just ground a failed filler repair off the roof of my 86. The roof was damaged years ago by a loader droping a hefty rock or something on it. Whoever did the repair put filler over the old paint in some area without grinding / sanding to metal. The filler/paint cracked many places and this let water in under the repaint. Result cracks, peeling and rust. For what it's worth!

I do have a related question! Should I get all the old filler out of the large dent. Not sure how deep it is but I cut down about 3/16 and did not find metal. If so, what is the best method to dig / pick the filler out? I would then pull the dent out more before refilling.

retro48/52 · #10 (**permalink**) 10-09-2009, 07:29 AM

Some of my fenders had at least 3/16 inch of filler and I used 7", 40 grit sanding disc
on a fairly fast speed angle sander. Took it out very quickly and I got it all out.
Then hammered it out til almost perfect shape of the fender. I wanted metal to have the filler to attach itself to, not old filler. Did not trust the PO before me and wanted to make
sure all was clean and straight.

Just my opinion.

E30tdf · #11 (**permalink**) 10-09-2009, 07:44 AM

Quote:

Originally Posted by retro48/52

Some of my fenders had at least 3/16 inch of filler and I used 7", 40 grit sanding disc
on a fairly fast speed angle sander. Took it out very quickly and I got it all out.
Then hammered it out til almost perfect shape of the fender. I wanted metal to have the filler to attach itself to, not old filler. Did not trust the PO before me and wanted to make
sure all was clean and straight.

Just my opinion.

Unfortunately I cannot get behind the roof panel as it has a sheet metal inner liner. I'm thinking I will weld on some pull tabs and use a slide hammer to yank the panel back to a shape as close as posible to the factory shape, before grinding/sanding and applying the new layer of filler to bare metal. I'm hoping the sheet metal did not get punctured in the acccident or there will likely be hidden rust inside my roof. There is no evidence of that. This old repair was done by the PO or someone for the PO prior to 1998 when I purchased the truck.

Thanks for you reply!

Malu Lani Farm · #12 (**permalink**) 10-10-2009, 05:29 PM

I have always put filler then primer. There was this one time someone didnt know what they were oding to my dads truck and put filler on without putting the hardner in it. The best thing to do is clean it all out before applying more filler to it. That is also after you try to get it back to original if possible.

Chaosracing · #13 (**permalink**) 10-10-2009, 06:39 PM

You always want to try and fix the metal back to as near perfect as you can. You want to limit the thickness of body filler to as little as possible. If it gets to thick, it can crack and bubble. Possibly even just pop off, especially on big flat areas like the hood and roof that get a lot of vibration and flex.

gt350h · #14 (**permalink**) 10-24-2009, 11:56 PM

I know this was originally started in April, but in case other people look at this I wanted to point some stuff out. When taking a panel to bare metal it is ALWAYS better to prime the panel first then filler. For the old timers that don't believe filler sticks as well to primer, you can sand the areas you want to fill to bare metal before applying filler. The reason for primer before filler is for corrosion. Even sitting in bare metal in your garage, corrosion can begin very quickly after getting to bare metal. Especially if you're handling the piece. Filler has made huge improvements in the last ten year also. Adhesion to a good epoxy primer is tremendous. We've done tests on bare metal and primed panels and the amount of damage that either would take before failing was well beyond the normal wear and tear of any product. Also, as another guy stated, filler is porous and has little or no corrosion preventative properties. If you go direct to metal with filler and you chip your paint where that filler was, water can be absorbed, go direct to metal, and rust from the bottom. How many times have you seen rusty bondo chunks fall off of cars in big chunks? I've got a few samples from people asking "why did this fail". Its always the same answer. One more thing and I promise I'll shut up. Bondo isn't meant to be a "panel maker". As the other guy said, buy yourself an Astro body hammer and dolley kit for $30 and see how close you can get the metal back to pre dent condition. I hate body work more than anything, but you'd be amazed what will hammer out. Thick bondo fails. Always has, always will. Sorry this post is so long.

Sand_Man · #15 (**permalink**) 10-25-2009, 08:06 AM

Very good info in that post and it pretty much says what I was gonna say. But I'd add one bit of evidence, ever see a car that's been hit that had filler work done? It seems to me that there's always rust between the metal and filler after the filler has broken off. Now I know some guys will slap bondo right over rust, but most don't. That means the rust occured AFTER the filler was in place. If you use a good-quality epoxy, that won't happen. I prefer House of Kolor's epoxy and I haven't had it fail yet.