Troubleshooting Wrinkling in Conversion Varnish Job
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Pros analyze a case of wrinkled finish, looking at formulas, shop conditions, and more. April 14, 2005
Question
We are finishing some tabletops with Krystal. We used the proper sealer and the first coat of Krystal went fine. Some of the tables needed a second coat. We waited until the next day. Some of the tables (not all) started to wrinkle as they were drying. Is there a recoat window? What might cause this to happen? I ran into this once before but don't remember what the outcome was.
Forum Responses
(Finishing Forum)
From contributor D:
Whenever a catalyzed coating is being used (post-cat or pre-cat), you can create recoat windows, you can have recoat window issues. That includes the class of coatings formulated to have no recoat windows.
The coatings which have no recoat windows need to have their marketing modified to be more accurate and less misleading. If the phrase "virtually no recoat window" were used, then this would be accurate, certainly in your situation. Similarly, how about throwing in the phrase "no recoat window to speak of"? That would be just as accurate.
What temperature did you spray and at what temperatures did the object flash and cure out? How thick did you spray?
Did you scuff sand first? How much? You may have scuffed through the layer of coating in which you will usually get wrinkling (the workaround if you sand too much is to lay down a light barrier coating of vinyl sealer).
What reducer did you use? If you use a reducer that is too "hot" (too high in solvency), this could surely kick a recoat window.
Did you follow all the catalyzation guidelines (10% catalyst by volume to straight, unreduced coating material)?
Understand what happens when you get wrinkling. Your coating has already knitted itself together into a continuous film. It was now undergoing a further process of crosslinking (think of how Tonker Toys are connected to one another). A new coating is introduced and the solvents in that newly laid coating want to burn into/melt/react with the coating already there. The film has no choice but to wrinkle. Many conditions can cause this reaction of the two coatings and I listed and asked about some of them in the previous paragraphs.
Sometimes, rarely, recoat window issues just happen for who knows why. The problem is still operator error because they do not happen from faulty product material (that happens too but it is too rare).
From contributor D:
What to do? Remove the defective finish and start fresh. Or sand out the wrinkles and lay down a light coat of vinyl sealer as a barrier coat and shoot your Krystal over that.
From the original questioner:
We laid down the first coat and all went well, however we had some small particles in the finish and wanted to lay down another coat. We first started with Magnasand sealer and then topcoated with the first coat of Krystal. We did catalyze correctly at 10% and we retarded the finish with MLC retarder at 10%, as without it we were getting lap marks. The temperature in our shop is probably not the greatest, although we were probably at around 65-70% in the shop when spraying and drying. The wrinkling appeared on about half the tables we did and the other half, which were finished at the same time, had no problem. We did scuff sand between coats with 220 grit paper. I sanded pretty well because of the particles that needed to be laid down in the previous coat. The finish did not wrinkle completely over the entire piece but only in areas. We let the original finish dry overnight before the second coat of Krystal.
From contributor J:
Were the particles of sand only in the ones that crinkled or in all of them? Maybe these tables had a breeze that not only flashes off cold, but also brought in dust or dirt. Any pattern as to where the good tables sat and where the failed ones sat? Also, did the finish start to crinkle right away or was it noticed the following day? Were the sealer coats dry when topcoated?
From contributor J:
That's one heck of a lot of retarder! What does the manufacturer recommend?
From the original questioner:
Perhaps I was unclear. The particulate that was in the finish was just minute dust particles that were airborne and landed in the wet finish as it was drying. 10% retarder is not too much, according to the MLC rep, if it is Campbell's retarder (I think it is a blended retarder). I think in retrospect that the problem may be in the areas where we sanded the most to get rid of the dust. It seems after talking to my rep and reading contributor D's post that perhaps the coating was sanded not all the way through, but thin enough that it let the solvents through enough to cause the problem. Also, we are having unusually cold weather and maybe a cold draft worsened the problem, although I don't think that as much because some that failed were right next to some that were perfect.
From contributor D:
The retarder is not the problem as long as it is MLC retarder. The reducer is not the problem only as long as it is MLC reducer. Their retarders and reducers are formulated to be weak enough not to cause recoat problems, but balanced enough that they do their expected jobs of retarding and reducing MLC coatings.
Unlike what you read in Bob Flexner's book "Understanding Wood Finishing," there are many products where the reducer is formulated to fit the coatings. MLC materials are formulated just this way.
Only nitrocellulose lacquer is the forgiving coating with which you could practically (virtually) get away with murder, so to speak. Conversion coatings are not the ones with which you want to play alchemist/formulator.
It sounds to me like you had some sand through areas. To sand out dust and debris with 220 is too much. Go with 320 grit and use a sanding block that has a soft cushion. Check for corms in the sandpaper and get rid of them.
It seems that by itself both Krystal and Duaravar do need to have the retarding additive or you get bubbles. As long as you are using their Care Retarder, either 1 or 2, you are safe. If you decide you want to dump in your own MAK (Methyl Amyl Ketone) or butyl cellosolve, then you are on your own. Their retarders are based on different formulations which do not have the high solvency that you find with MAK and butyl cellosolve.
From contributor J:
To me, adding any retarder, whatever strength, to extend a coating's flash and cure rate is the root of the problem. That critical recoat time is when all the solvents haven't sufficient time to evaporate when another coating is applied on top. Longer dry time, longer critical recoat time. Although my question on where the wrinkling occurred on each table was not answered, given the fact that the tables were all re-sanded almost to same level, pieces of this puzzle are left out. I guess we not only are told that material is ready to spray out of the can to comply with V.O.C. regulations, we have to buy and break the law to make them work! Time for this nonsense to stop.
From Paul Snyder, forum technical advisor:
When the second coat of CV causes wrinkling, the sealer would be my first guess. If you're going to use a sealer with CV, it's best to use a catalyzed sealer. You said you used Magnasand. That's a pre-cat lacquer sealer. It's designed for use with pre-cat lacquer.
Krystal is self-sealing and the tech sheet states "For best results and maximum durability, 550 Krystal Hi-Solids should be used as it own sealer. The use of conventional nitrocellulose sealers containing stearates is never recommended." I don't know if Magnasand contains stearates to make it easy to sand or not, but I still wouldn't use it with CV.
Try skipping the sealer in the future and see if the problem doesn't go away.
From the original questioner:
I talked to the MLC tech department and they said you are correct in that Magnasand should not be used as a sealer, although technically I don't think that is where the problem lies. The problem seems to be a recoat window and they recommended that if you cannot do a recoat of Krystal over Krystal the same day, that you should wait approximately two days before recoating to allow a full cure. It seems that there is a time when it is in between accepting a new coat and full hardness that can cause this problem. I have had it once before when I used the Krystal only and no sealer, so I don't think it is the Magnasand, although I won't use that again for Krystal either. I had asked the local rep and he told me it would be no problem. Wrong! They do make a Krystal sealer that is made to go under Krystal as a first coat. Thanks to all for your help!
From contributor B:
You're right, they do make a Krystal sealer which is catalyzed as well. What's happening underneath and one of the reasons you may be getting wrinkling is that the layer is not completely cured or dry enough. When you sand, it breaks into this area, so when you lay another coat of Krystal, it reacts to uncured layer. A catalyzed sealer does supposedly prevent that. Also, there is a window for Krystal, I don't care what the label or reps say. It's happened to me also. I just missed the appropriate shooting time.
From contributor R:
From my experience with this product, the recoat window is usually caused by a low temperature. Cool weather slows down the reaction and when you get a sand-through, you will usually get a wrinkle. This could be further aggravated by the fact that you added a retarder, which slows down the cure even more. While technically the product will be okay with 10% retarder, you again have to consider the temperature. The precat sealer may or may not be further complicating things. It seems that if you had to err, I would recoat sooner rather than later. I know that this isn't always possible.
From the original questioner:
We are in a deep freeze here and the temperature of the material could have been a factor also. As far as the retarder, the problem was that any less and we were getting lap marks in the finish. You could see every pass that the gun made. When we used the retarder, it stopped that from happening. We tried it with less retarder but it still happened. I am not sure how to deal with the temperature issue, as this is a concrete building and difficult to keep a consistent warm temperature in the 70 range. We do what we can but it is sometimes a problem when the weather gets really cold.
From contributor M:
That's interesting that the MLC told you to wait two days to recoat. I was once told by them that if I don't get all the coats on in one day, I should try to get them on first thing the next day. I don't know what to think now. I always try to finish everything up the same day, though. I usually spray one coat, then wait at least an hour and scuff sand with 320 and spray again, then wait at least another hour and sand and spray again. I try to keep the booth a minimum of 70F during spraying and curing. I do sand fairly aggressively at times and I know that I have sanded through the first layer. I never have had a problem with doing this and didn't realize it could be a problem. Maybe finishing everything within 8 hours or so helps? What happens if I decide to add another coat of Kyrstal, let's say 3 weeks after the initial finish, because I put on 2 coats and feel it should have another? Are there going to be any wrinkling problems here if I scuff sand first?
Sometimes I think I should just start using Magnamax on the kitchen cabinets and not have so many worries. Has anyone been using it long enough on kitchens to see how it holds up over time to general use and abuse?
From contributor J:
Set up a thermometer in your spray area, one in your coating and one on your piece. All these temps must be at least even with themselves to have success finishing. A wind current (hot or cold) rushing over the top of a coating will skin or flash off faster than either the areas free from this breeze and/or its own underlying layers. Add to this cold temps which slow its bonding process, a thermal layer that will build up containing quick solvent flash into the free air and the addition of still more retarded thinners to make this material flow in needed conditions (77' + 50% H.).
From contributor R:
Your finish probably wasn't flowing because it was cold. A retarder is, in essence, a slow evaporating lacquer thinner. There are different thinners/retarders for different temperatures. Try the C189-36 in cool weather and it will help the finish dry faster.
Contributor M, I wonder if because the questioner said he was having a wrinkling problem they told him to wait two days. If your question only addresses adhesion, then I could see why you were told to spray the next day. Also, if you want to recoat a few days/weeks later, wrinkling shouldn't be an issue. It is usually a problem when the coat below has a surface skin, but the inside is still uncured... Contributor D gave a great explanation of the situation.
From contributor E:
The time frame of overnight is the problem. For some reason, all catalyzed coatings seem particularly vulnerable at about 12 hours after spraying. I've never had a problem under 8 hours or over 24, but anytime I've done the overnight thing, problems have occurred.
From contributor N:
I sell finishes, and 90% of the coatings I sell I have personally formulated. I stand behind them 100%. That said, catalyzed finishes will wrinkle! I believe there are several reasons for this. In no specific order, I have proven through lab work as well as at furniture shops that you can get wrinkling if you: A) Use heavy pigmented stains that will effect the crosslinking of the catalyzed sealer. B) Use uncatalyzed sealer. C) Use material that has been catalyzed too long.
Temperature will also play a big part in this equation because the warmer the material, the faster the crosslinking process takes place. Eight hours of dry time in one shop is not equal to 8 hours of dry time in another shop, thus changing the so-called recoat window. As soon as I see wrinkling, I have the finisher apply a thin coat, let it flash for 10-15 minutes, and then apply a heavier coat. I make sure my customers don't use wiping stains loaded with pigments (use a dye stain and then a light pigmented wiping stain to get darker colors). They use a catalyzed sealer (my CV is self-seal anyway). And they mix fresh batches as often as possible. This procedure will virtually keep the dreaded wrinkling away.
From the original questioner:
Obviously, I am not the only one who has experienced this problem. I let the tables that failed dry for two more days, sanded them out and resprayed and everything went fine. I would like to know what others do about the dust problem which we seem to always have a little of on the darker finishes. We clean our booth every 3-4th day and have filters on the doors to keep out the shop air, but still seem to have the problem. It only seems to show for the most part on black stains or black painted finishes. Some of it will settle out as the finish dries, but not all.
From contributor B:
Static electricity could be part of the problem. The piece to be sprayed probably has a charge to attract these particles that still are flying around in air. Real bad about this time of year it seems. There are ways to static ground your object, but not familiar with them enough. Also, black will show up when nothing else will, black being one of the toughest colors to keep perfectly clean.
From the original questioner:
Contributor B brings up a really good point that I had not considered. Airborne dust lands in wet finishes, especially showing up in darker colors. We keep our booth as clean as we can and filter the air coming into the booth from the shop, however it seems to still be a problem. Static electricity seems to be a potential problem. We scuff coat the sealer, then brush it off and blow it off with a filtered clean air line and then tack rag it off with a commercial sticky tack rag. All of this would create a static buildup, meaning that it would attract airborne dust back to the board again. We, like other finishers, are not in a perfect situation for spraying and I am wondering if this is one contributing factor to the problem of dust in the finish. What could be a simple solution? We are already trying to control humidity and heat as best we can.
From contributor O:
I have a plastic two gallon sprayer that I can fill with water and mist the floor and wall. I haven't done an opaque finish in awhile, but it did seem to help keep the dust at bay. Besides keeping the booth as clean as possible, I don't have any dust collecting objects like shelves or open cabinets.
From contributor J:
I solved our problems when I stumbled upon the Lonix blow gun in an electronics magazine and convinced my boss that this could possibly be the answer to our problems. Like you, we did everything humanly possible to remove dust contamination till we pulled our hair out. Especially around this time of year, static charge is at its worst. The misting of floors I also do to prevent leaks under doors or wherever from stirring up any dust problems also. You'll know you have a static problem when you tack your job off and two seconds later your hand feels more junk back on the surface.
From contributor H:
I have seen conversion varnishes have static issues more than other coatings types. This is a general statement, of course. One experiment you could try is spray a test door/panel and flip it over (right away), propping up the four corners with gallon cans. Although this is not scientifically controlled, at least it will eliminate the particles that would fall onto the surface because of gravity. On occasion I have seen airborne particles actually turn and move to the upside-down finish. Usually you can't actually see it happening. Sometimes you still come up with trash on the surface that seems to appear more prominently as the CV begins to tighten up or get a little further in the crosslinking process (20 minutes). After examining the trash more closely, it was determined not to be from an airborne source, but delivered to the surface in the coating. More frequent and thorough cleaning/maintenance, better fluid filtering/straining, don't use material close to the end of its potlife are just a few measures that can be taken to minimize the trouble.
Another thing to consider with CV is overspray. This tends to be more visible on darker pieces but you can still feel it on lighter colored projects. Are you laying several doors/parts down and spraying them all in one group? Try spraying one door/part at a time, right in front of the exhaust. Then move that piece away to a remote drying rack and bring the next one in. I've seen too many spray rooms/areas filled with doors, frames, range hoods and entertainment center boxes being sprayed in what seems like a traditional method, however, the CV overspray is not making its way to the filters, but landing on everything else and not melting in. Hope you find something in this that you haven't already tried.
From contributor J:
All you have to do is feel it with your hands after you tack off the surface a couple good times. That should be adequate in removing debris. Static caused by dry air from heaters and electrical equipment such as sprayers and the field that the high pressure hose creates along with the rubbing action of sanding and tacking all add to this problem of charging the surface. Grounding is a hard thing to do but de-ionizing the surface seems to work good.
From the original questioner:
I ordered one of these Ionix blowoff units today. The people who sell it say you should not use more than about 10 lbs. of air pressure when blowing off with it. They said you want it to push off the particles and have them drop to the floor rather than up in the air. If this works as well as it should, it will be the best $129 I have spent in a long while. Thanks for the info! This forum is the best, as almost everyone on it brings something to the table and everyone benefits!
