I read the "filler over epoxy" vs bare metal thread, thoughts on SMC/epoxy & fg?

[74-Roadster]

My home-made flares on my 2001 Corvette are epoxy resin based fiberglass parts I made. I use Lord Fusor products to bond and splice new parts to the SMC as well as fill any low areas etc. and then spray multiple coats of epoxy primer. After blocking the epoxy, if any low areas are revealed, I then use Rage Gold "over" the epoxy primer, block the filler and then spray more epoxy primer, block (if needed), seal and paint.

Any suggestions? Confirmation?

So far, the flares I built have held up very well for 26 months and 19,000 miles. And thanks to help from this forum too for my successful results. The only ghosting I have is on the seam and is about 3" long. It shows up on hot days (black paint) and is located in the area where I busted through the epoxy primer and did not respray epoxy primer, just a couple quick coats of spray can poly primer before I put down the PPG bc/cc. One of these days I'll quit cutting corners . . . :o

FWIW, here is a link to the albums on my flare build I completed 2-1/2 years ago and my current rocker panel modification project:

http://s18.photobucket.com/albums/b127/74-Roadster/

Coming soon, I'll be building mini flares for the front fender to compliment the rear flares. Since the front fenders on a C5 vette are urethane, I'm gonna try using either Fusor or Duramix to bond a fg flare to the urethane fender. If it doesn't hold up, I'll buck up and buy the aftermarket fg fenders and do it again.

[johnnyrock]

i`ve worked on many vettes in my time(32 yrs)in the biz and i have learned many things the hard way,I think epoxy primer is the only way to go for fiberglass.seems to me that you did everything right except cutting corners,i personally don`t cut corners on things i do for myself,if you have the time do it right.cutting through the epoxy coat compromized the sealing properties of it and you should have reprimed but it looks really good,if a three in. spot is all you have then consider yourself lucky.keep up the good work.

[Len]

I also use epoxy primer on fiberglass and over filler but I rarely use it UNDER filler. I've never seen the reason for it and, if anything, I would think that it could hurt adhesion.

[74-Roadster]

I also use epoxy primer on fiberglass and over filler but I rarely use it UNDER filler. I've never seen the reason for it and, if anything, I would think that it could hurt adhesion.

Len,

After working bare fiberglass, especially home-made one-off stuff, I find it nearly impossible to see all the tiny flaws etc that exist. On the rocker panel project I'm doing right now, I applied 4 coats of HOK epoxy primer. Upon review the next day, I could see several tiny pock holes that needed filled and a couple of low spots. I spread a very small amount of Rage filler and then blocked them flat and smooth with 120 grit wet. I then sprayed 3 more coats of HOK epoxy and they look like 99% perfect now.

What other option(s) should I have considered after locating the areas in need of filler?

Here are pics that show the poly filler on them after blocking:





Tonight, I'm going to blocksand them again but will use a finer paper. After sanding, I'm going to spray 2 coats of HOK's sealcoat over them. After sealing them, I'm going to leave them alone for a week or two, clean up the garage and get the car cleaned up again and get ready to spray the bc and cc.

Here's a good shot after the 1st priming session:

[74-Roadster]

johnnyrock,

Thanks for the nice comments and support. I do this stuff as a hobby and I'm still trying to get past the, "let's just get it done" paradigm. I really want to hurry-up and apply the paint, but I'm forcing myself to wait and let it all cure out for a couple weeks to yield the best results.

[old man]

thats the hardest part, taking your time and going slow. wife will call me and ask what i'm doing. i tell her i'm watching bondo dry or watching paint dry.

[Len]

johnnyrock,

Thanks for the nice comments and support. I do this stuff as a hobby and I'm still trying to get past the, "let's just get it done" paradigm. I really want to hurry-up and apply the paint, but I'm forcing myself to wait and let it all cure out for a couple weeks to yield the best results.

It sounds as if you're using the epoxy primer as a "guide coat" so that it shows you irregularities in the surface. If you use a dedicated guide coat you would find that it shows these areas much better and you don't need to wait for it to dry. I usually use 3M Dry Guide Coat on my fillers and an aerosol guide coat on my primers when I wet sand.

[Serge]

I guess you are using KP2CF juging by the color.

In working with fiberglass, I prefer working with polyester primer (slick sand).

If you see pinholes and air entrapment in your layup you should use a sharp point to open them up some and then use filler to fill them, then prime. Low spots can be revealed when sanding at any point by using a guide coat. Like Len, I use the 3M dry powder most of the time but sometimes I will put some over reduced black basecoat (which I guess you have in stock...!) in my touch up gun and give the area a mist coat before sanding.

You will also find that polyester primer like slick sand builds much more than KP2 or any surfacer out there...It is also made to build thicker surfaces. KP2CF and other surfacers are not designed to build thick layers or be used to fill large surfaces, they are too week when layed up thick compared to polyester or filler. Remember that an epoxy primer is not the same as an epoxy resin. Do the test with some dried up KP2CF in the bottom of a mix pot....you will see it is pretty weak resin wise...

That's a great looking vet...very nice work you do there. I like the tasteful way in which the work blends in with the lines of the car....very nice.

[johnnyrock]

I remember back in 1978 when the local paint reps came around to our shop to sell us on the idea of using epoxy primer.they said to use it on the bare metal BEFORE putting on filler, i was skeptical about that then but after trying it and seeing the results after many years i was sold on the idea.Although being a commission man for many years i found that for every day body work it wasn't cost effective to use on every job.I have had lots of good luck using it but like everything it has it`s specific uses.I have found no harm in using filler OVER epoxy primer.

[74-Roadster]

I guess you are using KP2CF judging by the color.

In working with fiberglass, I prefer working with polyester primer (slick sand).

If you see pinholes and air entrapment in your layup you should use a sharp point to open them up some and then use filler to fill them, then prime. Low spots can be revealed when sanding at any point by using a guide coat. Like Len, I use the 3M dry powder most of the time but sometimes I will put some over reduced black basecoat (which I guess you have in stock...!) in my touch up gun and give the area a mist coat before sanding.

You will also find that polyester primer like slick sand builds much more than KP2 or any surfacer out there...It is also made to build thicker surfaces. KP2CF and other surfacers are not designed to build thick layers or be used to fill large surfaces, they are too week when laid up thick compared to polyester or filler. Remember that an epoxy primer is not the same as an epoxy resin. Do the test with some dried up KP2CF in the bottom of a mix pot....you will see it is pretty weak resin wise...

That's a great looking vet...very nice work you do there. I like the tasteful way in which the work blends in with the lines of the car....very nice.

Serge,

My home-made parts are made with epoxy resin. Because they are an epoxy based fiberglass, I thought it'd be best to use an epoxy primer to seal it all up. And then, if needed, add some poly filler over the epoxy primer. Although my home-made parts are pretty good (and I'm getting better and faster), they still need quite a bit of work to get them perfect. I've left the black HOK sealcoat on them for ~ 10 days now and keep looking at them in the sunlight. I finally concluded this morning, the passenger side needs a little more filler to get the shape to match the drivers side. At the most critical spot, the filler will need to be ~1/8" deep and will feather into the part over ~14"-16" from the deep area. Based on the path I took to get to this point, I'm going to sand the area with 80 grit and use Rage filler over the epoxy primer. The only other option would be to sand the area back down to bare glass and use Fusor 100 EZ. The Rage poly will be much easier as it's difficult to build up a vertical surface with the fusor products since they are so fluid.

Now back to your suggestion:

So I could have sprayed a high-build poly primer directly over the bare glass and blocked it down and then applied some poly filler (Rage) to get the new body lines just right and cover a 2nd time with a high-build poly primer, then use the dry guide coat Len mentioned, block it down and if all is okay after blocking, then spray the HOK epoxy?

When reworking panels, I prefer to unmask the car, block the areas to be painted, wash the car, set up the paint, mask the car off and spray a sealcoat, basecoat and clear.

FWIW - This project has grown . . . I've decided I might as well sand and repaint my front fascia (too many miles and too many rock chips), the headlight covers and the door jambs since they are integral with the rocker panels. Today I'm sanding the fascia and when I'm done sanding, I'll remove the fascia, the front fenders and eventually the doors. So much for a quick little project. :o :o

[74-Roadster]

It sounds as if you're using the epoxy primer as a "guide coat" so that it shows you irregularities in the surface. If you use a dedicated guide coat you would find that it shows these areas much better and you don't need to wait for it to dry. I usually use 3M Dry Guide Coat on my fillers and an aerosol guide coat on my primers when I wet sand.

Len,

Yes, the epoxy primer ended up becoming a guide coat. Not my plan . . . I though my parts were much better but when I blocked them down, the high areas certainly appeared. I guess I could have used a high build poly 1st to get the shape right like Serge suggested and after they were good-to-go, then I could've hit 'em with hok epoxy. I keep wasting time and money learning tricks of the trade. Before I make any more home-made parts, I plan to get a gun to spray gel coat and I need to figure out how to vacuum bag a home-made part to get rid of or at least minimize air bubbles.