I’ve followed the instructions for rubbing out finishes in Jeff Jewitt’s and Bob Flexner’s excellent books. However with both industrial quality waterbornes and nc lacquers , the completed surfaces look very nice, but scuff and scratch easily.
Before rubbing out the finishes seem much harder and don’t mark easily at all. Is this normal, or am I missing something?
Replies
I noticed this same thing. I found that a short while after the rubout, the scratch resistance increases substantially. I did not have this problem when using varnish, but I did find it when I recently switched to Ultima Spray Lacquer. My theory is when rubbing out, you cut into a less fully cured layer, although I could be completely wrong about that.
Rob Millard
http://www.americanfederalperiod.com
I don't know what Bob or Jeff say about rubbing out or what materials they use. By and large, the more polished a surface, the easier it is to see a scratch or mark. There can be a difference between lacquers. A spray can of Deft isn't quite the same as a catalysed nitrocellulose. Heat, friction and chemicals can also degrade some finishes. You can remove the majority of the finish through aggressive polishing, too.
It might help to say exactly which finish products you used and how you applied them, as well as how you polished them out. There are finishes that are far superior to NC lacquers when you want that highly reflective, durable finish. There are also methods and materials for polishing that are more advanced than using something like oil and pumice.
There is a tendency among woodworkers to over do. If one coat looks good, ten coats must be ten times as good. Often, the opposite is true, particularly with some finish materials. You can shoot yourself in the foot with good intentions.
Beat it to fit / Paint it to match
Hi
Thanks for the responses.
Imediately after the rub out , I'm very happy with the appearance, but even a featherlight touch with the back of my finger will show up as a scartch. The marks are most notable on dark stained wood
I've been spraying Sherwin Williams Kem Aqua waterbase, and Chemcraft NC lacquer with an Asturo gun. Both gloss. No sealer with the waterborne, 3:1 thinner-lacquer for a sealer with the NC.
With waterborne, 4 coats sanding between coats, level with 400 to 600 grit, and rub out with abralon pads.
With Nc; 3 coats, sand , 3 coats, level, rub out with 0000 steel wool and antique wax on a block, buff with a soft cloth. Lacquer thinned 25%.
On my last project, after flattening the NC, I flow coated with 5:1 thinner to 20 deg. satin lacquer and it looks good but not as good as a rubbed finish. I don't use box store finishes.
Solvent based finishes cure with the evaporation of the solvents. With NC, the solvents will reactivate previous coats, essentially making them a wet coat again. Just like the way a can of varnish will skim on the top, this can happen with NC on a work piece. This can trap solvents and prevent the NC from curing completely. As you abrade the top layer, you expose a softer undercoat. In time, it will get harder but if heavy coats are applied, the escaping solvents can crack the finish and it can take months before any problems show. I doubt that will be your issue but the more solvent, the more likely it may be trapped. In addition, a lot of solvent can make spraying vertical surfaces a nightmare, as you watch the lacquer start to run.Catalyzed finishes don't depend as much on solvents, the finish cures due to chemistry. They aren't trouble free and often require retarders of different types for varying conditions. However, trapped solvents are not as much of an issue.Both types of finishes are often done they way you describe, using a final wet coat. This is normally done so that rubbing out may not be required. Lacquer can be a bear to spray properly. Using a compatible sealer first, helps seal in stains or dyes, starts building a surface and is easy to level out. It will take less lacquer and reduce the need for thinners. My guess is that you are using too much thinner and it's not curing all the way. Lately, I've been using Mohawk lacquer. It's available both post and pre-cat and it's ready to spray out of the can. Currently, I'm only using lacquer in matte and flat sheens. That's a different animal than high gloss and I want it off the gun. Shiny finishes have lost their appeal to me for the time being. The last one I did, I used an isocyanurate catalyzed urethane/polyester, wow! The best part was, it's almost fool proof. Potentially very dangerous for the lungs, though.Do you use a viscosity cup and a mill gauge? You may be able to limit the solvents you are using. I don't spray everyday and I don't use the same materials every time. I have to retrain myself each time I pick up the gun. Gun distance is the one that gets me the most.Beat it to fit / Paint it to match
hammer,
Shiny finishes have lost their appeal to me for the time being. The last one I did, I used an isocyanurate catalyzed urethane/polyester, wow! The best part was, it's almost fool proof. Potentially very dangerous for the lungs, though.
I agree about the high gloss finishes, however I am looking for something like this for small projects like jewelry boxes/humidors.
Can you tell me more about this polyester (where to get, price, ease/difficulty of application, etc?) I have a spray booth w/ explosion proof fan.
My apologies to the OP for hijacking
Lee
Maybe you could shed some light on a problem that I recently had. I have been spraying Behlen's Qualalac on some kitchen cabinets. Initially I only used the lacquer. On later section I started using their sanding sealer, spraying a couple of light coats, then fininshing with 2 -3 coats of lacquer. On these I found that the slight ding left white marks in the finish.
I wonder if this may be due partially to the finish not being fully cured and somehow exposing the sterates in the sanding sealer.
Any thoughts and recommendations for repare?
Sneezy: As others have already said - NC lacquer or nitrocellulose, cures by the solvents evaporating out of the film. Most of the NC lacquers that you buy, if they do not specifically say, will be what is called pre-cat or pre catalyzed lacquers with less than 5% catalyst already added to the base mix. It will be a very mild acid catalyst as well and will have therefore a reasonable shelf life, probably a year. These one component lacquers tend to lose their entrapped solvents rather slowly . Initially within a few short minutes the film will dry and about 80 to 90% of the solvents will evaporate, depending on temperature. Then the remaining solvents will cure the film by evaporating slowly over the next week or so. I usually wait at least 10 days before rubbing out a NC pre- cat lacquer. It will not be hard enough through the entire film thickness of approximately 2 to 4 mils until then. If you rub it out before then you may get away with rubbing the top layer but the film beneath that is still curing and will be somewhat softer. The top part that you rubbed out is basically sitting on uncured lacquer. If you use a post-cat lacquer ( whether or not it is synthetic or nitro ) you are dealing with an acid catalyst and a base film. This catalyst will set off a chain reaction that will both cure the film and force the solvents out of the film at a rapid rate. A lacquer that I use regularly for cabinets is Becker-Acroma's Reliant. This is a post cat lacquer that I can stack chairs or doors on top of each other in 2 hours time. In other words ,they are definitely fully cured enough for my purposes. Now if I did want to rub the Reliant lacquer out (and I don't), I could do so within 4 hours without risk of a soft film underneath the rubbed out surface. One thing to keep in mind though; is that unless you want a shinier surface than the lacquer is rated, I would shy away from rubbing out my work. Lacquer is rated in degrees of shine - 40º, 25º etc. By rubbing out the surface , you will be rubbing out the silane additives (or flattening agents) and therefore producing a 90º surface. When viewed in a sidelight it will look like a gloss surface and will only look like the original say semi-gloss you intended when viewed directly looking down at the surface. Better you should perfect your spray technique and leave the last coat as is. Hope this helps somewhat.
Lorne Steed
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