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Old 03-16-2005, 05:18 AM
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Barry, epoxy adhesion testing?

Hey Barry, I took on a project a few months ago that had been started by another shop. The car was dipped and then put in epoxy then delivered to me. The amount of epoxy that was dumped on this car in one application is unreal with runs and sags over the entire car. Puddles of epoxy were found in all the window openings, door bottoms and any place it couldn't run out of. Where the epoxy was really thick there are adhesion problems with chunks of it that break off with ease. Where the epoxy was put on in a reasonable amount the adhesion is good. What I'm thinking here is the amount of shrinkage that took place where the primer was heavy actually pulled the primer loose. Similar to what you see in a paint mix cup when letting left over material harden and it dries and pulls away from the edges of the cup. This leads me to believe that there must be an increase in adhesion if the product was applied in a few thin coats initially. Hope this makes sense. Have you done any testing of adhesion related to how much material is applied at one time? Bob

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Old 03-16-2005, 07:19 AM
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If I may

Bob,
Yup epoxy does shrink as it cures..in thin layers such as we would normally apply it does not hurt a thing..if as you say someone poured it in the dorrs and such you will have the result you are dealing with..

What to do? well in the areas you can chip out the loose stuff and make a fill with epoxy and micro ballons to fill the cracks and such to keep moisture out of those areas..the outside that you can get to can be sanded out till it is smooth..

BTW: micro ballons are little glass ballons that we use to make filler with epoxy..new tech for the car guys..used it in boats for a long time..Dunno if Barry has a product that is compatible with micro balloons..will have to ask him..???

Hopefully the epoxy is not so thick that it interferes with the glass channels and such..

You are correct in the left it in a cup analogy..Epoxy is very forgiving but not quite that forgiving..and we probably have no idea of just what product was used other than it is some kind of epoxy..

Good luck

OMT
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Old 03-16-2005, 10:36 AM
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Bob........sounds like your theory is on the money.........


and OMT........These "Micro Ballons", can you tell us more about them and how they work?........oh, and were to get them?
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Old 03-16-2005, 10:38 AM
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Yes, because epoxy is so weird the way it reacts, I have tested about every scenario you can this of.
Summery:
To thin a coat will result in about 40% less adhesion.
To thick, such as poured on or three to four coats back to back with no flash
70-80% loss of adhesion.

Now the poured on coats will gain adhesion after the solvents escape but I have seen it take as long as a year for this to happen.
What you might try is DA 180 to smooth out the heavy places than let set and see if you start gaining adhesion (epoxy will do this, but clears and 2K's will not) However this is not going to happen over night, it might take 1-2 weeks at 80 degrees to see an adhesion improvement.
Or after sanding if you have a short or medium wave cook each panel getting the metal temp up in the 140-160 area for 4 hours and when cools off check adhesion. Of course you can sand off and start over. joy!

In a short, you don't have adhesion now because solvents are trapped in those areas but you have not lost adhesion yet! If this was a clear you would be toast for any future adhesion.
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Old 03-16-2005, 10:59 AM
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Some more good, and surprising information........thanks again Barry

So at what point do you loose adhesion for sure?
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Old 03-16-2005, 11:09 AM
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To thin a coat!

Like a one coat drysprayed.
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Old 03-16-2005, 03:03 PM
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Thanks for the epoxy info. I've always applied two to three nice medium wet coats to the bare metal without any problems and will continue to do it this way untill a better proceedure is found. The idiot that started this job must have put two gallons or more of sprayable product on this shell all at one time. The areas where the stuff puddled up to 1/2"! thick cracked loose from the steel and were easily chipped out, I sanded away any other thick areas that looked like a problem and found good adhesion on the rest of the sheetmetal where it was applied ok. I just figured if the extreme amount of epoxy that was applied shrunk to an extent to overpower the adhesion from the metal then this definately supports the need for proper application. Not too thin and not too thick for best results.

The crazy thing about this deal is the shop that started the project is nationally known for street rod work, they even produce thier own alluminum bodies. I would have expected better from them, I'm guessing an apprentice must have applied the primer.
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Old 03-16-2005, 03:52 PM
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Your application idea is right.
I have always promoted, spray the first coat of epoxy like you would your first coat of clear, wet and slick. Let flash good than second the same way.
Many of jobs I have let the first coat of epoxy set overnight (kinda overkill)
than sprayed the second coat.

Epoxy is more sensitive to proper flashing than any other product.
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Old 03-16-2005, 05:44 PM
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Micro balloons

Quote:
Originally Posted by myfamiliacc
Bob........sounds like your theory is on the money.........


and OMT........These "Micro Ballons", can you tell us more about them and how they work?........oh, and were to get them?
Actually they are called micro spheres and are available from the better providers of fiberglass components..they only weigh about 4oz per 1/2 gallon and are mixed into the part A of the epoxy and then the part B activator is added to the mix..makes a thick paint that can fill a scratch or gouge and is easily sanded...Used ofr those times when a surfacer with a bit more body is needed..Have not tried them with the SPI products yet so cannot tell how well that would work..

Note: Talc is sometimes used for this..talc tho weighs about 3 lbs per 1/2 gallon but is cheaper..

The other strategy for making a fill..epoxy bondo if you will is to use chopped glass strand in the epoxy to give it body..

Hope this clarifies things a bit

OMT
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Old 03-16-2005, 07:14 PM
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Sam,

Did not know the public could buy them?
They are compatible with majority of the products today.
Used in bodyfiller, some two part adhesives (3m structural)

Overdoing it can cause weakness, so be careful.
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Old 03-16-2005, 08:43 PM
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Actually they are called micro spheres and are available from the better providers of fiberglass components..they only weigh about 4oz per 1/2 gallon and are mixed into the part A of the epoxy and then the part B activator is added to the mix..makes a thick paint that can fill a scratch or gouge and is easily sanded...Used ofr those times when a surfacer with a bit more body is needed..

Interesting stuff. I bet the filler materials would compromize adhesion some but if applied over a straight epoxy primer it would work alright, your coats would probably be thicker though. Has a paint company marketed such a product?
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Old 03-16-2005, 09:13 PM
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Micro balloons were real popular back in my R/C days (circa late '70's). they were mixed into epoxy resin and used for smoothing wings and fuselage without adding much weight. I still have a 4 oz container from the "old days"...

Russ
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Old 03-16-2005, 09:22 PM
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Filler materials

Quote:
Originally Posted by BarryK
Sam,

Did not know the public could buy them?
They are compatible with majority of the products today.
Used in bodyfiller, some two part adhesives (3m structural)

Overdoing it can cause weakness, so be careful.
Actually Talc, micro spheres, thixotropic silica (cab-o-sil) chopped glass strands are all available from the glass suppliers that provide laminating resins..All the filler materials that I am aware of are chemically inert and do not affect the chemistry of any epoxy or laminating resins that I know of..

Now that I am more aware I probably should have thought that unless someone has done quite a bit of fiberglass laminating and such they would not know of these materials and how to use them..

If a fellow was building fiberglass body parts then he might have a reason to know about this sort of thing..

Did not mean to hijack the thread..

Sam
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Old 03-17-2005, 04:22 AM
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I had no idea!
this just blows me a away.

If were talking about the same micro-spheres 3m is the manufacture of them.
They are being used in (all) the new hyper resin mixes (not semi ) Because of this in last six months there has been a shortage and its been a major problem for anyone making the hyper clears.
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Old 03-17-2005, 09:37 PM
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about 10 minutes from my house is the major distributor for FRP products up and down the east coat. they carry all that stuff. micro baloons, fumed silica, mill fiber and a couple dozen other fillers. i find it very interesting thay they use it in clear. i would think it would just make it thicker and affect clarity. why would they want to do that? there must be another reason for this.
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