Troubleshooting Lacquer Adhesion Problems

      Advice on improving adhesion of lacquer over a wiping stain. May 17, 2010

Question
I have a few questions about lacquers and spray systems that I am using at work (a small construction company). I am the only journeyman cabinetmaker in the company, so everyone relies on me to get the finishes right. I primarily spray new wood, stained or bare, mostly oak/maple/alder.

We have a dedicated spray room, and inside the room is a spray booth, with an exchange air system and a heat toggle (can't adjust the temp with the heat turned on, but it feels like it keeps the room around 20-30 degrees Celsius). Overspray isn't an issue for me with our room setup.

The only spray system we have currently is a Graco HVLP 2500 turbine along with the Graco HVLP cup gun. I have only been spraying lacquer for about 2 years. It's pretty much been trial and error to get a good looking finish.

The lacquer I use is Cloverdale Excel Plus (pre-cat, 25/40/60 degree sheens), thinned anywhere from 5 to 40% with Cloverdale Clovathinner #19. This is the only lacquer I've tried, as it's readily available.

I can get an awesome looking finish. The problem is, every piece I spray has very poor adhesion and scratches very easily. I feel bad taking anything out of the booth that looks so good, but has basically 0 resistance to scratches/scuffs. Even after the pieces have dried over a week, if you scratch them with a fingernail to make sure they have cured, they scuff easily, and the lacquer chips off if you scratch it in the same spot a few times. It seems like it's taking it off right down to the stained/bare wood.

I use the lacquer as a self-sealer. My first coast is fairly light so it doesn't take a lot to sand (oak/maple/alder), and I usually put on 3 topcoats after the sealer to get it looking how I want. I generally sand after 20-30 minutes for my seal coat, and try to leave every other coat at least 1 full hour before I sand/recoat.

I have done a lot of testing lately with the HVLP gun and different thinning amounts to see if I can get any different results, but it just seems like it's doing it no matter how I spray it. Cloverdale suggests only thinning the Excel lacquer to 5% max, so I tried that a number of times, and even though it has trouble spraying through the tip (#3 fluid tip/needle) with such a low powered turbine, it doesn't orange peel, I just have to spray a lot slower. When I thin it around 20-30% I get the easiest spraying, but the results are still the same.

I have tried all the settings for the air adjustment on the gun, from max to the lowest I could get while still being able to spray a proper spray pattern. At each of those settings I have also tried different amounts of thinning from 5 to 40%, yet it still scratches and has very poor adhesion.

The fluid I have set to max, which isn't a lot for the gun - I just have the trigger wide-open and adjust the air as needed. My topcoats are applied around 5-6 wet mils. Has anyone had experience with finishing problems like this? I really want to produce the best finish that I can get with my current spray system. Upgrading our system to a pressure pot or air-assisted airless is still a ways away.

Forum Responses
(Finishing Forum)
From contributor R:
Poor adhesion has nothing to do with the gun. On stained wood it could be that you are leaving too much stain on the wood (not wiping off enough), or you are not letting the stain dry enough. On unstained wood, you could be burnishing the wood (sanding with too fine a grit of sandpaper). 220 grit or finer on maple will cause problems, 220 on alder is fine.



From the original questioner:
I have tried a few different stains. Some of them I have left on fairly heavy to get the color desired, while others I wipe off as much as I can. It seems to do it no matter what I do. The stains I have been using lately are Intermix from Cloverdale. I usually leave the heavier stains dry overnight, and try to wipe off all pigment while keeping the color I want. The pieces I stain are usually finish sanded with 150, no matter what species of wood I use.


From contributor C:
It says your stain is a wiping stain, meaning you should always wipe the excess off. I would find better material - Chemcraft Sadolin is around you and they have decent products.


From the original questioner:
Cloverdale does supply Chemcraft products, but the only experience I have with them is from my apprenticeship in school. Does anyone recommend a certain kind of pre-cat lacquer from Chemcraft that would spray well from an HVLP system?


From contributor G:
Opticlear.


From contributor B:
I always wipe stain within 5 minutes max. Oil takes a while to cure, especially if not wiping the excess right away. I would recommend using a sanding sealer for a first coat rather than lacquer. Sealer is basically lacquer with a paste that allows for easier sanding. Make sure you stir it every 20 minutes, because the paste will settle on the bottom. I use one coat of sealer and one coat of finish (usually satin 40 to 60 sheen). I apply the final coat as heavy as I possibly can without runs or sags. I currently use Rudd sealer and finish. Dries rock hard. Thin sealer and finish about 10% with lacquer thinner. I have also used Sherwin's pre-cat and Valspar without problems.

If doing more than 2 coats, I recommend using multiple sealer coats, and only a final finish with lacquer. Each coat will sand easier, and the finish coat seems to dry smoother and more even when applied over sanding sealer. Also, if you accidentally get a run, it will sand out easier during a sealer coat.



From contributor Y:
It sounds like you need better quality material. You also might want to make sure the lacquer you are using can be used as a self-sealing system. If not, that could result in adhesion problems. Try using a good quality vinyl sealer. It sprays like lacquer and is easier to sand.


From contributor G:
Seems like two issues here. Poor adhesion could be attributed to letting too much stain dry on the wood, but that shouldn’t affect the hardness/scratch resistance of the coating.
How long has this problem been going on? Could you have run into a faulty batch of lacquer? Does it cure when applied to wood without stain? Is the curing area temperature 25°C (77°F)? If Cloverdale can’t help solve your problem with their lacquer, they should have no problem giving you a free gallon of Opticlear to trial.


From the original questioner:
Thanks for all the responses. I just ordered 2 gallons of MagnaMax from the distributor in our area, to see how I like it. Does anyone have experience spraying this lacquer (or any lacquer) from an HVLP gun/turbine? I'm not really sure what's a good HVLP system to use. This was with the company when I joined 5 years ago and I've been using it ever since. I've had my doubts if our small turbine is even strong enough for lacquer to atomize properly without thinning it a lot.

Will I need to thin the Magnamax at all, and what air/fluid setting should I be looking at? I have been leaving the gun wide open to get as much material out as possible with the small turbine, and like I mentioned before, usually try to spray 5-6 wet mils. The only real setting I have been playing with is the air.

Looking up the specs of the Graco 2500, it has an output of 58 cfm, 5 psi. It's their lowest model and is only a 2 stage turbine, it doesn't have a built in compressor like the larger models, and is said to be used for "light materials such as stains, clear finishes, and light paints."

I have been experiencing this problem for quite a while, but never really looked into it and just figured it was normal. I will test a piece tomorrow without stain; I never even thought to test that. Our spray booth/room when the fan is on stays a nice warm temp - I'm fairly certain at least 25 degrees but not over 30. I will look for a thermometer to check.

On another topic, I was looking at ML Campbell's website and noticed another pre-cat product called MagnaKlear - some type of conversion varnish? I've never really understood what a conversion product is and what the advantages/disadvantages are over lacquer. I should be looking at this for kitchen cabinet doors, or just stick with lacquer?

Also, I got the go-ahead from my boss to start looking/researching a pressure pot/conventional system that I assume a lot of people use. It's a lot cheaper than an air-assisted airless setup, and can at least hook it up to a regulator/filter and have a bigger pot instead of filling the cup gun 100 times, and the added agility of a gun with no cup. Was looking at a Lemmer system, but is there a better system for moderate use?

We want to eventually convert to water-based finishes, probably within the year, and want to make sure the system we buy will be good for both lacquer and water-based.



From contributor F:
Something to check is that the lacquer is being properly catalyzed with the proper catalyst. There is a shelf life after the catalyst is added, usually 6 months. Most sellers add the catalyst at the time the product is sold or sell the catalyst for the purchaser to add. There is also post cat lacquer where the catalyst is added just prior to use. It dries even faster and harder. If they are not adding the catalyst or adding the wrong catalyst or have old catalyst, any of these situations could be causing your problems. I've sprayed several pre and post cats, and most dry to the touch within 30-45 minutes. You can't dent them with your nail after 12-24 hours, and they are very hard after 1 week.

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