Still having epoxy adhesion issues

mrennie

Promoted Users
You may remember my first post last fall asking a similar question. I was having issues with epoxy not feathering properly near areas that I had applied filler, this was on the body of my project car. In that case I had used a metal conditioner in several areas, and was advised to strip everything, neutralize and start over, which I did.

My current issue is on the front fenders that I primed and filled last fall, and just started blocking yesterday. Problem is the same as before. When blocking the filler and epoxy, I have areas that the epoxy seems to tear instead of feather. This is happening is areas close to where filler was applied, but also in areas where no filler was used at all.

Today I grabbed my air gun and in places where the primer won't feather, I can blow it right off, and using a scraper, it comes off easily. Other areas the scraper will not get under it.

The primer and activator were bought in 2014, kept stored in a 60F storage area, and never opened until late 2015 and and I used the last of it in late 2016.

My prep was:

-cleaned fenders before starting with jobber (Pro-Form) W&G remover (spray on, wipe off with wiping cloths)

-sanded with 80 grit on DA to bare metal

-no acid or metal conditioners were used!


-cleaned fenders with SPI 700 (spray on, wipe off with wiping cloths)

-let dry for 2 hours

-mixed SPI epoxy 1:1, induced for 30 minutes

-sprayed 1 wet coat, waited 30 minutes, sprayed another wet coat

-waited 4 days, then applied filler to a few areas

-garage, primer, and fenders were 72F when sprayed, and temp kept at 72F for one week after spraying. Temp never went below 60F since I sprayed them last fall.

-fenders looked great after priming, nice gloss and no orange peel


I am at a loss as to what I am doing wrong? My only other experience with SPI epoxy is the second gallon I bought this spring, I sprayed it on my doors a few months ago and any areas I have sanded through while blocking feather nicely and I have no issues. My prep is the same as what I did with my fenders.

Please help!

Thanks

Michael
 
If it went exactly as you wrote, it's going to be difficult to find what happened. What brand of prep wipe are you using?
 
The wipers I have been using are made by Prematex, part # 320-20, blue in colour.

Here is a description from their catalog:


PREMATEX NON-WOVEN WIPERS

The premier wiping cloth for low lint applications. Prematex is made with a hydro-entangled

binder free technology which results in a highly absorbent, durable & reusable wiper.

• Superior wipe-dry properties

• Low linting

• Solvent resistant


Do you think they could be the problem?
 
Probably not, just wanted to know for sure that you were using something appropriate. I'm going to wait for others to weigh on this, because I honestly don't know. All I do know is that I have used SPI epoxy successfully hundreds of times, but there is always a chance of something going wrong, which means I've had a few unexplained failures, too.
 
I am not a pro, but I had the same thing happen to me before. This part in your process sticks out to me; "-sanded with 80 grit on DA to bare metal" and I have done the same, the sandpaper wears down by the time you get to bare metal. You do not end up with a true 80 grit anchor pattern on the bare metal for the epoxy to hold on to. I suggest that once you remove the old coatings in the first part of your process and hit bare metal, that you switch to a fresh piece of 80 grit and go over the panel again so that you can get a nice anchor pattern. Switch the paper out the minute you feel it wearing down, save it for removing old coatings, etc.. no need to waste.. I hope this helps. Maybe a test panel using this method before continuing forward..
 
Good point, @Painting Mechanic ! Dull sandpaper and other things like wire wheels can start to polish the metal instead of scratch it up. This is where a good brand of sandpaper really shows its worth. We have a different, more expensive grade of 80 that is used when working with metal.
 
Good point, @Painting Mechanic ! Dull sandpaper and other things like wire wheels can start to polish the metal instead of scratch it up. This is where a good brand of sandpaper really shows its worth. We have a different, more expensive grade of 80 that is used when working with metal.
So....what's the brand? Always looking for better sandpaper!
 
So....what's the brand? Always looking for better sandpaper!
Norton BlueFire 23573 is what we use for sanding metal. It doesn't work well for filler or paint, believe it or not. For all-around work we still use 3M 01506.
 
Definitely good point on paper used to sand metal. Most paper meant for paint, wood etc will quickly turn into finer grit cutting on metal.

Silicon carbide & zirconia type grits will cut sharp longer on harder materials such as metal & stone.
 
I sanded both fenders back down to bare metal yesterday. I am using Norton 80 grit PSA aluminum oxide discs.

This morning I went over both fenders again with several fresh discs and got into all the hard to sand inner corners with 80 grit paper by hand then wiped everything down 3 times with 700, this time using a different brand of wiping cloths from the body supply store (just in case), and they were so clean I could have performed surgery on them!

After waiting 2 hours to ensure everything was dry, I applied 2 coats of epoxy that had induced 2 hours and waited 1 hour between coats. By the weekend I will apply some filler and block it down, and should know soon enough if I still have an issue or not.

Painting Mechanic's point about sanding scratches not being deep enough may be one possible explanation. Thanks for the feedback, I am not sure if that was my issue but it is something I was not aware of and could have happened the first time around.
 
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Let us know how this works, a lot of good advice here and I can't think of anything else to add.
Maybe old activator was weak from setting? Unlikely but never know if it is the activator it will do the same thing on all the panels.
 
One thing I have noticed is that this newer can of epoxy settles a bit different after mixing compared to the first can I used.

The first gallon, if I mixed up a quart 1:1 and let it induce for 30 minutes, there would be a small amount of separation on top, maybe 1/8", which went away when remixing prior to spraying.

This newer gallon, when I mix up a quart 1:1 and let induce, I get a much more pronounced separation of maybe 3/8" on top, but it still goes away when remixing, and both gallons seemed to spray the same.

I don't know of this means anything useful?
 
Tints do nothing but add color, we increased the titanium in the white a few times a little at a time to make it hide better and white is heavy so will settle more.
 
The gold Norton DA won't sand metal well at all. I got a roll of that once and the only thing it was good for was knocking off the top layer of paint or filler, imo. The white DA is middle of the road, it's better but still goes dull real quick on metal.
 
LOL, only second time for the fenders. My wife says I usually get pretty good at whatever I'm doing by the third attempt...hope I don't need another try, this is getting expensive.

The only thing that seems like a smoking gun is my sanding. It may not have been rough enough and the metal might have been too smooth. I did try different cleaning wipes this time, but the other ones I was using before should have been fine. I thought my panel cleaning was good before, but did another round this time "just in case".

I may have laid the previous coats on too thick as well...I read some posts about potential problems when too heavy a coat is applied but not sure if that was a factor or not.
 
Yes that is an odd situation. How ironic is that when you spill some on a dirt greasy floor, it's there forever! Although I will confess I've had this happen when the epoxy was too cold and didn't cure enough, the filler acted like paint remover and I was able to peel the epoxy and filler right off. Not saying that was the problem, but I know it can happen.
 
If something is smooth enough , it will act more like a release mold rather than a bonding surface for even a strong product that only can adhere to it by a mechanical type bond.
 
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