Q&A's on MIL-P-23377 primer

Q. Hi,
Did you receive a response to your question around the differences between MIL-PRF-23377 type 1 and type 2?

We are having trouble sourcing the type 1.

Thanks,
Scott Park
- Kalkaska Michigan
December 5, 2022

A. Hi gentlemen. Unfortunately, I think Mike's hopeful interpretation is a bit of a reach. We may feel that Type 1 is "standard" and Type 2 is "premium", but we cannot read the mind of the specifying authority. If it is becoming accepted that Type 1 is hard to find, I think the spec and/or P.O. should be revised to "Type 1 or 2"; "or equivalent" seems to add confusion rather than options.
Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Have you tried having the parts primed before application of the top coat? Try a coating of MIL-PRF-23377 [on DLA] or MIL-PRF-85582 [from DLA] before the top coat, this should improve adhesion as well as improve the colour.
Brian Terry
Aerospace - Yeovil, Somerset, UK

A. More than likely it is the paint. But switching to another paint is not going to solve the issue. Now that most all bright colored paint is made of organic pigments you are really limited on hiding ability. Yellow is probably the worst about inadequate hiding.

I would try applying many light mist coats. You could also have them add a few drops of a product called Smoothie to the paint to lower the surface tension. Lowering the surface tension of the paint will not only give you a smoother finish, it will help the paint remain on the corners.

The biggest thing, in my opinion, is to give it several light coats. Suggest 6-8 VERY light mist coats to achieve your desired DFT.
Jim Adams
- Lubbock, Texas

A. I caution anyone from making an addition (Smoothie, or even applying primer coat, to a paint certified paint (or other material) without approval from the engineering function approval for the application (the hardware painted, not the paint). These paints are tested for their physical properties...and aerospace environments and applications aren't exactly the barn door. This might be construed as "product substitution" per FAR 21...or maybe not. I'd err on the side of caution. I'd want to check the engineering drawing from your customer...and most likely his customer...most likely it calls for primer coat. If not and it is a very old drawing, revision may be needed ... prior to your doing the work.
Douglas A. Hahn
- Saint Charles, Missouri

A. Douglas,

I agree with you totally, it is important to make sure that you have permission from the OEM before modifying any process. If the drawing and/or the specification is not explicit about the use of a primer do check before going down that route.
Brian Terry
aerospace - Yeovil, Somerset, UK

A. Shantel, it sounds like someone needs to start from square one and flesh out a process for this job. Can any of your painters do that for you other than just saying "I think it's the paint"?

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina

A. I agree with Brian Terry. After the chem film application, MIL-PRF-85285 [link is to free spec spec at Defense Logistics Agency, dla.mil] D gives:

"4.5.2.1 Primer coating. Spray apply one cross-coat of primer coating to a dry-film thickness of 0.6 to 0.9 mil (15 to 23 ìm) in accordance with ASTM D823 that conforms to MIL-PRF-23377 [on DLA] or MIL-PRF-85582 [from DLA] and air dry for no less than five hours or one hour respectively."

The 85285 is then applied per "4.5.2.2 Topcoat." which gives additional crucial advice.

Although this is the procedure for test panels; unless otherwise specified, there's no reason to deviate.
Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

A. I endorse some of the previous comments. you cannot modify the recipe of the paint by using an additive, as it will no longer be the qualified formulation.

In addition to the absence of lead pigments this is a high solids topcoat and typically builds up either side of the edge leaving hardly any layer over the sharp corner.

I am sure that a primer is being used, however check if it is MIL-PRF-23377 [on DLA] type 1 or Type 2. Type 2 is a dark green which will grin through. Type 1 is yellow and will not show through to the same extent. The customer needs to agree to the change however. Otherwise the comment about building up a lot of thin "mist" layers is the only real way to crack it.
Jim Rowbotham
- Halifax, West Yorkshire, England

A. It's always been a problem getting gloss paint to sharp edges, suggest that you brush touch the sharp edges when the spray coating has cured, or if you can prior to painting, sand down the sharp edges prior to refinishing making sure that you don't go to far, just enough to round off the edges.
Peter Courtney
- Sydney, Australia

A. Shantel, your painters are going to tell you that the finished product will come out hazy and textured if they try to mist a few coats instead of smooth and shiny. Plus the application cost will increase because they will be applying several layers of paint with tac time in between coats. What did your search for applicators that are certified and experienced with this type of material turn up? Maybe the local guys aren't qualified for this type of work.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina
2007

A. In agreement with Brian and Jim.

The initial application of primer is a must. The break-away from the edges is a common issue on the gloss finishes. The only way to successfully obtain coverage is by allowing a couple of light mist coats to flash off, then follow on with a full finish coat to obtain the specified film thickness.

As for the addition of additives, normally not acceptable in the aerospace industry
Adrian Yeo
- Chelmsford, Essex, UK
August 22, 2011

A. Make sure parts are clean, any contamination i.e:.finger prints (even when using gloves) will cause primer and or paint to flash off down to base metal or the primer coat.Handle parts as little as possible before any paint application and if you have to handle parts, hang parts and spray with iso alcohol then let the alcohol evaporate before applying paint or primer.
B. Broesamle
- Munith, Michigan USA
September 9, 2011

A. The two primers are similar, the 85582 being water reducible. They are usually considered interchangeable, but make sure that you have permission from the design authority before you try to make any changes.
Brian Terry
Aerospace - Yeovil, Somerset, UK

A. DC-
All of the above.

Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina

A. Hi Cannon,

I don't think that you will find a color chart specifically for primers. If you wish a particular color you could use MIL-STD-595 as a reference tool.

All primers released to MIL-PRF-23377 [on DLA] should be listed on the DoD QPD that that can be found on their assist quicksearch website, these tend to be standard colors, with a little variation.

You could try talking directly to the manufacturers of the primers if you wish (the likes of PPG, AKZO, Deft, Randolph etc...) to see what they have or what they may be able to generate for you.

Best of luck.
Brian Terry
Aerospace - Yeovil, Somerset, UK

A. Hi Chris,

MIL-PRF-23377 [on DLA] paints are usually pretty good at doing exactly what it says on the tin when used in accordance with the manufacturers technical data sheet (TDS). Does your customer have some sort of strange mixing or application requirement that doesn't meet the manufacturers TDS?

As stated in the previous posting many things can affect gloss levels, but I have found some paints are very sensitive to the mix ratio and the level of thinning, so make sure that is strictly controlled and that the viscosity of the paint is right before you spray it.
Brian Terry
Aerospace - Yeovil, Somerset, UK

A. We use the MIL-PRF-23377 [on DLA] from Akzo and it is most definitely glossy when used as instructed by the TDS.

When we switched from the MIl-P-23377 product we thought we had missed something as that was as flat as a pancake!

As Brian mentioned, stick with the manufacturers instructions and you won't go far wrong.
Adrian Yeo
Aerospace Surface Treatments - Chelmsford, Essex, UK
June 27, 2014

A. Hi David. It looks like MIL-DTL-53030 [on DLA] coatings are chromate-free, and that MIL-P-23377 was superceded by MIL-PRF-23377 more than twenty years ago. Although MIL-PRF-23377 lists type "N" coatings which are chromate-free, it also says they can only be used in special circumstances. So my guess is that your customer is telling you that they want chromate-free coatings these days.

Although that is what I would assume is going on, we all know the consequences of assumptions, and you should now probably verify with your customer exactly what they've ordered and that you have the permission and authority to ignore the requirement for a MIL-P-23377 coating. Please note that per MIL-PRF-53030 section 6.1 "Intended Use", it seems that this water-based chromate-free coating cannot be used on aircraft.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Mark,
At some point a few years ago, the designations of most of the military standards got changed a little. The numbers all stayed the same, though.

If you look up this spec at https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=16259
you can see that it used to be MIL-P-23377 and is now MIL-PRF-23377.

It looks like M23377-1-C2 is the part identifying number for parts done with MIL-PRF-23377 Type I Class C2 designated coatings. (Paragraph 1.3 of the spec.)

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

A. Hi Ian. There are paints which comply with both, so in that respect, yes, they are 'equivalent'. But specs can have different inspection criteria or other requirements in them, so complying with one does not guarantee compliance with another even when they are generally similar and a product is qualified for both. You must get access to the spec in question and insure that you are actually fully complying with it :-)

Luck & Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey