Filler to bare metal causing metal to sweat ! What

stay in this business long enough and you will earn the truth about tech sheets. no mfgr is going to say anything that could possibly cost some sales nor anything that is not 100% proven . just like letting paint freeze. do they say no don't do it ? nope but they do recommend keeping it above 45 degrees. the biggest problem comes from too many folks with AI getting into this as a hobby and then spreading bs about things they nothing about . you can not google experience . you learn by your failures or successes .
 
you learn by your failures or successes ....... well we should shine!!!!
 
My first post but have been monitoring the forum for awhile - lots of good information here! Have always put the filler on the metal in the past - but it seems there is a good case being made for putting down epoxy first. Questions about proper technique:

1) What is the time window for applying the filler after the epoxy is shot?

2) If the time window is exceeded, what is the procedure - A) sand and apply the filler or, B) sand, recoat with epoxy and apply filler?

Thanks.
 
I read about this question a bunch when I first started 'educating' myself about body and paint work. I chose to follow the epoxy first reasoning and carried on. Then as I was taking the grill down to metal I came across this repair. I had no idea it was there and was surprised to find this underneath what appeared to be good solid paint. whether it was from absorbing moisture, trapped moisture or chemicaly induced... It rusted between the filler and the metal. That's all I needed to know.

View attachment 1857
 
common practice , common problem , but if you say anything the bondo slingers will be all over you .
 
trdrew;26445 said:
My first post but have been monitoring the forum for awhile - lots of good information here! Have always put the filler on the metal in the past - but it seems there is a good case being made for putting down epoxy first. Questions about proper technique:

1) What is the time window for applying the filler after the epoxy is shot?

2) If the time window is exceeded, what is the procedure - A) sand and apply the filler or, B) sand, recoat with epoxy and apply filler?

Thanks.
Click to expand...
This information is from my own personal experience with SPI epoxy, and should not be taken as gospel, or as valid with any other epoxy.

I like to apply filler between 48 and 72 hours after spraying epoxy. To soon, and the epoxy will ball up on the sandpaper, too late, and sometimes early adhesion seems not what it should be. After 72 hours and before 7 days, a good scuff with a red pad is all that is needed to get perfect adhesion. From one week to about one month, full sanding with 150-180 is necessary. Fully cured, aged epoxy from around 1 month on should be fully sanded and recoated with itself before proceeding with ANY other material.

All these times are based on surface temps in the 65-70° range. Hot temps shorten times, and cooler surface temps are not recommended.
 
crashtech;26450 said:
This information is from my own personal experience with SPI epoxy, and should not be taken as gospel, or as valid with any other epoxy.

I like to apply filler between 48 and 72 hours after spraying epoxy. To soon, and the epoxy will ball up on the sandpaper, too late, and sometimes early adhesion seems not what it should be. After 72 hours and before 7 days, a good scuff with a red pad is all that is needed to get perfect adhesion. From one week to about one month, full sanding with 150-180 is necessary. Fully cured, aged epoxy from around 1 month on should be fully sanded and recoated with itself before proceeding with ANY other material.

All these times are based on surface temps in the 65-70° range. Hot temps shorten times, and cooler surface temps are not recommended.
Click to expand...

Thanks, Crashtech. This is exactly the info I was looking for.
 
I just thought I would give my experience with filler over epoxy. I have 2 vehicles that back in the mid 80's were stripped to bare metal, sprayed with the old PPG DP-40/401 epoxy and then had body filler work done on them. Both of them had numerous repair panels welded on them and to this day there is no issue with rust bubbling on them any where that they were repaired. At the time I restored these cars I was working at an Auto parts jobber that sold PPG paint. I followed the PPG recomendations for epoxy first and have been doing it every since. Since I learned of SPI products that is what I am currently using. I will say that when PPG switiched to the lead free DP products that they do not provide the corrosion protection and adheshion properties that the old leaded product provided. Just thought I would share some long term experience
 
This thread has once again reinforced why it is the only paint forum I go to for advice.
No crap, no half baked theory's, no innuendo. Just facts backed up by experience.
Please carry on :)

Dean
 
crashtech;26450 said:
I like to apply filler between 48 and 72 hours after spraying epoxy. To soon, and the epoxy will ball up on the sandpaper, too late, and sometimes early adhesion seems not what it should be. After 72 hours and before 7 days, a good scuff with a red pad is all that is needed to get perfect adhesion. From one week to about one month, full sanding with 150-180 is necessary. Fully cured, aged epoxy from around 1 month on should be fully sanded and recoated with itself before proceeding with ANY other material.
Click to expand...

How about when one accidentally sands through the underlying primer when taking filler down? I did this a bunch on the car I painted and just would respray the bare area, let the epoxy cure for an hour or so (this was in the summer, so it was 90+) and then reapplied more filler. Mind you, I'm talking about the thinnest of skim coats. The filler ended up being probably 1/16" at maximum. If I would have waited 48 to 72 hours on this car, I would still be getting it ready for base coat. I imagine that for such small areas, no bigger than a quarter, an hour or so is acceptable.
 
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