Uneven Sheen with "Dull" Conversion Varnish
May 15, 2012
Question
After the third coat of MLC Krystal on some big cherry table tops, I ended up with a few dry spots. Is there anything I can use to buff the tops out, or would I be better off sanding them down with 220 and shooting another coat? I don't want to spray a fourth coat because of the mil thickness limits, but I'm thinking if I sand off a bunch, I should be able to.
Forum Responses
(Finishing Forum)
From contributor R:
What sheen are you trying to achieve? High gloss? Gloss can be buffed nice, but any other sheen like a satin will be very difficult to buff and have even appearance on large surfaces to get same satin sheen.
From the original questioner:
I'm using dull. If buffing it brings up the gloss a bit that's fine, just need to know how to go about that. Still thinking about sanding a bunch off with 220 and shooting another coat.
From contributor R:
Dull will not be easy to fix. I agree with you, sand down with 220 and then 320 and shoot another 4 wet mil coat. As long as you sanded some between coats and kept your wet film build down some, you should be good. Try not to sand through coats when you scuff and get halos. You might run into other issues.
From contributor G:
What kind of equipment are you using to spray the Krystal? I recently upgraded to a Cat AAA because I had a 14' x 4' wood island to shoot. I don't think I could have kept a wet edge if I had to spray it with my cup gun. AAA (for me) is the best equipment upgrade I've made and I should have done it sooner.
I'd sand and respray.
From contributor A:
If it makes you feel any better, I'm having the same problems with Krystal in dull. Kind of like patchy spots. My MLC supplier tells me it's dry spray, but it's not something I've ever noticed before using any of their other products or sheens. I just sanded and recoated since there was really no other fix that would work. I'm also using a AAA.
From contributor O:
I also have had problems this week on a table top. Glad to hear it is not just me. I had some rough spots show up on the third coat. I sanded it down with 220 orbital, then went back with scotch bright pads to get the swirls out. I recoated and now I can see overlap marks down the table if you look with the light just right. Any Ideas?
From the original questioner:
I sanded the tops down and shot one of them, and the same thing happened - bunch of dry stripes, even with all my spot lights shining on the surface. Then I figured out my problem, I think. I took the gun apart and found a bunch of Krystal congealing in the guts of the gun. I broke my #1 rule, make sure the gun is clean. I'm going to do a bunch of sanding tomorrow and shoot the tops. Just makes a person feel real stupid overlooking the obvious.
From contributor O:
Hope that works for you. I did the same thing before I shot another coat on, but it didn't help.
From contributor A:
Thanks for the update - and I think I'll check my gun tomorrow as well!
Contributor O, try increasing the amount of solvents you're using in the Krystal. I went to 15% care reducer and it seemed to help, as well as spraying in a cross hatch pattern (which is not how I normally like to spray). Seems to have worked for the most part.
Anyone know if MLC has changed the formulation of Krystal/Resistant in the last little while?
From the original questioner:
My gun for this is an eight year old DeVilbiss HVLP gravity feed. This gun has produced excellent results with Krystal for the past couple years.
After sterilizing the gun and adding 15% retarder, I got a beautiful spray pattern. I've never reduced Krystal before. Fact is a little over a month ago I shot a maple top a lot bigger than these cherry tops with no problem, same finish, gun, and everything. I think a big part of the problem was garbage in the gun, but like I said I have never needed to reduce Krystal. I shot them at 10:30 this AM. At 2:00 I could see some striping, not dry overspray. I'm thinking it's still drying, flashing off. I really hope the problem was my gun - I love this finish and so do my customers.
From contributor R:
The main reason for sprayed uneven sheen in Krystal Dull or similar products that are low sheen is typically the significant amount of flattener in the product and poor atomization from the gun. The lower sheen and the higher solids of the product make the flattener stack up unevenly with poor atomization. The flattener will actually move around inside the coating when sprayed, and if it builds up unevenly from the spray pattern, you will notice uneven appearance and gloss in areas. This is most noticeable on dark stains and dark pigmented colors.
It is very important that your gun atomizes well and even to avoid this problem with low sheens. Plugged guns and aircaps really struggle breaking up the coating, especially with the lower pressure used today. Lower solids conversion varnish, like MLC HP CV, can help and are more forgiving because you have less overall flattener throughout the film because each coat is thinner due to lower solids. MLC does not make Krystal Flat anymore and everything moved over to HP CV Flat for the very lowest gloss level for ML Campbell. It is a very clean and easy to spray finish and works great over dark colored stains and paints.
From contributor O:
I was using satin Krystal and got the same striping look. I reduced only 10%, usually less, but rep said to reduce 10%. I am going to remake the table and try again. I might use 2k poly this time.
From contributor R:
Use a crossing pattern when spraying. You should not have the problem with satin Krystal. Are you going over a darker color?
From the original questioner:
What is MLC HP CV? I need to ask because my supplier is worthless unless I tell them exactly what I want. Also, if I'm reading all of this right, I should get more even results with satin, true?
From contributor O:
Yes, it is very dark brown with black glaze. What do you mean by cross hatching? Do you spray once cross ways and go back over it again lengthwise?
From contributor R:
ML Campbell HP CV is really called High Performance Conversion Varnish. Sorry about the abbreviation. Takes the same catalyst as Krystal. It comes in flat, dull, satin, and semi-gloss pails. It is a non-yellowing CV that has a real nice soft feel and provides more of a close-to-the-wood furniture finish. It is really clean and rich in appearance.
Something else you might want to check out is Envirovar. It is a new formaldehyde free CV. Takes a different catalyst, though, at 5%. Comes in dull and satin. It is not non-yellowing, but I have not seen anything that looks so good. Simple drop-in solvent CV for green jobs instead of waterborne stuff.
From contributor R:
Yes, you are correct. Spray one way and then the other on same coat. Might want to try increasing your air pressure some, but typically gun related/uneven application. Some guns spray better than others. Krystal satin is easier to spray than dull on bigger items.
From contributor A:
Their satin is also quite shiny at 35 degrees. To see the difference between a dull and satin, place some transparent tape on your dull finish and you'll see what it'll look like. Just a tad too shiny for my tastes - I prefer 25.
I've heard about the HP CV and wonder how it compares to KlearVar. I've been given a sample of Envirovar to test out but haven't had the time to try it yet. It's supposed to be a very nice spraying coating, though.
From the original questioner:
Well, after hoping everything would end up nice and even after drying all night, no such luck. Still striped, although much less noticeable than before. Sterilizing the gun and adding 15% retarder did make a big difference. So today after reading that satin might work better, I got a gallon from a buddy. Sanded all the tops, blew off all the dust, and wiped down with the good thinner, mixed up 1.5 liters of the satin, added 15% retarder and a shot of fisheye eliminator, which I always use.
Sprayed the table leaves - laid out like glass. I'm laughing and pissing in my pants I'm so happy. Ten minutes later, I have fisheyes everywhere. Now 5 hours later, the only recourse I can come up with is to sand these tops down to bare wood and start over.
The thing that's really bugging me is I've been using Krystal since it came out, and I love the stuff. 3 weeks ago I sprayed a 72" x 72" maple top in dull and it came out perfect. Now on a standard 42" wide I can't get anything to work!
From contributor T:
Could be a bad batch. Order from outside your area or demand a new batch number from your local. It happens. Otherwise I would go into technique. As you said, you have used it for years. Something has changed... Bad batch would be first guess. Or gun has a foul.
From contributor O:
I know what you're going through. I delivered the table I was having trouble with and of course in the customer's house, their lighting made the striping stick out like crazy. The table I made has sort of a picture frame around it with MDF core ply in center, so I told them I would just build another table. Even though I thought I had sanded enough of the finish off between coats, I can see that the finish is getting too thick, getting a little cloudy look to it. My rep told me that the striping is caused by either a plugged air cap or not spraying correctly. I told him I just cleaned the gun good before I sprayed the last coat and am not spraying any different than I have for the last 15 years. Maybe next week will be better?
From the original questioner:
Any ideas as to what will strip Krystal?
