Brushing a Topcoat Onto Lacquered Trim

Brushing a coat of lacquer onto already installed lacquered trim is not a great idea. May 17, 2010

I use ML Campbell mainly and have a client that wants his onsite finishers to brush on a final coat over the trim, doors, etc. I was thinking a fast drying water base poly might be the best option? Has anyone out there topcoated lacquer with a brushable finish? I am asking about clear coats.

Forum Responses
(Finishing Forum)
From contributor E:
Absolutely the wrong thing to do. Your brush on finish will fall off and I learned this the hard way. We just finished a house with 4200' of 6" Trim and baseboards and 37 maple interior doors and jambs and we shop finished everything and then the trim carpenter installed it all - beautiful job. We used Amazing Stain 3 with vinyl sealer and two Magnamax topcoats on everything.

From the original questioner:
"Wrong thing to do"? Are you saying that any brushable topcoat will fall off of the lacquer finish? I have talked to several sources (ML rep, ML coating department, other finishers, etc..) I am getting conflicting information from these sources. I am doing test samples and testing brushable topcoats next week. If the lacquer if cured, scuff sanded I don’t see how the brushed coat would be falling off?

From contributor E:
I was wondering if the final brush on finish would look ok as compared to a shop finish. In our case it would not have looked as good as the whole project was a satin finish that could not have been done on site with brushing but we could not spray on site either. That being said, if you scuff sand and use the same MLC finish, say magnamax, it will burn into the dry topcoat and adhere but will not have a smooth sprayed look.

I used a waterbased polyurethane finish over magnamax and after a few days I peeled the sheet of waterbased right clean off the lacquer, so it was an obvious adhesion issue. Perhaps I didn't prep well before the waterborne topcoat over the MLC MM. If your trim guys can install it with 22ga or 23ga pinners it will look way better shop finished.

From contributor Y:
Best thing to do for sure - samples and more samples. Make sure you wait six months and keep them in the same environment you plan on using them in.

From the original questioner:
It seemed like a very simple question - "what coating can be brushed over lacquer"? I am getting the feeling that once you lacquer you can’t go back?

From contributor Y:
Lots of products "could be brushed over lacquer" as you say. The answers you may receive will probably all be reasonable, be they aqueous or solvent types. In the long run it's not a matter of “what” but of long term success. Your rep's on the line with anything you recommend that you don't know first had will really do the trick.

So either wait till someone recommends something they know for sure by having done so many years ago and can show how it's held up over the years be it individual finisher or finish mfg.'s samples using identical products, or do as you said you would do and test out samples for yourself.

From the original questioner:
Help me out here, what am I not getting? My rep aside, I am just trying to figure out if the onsite guys can brush on the final coat?

From contributor R:
You can brush anything over anything but how long it will last is the real question? Perhaps you’re not liking the answers you’re getting and you’re wishing for someone to step up and say “yes, go ahead and do it, everything will be fine from here to eternity.” As you have been advised it is not a good idea to put a water based coating over a solvent based coating because it won’t melt into the solvent coating.

Sure, you can scuff sand the solvent and apply the waterbased coating over it, yes it will dry, and yes it will adhere but it won’t become "incorporated" with the solvent coating. You want something that will "incorporate" itself into the previous coating and a waterbased just won’t do it.

Yes, you can buy a brushable lacquer and tint it if you need to but when you attempt to brush it on, it will soften up the initial coating and create a huge mess for you, your contractor and your customer.

From contributor M:
Go to Home Depot and get a quart of Deft (which is brushing lacquer, as noted by the previous poster). It will "bite" into your sprayed lacquer finish and will never have an adhesion problem. You don't even have to sand before putting it on. Since your sprayed lacquer has probably had some time to cure in hardness, brush on the Deft on some trim with similarly aged lacquer on it. Brush it on as quickly as you can given the fact that it is trim, and you can probably go down a stick of it pretty fast, but not so fast you can't brush it out sufficiently to level it. Let it dry and see what you've got.

From the original questioner:
Sounds like I will have to go onsite and final coat (spray) this job if I want to sleep at night.