Checking for Contamination in Conversion Varnish

      Ideas and a checklist for troubleshooting a "gritty" CV finish. June 10, 2006

Anyone out there had trouble with 4140 CV from Chemcraft having a really fine grit in the product? It seems like there is sand in your finish when you lay it down. The finish tech was just here and we are not sure what happened.

Forum Responses
(Finishing Forum)
From contributor S:
Isn't that comforting, when the tech isn't sure? Did he bring new product (different batch) to see if it may be the product you have? Most of the time, issues such as these are solvent related. Is it a Chemcraft reducer you're using? Are you spraying with an AA? Is it happening on whatever substrate you spray onto and with all your spray equipment? Has your compressed air been checked?

From the original questioner:
Yeah, he brought with him new finish, catalyst, reducer and 2 guns. I also had the problem when I shut the air fan regulator down on my AA. No matter what we put it on, we had the problem. When he got back, he got some CV from the same batch number and couldn't duplicate the problem. He is thinking it might be the catalyst. We will see tomorrow.

From contributor B:
Have you tried shooting it in something besides a AAA? Try shooting it with an HVLP and see if you still have the problem. Could your pump or lines be contaminated?

From the original questioner:
Yeah, we shot it with 3 different HVLP gravity feed guns.

From contributor B:
Hmmm… Are you sure that your air supply is dry? That is the only other thing I can think of.

From the original questioner:
We think it might have something to do with the catalyst, so that is the next thing we are going to try, that and one more batch of finish. This is one that is really odd.

From contributor D:
Clean a piece of glass with acetone. Mix up your finish and pour some out onto the glass. Try to get it so that you end up with a poured film of maybe 5 wet mils. Brush it out if you have to. Wait for it to dry. If you end up with gritty finish, then it's the finish or there's a remote chance that you have a filthy spray environment (you know best on that and all I am doing is citing the variables). But if you end up with smooth finish, it's your equipment.

From contributor N:
Below is our SOP for checking contamination. A little long, but checks all your possibilities.

1. Obtain clean glass or metal plates. Wash with thinners to remove any surface contamination.

2. Dip plate in product ready for application and check for contamination.
* If no contamination found, check equipment or application environment. See (7).
* If contamination found, see (3).

3. Dip clean plate in uncatalyzed, unreduced product.
* If contaminated, change batch of material and contact your local paint representative.
* If no contamination is found, see (4).

4. Dip clean plate in catalyzed, unreduced product.
* If contaminated, change batch of catalyst and contact your local paint
* If no contamination is found, see (5).

5. Dip clean plate in catalyzed, reduced product.
* If contaminated, change to new thinners.
* If no contamination is found, see (6).

6. Remix material, original product had external contamination.

7. Check oil lines and water traps for build up and drain appropriately. Respray and check for contamination.
* if contaminated, see (8).
* If no contamination is found, begin regular maintenance of lines and traps.

8. Spray clean plate with mixed material.
If contaminated, see (9).
* If no contamination is found, problem occurs with substrate. Wipe or resand panel and check earlier manufacturing or finish techniques for contamination.

9. Spray clean plate with mixed material and transfer immediately to non-connected area.
* If contaminated, see (10).
* If no contamination is found, problem concerns environment when drying. Possible contamination from air intake or make up.

10. Transfer mixed material to alternate area and respray with different equipment.
* If contaminated, see (11).
* If not contaminated, then problem is with spray or pump equipment. Contact your local equipment representative.

11. Neither product nor equipment appears to cause contamination. Problem could be nonlocalized airborne contamination or airline contamination. Contact your local paint representative for assistance.

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