Can someone tell me the differences between clear lacquer and polyurethane and the advantages ans disadvantages of each.
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Can someone tell me the differences between clear lacquer and polyurethane and the advantages ans disadvantages of each.
Polyurethane isn't the name of a kind of finish, merely the name of one particular ingredient, a plastic resin, in a number of kinds of finishes. Finishes that contain only polyurethane as the resin are almost always two part, or have specific curing properties, as requiring UV light or moisture. There are only a very short list of such products packaged for DIY use. (I only know one such product.)
Mostly what is meant in DIY usage is a varnish made using an alkyd resin modified with a bit of polyurethane resin ie. it is a uralkyd resin. This is very much like more conventional varnishes based around alkyd resin or phenolic resin (bakelite plastic) which are reacted with an oil, often linseed oil, but also tung oil or soya oil. The polyurethane addition makes this varnish softer but more abrasion resistant than the other varnishes, and poses special difficulties as far as adhesion, and the ability to be rubbed out to an even sheen, particularly a full gloss sheen. The polyrethane addition also makes these finishes subtly cloudy, creating a "plastic" look. All oil based varnishes, including poly, are quite moisture resistant and resistant to household chemicals. In my personal opinion, the only use for polyurethane varnishs is on floors where the abrasion resistance matters. Otherwise, conventional resin varnish is easier to use, and more attractive.
By lacquer I assume you mean solvent based nitrocellulose lacquer. It is an evaporative finish that doesn't cure, it just dries as the solvent evaporates. The solvent can redissolve it at any time, and does so at one particularly advantageous time, when the next coat is applied over the previous ones. That means that the coats melt together essentially making a single coat. Lacquer is dramatically harder than poly which means it rubs out much more easily. It is a little more resistant to household chemicals than shellac, and similar to shellac in water resistance. Most lacquer is designed for spray application, though there are several brands of "brushing" lacquers, who solvents are chosen to take long enough to dry that with quick work, they can be applied by brush.
There are waterborne finishes sometimes labeled lacquer or polyurethane. In both cases the dominant resin acyrlic, with small amounts of polyurethane for a touch more abrashion resistance than acyrlic alone. But these waterborne products are more alike than different, with the names being mostly marketing ploys.
Thanks for the response, interesting reading. In layman's terms, when would one choose a product such as "deft brushing lacquer" to finish the interior of wood cabinets as opposed to "minwax polyurethane finish", and why? Both say "excellent finish for furniture, cabinets, etc".
Maybe a more practical approach would be to say that lacquer is fast drying and even though some are advertized as brush-able, in all likelihood you be better off spraying it on. That would mean you’d need some type of spray equipment or bought the lacquer in a spray can. It’s hard but also more brittle then polyurethane or varnish. It’s also relatively easy to repair since it is an evaporative finish.
Polyurethane, the synthetic is a bit more user friendly in that it can be brushed and it has a slow setup time. The only equipment you’d need to apply it is a pail and good quality brush (ox or badger if you really want to go the distance). You can also rub out polyurethane after a full cure, about 30 days or so.
Personally, I would only very rarely consider a brushing lacquer. If I wanted something that dried fast for finishing the interior of cabinets, I would choose a waterborne acrylic. It dries as fast as lacquer and you can clean up you equipment or brushes with water.Quote:
Originally Posted by j milana
A good quality lacquer is a great product. I have never used the brushing lacquer because it would defeat the main purpose of lacquer which is quick drying.
I use a pre-catalyzed lacquer or a catalyzed 2 part lacquer which both are far superior to the normal lacquer used on cabinets. Looking through a good lacquer finish is like looking through glass. Looking through a poly finish is like looking through plastic.
Lacquer dries to a dust free hardness in a few minutes. Within 10 minutes or less, you can handle it. You can re-coat it in about 10 minutes on a warm day. That means that in 1 hour you can put on 6 to 7 thin coats and you are DONE !!!!. You can then go about your business without too much concern for dust - within reason. With poly, my shop is tied up for days trying to keep the air clean and dust free.
Lacquer finishes are very durable. That is what most of your furniture is finished with. Consider what a normal dining table puts up with on a daily basis.
Another thing about the quick drying time of lacquer is that most of it is dust before it hits the ground. That means that other stuff several feet away will not be tacky and sticky and have an unwanted new finish.
A cheap lacquer is a poor product, a good lacquer is a great product.
Any good lacquer MUST be sprayed. If you dont have a good air compressor and spraying equipment, lacquer is out of the question.
I hope that should about cover it for now. Oh, one more thing. The HVLP sprayers , in my opinion, are not good for spraying lacquer. They spray is too thich for the individual coats.
Tony B
Whether HVLP spray guns spray too thickly for lacquer depends entirely on how they are set up in terms of nozzle and air caps.
Also, be aware that beyond ordinary NC lacquer--ie. the catalyzed lacquers, you need fairly serious spray facilities unless far enough in the country that you can spray under the shade tree without problems from neighbors from fumes that are more noxious than ordinary lacquer thinner. Even for NC lacquer, you still need to consider the explosion and flamability potential.
That's why for most DIY finishers, waterborne finishes are more practical.
While we are on the topic of finishes, I thought I would throw this in also.
This rule applies no matter which kind of finish you select whether it be poly, acrylic, lacquer, etc.
If you want a satin finish, always build up all of your coats with a gloss and only use the satin on your last coat.
The reasoning behind this is that satin finishes have a 'flattening' agent added to it. For all intents and purposes, this flattening agent is microscopic plastic beads of sorts. The beads scatter and difuse the light and in effect make the finish slightly duller. If you were to build up all of your coats with satin, you wil be adding more and more flattening agents and eventually end up with a finish that looks dead. Even the grain will be obscured. So, build up your coats with clear in order to not hide your grain and use satin as your final coat.
If you are hand rubbing to a satin finish, only gloss only.
Tony B