View Full Version : Epoxy primer before or after bondo??


NYH1
05-14-2010, 01:01:44 AM
I had to weld some patches on the lower parts of my front fenders. Should I put epoxy primer on them before or after I put bondo on them?

Thanks.

Blu-By-U 79Z
05-14-2010, 01:43:47 AM
i say after. Because filler is supposed to be on baremetal. You can put filler over epoxy but you run the chance that it wont bond.

BusDriver
05-14-2010, 07:22:42 AM
Both. Seal the metal up, do the filler then use it as a sealer before basecoat.

Filler is porus and water will infuse it if given the chance, I dont want that next to the metal. Paranoid, maybe, but it makes me warm and fuzzy to know the metal is entombed and SEALED.

Scuff the epoxy well if adhesion is a concern.

leafs_11
05-14-2010, 07:55:03 AM
i had a lenghthy phone chat with the company rep from pro form.
bondo over metal can stick better but also chance it could let go.better to seal with epoxy first . it makes sense.sand blast or wire brush your welds real good.blow off dust and tack cloth. thats just common sense.
he also said to let the epoxy cure for 24 hours before applying bondo.
wenever i welded my patches i used a bright light to make sure all the pinholes were filled with weld.that way its sealed from backside.
im no body man or xpert im just extremely fussy.
all my patches i did required minmal bondo as my welds did all the work.
a die grinder will be your best friend.
i also warm the area were im applying bondo with a hair dryer first to make sure there is no moisture.
wen i sand bondo i reapply epoxy to any bare metal that i break through.

mscamp02
05-14-2010, 08:22:51 AM
wookie and SPI told me to use epoxy then bondo then epoxy then high build 2k before laying down base. So thats what Ill do

wookie
05-14-2010, 09:37:52 AM
wookie and SPI told me to use epoxy then bondo then epoxy then high build 2k before laying down base. So thats what Ill do

Yep.

Blu-By-U 79Z
05-14-2010, 11:41:19 AM
The autobody instructor at the college was the one who said to work the filler then epoxy because hes seen the filler not bond well to the surface over epoxy and pop off shortly down the road. Fillers designed to go on metal. Same reason you dont want it over paint. It just doesnt bond good enough. Now if its a small dent. Epoxy and use a glasze puddy. That is fine to put over primer.

wookie
05-14-2010, 03:49:08 PM
I hate to question the instructor at your local college but this is erroneous information in 90% of cases. The newer epoxies like SPI are designed to take filler and have excellent adhesion properties. Filler on the other hand does not tend to adhere as well to metal as it does epoxy.

At least in the 20+ years I've been doing this that was the case...Maybe he knows something I don't?

Blu-By-U 79Z
05-14-2010, 05:01:54 PM
I hate to question the instructor at your local college but this is erroneous information in 90% of cases. The newer epoxies like SPI are designed to take filler and have excellent adhesion properties. Filler on the other hand does not tend to adhere as well to metal as it does epoxy.

At least in the 20+ years I've been doing this that was the case...Maybe he knows something I don't?

Hes been doing auto body for over 30 years. Ive been doing it this way with no issues. Just prepwork regardless. We dont use SPI. We use PPG Epoxy primers. So idk if that is one in the same but i dont belive so. It could depend on what type of material you are using.

JR454
05-14-2010, 05:54:48 PM
got to agree- The best is to spray epoxy before and after filler.. Been doing it that way for many years on restorations. Im using ppg- and The tech guys at the ppg center actually said that the filler bites better to the epoxy than bare metal. I agree with wookie- I think most all of the paint manufacturers epoxy is designed to have filler over it.

Blu-By-U 79Z
05-14-2010, 06:41:18 PM
Well i did mine with out epoxy due to fear of it not bonding well. When we apply filler. We float the surface with 36-40 disk grinder to give it something to bite to. Just how i have been taught and i will more than likely finish it this way.

Blu-By-U 79Z
05-14-2010, 07:09:33 PM
http://www.autobodystore.com/filler_&_epoxy.shtml

Found this and decided i would share. Its interesting.

krabben1
05-14-2010, 10:04:58 PM
Ive seen body filler take in water and rust first hand.restoration guys seal metal first with epoxy,then fill.Because they dont want rust issues down the road.They filled first on the tailpanel of my car,then epoxied and painted.It looked fine from the outside,till it was stripped.

leafs_11
05-14-2010, 10:07:42 PM
that test is not even close,nothing was allowed to cure for 24 hours. it was a complete wast of time. the epoxy was cured for 20 minutes with a hair dryer.
what does the curing bondo do to the uncured epoxy??? weakens it.

Blu-By-U 79Z
05-14-2010, 10:09:27 PM
If body filler is sealed then no moisture should be able to get to it. Unless it was not properly applied over a dent in which it bridged over it creating an air pocket. Then when the filler heats up to cure, the air condensates and begins rusting the metal. That or if filler is used over a whole which in my opinion is a terrible idea and i would never do that. I believe it depends on which products you use to prep your metal and seam with.

Blu-By-U 79Z
05-14-2010, 10:11:59 PM
that test is not even close,nothing was allowed to cure for 24 hours. it was a complete wast of time. the epoxy was cured for 20 minutes with a hair dryer.
what does the curing bondo do to the uncured epoxy??? weakens it.

Only thing abuot 20 minutes i see is this.
"so the 20 minute induction time is not a problem…"

Which isnt cure time. Its how long the epoxy must set before spraying it to do a certain job. (different hardeners)

Also the thread says nothing about hair dryers... so i dont see where you are getting that from.

Marks71BB
05-14-2010, 10:14:08 PM
NEVER put filler on bare metal!
seal the metal, fill as needed and then seal it again. hi build over that and prep for paint.

earlysecond
05-14-2010, 10:22:23 PM
Interesting test on this one.

Leaf- he used a medium wave light, which is more than acceptable.

I liked the test and I will not argue with results. BUT if a car gets hit hard enough that the filler is coming out. . .the whole panel, or the whole car (haha) needs reworked. If you hit a panel hard enough for filler to come off you have way bigger problems than cracked filler! Get my drift.

NOW to make the test pertinate to restoration or collision work. Take a cupon totally coated with epoxy primer and a bare steel cupon apply filler and put in a salt bath or even plain water, then tell me which filler stays on. I had panel adhesive fail due to rust and am confident that filler would do the same.

I was of the understanding that oxidation protection was one of the bigger issues, especially over a welded patch. So while the whack and bend tests are interesting. . .are they valid real world issues. Serge deserves props for checking it out either way.

Brent

Blu-By-U 79Z
05-14-2010, 10:30:43 PM
Interesting test on this one.

Leaf- he used a medium wave light, which is more than acceptable.

I liked the test and I will not argue with results. BUT if a car gets hit hard enough that the filler is coming out. . .the whole panel, or the whole car (haha) needs reworked. If you hit a panel hard enough for filler to come off you have way bigger problems than cracked filler! Get my drift.

NOW to make the test pertinate to restoration or collision work. Take a cupon totally coated with epoxy primer and a bare steel cupon apply filler and put in a salt bath or even plain water, then tell me which filler stays on. I had panel adhesive fail due to rust and am confident that filler would do the same.

I was of the understanding that oxidation protection was one of the bigger issues, especially over a welded patch. So while the whack and bend tests are interesting. . .are they valid real world issues. Serge deserves props for checking it out either way.

Brent

I agree. They both are acceptable. There are so many factors that can cause cracking and popping off other than bare metal or epoxy. Thickness, amount of harder, temp of the substrate and out door temp, surface prep, etc. This is just the way i have been taught and have had great luck with it. Im using shoplines JH377 i think it is. Work my metal and do my skim of filler to lever then epoxy to seal the repair. I was planning on sealing then doing filler but was instructed not to. But as you said if somthings hit hard enough to crack either filler out. Thats not the majority of the work. Redoing the car that was hit is lol

As far as the other test you suggested. To be accurate. Apply filler over bare metal then epoxy over front and back. Then epoxy and apply filler to the other then epoxy again. See how much surface rust appears. If the sealers doing its job. None should form.

Rick WI
05-14-2010, 10:44:58 PM
NEVER put filler on bare metal!
seal the metal, fill as needed and then seal it again. hi build over that and prep for paint.

Never? Filler can be applied to bare metal without question. No problems with adhesion. In the application the. OP is talking about I would epoxy first. Its simply the newest primer technology which in this application should offer the longest lastin finish.

Even with that said. I could two part etch prime that area cover with 2K surfacer sand with 80 grit fill smooth and 2K and not loose a bit of sleep for a very long time.

Afte inspection of ther weld and treating the back of the repair I could also say after prepping the welded surface I could directly apply filler to the repair area block flat two part etch and primer surface with no loss of sleep either.

Either repair will last just as long if the base prep is correct.

What in the heck did folks think we did before epoxy? How many old cars have you stripped only to find a repair done likely before many on this board were even born and even worse were told prior to buying the car it was bondo free? .

I think is is very important to point out that there are a few ways to perform a very good substrate finish to this repaired area. The current industry standard is to epoxy prime then apply filler.

Before ypu do this a lot of excellent informatio is included in the P Sheet for the epoxy. Follow ALL the instructions for application and steps needed prior to applying the filler as well as recoating over a cured surface.

Blu-By-U 79Z
05-14-2010, 10:56:07 PM
Adding on to Rick.

Another thing about buying a buying a bondo free car is that alot of new cars have bondo from the factory. From transport damages that dealerships fix before you lay down the dough for it. But bondo isnt a bad thing like people think it is. They think its bad because people dont use it properly and try to cut corners. Well put Rick.

Marks71BB
05-14-2010, 11:06:07 PM
Well stated rick, but my point being, if ya have the skill and tools to be doing this kinda work to begin with why would you not seal the metal prior to doing the filler? steel has a tendency to oxidize, I would err on the side of caution and seal it prior to applying any filler. Filler is much more porous than sealer and would be more likely to promote oxidation than sealer..
Just my 40% of a nickle.

Rick WI
05-15-2010, 12:37:39 AM
I agree 100 percent Mark. Basically the industry has moved to epoxy and that's what a lot of us use in the shop. It should give someone like the OP the best chance for a long lasting and trouble free repair using it as a base over the bare metal. No argument on that at all.

Filler though does have excellent adhesion to clean sanded bare metal. If topcoated with a two part etch and primer surfacer that also is an excellent base.

In the industry a phosphate etch base with say a powder topcoat is a very common and durable finish that can pass severe salt spray test hours required by say Utility spec equipment. Of course some of the best companies such as John Deere use E Coat since the mid 80s as a prime over bare steel. You can guess what E stands for. John Deere always uses the best.

Just want to make sure someone doesn't wig out if they just got done painting their car andused filler over bare in some area thinking it would fall off.

NYH1
05-15-2010, 03:16:33 AM
I know this is probably a stupid question but can I get Epoxy Primer in an aerosol spray can?

krabben1
05-15-2010, 10:49:02 AM
I know this is probably a stupid question but can I get Epoxy Primer in an aerosol spray can?
I havent seen that anywhere yet.

leafs_11
05-15-2010, 11:04:43 AM
let me clear up some moisture/ condensation issues. im not a body man.but i do know this.
condensation is caused from warm air hitting a cold surface.warm air holds more moisture than cold air. thats why wen you shower the mirror and window are wet. the glass is colder than the air. wen the air hits the cold glass. the moisture comes out.
thats why you have dew on the grasss in the morning the hot moist air from the hot summer day condensates in the cool night air.
same thing in your shop.if you are doing body work on a hot muggy day and you have bare metal.if you lets say strip some parts in the morning later on in the day you can bet yur a@#$ there is moisture on the metal.the metal is cold.
early in the morning or later in the evening will be the worst times for condensation on metal.qwait till the middle of the day wen everything warms up.
ever have a wet concrete floor in the summer????
if you dont have a climate controlled shop you will have moisture on the metal
you must dry the bare metal before finishing.
a heat gun or a hair dryer on small areas.
or let the sun bake the panels first.
if you go in the shop in the morning after a cool night crank the heat up.
i am a contracter i have an electronic moisture sensor.one morning i tested some bare metal i forget the actual number (about %50 hunidity )but it was almost zero after i warmed it with a hair dryer
the average climate and house has about%50 humidity in the air at all times
the heat from the bondo does NOT cause condensation.if bondo got cold as it cured it would but it gets hot.it just traps watever condensation is under the bondo already
like im saying the moisture is in the air no matter wat. the idea is to keep it from forming on the cold metal.the warmer the air temp the more moisture the air can hold.

BusDriver
05-16-2010, 11:50:33 PM
I know this is probably a stupid question but can I get Epoxy Primer in an aerosol spray can?

Yes, but it's rare, and it's very expensive for what you get. I've seen it and the can has a device that you trigger to release the mix agent then shake to combine....

Downside is that once activated, you have about 8-12 hours to use it and your $30 can of primer will be a brick.

Some paint shops can mix anything and inject into a can as well, but again you have hours at most to use it before it's a solid lump. Also not cheap for any kind of bulk useage. Doesn't take many of these before you could have bought a cheap gun (~$30 tops) and a 2 gallon kit of SPI Epoxy (~$140).

Do you have a compressor? If so, a cheap harbor freight HVLP gun will shoot primer just fine.

HOGDADDY
05-18-2010, 08:29:22 PM
The autobody instructor at the college was the one who said to work the filler then epoxy because hes seen the filler not bond well to the surface over epoxy and pop off shortly down the road. Fillers designed to go on metal. Same reason you dont want it over paint. It just doesnt bond good enough. Now if its a small dent. Epoxy and use a glasze puddy. That is fine to put over primer.

This is some interesting tests done here with epoxy and bondo its worth a look.

http://www.autobodystore.com/filler_&_epoxy.shtml

earlysecond
05-18-2010, 10:51:28 PM
Now we have gone in a complete circle! Not bustin' you too bad Hogdaddy BUT that IS the test that we were debating.

I am not sure that, in most cases on solid metal (not rusted or welded) that it makes a huge difference. I have filler on bare metal on the driver's quarter on my Camaro and the front fender is epoxied first. 6 years later, all is well.

This issue comes down to personal preference, your own system is what matters. When your results aren't what you expected or do not last. . .consider a change!

Brent

HOGDADDY
05-19-2010, 12:54:00 AM
Now we have gone in a complete circle! Not bustin' you too bad Hogdaddy BUT that IS the test that we were debating.

I am not sure that, in most cases on solid metal (not rusted or welded) that it makes a huge difference. I have filler on bare metal on the driver's quarter on my Camaro and the front fender is epoxied first. 6 years later, all is well.

This issue comes down to personal preference, your own system is what matters. When your results aren't what you expected or do not last. . .consider a change!

Brent

LOL! Doh! I shoulda read all the posts sorry. :o ........:)

ChevyReb
05-19-2010, 09:31:36 AM
If you epoxy and then use filler why would you need to epoxy over the filler again instead of going strait to 2K primer? Won't this just add more mil's and you use the epoxy as a seal coat over the 2K just before shooting the base right?

leafs_11
05-19-2010, 05:09:24 PM
my understanding is only epoxy if you break thru to bare metal wen sanding bondo

Rick WI
05-19-2010, 05:58:06 PM
If you epoxy and then use filler why would you need to epoxy over the filler again instead of going strait to 2K primer? Won't this just add more mil's and you use the epoxy as a seal coat over the 2K just before shooting the base right?

It really isn't needed from an absolute standpoint. it will seal up the bondo so when you spray the 2K you'll get a nice smooth even surface. Even 2k can soak into the bondo and you'll see the "ring" of the bondo after the first coat dries. Once that coat is blocked and you apply another coat of 2K that won't happen. The 2k has cured and also sealed the epoxy.

As a side note, if you chip the paint through the clear, through the base, through the 2K primer and down to the bondo, you'll likey chip through the 1 mil of expoxy as well.

I don't see any harm in a mil or so with the overcoat of epoxy since 2k alone hoses on 5 mil, although a lot is sanded off between blocking.

JR454
05-19-2010, 06:05:42 PM
This has been a popular topic... Ive gotta say Ive lost a lot of sleep.!- I just finished a set of harley tins and I put epoxy on first and let it set over night, scuffed the next day and did some filler work, prime etc, paint.... all done now and looks great and ready for the customer.. My problem is- I just hope he never takes a fender or tank and whacks it against a corner of a table.!! If so my filler may crack.!!!! Holy crap then what.!!??? lol....

Its just the latest technology to have protection under your filler- some people are comfortable just sticking with what has worked for them in the past, And there is nothing wrong with that. Some guys may still want to work with lead- Hey if it works for them and they are happy- great...! Some guys like to stay current with what is supposed to be the "best" method and to date that is supposed to be the best way to ensure you have done your part to make a lasting repair.. I have had great results with epoxy first then finish with filler and prime etc. and that is the way I will continue to use That said, before Epoxy was so popular I did many cars with just filler on the metal and havent had any problems from doing it either way.. But then again I havent tested any of my repairs by hitting them against a table, I may be doing it all wrong...????

Another comment on the above question. Some primers being used today arent a dtm primer so by putting epoxy on burn throughs it will eliminate that problem..

cubfan226
06-11-2010, 12:53:36 AM
I know this is probably a stupid question but can I get Epoxy Primer in an aerosol spray can?

http://www.autobodytoolmart.com/spray-max-2k-epoxy-rust-cure-primer-3680032-p-14526.aspx