Glassing with Laquer Based Polyurethane

I use "DEFT" laquer based sanding sealer on my planes and put 3 coats on. I recently went to Lowes to get some more sealer and noticed that they just started carrying Laquer based Polyurethane. It is also by "DEFT" and costs 8 bucks a quart. I tried this and because I knew the properties wasnt surprised but pleased. For those not familiar with laquers they dry super fast and are extremely light weight finish as most of the carrier for the laquer based product evaporates off. You also have fumes to deal with but if you have a fan to draw the fumes outside or even do it outside you wont have a problem. Now this product states not to sand between layers and to put a layer on every 2 hrs. Within 15 minutes the entire surface was dry to the touch and the rest is time for it to breathe. I put a coat on every hour and had no problems and when I was done had a rock hard finish. you can get this in gloss or semigloss it doesnt really matter which you use. when I was done all I had to do was scuff the surface with 320 and apply me Nelson Hobbies Paint. For those of you that use nelsons one thing to remember is not to use laquer based primer for his paint but was told rustoleum has been used.

Question: Can you tell me more about this lacquer based polyurethane? I have searched several sites including DEFT.

Yes, there are a couple out there. I use "Deft" brand name which can be found at Lowes. A friend of mine, after I told him about it, found another laquer based at Tru-Value hardware stores but he couldn't remember the name. Basically, laquer based products especially paints have the product and a carrier. the carrier is 3/4 th volume of the product and evaporates away as it cures thus making it lighter. the polyurethane I have found works in the same way as I have tried sample pieces myself. I dont have a gram scale but could actually feel the difference in my hand. Laquer Based Polyurethane dries to the touch (by on the can) in 30 mins and is ready for second coat within 2 hrs. My personal experience is abt 10 to 15 minutes until dry to touch and I put a second coat on in 1 hr. You need at least 1 hour between coats to allow the carrier to evaporate. Now also if by chance you get a run it will sand extremely easy abt like you would do for hard balsa. now with 2 part epoxy or regular polyurethane you have the chance of getting a gummy surface that makes you go through several sheets of sandpaper to sand (not always but a lot of the time this is the case) with laquer based it dries hard and without the gumminess because the carrier evaporates. now if you finish glassing give it 24 hrs to make sure fully cured, sand with 320 to scuff it up and tack rag it off and paint its that easy. I will not be putting more than 3 coats on in a day and wait 24 hrs before doing final 3 coats. I have found it takes 6 coats to fill the weave on 1/2 oz glass. then after second 3 coats give another 24 hrs to breathe and paint. now 1 to 2 hours after you paint the final coat you can sand then leave to breathe its just you want it to have 24 hrs before you paint to make sure all carrier evaporated. thats abt it. It comes to a glass smooth finish and you are not supposed to sand in between layers only after the final layers dry.

Question: Why not lacquer based primer? Is that a problem for the paint to go over or for the polyurethane underneath?

Good question, and I got the answer for you. You can use a laquer based primer, but you have to be careful on the paints you use on top of it. let me explain: Laquer based paints and primers have a wax inside them called Styrene. What this wax does is help it when drying to get a good and hard and not have a soft gooey coating on top. It is the same thing and principals that are used when painting Gel Coat. Now on laquers you cant feel the wax coating as it is just a minute quantity, but trust me it's there. Ok now the reasons not to use certain paints on top of Laquers. First we will cover Laquers: Laquers have what is called a chemical bond. Basically what they do is (for lack of better word) is to melt or blend into the layer below it. You can paint certain laquers on top of each other and they will blend together to create a totally different color I also know this by experience because we use it like this in Taxidermy a lot when painting fish. that is a chemical bond Now for a Mechanical bond ie. Enamels and others A mechanical bond is one that you spray on top of something and it drys just as it was sprayed, it drys on top of something and doesnt join with it for a stronger bond. Now this is how it would work with a laquer based primer. The laquer sprayed on top the primer would melt into the primer joining with it creating a really strong bond. But an enamel like Nelsons Hobbies Paints will just sit on top the laquer based primer. Now what will happen is that the styrene in the laquer will work as a release agent. Just think of a fiberglass part in a mold. they use wax so the part doesnt stick in the mold, well same thing here. now it wont be over obvious it isnt sticking, but vibration during flight etc will shortly make your paint start flaking off. I hope this helps explain some things. Laquer is a good primer but only for paints with a chemical bond. now the laquer based polyurethane does not have this styrene in it so it will work as a mechanical bond thus all paints will stick to it.