What's Right? Body Filler Over Epoxy Primer or Bare Metal?

This video will help you decide if you should put body filler over bare metal or epoxy primer. Different dry times, filler types, epoxy primer types and sand paper grits were used in an extensive experiment to compare the bond strength of body filler over bare metal vs. body filler over epoxy primer. Tools, materials and Lakeside Merch and Apparel below -
*** Epoxy Primers: Auto Body Master Epoxy Primer, Speed Coat Epoxy Primer
*** Fillers: Auto Body Master Light Weight Body Filler, Evercoat Everglass

[davidgalea]

Filler can absorb moisture and cause rust to the metal underneath it. The level of moisture absorption will depend on the filler brand, humidity and the amount of time the filler is exposed to the humidity in the air. IMO Epoxy primer the bare metal first then put the filler on top of the epoxy primer, this method eliminates that risk regardless of how small that risk is especially considering all the work and money to paint a car.

[ShystySpokes]

Great way to actually put it to the test because a lot of ppl seen to have an opinion on which way is "right" or best but they dont seem to know why. This is right in front of your face. Black and white results. Great job!

[vincemajestyk]

Great video! I've done both depending on circumstances, but I would always prefer a good primer underneath depending on the size and type of repair. Most of the problems people have is with improperly prepared bare metal under the filler where rust has not neutralized.
Many people don't realize that regular filler is just talc and polyester resin. Talc absorbs water. If there's rust underneath it will rust again. You have a better chance with premium fillers like USC All-metal or similar that uses ground up aluminum or any of the 'fiber' fiberglass reinforced fillers like Tiger hair or Gorilla hair, maybe not that extreme but just a 'glass' filler which doesn't absorb moisture. You can see regular fill soaks up water wet sanding. They use that Bondo-glass fill exclusively in the marine and boating world just because it doesn't pick up moisture.

[LRSS]

In the early 90's I had to go to the PPG training seminar to become a PPG certified painter. They are the ones who require their DP epoxy primer to be sprayed before the plastic filler is applied. You still have to give the metal tooth for the filler to adhere to the panel. It has to have 40 grit scratches using a rotary sanding tool. The epoxy is to prevent moisture being transferred to the bare metal.

I don't know if it is still required or if any other paint companies suggest it being used this way anymore. I have been out of the industry for the past 10 years. If I have to now, I will still spray my epoxy before application of plastic filler.

[mickholgate]

Great video Jerry, well done. I personally use epoxy primer only to keep the car rust free while I'm carrying out body work. Seems to be the option for restoration type work vs collision repair work where body filler gets used on clean prepared bare metal.

[djhoffman]

Great info in your vids, thanks! I always find myself in the bare metal—>epoxy—>filler—>epoxy camp. Main reason being moisture protection. Since most fillers are porous polyesters in composition, my concern is moisture trapped inside the filler eventually causing rust through heat/cool cycles causing condensation. Being that you can never get the moisture levels in the filler to 0%, you can always reach a temperature at which condensation could occur. The only filler I occasionally use DTM in window channel areas is Adtech P17 because it cures to a solid. Again, potential moisture/corrosion down the road is my main concern as I never have had filler adhesion issues to begin with.

[rongamble]

I use epoxy primer all the time on my restoration and custom jobs but not recommended for typical collision repair but I let my epoxy set for 5 days then sand whole car with 150 then the areas for filler I hit with 80 after my filler work is done I spray 1 coat of epoxy over everything flash off then apply my polyester

[russdavis]

NICE!!!

As long as the substrate is sound and properly prepped, the bond of the filler should hold.

[moesizlac]

Bond strength isn't the central issue on this question, moisture is.
Epoxy is moisture barrier. Metal needs to isolated from moisture asap. Get the epoxy down first. Then take all the time you need on filler. Just don't sand past the epoxy.

[BruceLyeg]

It's all in the prep. Like you, I've never had a filler failure on any substrate. Great demo

[paulking]

First, I LOVE your channel. This is the video I've been waiting for! I've been restoring our '65 Chevy C10. I ook it all the way down to bare metal, which meant taking off who knows how many gallons of body filler! Now, in searching for the proper way to work the metal BEFORE applying and covering the 1/2" to 3/4" dents with body filler like the cheapo BIG name body shop did. Ya, watching to many different people do it in MANY different ways can leave a Fellers head spinning LOL

[blueblood]

I always make a chart so peeps can see different out comes at a glance. Good vid.

[gwcastle]

It’s best over scuffed metal but it really doesn’t matter if whichever base primer is used as long as it’s s properly cured and the metal has been properly prepped before whichever base primer is used and scuffed before the filler is applied . It’s going to stick

[JH-vfrm]

Everyone has debated this topic for years so it’s nice to finally see an actual scientific test to put myths to rest. As usual another awesome, informative video. Thank you for sharing your knowledge!

[unclemarksdiyauto]

I have always wondered this exact question. Thanks for doing a experiment that is actually measurable! Thanks for taking the time to do this video as well as this took some patients! (I guess bodywork is something you can’t rush so your use to this) I think this does answer the debate. Good work Jerry!

[lismsthebenchandthebooth]

Very interesting....I was always told that filler to bare metal would cause moisture between the 2 over time...however I only hear the filler over epoxy in restoration...but in a production shops I've worked at, it was always filler to metal, 2k prime, , seal, , etc...Very nice video!!

[TheDocrock]

Thank you for this debate answered! I did one thing that was suggested by you, which was verify with the vendor how and in which order should the filler and epoxy primer be used. The answer was, do all filler over properly prepared bare metal, then epoxy. I saw a video with Kevin Titts and he stated the same thing using Eastwood products. I feel comfortable now hat the methods I have used over the years have been correct, accept for, one time I sprayed rust converter over rusty metal and the put primer and paint, and it didn, t last long before I had bubbles. From now on it is strip to bare metal wash with metal etch. The parts look like they are fresh stamped steel . Keep up the great work

[robertmccully]

It not the epoxy or the filler that causes fails, , it’s if the surface is clean on the metal, epoxy, or paint that you apply it over. You don’t put anything on a dirty surface. The reason some people strip down to metal is to get down to a clean surface, versus any possibly contaminated layers in between.

[sidney]

Excellent test, I done my car in epoxy primer over bare metal first, but still ended up sanding through it on some spots. Good to know it's all good in any case. Thank you!

[Chad_N_Stacey_Hopson]

This is an ingenious experiment brother.... very informative and well thought out!!