Urethane-- A Viable Alternative to Varnish?

by Sherwood Heggen


Why put a finish on a wooden boat? Is it what has always been done and therefore is continued without question? Is it necessary? Well, the reasons are obvious if the boat is intended to be useable for any length of time. Wood with no protective finish soon results in gray, rotting wood when it is exposed to the elements. Wood is a result of killing a tree by cutting it off from its life supporting roots. Sounds rather gruesome, but that is what happens. Unless something is done to preserve and protect the resins in the wood, it will soon begin to dry up and deteriorate.    

For centuries, it has been the practice to preserve wood's natural resins by capturing them with some type of coating and protecting the wood from exposure to sunlight, moister, and air. If the natural resins are destroyed, so is the integrity of the wood. Once wood is properly seasoned, sealing it in wax and keeping it in a cool, dry place would stop air and moister from having its effect. That is not possible for a boat, however, so a more practical solution is required.

Spar varnish has been the answer for a long, long time. The reason spar varnish is a great finish on boats is because it provides a smooth, glossy, flexible film that provides a barrier between the wood and the elements. It can be re-coated as necessary to maintain its protective quality and it beautifies the wood that it protects. The idea pursued in this Gadgets and Kinks is an alternative to varnish. It is not necessarily portrayed as a recommendation nor has it been tried personally by this writer. There are a lot of varying opinions whether this is a good alternative or something that should be avoided altogether. From what is available for reference on the subject, the choice of this finish would be at best experimental if you should decide to try it on your project. We are talking about a urethane finish here - car paint, if you will. There is a boat builder out West by the name of Don Philbrick who built the Philbrick wooden runabouts. The finish he applied to the hull was the urethane. The finish reportedly stayed intact and glossy for years as it would on an automobile. That is much unlike a varnish finish that needs re-coating far too often. Let's explore the positives for using a urethane finish.  

Urethane is a very tough, clear coating designed for the automobile industry. For a few days of effort, a shiny finish can be applied. It has been used successfully on cars for years in very demanding extreme conditions of heat, cold, and direct sunlight. Urethane requires a catalyst that causes it to cure very quickly. As a result, multiple coats can be applied in one day, or before morning coffee if you start early. After about 30 minutes, another coat can be sprayed on without sanding between coats. It is necessary to sand to level the finish as it is built up, but far less frequently. Dust is not as big an issue as it is with varnish. With urethane, the final coat can be wet sanded with 1000 and 1500 grit paper, eliminating all of the dust. Then, a little polishing compound and a power buffer will bring up a high gloss that will make you proud. The time required for putting on this type of finish is less than a comparable spar varnish finish. 

What about the negatives? Urethane is clear - no color. That causes the finished color of the stain to lack the warm, amber glow provided by a varnish finish. The knowledge of and addition of toners would be necessary to accomplish the proper color. Gleaning information from the Internet, the general opinion of those who know say that a urethane finish is not the best serviceable finish. The reason is because a urethane finish, unless the correct catalyst is used, can crack due to the flexing and dimensional changes of the wood it is applied to. A complete stripping of the finish and application of a new finish may then be the only way to correct the problem. The proper way to apply urethane is with a spray gun. A high volume/low pressure gun is recommended to minimize the over-spray problems. The negative here is that this can be a bit of an investment if infrequent use of the equipment is expected. Here is a big negative. You must cautiously protect your lungs from the vapor and mist produced with a high quality mask when applying the finish. Definitely follow the warnings and directions on the can. Your health may depend upon it.
   

Whether the urethane is more or less expensive than varnish is hard to say. It all depends on how much you put on and how many sheets of sandpaper, foam brushes, foam rollers, or special equipment are needed. It is going to cost, regardless. Fellow BSLOL'er Ken Patz is currently experimenting with a urethane finish on his 1957 Chris Craft Cavalier 17' runabout. He is expecting success with the method with regard to overcoming cracking. Ken has sprayed urethane on a flexible sample of material and allowed it to cure completely. Bending the sample produced no cracking or flaking. His method uses a catalyst that allows the cured urethane to bend and flex with the sample.
   

What is the correct choice for the new finish on your boat? By the way, that reads "new finish". Don't try to put urethane over and existing varnish finish. Having seen some boats with urethane, it is hard to say. If you know no difference between the appearance of urethane and varnish, the urethane is certainly shiny and dust free. However, as stated earlier it doesn't have that warm amber glow of varnish. A nightmare of spider web type cracks all over was witnessed on one boat's finish that was barely a year old. Another boat's finish was over six years old and had sat outside every summer with no more than a covered slip to protect it. It looked shiny and new with no cracks. The owner of that boat went on to finish his cruiser's brightwork confidently with urethane. The success of the finish appears to depend on the proper catalyst to provide a flexible cured urethane.
   

A potentially successful method for applying a urethane finish is offered here in the name of experimentation. "Potentially" is the word used because this description is the common sense method with no actual application experience to personally back it up. Try this at your own risk. The basic supplies you will need are:
   

  • Paste filler stain

  • Smith & Co clear penetrating epoxy sealer (CPES)

  • Urethane clear coat (NAPA 8853 or equivalent)

  • Catalyst (NAPA 8850 or equivalent for flexible finish)

  • Reducer (NAPA 8832 or equivalent)

  • HVLP spray equipment

  • Various grits of sandpaper, i.e., 220, 320, 400, 600, 1000, and 1500 and hard rubber sanding blocks

  • Polishing compound and power buffer
       

Start with a hull completely stripped of all paint or varnish. Sand it thoroughly in preparation for stain. Stain the hull and let it dry thoroughly for a day or longer if the air is very humid. Then, spray on two coats of CPES sold by Smith & Co., who advertise in The Boat House. This will seal the surface of the wood through the stain and create a great base for the urethane to adhere to. Lightly sand the CPES with 220 paper dry and then clean off the sanding dust with a vacuum and tack rag. Spray on the a couple of coats of urethane and let it cure. Wet sand lightly with 320 paper, clean thoroughly, and spray on two more coats. Let it cure and wet sand with 400 paper. Urethane goes on thinner than varnish so sand carefully to avoid sanding through on sharp edges or high spots. Continue to spray on coats of urethane until the surface meets your satisfaction. Let it cure for a few days to let the reducer gas off. During this time, sand with 600 wet paper in preparation for the final coat. Do a thorough cleaning job again by washing the surface with water and then use a tack rag to get as much dust as possible. Spray on the final coat of urethane and let it cure completely. Sand out the dust nibs with wet 1000 grit paper on a hard rubber speed block. Follow up with wet 1500 paper using the speed block again. Finish up with polishing compound applied with a power buffer. Then step back and admire the dazzling shine with no annoying dust.
   

This seems like a lot of work when you consider that a spar varnish finish is relatively easy and friendly to apply. The original factory varnish finish on a Chris Craft was: stain, a sealer coat and three coats of varnish. Shine - it did, but when did this thing start that we need a mirror finish to protect the wood. Certainly more varnish is better for UV protection, but 12-15 coats of varnish for shine is a little work intensive. Other than that why would it even be considered. Maybe it is because we can and therefore we do. With urethane, it may look like 12-15 coats of varnish, but unless you know the method, and have the equipment, it may be a disappointing effort.
   

The choice is up to you. There is no harm done trying and you will more than likely succeed if the urethane is properly catalyzed. It would be greatly appreciated if you would pass on the results of your effort to Gadgets and Kinks so that others may learn. Whatever the extent of your effort, keep in mind one thing and pass it on to everyone else:
Don't destroy it; restore it!

 

 

 

 

 

 

 

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