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Epoxy primers - not a war

Posted By:
Kas Pranskunas
Homebuilder or Craftsman
5
Posts
0
#1 Posted: 8/8/2010 06:19:26

An old topic but one that will continually change:

It is a given that every Epoxy primer manufacturer advocates that their product is the best in the business. Now that the likes of Consolidated have indeed done just that - consolidated several manufacturers under  a common banner, I need some honest advise from all you builders / restorers about their experiences with Epoxy primers.

I need to prime a 4130 frame that will be exposed to the elements and would be grateful to anyone who has the time to throw in their to bits worth.

In your experience, have you found variation between brands in the way they apply, finish and ultimately protect? It kind of boils down to about four or five basic brands - Poly Fiber, PTI, Azko Sherwin etc etc.  Has anyone had more than favourable outcomes with a particular product -  or indeed and unfavourable one.

You guys have done the work and shot this stuff out of a gun which to me means a lot more than the hype that comes from the product brochure. Not interested in cheap (almost a prerequisite in this game) - interested in good.

 

Thanks for your time



Aaron Novak
AirVenture Volunteer
14
Posts
2
#2 Posted: 8/8/2010 09:09:53

Kas,

I understand where you are coming from. From paints to welding to covering material to engines there is many times more marketing information than anything out there, and frankly marketing information is usually inflated to say the least. We did some pretty extensive testing at work on primers and found that "epoxy" primers did indeed perform the best for corrosion control. The testing also showed that they all perform at about the same level. In out aircraft and other restorations at home, armed with the knowledge of our testing at work ( in environmental chambers ) we used PPG DP-40 ( not DP-40LF ) and have found its performance exceptional. However DP-40 no longer exists, and so to replace it we are using the "stitts" epoxy from Consilidated with equal results. The drawback now to automotive epoxy primers is they have removed the sacrifical pigments for EPA reasons, unfortunately that was what made them perform. Think of those pigments as an "annode" for your tubing. Aircraft industries can still use the chromates and oxides in their primers as pigments, so the performance is still there. Hope this helps!

-Aaron



Joanne Palmer
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
276
Posts
68
#3 Posted: 8/8/2010 18:58:57

For a two part epoxy primer for metal, it is very difficult to beat the MIL-PRF-23377 primer.  PTI has theirs under their part number PT-500 and PT-500FG.  If it meets the MIL-specs then the corrosion protection has been tested.



Kas Pranskunas
Homebuilder or Craftsman
5
Posts
0
#4 Posted: 8/12/2010 17:28:24

Thanks Aaron,

Your input is most welcome.

I was a little concerned that if I was to leave the epoxy primer without a top coat, ie a finishing coat, for an extended period of time, I may have had issues with the two coats adhering in the future. A lot of manufacturers stipulate that the top coat should go on within a specific timeframe so as to allow the two coats to "key" in together.

My problem is that I need to assemble and them break the whole structure down before final assembly hence my reluctance to lay on a finishing coat.

Maybe a light scuff should be enough prior topcoating???

Thanks again for your time.

kas



Michael Dooley
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
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#5 Posted: 8/12/2010 20:55:55

I've had excellent results with Akzo-Nobel two-part epoxy. It mixes easily, has a short induction time (30 min) and can be kept mixed for several hours. It sprays evenly, covers well, and dries quickly (parts can be stacked within an hour with no problems).

After 24hrs of cure, this is an extremely durable finish. Very resistant to all types of fluids and solvents.

I have top coated it after several months (using Jetflex water reducible interior finish); lots of scuffing required, with an MEK wipe before spraying the finish. No problems. Having said that, I don't have any experience using this primer on exterior surfaces or with an exterior finish coat.

Good luck,

Mike




Aaron Novak
AirVenture Volunteer
14
Posts
2
#6 Posted: 8/13/2010 07:42:58

 

Kas,

If your going to have an extended time between prime and topcoat, usually a light scuffing is suggested. The maroon scotch bright provides a proven surface for topcoad adhesion. Like I said before, between brands is splitting hairs when it comes to performance. Although some put talc in their primer to promote adhesion with the topcoat and this actually is a help.  The epoxy binder is just there to keep the pigments in contact with the material being painted. Also as a side note, topcoats can affect performance of the primer. Too heavy or one of the wrong type can prevent oxygen from reaching the primer layer, then you get the "worm track" or filiform corrosion. Good Luck!!