I am spraying coats of Black Gloss Lacquer (spray can – Valspar) onto a surface. The usage direction on the can is minimal. They state two light coats recommended. Recoat anytime. Dry to touch in 1 hour.
I have a call into their 1-800 #, but I’m not holding my breath waiting for a return call (it was an answering queue).
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So as a general question for folk’s experiences with Lacquer.
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1. If I want to do more than two light coats for added durability and sheen, should I scuff up the surface between additional coats with perhaps 400- 600 grit?
Should I wait longer than 1 hour between additional coats to be safe?
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2. I did the best surface ceiling prep I knew how, I detect a very slight amount of fine pebbling, can this be corrected by sanding between coats with a finer grit than 400- 600 and thereby building up leveled coats, if so would 400- 600 be the correct grit to address this?
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3. I got a few small runs when spraying, how can this be corrected?
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4. What would I expect as the actually fully cured time?
5. I know whats is in polyurethane, shelac, varnish and other finishes; what makes Lacquer, Lacquer?
Replies
Bioman,
The instructions on the can, to spray 2 light coatings is utterly meaningless. Without the type of wood known, and the final result desired, no advice can be given.
You have not said which wood you are finishing. Is it a very open grained wood, a medium grained wood, or a wood with no visible grain or pores?
Open grained woods are often filled with a silex (or equivalent) filler slurry so that the final lacquer finish is perfect and unbroken. This is almost always the case with a gloss black lacquer.
But any lacquer, including gloss black can be controlled to look like an oil finish on an unfilled open grained wood, depending on the number of applications and the "rubbing out" (leveling/sanding).process. The decision is yours.
In general, no sanding sealer is needed for a black lacquer finish.
Here is a general finishing schedule for lacquer.
Sand the wood to 220 or 320 grit (I prefer 320). Apply a thin but complete coat (make sure the entire surface is wet by the lacquer spray. Wait an hour, recoat, wait an hour, apply a third coat. Work quickly, but carefully, avoiding enough spay to cause runs, drips. Let dry overnight (at least 8 hrs, preferably 12).
2nd day - using a rubber or felt sanding block, level with 320 grit paper used dry. Take down all ridges, runs, etc. The goal is to take down the "mountains and hills." Valleys of shiny, untouched lacquer will remain. Don't try to achieve a perfectly uniform result at this stage - you'll sand through to the wood.
Spay a light, complete coat. let dry one hour. recoat, let dry one hour, recoat. Let dry over night.
3rd day - level with 320 on rubber/felt block. The "mountains" will come down quickly and the areas of smoothly-sanded lacquer will be much larger, leaving much smaller "valleys" of shiny, unsanded lacquer. The purpose of this leveling sanding is to eventually achieve a completely uniform, dull surface devoid of any irregularities, ridges, dust nibs, drips, etc. Apply 3 coats as above, one hour apart. let dry over night.
4th day. Level the surface as above. It should sand very easily and the valleys should completely merge with the hills. The entire surface should look completely uniform and flat with a ground-glass appearance. If there are still some shiny valleys that do not easily sand out, go through another day's spraying schedule.
When the surface easily sands perfectly level with 320, you are ready for the final step. You can proceed with two slightly different approaches. 1. apply one final light coat of lacquer, then start "rubbing out." Or 2. start rubbing out the existing ground glass lacquer surface. In either case, let the job dry for at least 3-4 days. I wait at least a week. Lacquer does not "cure." It dries by evaporation of its solvents and thinners. It is dry to the touch and ready for recoating in an hour, and certainly feels very dry and hard after 24 hours. But solvents still remain and slowly outgas for many days. The lacquer gets harder and achieves a much higher-quality surface if given about a week to dry before rubbing out and polishing.
"Lacquer" is a solution of a synthetic resin (nitrocellulose, cellulose acetate butyrate acrylic), plasticizers, other solids which affect adhesion, evaporation retardants and solvents and thinners. When dry, it's the residual resin, modified by the plasticizers and other solids that is the actual finish.
Start with 400 grit wet-or-dry abrasive paper. You can use it dry, or wet it with paint thinner or naphtha or with a water solution containing one drop of liquid dish washing detergent per quart of water. Achieve a perfectly uniform scratch pattern at that grit. If working dry, you can see your progress as you sand. If working with a lubricant, you have to dry the surface from time to time.
Then switch to 600 grit. It should go very rapidly. You simply want to remove the 400 grit scratch pattern with the 600. No leveling is done at these grits. That all was accomplished at 320.
Then use 4-0 steel wool, then automotive polishing compound (white). This will leave a highly polished, glass-like surface that may appear slightly cloudy. Follow with Meguiar's "Scratch X" (a fine clay called Kaon). For small jobs a soft cloth and hand power will work beautifully. For large jobs you can get a power polisher at the same auto store you got the polishing compound and Meguiar's for about $20.
In a few minutes, you will have a blemish-free, mirror finish that looks a foot deep.
Rich
Edited 12/28/2007 4:36 pm ET by Rich14
The substrate is MDF Rich.
I'll follow you're advise. Thanks for the very detailed response.
I forgot you had asked about finishing MDF before.Treat the MDF as you would any wood surface. Sand to 220 or 320. It should give you a very good surface to begin the finish film.Then "build" the lacquer finish as described. You can build a film which will become very level, smooth and blemish-free. You will certainly need more than the 2 applications that the product suggests (I guess they had to put SOME kind of instructions on the can. And they didn't want to scare anyone off with a description of how much effort is really needed to do a decent job). How many applications it will take will depend only on your satisfaction with the appearance.Rich
fyi- lacquer spray cans have a much higher ratio of solvents to solids than regular cans of lacquer. light coats are a must to avoid runs, and many more coats than two are needed to build body, or depth.
Expert since 10 am.
Thanks, good tip. I've been noticing a tendency to runs.
jackplane,Good point. Once one knows how to spray lacquer, it's hard to do it wrong, even using a spay can, which gives a terrible spray pattern compared to even the most inexpensive gun. But if one has little experience, the spray can stuff can quickly becomes a runny mess.bioman,I don't know here you're getting the lacquer. But if it's one of the big boxes or Ace, there should be a can of brushing lacquer near where the spray cans are stocked. Brushing lacquer has more retarder than lacquer intended strictly for spraying, to slow down evaporation and give you a chance to apply. You might get better results brushing than using many spray cans for that project.Rich
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