[3goats]

I have no idea what we did to cause problems with this 69 bumper but stumped. Followed instructions from py members. Started out with a 40 year old bumper with typical cracks. Sandblasted down to bare endura and repaired cracks with two part epoxy. Filed the deeper cracks filled and blocked smooth. Sprayed three coates of epoxy primer (20 min between) and let dry for 24 hours or more , blocked bumper and it turned out nice and smooth. Week later noticed crack on top. Started pressing and flexing different areas of bumper and bang,, Cracks like bondo???? WE used pro form epoxy primer. Is that our problem? It sanded out really good. Now what?
Need help thanks

[Tim66]

Maybe you need to use a flexing agent in the primer.???

[JUDGE3]

did you use the 3m #5896 flexible parts epoxy kit? I used this, and plenty of flex agent in my primers/paints. didn't spray any epoxy primers on it at all with excellent results. and i had a lot of repairs on mine.

[3goats]

We used a 2 part epoxy made by Dominion Sure Seal . It is blue in colour and we used the adhesion promoter. The stuff sticks like glue to the endura and did not crack when flexed. We then sprayed Pro Form 2k epoxy primer only. 3 coates and blocked. Did not use any flex agents at all. Booth temp was 70 deg or so if that matters.
I was told by a very reputable bodyshop guy from py here that we didn't need flex additives at all.
I think it has something to do with the primer but don't know. I can't buy the SPI epoxy here which was suggested to me. Should we sand the epoxy and try flex with ppg 2k? Or try a different epoxy primer?

[68gtoMN]

contact PaulAtFast on this board - I'd call him the expert

[anewtoi]

ive read in a recent post that you shouldnt use flexible primers because they dont allow full curing, however, i read @ endurabumper.com that everything you put on the endura should be flexible. confusing to say the least

[Forrest]

Not sure what that epoxy you used but it should not be easily sand-able. Sounds like yours is hardening way too much( I use one coat of shop line jp375) and it will "ball up" when you try to sand it because it is more flexible. Also 3 coats seems alot..should use very minimum (1 coat). Then I use a thin film of sandable polyester primer.( I use featherfill g2.) And then block till you just see the epoxy primer underneath.. The whole point is MINIMUM coverage/thickness of the primers and final paints.. Of course all this works for me MOST of the time but painting is unpredictable at times!

[3goats]

Thanks guys
We decided that maybe we did go too thick on the epoxy primer. It wouldnt sand easy with 320 but ok with 220. I'm going to block it down until it's almost through to bumper and re-spray one light coat. If that doesn't work i'll let you know.

[salem1912]

Do a search there is plenty on the subject. I used 3M 2 part epoxy and 1 coat of epoxy primer.

[3goats]

Forrest
I think you nailed the problem by the head. Thanks. We re-blocked and took your advise and so far we think this is the ticket. I will let you know if any problems arise from this.
I have done bumpers in the past and used the flex agents. 15 years later i've had one crack. The products we used back then are not availible anymore. I thought I would try a different method this time. I'll let you know if it holds up.

[Forrest]

Great! I hope it all goes well...I'd say 80% of the time it works for me but then there are always times when "something" goes wrong and there really is no explanation?? (maybe it was the full moon, solar flares?!) Well, that's painting! Let us know..

[GoatDr]

I'm no sure about the epoxy. I used SEM weld a 2 part rubber repair and it's not an epoxy. It's a flexible rubber stuff, grey in color when dry and it sands very easy.

[Cammer-6]

I use Lord Fusor repair with good results
no flex agent and prime with epoxy before any repairs

[PaulatFast]

Originally Posted by Forrest

Not sure what that epoxy you used but it should not be easily sand-able. Sounds like yours is hardening way too much( I use one coat of shop line jp375) and it will "ball up" when you try to sand it because it is more flexible. Also 3 coats seems alot..should use very minimum (1 coat). Then I use a thin film of sandable polyester primer.( I use featherfill g2.) And then block till you just see the epoxy primer underneath.. The whole point is MINIMUM coverage/thickness of the primers and final paints.. Of course all this works for me MOST of the time but painting is unpredictable at times!

From my experience that polyester primer does not expand and contract at the same rate as endura, garanteed to fail in time... at least the stuff we've tried.

Your epoxy primer must be the problem. We only use the SPI because it sands nice, very nice actually, and never hardens enough to crack. We end up with at least 6 coats of epoxy in places on every nose we do. NEVER had an issue!

That polyester primer has NO qualities that make it compatable with endura repair. The stuff may work for awhile, but I have never seen it hold up to temperature swings... or the passing of time... It is the most common product used in failed endura repairs that I come accross.

I'd start over and blast the nose again... It would be easier than pulling and repainting it in two years.

Why can't you get SPI products?

[PaulatFast]

Originally Posted by GoatDr

I'm no sure about the epoxy. I used SEM weld a 2 part rubber repair and it's not an epoxy. It's a flexible rubber stuff, grey in color when dry and it sands very easy.

What is the part number?

[Forrest]

Sorry I goofed on the g2 poly..( I was using the g2 all that day) I use the acrylic ppg K36 primer (K201 hardener) over the shopline jp375 epoxy primer. jp375 does not get "hard" and doesn't get brittle from my experience. The K36 works very well, sands well ect........ finished many a car this way ( many years), not a problem as of yet that I know of..I guess the total minimal film build (repairs,epoxy, primer, base, clear) is what works for me also..everybody has their way..

[PaulatFast]

Agreed. I wish everyone's epoxy primer was similar in make-up. Some stay wet, as the epoxy you use must, and others harden and dry out over time, as the stuff used by the OP. The SPI epoxy is the key ingredient for me. It is the perfect mix of flexibility, sandability and consistancy.

I am truly hoping the epoxy 3goats used is not going to be used again... I see bad things from that product!

[3goats]

Paul
None of the paint shops I checked with have even heard of SPI products here. I did a search on SPI and found one distributer in canada located in ontario. I think its called JC Restorations. I'll contact them and see if I could possibly get some from them.
Do you have a name/part number for the epoxy and catalyst etc. that your shop uses?
Great Thanks
Forrest
I used the ppg dp50 epoxy and then the k-36 in the past but they quit making it or can't buy it here anymore.

The Pro Form epoxy actually was going to be re-sprayed but a thinner coat with a bit of reducer added. Maybe not a good idea?

[paint guy]

Thinner films are typically slightly more flexible. Adding reducer will make it easier to spray to a lower film thickness, but adding reducer by itself will not change the chemistry of the primer to make any more inherently flexible. If the dry film ends up being more flexible, it will only be because there is less of it on the bumper.

[PaulatFast]

SPI epoxy is sold as... SPI EPOXY. No options.

I sure wouldn't go down that road again!