Process/Procedure for Cross Hatch Test - Measuring Adhesion by Tape Test

A. ASTM has a spec for the crosshatch test, but I can't remember whether it says anything about how long to wait before testing. Just be aware that freshly cured paint will frequently do better on flexibility and adhesion tests than when allowed to age. As long as you do the test the same way each time you don't have to worry about that effect.

The key is to do testing on enough parts personally so that you know what the result should be on a given part, then if you get a different result you'll know it's something unusual and not simply a timing issue.

A. I don't believe that the ASTM spec calls out a waiting period. We paint to a lot of military spec and some of them do call out times. Mil-C-53072 [MIL-DTL-53072 [link is to free spec at Defense Logistics Agency, dla.mil]] (this is for CARC paint) calls for 168 hours cure (at 70/50) prior to testing. Mil-C-193 simply says to do the testing after the top coat has been allowed to cure.

You might want to talk to your paint supplier about the time needed for cure and what they would recommend. Depending on your type of customer, you may need their buy in too.

A. Mac, I ran into the same situation and decided to wait until the parts (and test panels) had completely cured before testing. In my case this involved a 24-hr room temp cure then a 24-hr low temp bake. I figured that the process wasn't complete, and therefore wasn't ready to be evaluated, before then. Good luck (adhesion!)

I would like to thank those who answered my request for a "consensus" on how long after the last coat is applied, and the time when a "Cross Hatch Adhesion Test" is done.

I was writing an article on this test, and after doing much research with coating manufactures, companies that make the "CHAT" test kits for doing this test, a few chemists, and also checking with ASTM and ISO --

There was no consensus, there were too many different answers, no standard to really use in my article. I would like to share what I consider one man's opinion, and what I wrote in my article concerning the test.

"Because of the numerous coatings, and methods of applications, and different systems for drying on the market today, I cannot give a definitive answer as to when to do this test on the coatings you are using, I personally prefer doing the test after a week to ten days, and then doing another test two weeks later to double check any differences, always keeping notes on the two samples to make comparisons for future references. This suggestion includes the air and heat dried coatings.

If a faster test must be done, then these calculations could be used, If less then 20% of the coating is removed this is considered passable, if greater then 20% of the coating is removed this is considered poor adhesion between the coatings and substrate."

I hope someone will find this helpful.

Thanks again for your answers. I considered all of them.

Mac Simmons

A. See Method B of ASTM D3359, 'Standard Test Methods for Measuring Adhesion by Tape Test.' For flat substrates and paint up to 125 microns (5 mils) thick, it's easiest to use a commercially available test kit: http://www.gardco.com/pages/adhesion/pa2000kit.html

For non-flat surfaces and/or thicker paint, see Method A (X-cut) of ASTM D3359.

A. The most common method is ISO 2409 so I would suggest you buy that spec. It is a destructive test so you need to spoil a part to do it as QC but it is ok for test panels.

Basically cut down to the metal with a knife in a cross hatch pattern and use pressure sensitive masking tape to try to pull off the paint. The ISO method is basically 10 scribe lines 1mm apart and the same perpendicular to those which gives you a set of boxes. You can use a special tool or a sharp knife with a steel ruler.

You can determine the number of lines and distance apart depending on your needs. The tape used also needs to be standardised. We supply the 3M #250 1" tape which is a commonly used standard.

A. There is no spec or standard to advise when we should test (ASTM 3359 or ISO).

The one and only answer is it should be tested after initial curing and long term curing.

To know when it is initial and long term curing severals factors should be noticed:

1- Numbers of Mils applied to the surface.
2- Ambient air drying.
3- Forced curing ... heat room
4- Method of application
5- Type of coating , epoxy , polyurethane, organic zinc, etc.

By the end, there are so many systems that the only one who can send you in the right direction is your paint supplier.

Never forget to ask for an official email about the lapse of time before testing -- too many answer come from sellers instead of a real technician from the company brand name.

Hi Dante. Personally, I would expect this test to be fine for a drum (a fairly large diameter cylinder).

Regards,

? Hi Dipak. I'm not hearing a question. Sorry for perhaps being dense, but what do you want to know?

Regards,