A Better Way to Apply Spar Urethane?- Question of the Week
February 13, 2007 | Filed Under Blog, Question of the Week
This week’s question comes from Jeff. He writes, “I am using Helmsman Spar Urethane to refinish the front door of our house. It’s a one piece flat door — no recessed panels. I am applying it with a quality brush but I still get brush marks and hi-low points, also tried a sponge brush with same results. I know it’s barely noticeable but I absolutely abhor brush marks. After 4 coats, I have managed to sand it down fairly flat. Is it possible to thin Helmsman and spray it with an HVLP gun? There is a Helmsman spray can available but I have so much Urethane left over. To thin or not to thin.”
And here is my reply: “Hello Jeff. You can absolutely thin your urethane. In fact, you might have been better off thinning from the beginning. Thinning about 20% with mineral spirits allows the finish to self-level a little better which helps avoid brush marks. The only disadvantage is you need to apply more coats to get the finish you are after. But if the payoff is a smooth finish with no brush strokes, who cares, right?”
“Now when you thin, bubbles are going to be your worst enemy. So take special care when mixing. If it were me, I would abandon the brushes all together. I would thin the urethane 50% and wipe the material on with a soft cloth. Just remember you will need to apply twice as many coats to get enough urethane on the surface. But since the solution is thinned out, you could easily get away with applying one coat in the morning, and another at night (if the weather is cooperating). And remember when wiping on a urethane, you aren’t really flooding on a thick layer. You are just coating the surface.”
“Now if your surface is sanded flat and you are ready for what will hopefully be your last coat, then I say wipe on your last coat. I think you will be pleasantly surprised with the results. And to directly answer your question: yes you can thin and spray urethane. But the real question is whether you should. If the door is flat and you have a reasonably dust free environment, I see no reason why you couldn’t spray a coat on. But due to the simplicity of the wipe-on method, i never bother spraying oil-based finishes.”
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21 Responses to “A Better Way to Apply Spar Urethane?- Question of the Week”
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Thank you Marc for a great website, It’s very informative. I myself am in the constuction trade learning what is to know and I use your site as a tool to increase my Knowledge in fine wood working.As you probably know working for contracters they are allways looking for the quickest and not so safest way to GET UR DONE. I was wondering what your expierance is with water based poly’s. ie with brush hash marks.
Thank you for your time, I now have to dig myself out of this snow storm that we are getting blistered with.
Thomas
Marc,
What is the difference between Spar Urethane and Polyurethane?
Thanks,
Ron
Hey Thomas. I don’t usually use water based poly, but when I do I usually apply it using a HVLP spray system. It sprays alot like lacquer and gives decent results. Its a water-white finish so it suitable for light-colored woods that you dont want to yellow over time, like maple and birch. If you do have to brush it on, I recommend using a synthetic applicator taking care not to produce bubbles. When you stir the product, use a stirring stick and stir in each direction about 100 time. Dont shake the can. And since it flashes so quickly, you might want to dilute with a bit of water. This will give you a bit more working time between application strokes.
And Ron, Spar Urethane is intended for outdoor use and contains a higher amount of solids. It tends to be a softer, more flexible finish. This is primarily because of the temperature changes and harsh conditions outdoor pieces will experience. The finish needs to be flexible in order to survive. Spar urethane may also contain UV inhibitors which help to preserve the color of the wood and avoid graying.
Hope that answers your questions guys!!
marc
Great! Just what I was looking for thanks!
Marc,
I have to say Wow, my hats off to you and your wife.For doing such a wonderful job.
This past summer I lost my lower left leg.While I was off an setting around, I got interested in woodworking.I started by watching New Yankee Workshop and then I started to read books an magazines. Looking at websites, thats how I stumbbled across yours. Man,I am impressed.
How a person can take a piece of wood an create a work of art.I myself would love to learn how to become a craftsman.But i know it takes time an tools.As far as skill I believe I have the abillaity.But the question is can you teach an old 50 year old man .Where do I start in what direction. These are questions I ask myself.
I dont have friends that have this skill.As far as classes, I have looked but can not find any near Cincinnati,Ohio.
Hello again. I finished my hardwood floor and applied water based Trek + one of three different ways. The first coat I used a brush and all went well - some lap marks but no big deal. The second coat with a paint pad for water based poly - went well but not as good as a mohair roller. No air bubbles and dried perfect and took so little time and effort. One question though. Before the floor was finished and just bare wood it looked and felt like glass. After the coats and buffing in between each it doesn’t look as flat. Almost like the poly seeps between the cracks and lowers versus the center of the wood which gives a less than flat look. I was thinking of buffing after the final coat with 600 grit paper. Any suggestions? Thanks again.
Hey Moe. By no means am I a floor finisher. I can only apply what I know about furniture finishing to your situation. Perhaps someone with floor experience can chime in.
Usually with furniture, you can sand your finish coat flat after you apply a coat or two of the finish. So any little dips or valleys will be taken care of. Then when you apply your final coat, it is glass smooth and flat. Now doing this on a larger scale is a whole different story. And hopefully someone else can chime in.
As for the final buffing, 600 grit would work fine but it will give you a satin finish. Assuming thats what you are looking for, you are good to go. Just let the floor cure for several days to a week before sanding. And use mineral spirits as a lubricant.
Hope that helps.
Thin Urethane, love it! Solved my bubble, speck and brush stroke problems on my dashboard.
I am refinish a wood garage door that the original finish has deteriorated in some areas, but not others. I used a finishing sander to remove the discolored wood and finish as well as to taper out the edge. I thinned the helmsman spar urethane about 20% on the first coat, and used it straight for two more coats. The areas where I sanded have a darker appearance than the unsanded areas, even though it is the same varnish being used and it occurs not only on the exposed wood but the areas that I sanded the finish off of (that had not been damaged), just in order to be able to feather the new finish in easier. I don’t understand why reapplying the same finish to wood that was originally only sanded, with no other sealer or finish, has caused this difference in color to appear. Is it possible that it will lighten up to match the other finish as it dries, or that the mineral spirits thinning caused my finish to penetrate differently?
Hey Rick. Its really tough to say. Since we are talking about weathered wood that has been previously finished, and the finish was damaged, there are a quite a few variables at play. One thing I know though is that once you sand off a finish and refinish it, the wood almost never stains or finishes to the exact same color. At least part of the reason is the fact the sanding can actually drive some of the finish into the grain.
So it is possible that the color will even out over time, but I wouldn’t hold my breath. Just keep in mind that poly finishes are usually not the best finishes for the type of repair you did. The repair is nearly impossible to hide (as you can see). In many cases its necessary to remove finish from the entire surface in order to achieve an even appearance and a smooth finish. So at this point, you may just need to give it time. But if it really bugs you, you may need to refinish the whole door.
I might also suggest trying a higher quality spar urethane that will last alot longer than the Helmsmans. One that I recommend is Epifanes.
he absolutely correct! if need to spray, then spray, like me, im a sprayer beleiver, but you gotta know what ya doin. A tip , use min spirits mixed with naptha for your thinner blend, this is to thin and be a delivery solvent for coating. HVLP, Conventional, ok, no airless!!! !st two u can control air atomization, by feel. forget reccomendations by mfg!!! Im an old coatings guy from the industrial side, not local joe blo painters, which normally give u same info, cause they dont know!!! But thin n spray, have fun!!!
Hi Marc, my name is Chena I have a question for you, how do clean bristle brush after using Spar Urethan?
Thank you
Regards,
Virginia Jimenez
Urethanes are cleaned from brushes using mineral spirits. Purdy makes a metal toothed comb that separates/aligns the bristles to aid in cleaning.
Some people prefer to toss a brush after each use, but when you buy a quality brush it can last for weeks of use with proper care.
can you use spar urthn on an acrilic painted surface?
Hi Sue. You can apply spar urethane over acrylic. Just keep in mind that it could very well yellow the finish over time. Im not sure what your application is, but you might consider a water-based poly for this job. It is fairly protective and won’t yellow over time.
I understand spar urethane is better for water and uv rays than polyurethane. My window sashes have one coat of poly, can I use spar over the poly?
Hi Randy. You are right on about spar urethane. They are engineered to have better water resistance and added UV blockers. But in reality, its all just varnish. So if you scuff up the current poly layer with some 220 grit sandpaper, just apply the spar urethane right on top. They should be completely compatible.
Good luck!
HI,
Would like to know if you can apply spar urethane over a formica countertop? It is an ugly speckled white countertop and I want to first stain it a different color than coat it with Spar urethane. Will it adhere and hold up to moisture in a kitchen??
Thanks for your input.
Great website, lot’s of very good info. I just built a tiki bar in an semi covered outdoor pool area. The top is Tigerwood flooring and sides and trim are stained Mahagany. Would a spar urethane be the best finish for my project and what brand do you recommend? Also I am considering doing a 2 part epoxy finish over the tigerwood top, at some point, will I be able to apply this over a spar urethane?
Mahalo,
Lee
Hey Lee. Spar urethane would be an excellent choice for that job. My favorite outdoor finish is actually a marine varnish known as Epifanes. The 2-part epoxy would certainly give you a good amount of protection on that bar top. Now if you already had some spar urethane on the top, my best guess is that you would be fine coating over that with epoxy. My guess is that the epoxy isn’t going to be too picky about what it sticks to. But its probably not a bad idea to lightly sand the poly top prior to applying the epoxy layer.
Hope that helps.
Pam. To be honest, that’s a little beyond my expertise. Im not 100% sure how the surface would respond. My guess would be that you need to rough up the formica surface a bit. The urethane will need something to bite into and a smooth formica top is not exactly that. So I guessing that if you sand the entire surface with 180 or 220 grit, apply your coloring agent, and then apply the urethane on top, you MIGHT get a decent final product. But its not something i can whole-heartedly recommend unless I experiment with it myself. Maybe try the operation on a scrap piece of formica from the home store and see how it holds up.