This thread is in response to Larry's questions about comparing two part McFaddens Urethane Lacquer to McFaddens Nitrocellulose Lacquer. I don't want to clutter up Lance's SJ thread so .... her goes it:
Is Urethane more user friendly than Nitro? Well.... Yes and no. Urethane fumes are really bad so you need a GOOD respirator to spray it or even mix it. Once you mix the hardener you have a 6 hour pot life and then it sets up like epoxy!!! I keep a real close eye on the clock
Clean up with lacquer thinner.
How do you mix it? Mix ratio is 4 parts urethane, 1 part hardner, 1/2 part Butyl Acetate (optional) as this finish is a bit thicker consistency than nitro. Don't leave lacquer thinner in the guin or you will have problems. Flush the gun with Butyl Acetate before spraying Urethane.
Costs? It's about 3 times more expensive than nitro. About $80.00 per gallon with hardener vs. $28 for Nitro
Special spray equipment? No, just use the same gun, tip and nozzle you would use for nitro.
How does it spray? It is thicker so I had to thin it a bit and increase the air to around 50 psi to get better atomization. It flows out like glass with vey little orange peel IF you spray it wet.
Does it tack up as quickly as nitro? Yes about the same or maybe a bit faster.
How many coats of Urethane are required? I have been using a total of 6 coats. Spray a maximum of 3 wet coats per day. It is important to wait 1.5 hours between coats or you may trap gas. Wait 48 hours, level sand with 220 (sterated paper is OK) and spray final 3 coats.
How does it sand? Great, in two days, unlike nitro which will clog paper. Sands to a nice dry powder.
How long until you can buff it? It can be buffed in 3-5 days but 7 days is better. It off gasses quickly and the fumes are mostly gone in 3 days, unike nitro which off gasses for a a couple of weeks. It buffs a bit harder than nitro and doesn't burninsh. If you sand it properly (up to 2000) it will look just as deep and glossy as nitro. I use fine and very fine Menzerna compounds.
What is the sanding schedule before power buffing? Sand with 600 Abranet (only if you have runs or orange peel), 1000 Mirka gold, 2000 Abranet, then buff.
I noticed a slight bluish tint on RW the first coat that I applied. Very similar to a faint bluish color of waterbourne. I added 10 drops of yellow and 20 drops of amber dye to the gallon and the blue cast went away. It's is as clear as water in the can and when I called McFaddens they were baffled as to why I had the blue cast.
What about repairs and witness lines? It will not burn into the previous layers if you wait over 24 hours. After 24 hours you must scuff or level sand to provide a good mechanical bond. You can't drop fill like nitro. I have made repairs with CA but it will shrink back so you will have to wait a week before leveling and buffing or you will see tell tale signs.
Is it worth the higher cost over nitro? It has a lot of benefits: More durable, resists scratches better, shorter duration of off gassing, you can buff it in 1/4 the time as nitro (which is probably the most important factor to me).
What about cold checking and finish crazes? I don't know the answer to this question. If nitro is applied to heavy it WILL crack and craze.
