Slow Curing Times with Post-Cats

A finisher gets some feedback about why post-cat primer and varnish may be taking too long to cure. May 2, 2011

I have sprayed some sample MDF pieces with Clawlok - white then Krystal clear. My 10.1 mix is right, but my shop is only 60-65 degrees. It has been two days and the leftover mix in both products has not hardened. Is this normal? The cans have about two inches left inside. I can still mark the finish with my thumbnail.

Forum Responses
(Finishing Forum)
From contributor L:
This is not an epoxy and the large quantity you have left over in your cans will take quite a while to cure hard. This is normal. Now, did you say you can mark the parts that you finished with your fingernail? This is not normal. The Krystal should have hardened within a half hour and started to cure overnight. However, 65 degrees is the minimum you should be spraying and curing your finish at. 72 degrees seems to be optimal.

From the original questioner:
Thanks for the reply. It is the sample that is marked. I sprayed the Clawlock and Krystal with my Kremlin 10.4. I sprayed one coat, let flash 10 minutes, sprayed another coat. I let this dry 2 hours, then flipped them over and did the same with that side. Let dry overnight. When I went to sand them the next day, I noticed that the samples had an imprint from my dry rack. I sanded the imprint out and sprayed the Krystal the same way and left them overnight only to return with the rack imprint in the clear. The humidity is 40%.

From contributor L:
The stacking time on Krystal is 4-8 hours. Flipping over after 2 hours should be sufficient to not have print marks. One thing might be the two coats you are applying. You might try spraying one coat, waiting an hour and flipping. This is the way I do it and have no printing problems.

From the original questioner:
Thanks. I will leave the next test longer in between coats. I did not use MLC lacquer thinner for thinning. Do you think this could be an issue?

From contributor L:
What are you using? One thing I have learned is that when you are using a product that is part of a system, it is always wise to stay within the system. It is unlikely but still possible this rogue thinner might be part of your problem. If you do get MLC thinners, get the standard thinner for the Clawlock and the reducer for Krystal.

From the original questioner:
The name is Recochem, made in Canada.

From contributor L:
Looks like your thinner has a lot of toluene in it. Not sure if this is good or bad. But I would recommend that you use the MLC thinners.

From the original questioner:
I will try again with the company solvents as you suggested. Thanks for your time... Love this site!

From contributor L:
Glad to help. Krystal and Clawlock are great finishes. You shouldn't be having this problem if everything is set up right.

From contributor J:
Conversion varnishes take a little longer than lacquers to harden to the point that the racks won't mark them. This is especially true with your cool shop temps. I find in the winter when it's cool, I turn my spray job into a two day job. Spray the seal coat on the first day, then spray the topcoat on the second day. Back side gets sprayed first thing in the morning, front side gets sprayed at the end of the day.

If you are rushed and need to get it done in a day, try to get the interval from spraying the backs and fronts as far apart as possible for your topcoat, then keep going back to the rack every 15 minutes or so and just slightly adjust the parts on the racks so they don't sit in one place too long.

I use one of the Hafele racks, and do get the marks if I flip too soon.

From contributor R:
I commend the questioner for finding out through making his sample board that there is an issue with his finishing schedule. Exactly what the issues are have been discovered on the sample and not when he has proceeded with the entire project, nor after he has completed it. Many a finisher will post an issue after they have completely finished their job, and it's too late to rectify.

This is just a gentle prodding for up and coming finishers to make samples before jumping into the whole job. If your samples come out the way you expect, proceed with the project and follow the same schedule that you performed on your sample. The temperature and drying times and spraying techniques can be jotted down on the back of your sample. You can refer to your notes as you progress through the project, and if all goes well and Murphy doesn't rear its ugly head, the chances of smooth sailing are surely in your favor.

From contributor L:
I learned to finish through WOODWEB and the school of hard knocks. It took me about two years before I really was confident enough to start experimenting and posting help on WOODWEB. I am no expert, and still consider myself a sprayer more than a finisher. I do not mix up colors except for trying to tune in what my color guy at MLC mixes up for me. I do use the stains and dyes I have in house to develop colors for clients, so I don't need to get the samples from my MLC guy. I assume it will take me about a decade to complete my self taught education. Only expanding when the project requires it. Just lazy I guess.

From contributor G:
I have found with Clawlock and the Kremlin you can get too much product laid down and it will take forever to set up. I thinned it a bit and dropped a tip size to 06 and it set up much better. It is 30 below here, so it is hard to keep the drying room as warm as we would like.

From contributor T:

I am curious about one thing. You state that you shot a coat of Clawlock, flashed 10 and shot a coat of Krystal over that. I use a ton of Clawlock, straight white and tinted. I always go two coats Clawlock, thinned, let flash 45 minutes to an hour, cut back hard and tack. Final color (mid coat). Scuff 320 - 400 when dry. Then proceed to Krystal dull as topcoat. First pass light, second as a full finish coat.

I have used a Kremlin for quite a few years now and I am nowhere as enamored with it as I was in the beginning. If you have the standard setup from the factory with the 09-94 tip, then take contributor G's advice and invest in an 06 tip. The 09 is an absolute firehose. If you are doing panel work, wainscot, etc., consider jumping to a 114 or 134 fan pattern. This is the major drawback to Kremlin in my opinion - the inability to change patterns or flow without physically changing the tip. For almost all my samples I use my trusty DeVilbiss Gravity with a PPS setup. Much faster for color adjustments, etc.

Has anyone used a Kremlin in the past and moved onto something different? If so, what? I know this is not common to do after the initial cost outlay, but I am curious.

From the original questioner:
I sprayed a coat of Clawlock, let flash 10 minutes, then sprayed another coat and let this dry for two hours before flipping over to do the same on this side. This dried overnight before spraying the Krystal in the same way. I followed contributor L's advice and it worked. But I do seek any advice on what tips would be helpful. Yes, I do have the factory 09 tip and have not been happy with it.