Lacquer Crazing

[Michael Pyron]

did you sand just before spraying after you let the frames sit for 24 hours?

the rule of thumb I was taught is that after 24 hours one must sand the lacquer before spraying over it...under that time and sanding is not required except to remove any trash that gets in....

I skip the wearing of gloves and do my sanding then put a bit of mineral spirits on a rag and wipe it down...let that dry thoroughly then hit with a tack cloth moments before I spray...I find the mineral spirits both decontaminates and also makes the removal of sanding dust a heck of a lot easier with the tack cloth....

[Ken Casser]

Sorry I took so long to reply. Busy, busy.

Well, the thin coat did nothing for the crazing, so I wet-sanded and put on another coat. It looks better, but needs more coats to cover the flat left after sanding.

I think it will be alright, but still don't know what caused the crazing. Oh well...

Michael - Interesting. I spray at about 5 PM. Then, the next morning, if I need to, I'll wet-sand any imperfections and let that dry the rest of the day. Then recoat at 5. I hadn't heard the 24 hour rule, but it makes sense to me. Maybe after 24 hours the lacquer cures too much to be melted with the new coat. Maybe I need to revise my painting schedule as I sure don't want to have to sand all these frames every day. Are you wet-sanding? What grit?

Thank you.

[Michael Pyron]

as a note that 'rule of thumb' was told to me by a PPG representative and it was specifically for their DCA468 acrylic lacquer (for autos)...that is an air dry product and I would suspect that for a catalyzed product the time might be less...I know that with that specific product when I sand it 2 days later I can smell the solvents being released that are still in the stuff...I reason the sanding does 2 things: gives the new coat a slight mechanical bond and also allows more of the new coat to get into those scratches and 'lay there and melt in better'...also the smell of solvents makes me think that beyond the mechanical bond it also makes burning in of the new coat easier as you are now spraying onto a more uncured area of the lacquer....

it sounds like from your last post that you are actually going 12 hours between coats...though I have sprayed about 20 gallons of pre-cat lacquer over the last 4 months I am still a 'n00b' with the product and haven't even attempted to do a new coat in any time beyond 4 hours (as I haven't had to...YET (knock on wood))

I only wet sand at the final polishing stage using 1200, 1500 and 2000 grit before I whip out the buffer then my ROS with 3M machine polish for the final step...if I am sanding a dried surface (for example pre-cat products after an hour of drying) I use 320 grit as I find that a single coat over those light scratches covers....220 usually leaves marks with only one coat over it...if I am simply removing any nibs that are in the finish between coats I use 1200 grit to just knock off the bump....

I presently do two types of spraying schedules with lacquer...with 2 or 3 coats of pre-cat material I do them as quick as possible (the first coat being vinyl sealer)...its annoying some times to have to wait for the stuff to harden for 30 minutes to an hour, but oh well...I've seen plenty of finishes sprayed on real thick fail so I prefer to do three coats maximum with pre-cats as since they are far harder than an air dry they will tend to fail when the wood they are on moves and the finish thickness is too thick to allow some slight movement of the surface film...

with the PPG product I mention I usually spray 2 coats of vinyl sealer (air dry, as one must use air dry sealers with air dry top coats and pre-cat sealers with pre-cat top coats) sanding lightly on the first coat to remove any nibs and raised grain....I let the second coat dry thoroughly and sand the hell out of it to level it out and leave a 'perfect' substrate for the top coats...I then proceed to shoot 5 coats maximum on that session (sanding any blemishes between coats with 1200) and then let it sit for 3-5 days so that the majority of solvents are released...I then sand with 800 grit and shoot 5 more coats (usually the first coat being thinned a bit more than usual so that it burns in better, then I thicken up the next 3 coats, and the final coat again gets shot being thinned out so that it flows out better)...if I am going for a 'show car finish' I will then allow the project to sit for at least 5 days (maybe more if the weather is wet and cold...and especially more if I use any retarder) so that the rather thick build has ample time to release solvents....I will then proceed to do a good sanding with 800 then 1200 grit and really level the stuff and shoot a final 5 coats...I then let sit for at least 2 weeks before I even think of attempting to wet sand and polish to a jewel like finish...its better to wait even longer as the dry time for air dry lacquers is around a month and if you wet sand and polish too soon the lacquer will shrink afterwards basically making the whole tedious process of polishing a waste of your effort...I've done the 2 week period of wait when it was real hot and dry for the whole time and the project was due for delivery...it shrunk a little bit more over time, but not enough for me to call it a total waste of my effort...take note of the fact the mentioned product is for autos, which means its a tad softer than most lacquers which allows for it to be sprayed this thick....the only negative I've found with building it that thick is that while it gives awesome scratch protection it tends to shatter when impacted...I shot 2 wet bars for a lounge 5 years ago with the above mentioned 15 coats (actually a couple more than that if I remember correctly)and they are showing NO signs of finish failure, though there are damage points from hard impacts....the customer is completely happy and prefers a few shattered areas of finish over abuse from customers with beer bottles sliding around and being ground into the top going through the finish...please take a note of caution that not allowing the 5-6 coats at a time thoroughly dry for the minimum times I give above will lead to trapped solvents, which then results in either tiny bubbles being formed deep in the finish or craters from those bubbles getting all the way to the surface then popping (don't ask me how I know that...lets leave it at that it took a hell of a lot of sanding to remove those craters and such)

I'm betting that if you start using a compatible vinyl sealer as a first coat you will never see any of your symptoms again if you don't shoot the top coats on too thick (and that includes the concept of wet film thickness of an individual coat and the total dry film thickness of everything)

[Ken Casser]

Michael,

Thank you for your very detailed response. It scared me! Much more work than I can put in, but I'm sure the results you get are worth it.

First, I am doing one coat in 24 hours - at 5:00 PM each day (when I close my shop) - but it's exactly 24 hours apart, so I guess I'm borderline there.

Clearly the job you are doing and my work are very different both in terms of the desired finished result, and also the wear that the finish is expected to withstand. A bar would get much more abuse than a picture frame.

I'm a bit confused over the terms "catalyzed" and "pre-cat". I went to my paint store and asked about that, and they tell me that the product I'm using (Lenmar DuraLaq 1A.97) is not catalyzed, and they led me to believe that "catalyzed" and "pre-cat" mean the same thing. Is that true? Do those terms only apply to acrylic? Either way, you're using different materials than I am, so I shouldn't really compare them. My paint guy tells me I only have to sand if there are blemishes. Of course, the can says 'sand between coats', so it is a little confusing. No mention was made of the 24-hour rule, but maybe it's different for nitrocellulose lacquer than it is for acrylic. When I do sand, I don't notice any hint of escaping solvents, so I think I'm okay there.

The can says, one coat of primer, followed by two coats of topcoat, sanding in between. I put on one coat of primer followed by five or six coats of topcoat, and you can still see wood grain showing through. My paint guys says I need a thicker primer, or more coats of primer followed by a couple of topcoats, so I guess I'll try that next time, plus a bit more sanding between coats. The finish I've gotten is the best so far in the four years I've been doing this project, but I think I could do better with a bit more experience. At least I'm getting closer. Thank you for your help.

[Michael Pyron]

to be honest I'm not even sure why I took the time to make that post last night...I only got 2 hours of sleep before that and I was (and still am) a tad messed in the head because of that....I obviously got completely confused about the concept of nitrocellulose and pre-cat....I also mis-read your comments about the time between spraying (yep, you sand the next morning then spray again in the evening)...

OK then...you are definitely pushing the time margin for re-coating in 2 ways...while you did sand, it is 24 hours between coats still...nitro dries real fast and arguably would need to be shot sooner (though perhaps if you thin the first re-coat a tad more it might help burn in)....also, you waited too long after sanding to do the re-coating and that is what makes me say you waited too long between coats...even though nitro dries real quick it is still curing, and when you sand during this period you really need to shoot immediately afterwards as the 'paint' is still shrinking and anything beyond 4 hours after sanding for all intensive purposes makes the sanding ineffective as a mechanical bond...or so I have read in perhaps different words...

I guess I used the word catalyzed as opposed to pre-cat even though I meant for the terms to be =....actually there is a big difference between pre cat and catalyzed....pre-cat has a shelf life of up to 6 months...catalyzed is when you yourself add the catalyst into the mix, let it sit for 30 minutes, re stir it then shoot it...it has no shelf life...it also cures harder than pre-cat products....the issue with catalyzed (in my eyes) is that many times a person is using pretty small quantities of the stuff which makes measuring the correct percentage of catalyst pretty hard....to me that product is best left for situations where you are using gallons at a time and also are willing to throw any leftover stuff away....

I also got lost in the moment and forgot you are using black lacquer...hmmm...not sure if a vinyl sealer (primer) is compatible with that...I would bet it is, but I'm not sure...I've found vinyl sealers to be the best of all as they make a great bond with the wood and allow the top coats to bond well to it....

you also state you are spraying so many coats to deal with grain showing....this, as a previous poster mentioned, is perhaps creating too thick of a final build....what you need to do is to repeatedly apply coats and sand the hell out of them so that you are almost back to the wood and are for all effective purposes using the lacquer (whether it be the primer or the black) as a grain filler...what is important is the total dry film thickness of your lacquer as that being too thick can cause various types of failures of the finish....many times people talk about how many coats they shot on a project....what is really important is how many coats were really left after they sanded....again, it is all about the final thickness of the dried film....

finally, I notice that you perhaps misunderstood my concept of being able to smell the solvents after sanding...to me that is a good thing as that indicates that new coats will bond better...

regards and good luck...

[Rick Lucrezi]

Rick, maybe someone else on SMC can help you with this, but all I can tell you is that I got an Accuspray turbine and gun, and the hose plugs right into the gun, no problem. I get very low overspray and it works great. I think there are two kinds of HVLP guns - those that work with the turbine, and those that connect to a conventional compressor. Maybe all of yours are the latter kind? The thing about the turbine is that it pushes a large volume of air through the gun which (I think) a standard compressor can't do. So the results will be different between the two types of system. I would try turning down the air pressure on your gun, turn down the paint volume, and narrow the pattern if possible, and see if that gets things under control. With my setup, and doing my narrow frames, I have the "pattern" needle open about 1/4 turn, and the "paint volume" needle out about one full turn or less, and that seems to work well. Anything more open than that and I get a real mess. The turbine has no pressure adjustment - it's full volume all the time.
Sorry I can't help more, but I'm feeling my way in the dark as well!

Thanks Ken, I found a gun for the Turbine set up but it has no fittings, gonna try to find them some where and give it a shot.

[Ken Casser]

Thank you, Michael! You've cleared up a lot of my confusion. I now understand "catalyzed" means it's a two part system, like epoxy or polyester resin, that you must mix together giving you a limited working time and a strong finish. "Pre-Cat" must mean 'precatalyzed', or already mixed.

Anyway, I delivered 70% of the job last night and the customer was happy. The other 30% will get finished this weekend hopefully all in one day. I clearly need to rework my schedule so that I get it all done in one weekend, and I need to put on more primer and sand more than what I was doing. Now, I'm back to the sanding question - wetsand or drysand? The last time I did this job, I tried drysanding and the paint would ball up on me. Maybe I was sanding it too soon, but I tried following the directions. Wetsanding worked much better, but it leaves the wood wet which isn't good for painting. Maybe drysanding will work better when I just prime and then sand and prime and sand, and then go to final coat. I'll keep working on it.

Thank you for your responses. Get some rest!

Good, Rick - glad you're working it out.

[Michael Pyron]

you make a valid point about the paint gumming up in the sandpaper...go ahead and wet sand with 500 or 800 grit, let it dry, then use some mineral spirits to help wash away the residue, let that dry for about 30 minutes and tack clock the product and spray it immediately (its rather a waste of time to tack cloth and then shoot an hour later, now isn't it?)...remember to keep adding water to wash away the residue created as your are sanding...as long as you don't sand to the bare wood you will be fine...

the pre catalyzed stuff I've been using on the project I am finishing up hardens real fast and unless I've had to use some retarder it doesn't gum up hardly at all an hour later, so I've been simply dry sanding.

[Ken Casser]

I'll try it again on Monday. I'm going to sand today. Let it dry, and then Monday morning hit it with mineral spirits and a tack cloth, and then spray all day until I'm happy. I also have some test pieces I'm going to try different methods with. I need to shorten the process as much as possible while still getting an acceptable finish. Otherwise I end up earning about $5 an hour.