[dataway]

I'm working on repairing my Endura bumper using the methods often suggested on this site. Using the 3M flexible parts repair epoxy. Carved out the damaged areas with a die grinder and sharp carbide burr. Stretched wax paper or plastic sheet over the surface to smooth it. (pics below). I have a few questions about the finer details of this process.

1. After a 30 minute dry time (approx. 65 degrees) I was getting a lot "worms" when sanding. Still sanded ok but was wondering if I should let it dry longer next time.

2. At what point do I stop using the epoxy paste and leave it to the epoxy primer to fill? I have some areas with scuffing, very shallow, some roughing of the Endura material but almost nothing that goes below surface level.

3. Noticed some pin holes in the epoxy paste after sanding ... will the primer fill these?

4. Any tips on spreading a thin layer of the epoxy paste over a previous coat of the paste? I noticed it really likes to cling to the spreader making it difficult to spread thin layer.

Thanks

[killakev]

On question #2 - The epoxy primer does an amazing job covering small imperfections such as those "spider web" looking cracks common on endura bumpers. I didn't have to do filling repair like you're doing but I did follow the recommendations here on using epoxy primer and the various steps. I used the primer from Southern Polyurethanes. Really amazing stuff. Came out fantastic! Barry at SU extremely helpful in guiding.

[dataway]

Yep, I plan on using the SPI epoxy primer due to all the recommendations here. I know I'm not supposed to use any filler/primers ... so the SPI is used as the "filler" primer basically?

There are some very shallow "impressions" that don't involve any damage to the Endura material that I would like avoid grinding down and filling with the paste if possible.

[JUDGE3]

Originally Posted by dataway

I'm working on repairing my Endura bumper using the methods often suggested on this site. Using the 3M flexible parts repair epoxy. Carved out the damaged areas with a die grinder and sharp carbide burr. Stretched wax paper or plastic sheet over the surface to smooth it. (pics below). I have a few questions about the finer details of this process.

1. After a 30 minute dry time (approx. 65 degrees) I was getting a lot "worms" when sanding. Still sanded ok but was wondering if I should let it dry longer next time.

2. At what point do I stop using the epoxy paste and leave it to the epoxy primer to fill? I have some areas with scuffing, very shallow, some roughing of the Endura material but almost nothing that goes below surface level.

3. Noticed some pin holes in the epoxy paste after sanding ... will the primer fill these?

4. Any tips on spreading a thin layer of the epoxy paste over a previous coat of the paste? I noticed it really likes to cling to the spreader making it difficult to spread thin layer.

Thanks

Iv'e used this several times. don't know what the label says for dry time but 30 min is no where near long enough. i always let my coats dry overnight. your probably getting the pin holes from sanding to soon/not dry enough.

i used a routine spreader, I wouldn't be concerned about getting a super thin coat on, but rather a nicely applied coat. you will find better cured it will sand much better anyway. be sure your mixing it right.

whats that wax paper for?

judgement call on what you feel the epoxy primer will and should fill. I put 2 or 3 coats of epoxy primer on mine. but whatever you deem minor enough for primer fill, just be sure its not a hairline crack etc.

[dataway]

Yep, just learned about the dry time, the stuff I let dry overnight sanded WAY better, night and day difference.

So basically instead of a thin coat, apply another thick(ish) coat and just sand ... not as much of an issue now that I've learned to let it cure properly

I was having way better luck getting a smooth coat by kind of globbing it into the depressions I ground, then pressing it down by pulling wax paper or plastic down over it and kind of squirming it around while I put some tension on the paper/plastic. Made it follow the contours of the bumper very nicely. Peels right off when it's cured. Again .. not much of an issue now that I see how very nice it sands after proper curing ... does save on the 3M product though since it pushes it into the depressions nicely without large high spots.

[mrennie]

In my experience, sanding after 30 minutes was difficult and gummed the paper until you cut through the top. One hour was better to wait before sanding.

I tried to get my Endura as level as possible with the repair material, and once I sprayed epoxy primer and started blocking I still found some low spots that needed more epoxy flex repair material added. My advice would be to do the best you can filling with the repair material, then spray 4-5 coats of SPI epoxy with one hour of flash between coats, then do some blocking with 180. You will find real quick where you are close and just need more epoxy coats vs where you need to add more repair material. The good thing about working with epoxy is you can add repair material on top of sanded SPI epoxy and it is going to stick very well, especially if done within 7 days of spraying the SPI.

For the pinholes, I would try to fill with repair material. The epoxy primer may fill but you don't want to miss one and have it show up later.

No problem with the repair material sticking to a previous layer below it, just make sure it is well sanded first.

I would estimate that I applied at least 12 coats of SPI epoxy, spraying 4 coats at a time, then blocking, then spraying 4 more, then blocking, etc. I probably should have applied a bit more repair material in a few spots. Mine turned out well.

Lastly: DO NOT use a solvent based W&G remover on the bare Endura material as it is somewhat porous and could cause problems with adhesion. Best to do initial cleaning with soap and water, and then use a water based W&G remover from that point forward. I used SPI waterbourne W&G remover and it worked well.

[n20ta2]

I waited about 45 min to 1 hr and it sanded well. I sanded my repairs with 80 grit then did a wipe over coat with the 3m to fill any minor holes and scratches then hit it with 180. It came out smooth and ready for epoxy. I used a small 1.5x4 inch Dura block to sand the entire bumper so I don't think I will need much work beyond the spi epoxy.

[dataway]

Ok then, I will continue with the 3M on the smaller imperfections also. The project is actually turning out to be much easier than I thought it would be. I'll have time to see how it ages as it will easily be a year before it's top-coated.
Thanks much for the advice folks.

[dataway]

Couple more questions.

1. Any tips for reconstructing the rear edge of the bumper where it meets the hood. Mine has been rounded a bit by years of being moved around an leaned on things. Currently I've taken a cut off welding rod and wiped beads of the epoxy down the length of the top and a bit on the rear of the edge to square it up some. Not sure how well it will adhere in the long run.

2. Is there some kind of paint I can use as a guide coat? Hard to get a feel for the outcome with the different shades of color.

Thanks

[mrennie]

I'm not sure what you are meaning about the welding rod, but as far as getting the shape correct, yes, if you sand the Endura with 80 grit and it is clean and sound you should have no problem building up the top edge to match the hood.

On my car, I found that with everything lined up with good gaps, the shape across the top did not match the shape of the front edge of the repop hood. To fix this, I taped the first 4" of the hood, prepped the endura, then mixed up epoxy repair material and applied it to the endura while running my spreader along the taped hood to match the contour. Several layers later, the endura matched the shape of the hood and I block sanded to get it smooth.

I was also going to mention that you should make sure you fit the endura to the car with your final gaps and make sure you are happy with it before final primer. I screwed up and initially fit the endura before the gaps were perfect, then did 80% of the endura work, then when I put it back on and got the gaps 100% found that the endura needed building up on the sides to match the fenders, so more repair material and sanding. It turned out great in the end.

I have also read about some guys stiffening the top edge by "gluing" metal rods to the underside of the edge with the epoxy repair material.

For guide coat, I used 3M black dry guide coat. It is mildly expensive and some pros think it is a waste of money, but I found it very straightforward and obvious where the highs and lows where, and unlike paint, there is no smell and you can sand 10 seconds after applying it. Anything that improves my chance of success at bodywork is worth it IMO. 1 container should do your whole car.

I should clarify that I did not use guide coat for the epoxy repair material on the endura. I did not want anything contaminating the endura and only used guide coat after I have started priming the endura. If you are trying to determine how close you are to level with the repair material on bare endura, you could use a ruler or straightedge and slide it across the surface to look for low spots/gaps. Once you get the first coat of epoxy on it and it is all one colour, guide coat and blocking will reveal where you still have work to do.

Sorry for information overload, I tend to analyze the crap out of everything. LOL

https://www.3m.com/3M/en_US/company-...3223475&rt=rud

[dataway]

Perfect, just the kind of information I need.

I just used the welding rod to spread the epoxy .... probably didn't need to mention it

For deeper depressions that require multiple coats of the 3M I have been using a wire brush to rough up the shiny cured epoxy in the depressions .. ok?

I probably won't get this bumper into epoxy primer until the spring, so I should probably do what I can with the 3M for now and give it a rest until I can test fit it on the car. Just trying to get some things done in between welding sessions on the body.

[mrennie]

I would sand with 80 grit instead of using a wire brush...but if you are re-applying the repair material within a few days there is probably a chemical bond helping too.

[n20ta2]

I built up the entire front edge where it met my hood as well, I ended up using a bare piece of sheet metal that I braced up tight to the bottom of the top edge. Once it started to cure but before it was completely dry I ran a knife between the sheet metal and endura to seperate it. I used a 3m powder guide coat on my endura that wipes right off once your finished with it, as mentioned above I would try to stay away from any spray on guide coat that might come back to haunt you later.

[dataway]

I ended up building a dam by sticking blue masking tape to the back edge of the top of the bumper and then running a bead of 3M in the corner between the tape and the bumper, much like the metal solution ... pulled it off before it was fully cured, so far so good.

That 3M sure sands nice with 80 grit doesn't it. I also had some drip on an unprepared part of the bumper and the adhesion is great, going to have to sand it off.

[dataway]

Tape method worked great ... jeez now I'm worried about making the bumper look so good that it doesn't look original With patience you could repair some serious damage with this 3M stuff. Now I'm tempted to use it for small areas of body work.

[n20ta2]

Its great stuff for sure! I wouldn't use it on any metal though, it will expand and contract far differently then the metal making a repair stand out after paint.

[dataway]

Never thought about that ... thanks for dashing my dreams

[LATECH]

The Pits are formed by gas escapement of the filler product.The gas is escaping and the product is setting before the majority of gas escapes.That forms bubbles which in turn are pinholes when sanded.
Try thinner multiple coats, instead of a thick heavy coat of material, that wil give the offgassing room to breath and should result in less pinholes.

[dataway]

Last few applications I've been warming the applied epoxy with a heat gun, you can see bubbles rise to the surface and pop. The heat reduces the viscosity quite a bit before it's cured allowing the bubbles to come up.

[mrennie]

Originally Posted by dataway

With patience you could repair some serious damage with this 3M stuff.

You sure can! Here are several pics of the bumper I repaired for my car. I also included some to show how I matched the body lines and hood shape.