I am constructing built-in benches in the waiting room of a veterinary clinic. The wood is all stained and I am ready to apply a finish. It needs to be durable as it must withstand animal claws, occasional pet urine, and occasional exposure to dilute bleach solution. I have selected Minwax¯ Helmsman¯ Spar Urethane (satin finish). Anyone have experience with this product?
Also, they recommend 2-3 coats for better durability. Is that a good idea?
They also recommend light sanding between coats, presumably to improve adhesion. Is this necessary if the grain has not raised form previous coats?
Thank you for your input
poppi
Replies
poppi,
I did benches in a veterinary clinic in the early 90's. Used shellac. Owner recoats every 3 years. Still looks great when I get back to visit
Chuck S
I've used that urethane with excellent results! The uses were a front door (oak) and a pine dinning table on a covered outdoor porch. The door is over 17 years old and the table is over 10 years old. Both look like the day they were finished.
Be sure to use at least three coats. If you need a really sturdy finish, go with 4 coats. ALWAYS SAND BETWEEN EACH COAT! The urethane will not stick otherwise. It isn't a glue and only adheres to a rough surface. You won't need to use heavy paper, only 200-400 grit between coats should work fine. I've even used wet paper but you can get dry paper that will work just as well and less messy.
Hope this helps. Fire away with any questions. Good luck!
If it's oak and you are going to use Poly...make sure you seal it before your first coat. Reduces drying time and makes for a much smoother finish.
The gloss finish will prove slightly more durable. If you don't want a gloss finish on the final product, then wait until it is thoroughly cured (at least 2 weeks, some folks will say longer), and rub it down with 0000 steel wool and paste wax. Rub lightly you're just removing the sheen.
But this may not be the right finish. First, it is fairly dark in final color, yellow to amber, and will effect the final color ofyour installation. Second, finishing with poly of any kind is time consuming. Ideally, you'd apply a sealer (shellac, lacquer or anything labeled as a "sanding sealer") rub that out, then start applying coats of poly, allowing each one a week to cure, then sanding with 400 grit, light sanding, but it must be thorough (covering all areas), then clean the surface, apply another coat, wait another week, etc. Depending on what kind of finish you want, and the species used, it gets more complicated. In this setting you want a very smooth, non-porous finish. If you started with a fairly non-porous wood, no big deal. If you started with flat sawn red oak, you've got a job ahead of you, to fill all those pores, sand it down smooth and start building a smooth film.
Shellac is not as durable, but is still quite durable, and enormously easier to apply. It dries very quickly, you don't have to sand between every coat (although for a good, smooth finish you'll still want do some sanding), and the chemicals involved are far less noxious. In addition, you can get it from blonde to amber even at home stores like HD, and can get it from clear to ruby at woodworkers' stores or online. Downside is that shellac won't stand up to some cleaning agents, including anything with ammonia.
Shellac's greatest feature is that everything sticks to it. So a good compromise would be multiple coats of shellac to build up a good smooth film finish. Rub out that last coat with 400 grit, clean the whole thing up with mineral spirits, then apply a coat of poly. You end up with an easy to apply film finish, the top coat of which is extremely resistant to chemicals, dirt and damage.
You might post this over at Knots, those guys really know their wood finishing.
I'm surprised at all the mentions of shellac here. First - the guy has already chosen his product and it is one of the best available for the job.
Second, shellac as a sealer should never be used under polyurethene. Read labels on both products. The only way shellac is compatable with poly is after a goood 30 cure and then sanding hard. Finally shellac is not suited to withstand the ammonia in urine.
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Piffin,Dewaxed shellac is an excellent first coat for poly. Use it as a prestain conditioner, stain and then top coat with poly. Zinser is what I have from the local yard.See http://www.zinsser.com/product_detail.asp?ProductId=72KK
if dewaxed and cut then well dried, yes.
Nobody mentioned dewaxed though
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Piffin, the guy asked if anyone had any experience with that product. I have substantial experience with that product and was sharing the results of that experience. From his questions it sounded like he does not have a great deal of experience with this product, or with finishing with polyurethanes in general.
As to "one of the best" for this application, I'd have to say it's a good tough finish, adequate for this job, but far from "one of the best." The UV inhibitors are likely entirely wasted in this application, and those are the main reason for the product's premium cost over many other polyurethanes. Shellac actually has similar moisture resistance and better water-vapor resistance than poly, which could be important in this application. It is easier to repair. Less toxic and, in my opinion, far easier to do a really excellent application. As I pointed out, the satin version loses some of its durability because of the flatteners, so even just switching to the gloss improves hsi finish somewhat. And overall I can think of several other finishes that one might choose over polyurethane for this application.
He also askd whether he really should do 3 coats, so I responded with an alternative method that would not require 3 coats of poly, could be completed much faster, and would end with a coat of finish that will stand up to the ammonia in urine and/or cleaning products.
Mea culpa, I should have specified dewaxed shellac. But in my own experience finishing wood (which spans the last 15 years), I find that the concern about wax in shellac under most varnishes is grossly overstated. Allow the shellac to dry and remove any and all surface wax by sanding and wiping with mineral spirits, which is precisely what I suggested, and you get a mechanical bond between poly and shellac that is esentially identical to the bond between two coats of poly.
Perhaps I should have explained all of this in the first instance, but somehow I don't think doing so would have prevented your response or the inaccuracies in it.
"If the trout are lost, smash the state."
There were no inacuracies in my responce. Maybe a difference of opinion on a good, better, best choice, but definitly no inaccuracies.You seem to have takena a technical response personally. Did you escape from Knots?
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Did you escape from Knots?
Check his profile ... legal services!"Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Nice cheap shot, FastEddie, you've added so much to this discussion.
Poppi, yes, you can switch from the satin spar to a gloss poly if you wish. As to how long to wait, check the instructions on the can for the minimum period. Problem is that if you attack it too soon the poly or spar is still soft and will gum up. What you want is that when you sand you immediately create a fine white dust. If parts of it seem gummy at all, you need to wait longer. When I wish to create the best possible finish with spar (I use it on bamboo fly rods where the finish takes unusual stresses, and aesthetics are paramount) I wait two weeks with the item in a drying box and that way I am assured a good solid cure. When I'm in a hurry, I test periodically by sanding, and only stop if I find gummy, uncured poly (normally in corners where it built up a little thicker).
Poly is relatively cheap, so if it were me, I'd switch to a high gloss at this point, and plan on rubbing out the finish at the end of the job to remove the gloss. That would give you 4 coats total, which should provide a finish more durable than the pine it is covering. Like I said, some 0000 steel wool lubed with either wax or mineral spirits will knock down the glos quite nicely, as will the finest grade of scotchbrite pad. It's best to wait as long as possible after appying the final coat before you try to knock down the gloss. But it also would be reasonable to do a couple coats of high gloss, and finish with a coat of satin.
Good luck.
"If the trout are lost, smash the state."
Cheap shot? No, just stating a fact.
And yes, I think I have added to this discussion. Look at post #13 where I mention getting dust when sanding, rather than a gummy residue. Sorry if I didn't use the eloquent words and a fly rod as an example like you did."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
There have been a few suggestions to do a final finish with a hard wax (Johnsons?) applied with 0000 steel wool and buffed out. I did this many years ago on doors with excellent results and think I will do it here. How long should I wait after the last application of poly before applying the waxTahnkspoppi
Everybody Duck!
Just kidding;_0
I've been using waxed shellac under poly for 25 years and I haven't had one project fail. . . I know, I know.
I would agree that the use of a spar varnish/polyurethane is not the best choice for your benches as it is like most have said, soft.
It's designed that way to "give" with exterior wood projects that will "move" as seasons and weather changes. I would also agree that the use of
a gloss finsh would serve you better. You can do as you have stated and rub it out with 0000 steel wool, but you could also just use a stain finish
as the last coat.
Good Luck
Edited 2/15/2007 3:30 pm ET by Joe
Great job Joe!I'm ducking
;)
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Just to add to the confusion...
I always thin poly by about 5-10%. It makes the material flow much easier and helps prevent that dreaded overnight "creep". It also helps get the bubbles out.
I've had a lot of bad luck with sanding sealers, so I never use it when the wood is to be stained (exception is very soft woods, like pine). A decent coat of poly makes an excellent first coat, and will perform much as the sanding sealer. I've done a lot of red oak with this method with excellent results. It does leave some grain showing, even after 3 or 4 coats, but I actually like that. I don't really want fine wood looking like formica.
I always wait at last a week, and prefer to wait even longer than that. A good, thick film of poly won't be fully cured for 30 to 60 days, and ideally, you'd wait that long. But let's face it, only a saint can put a finish on a project then wait a month or two before installing or using it. It's winter time, so humidity shoujld be low regardless of where you are. I don't know if your workshop/finishing area is heated or not, but if you can keep it warm and dry after applying your last coat, you should be safe rubbing out the finish after a couple of days. Do the same thing recommended before. Check it out for softness/gumminess in the most recessed, built up, inside corner you can find. When that corner is cured hard, the whole thing is."If the trout are lost, smash the state."
Eddie, I've actually read enough of his stuff here to know that he has done as wide a variety of stuff in construction as I have, in more of a DIY format, but still has a lot of experience and is on the ball in a lot of ways. My comment of escaping from Knots had more to do with his egalatarian haughty attitude than any attempt to slam his knowledge or experience. All top dogs have 'tude, we just display it in different ways. His seemed more like the kind that I see at Knots.
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Point taken. I still don't think I erred. You made a comment about Knots and I pointed out an element in his profile, without any added comments."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
Right, I was not criticising you, only clarifying my own...Hope poppi can manage to wade through and end up with a great finish now....LOL
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Piffin, I'll accept your criticism as honest and well-intentioned and give it consideration.
To answer your question, no, I don't go to Knots very often, but have on occasion, and believe that I'd probably agree with your analysis of the particular form of haughtiness over there (it differs only in form from one forum to another, every forum suffers its share).
To take a second shot at the post of yours that did set me off just a bit and to attempt to do so in a less abrasive manner let me try this: I would have to say that your statement that shellac should "never" be used as uner poly is, IMNSHO, incorrect, as you later agreed in reponse to another poster. Fact of the matter is that many of the best, most knowledgeable finishers out there recommend shellac as part of a finishing course that ends with a topcoat of poly for its durability. A recent example is Tim Leahy's artice in the January '07 FHB on finishing wood floors. While I don't know Leahy and his work, his article demonstrated a good understanding of wood finishing, and included a reocmmendation to use Zinser Sealcoat which is nothing more than a dewaxed shellac.
As to fast eddie, he appears to put a lot of stock in the labels people carry. I hope that approach to life serves him well, but I have my doubts.
"If the trout are lost, smash the state."
Right - we're beating a dead horse now with a broken broom. de-waxed was not the shellac mentioned is why I was definite in my language. I don't have a problem with shellac, having used about 24 gallons of it in the last couple of years.My fondness for the spar comes form the fact that this area has a lot of fine boats...
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Good product choice.
why question the manufacturer on number of coats?
Three is normally optimal. Let dry thoroughly between coats for hardest finish. catch it right at the minimum time they recommend and coats will have better cehmical adhesion but can end up with a softer finish overall. Do four coats and it is even more likely to be soft finish instead of hard.
Sanding does two things between coats. It provides "tooth" for mechanical adhesion, and it smooths the bumps, bubbles, and other flaws. Progressively finer sandpaper gives you a smoother finish. say 200 grit lightly with the grain between first and second, then 400 grit between second and third coats. Tack clothe to clean before wetting the brush of course. It'll finish smoother than a babies butt.
Pay attention to temperature and to fresh air when doing this also. Too warm and the surface will flash over and make it hard for oxygen to get to the subsurface molecules and cure them hard. Too cold and it will take forever.
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catch it right at the minimum time
Are you saying that you should recoat at the minimum time? I don't have a can handy, but I thought it said something like "recoat within 1 hour or wait 24 hours""Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
I wasn't recommending either or, simply reporting what to expect for each or which to aim for if certain results were desirerd.Here is the thing - The oil poly cures rather than drying. It cures byu oxygen.if it is still slightly uncured, then the next coat will be able to bind chemically to it for a stronger bond between coats.But this is not especially desireable. If you build 3-4 coats without adequatecure time for each, then you have reated a thich mucous that will take forever for oxygen to reach the center molecules. It will look fine and be OK on something like a wall, but for heavy use on a floor or this project, it will be soft and easy for pets to scratch.So it is in this case, best to wait a good day in optimal dry warm setting betwen coats, sand lightly, then recoat. I thought a rec above for waiting a week was excessive normally, but in cooler humid air, it can take that long to get a good cure. water molecules filling air space make it hard for the volatiles to float off so time is extended.Cool or cold means less air movement too and less energy to help those oils escape and less movement equals less contact with oxygen for the chemical cure.
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Ok, I understand and agree. Better to wait a little longer. Been there, done that. Removing a gummy finish is no fun. And sanding between coats is a good indicator: if you get dust, it's good. If the sandpaper gets the least bit gummy, it's too soon."Put your creed in your deed." Emerson
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
That is a good signifier.
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I wouldn't use spar because it's a softer finish than a regular polyurethane. That's why spar isn't used or recommended for floors. It's perfect for low traffic uses exposed to high humidity, but not my first choice for what is essentially furniture.
The poly finish is essentially a layer of plastic and the more layers the longer it takes to wear through 'em.
Fine woodworking did some real world tests on various polys and like the cheap stuff or not, minwax was pretty highly rated over the more expensive stuff.
For a number of years we used Valspar floor poly, so that's what we used on everything from builtins to trim in addtion to floors. It's very similar to regular minwax.
I had a chance to use some varathane variations from their cheap poly to the top of the line stuff and it's very similar to the others.
There are high tech two part urethanes that are more durable and $200/gal, but regular poly is typical for your application.
The water base acrylic polyurethyanes are good as well, but harder to apply. For a brushed on finish nothing is more forgiving or better performing than the oil-based polys.
Poly doesn't really need a sanding sealer of any kind, but the sanding sealers build up thickness faster because of the fast dry time. Some sanding sealers change the final apperance and some don't.
Like a wood floor, each layer should be lightly sanded and tacked off before the next layer. There is no way to prevent lumps and bumps from dust and whatnot and not sanding between coats is asking for a rough finish.
If you don't use a sanding sealer, it's commonly accepted as a good idea to thin the first coat to ensure good saturation of the surface. Thinning 25% works well with oak.
Good luck.
Beer was created so carpenters wouldn't rule the world.
Every can of sanding sealer I've ever read said not to be used under polyurethene and every poly said do not use over sanding sealer.Eventually I learned that it was because of the waxes in the sealer. You have to let it cure for thirty days and then sand it welll to avoid bond problems. That might be no p[roblem in some situations but for a heavy use location like this it is essential to have good bond and good cure.
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<Every can of sanding sealer I've ever read said not to be used under polyurethene and every poly said do not use over sanding sealer.>I don't know if it's common or not...when I choose to use sanding sealer and the final finish is poly I use standard poly thinned 50-60%, seems to work well. Grain filler also works well to condition raw wood.Rip
Every can of sanding sealer I've ever read said not to be used under polyurethene and every poly said do not use over sanding sealer.
The sanding sealer I mentioned is specifically designed for use with poly floor finish.
You're right about being careful with sanding sealers and their compatibility with finishes.
There's nothing worse than spending a great deal of time on a finish and have it turn sour for lack of reading the directions on a can.
Beer was created so carpenters wouldn't rule the world.
Poppi,
You have had a lot of advice here, mostly sound.
I agree that the extra money spent on the exterior "spar" urethane is wasted in this application. A solvent-based polyurethane gym floor finish in gloss is ideal for the performance requirements of this job.
Since nobody else mentioned it, you may want to fill the open grain of the oak after sanding and vacuuming the first coat of poly. Otherwise, it takes a lot of coats to fill the grain with only the finish.
Another point concerns time. Doing the polyurethane properly will take many days. Is this clinic already open, or do you have enough time before they open to spend a week finishing the lobby benches? A professional finisher might use a catalyzed lacquer, which can build the coats needed in a single day. The fumes are awful, but the turnaround time is way faster.
My own experience is that oil poly takes up to a month to reach full hardness. Kind of like concrete. I did a job and left the lid of the first can in the area and checked it over time. It took 3-4 weeks to reach a point where I could no longer detect a difference in cure with my fingernail.
Shellac is a great finish, but not for a veterinary lobby IMO. Like others said, ammonia will strip it. However, the lack of sanding and speed of build is seductive when compared to oxidative finishes like the poly. And the fumes are gone very fast indeed. Good luck, and let us know how it comes out.
Bill
I came back to the first here because a couple of other posts mentioned your oak and I did not recall reading anything about the kind of wood here. Did I miss something?
Another thin mentioned a couple times is that gloss will be harder and longer lasting. That is because gloss has a higher percentage of solids in the mix. Satin has had de-glossers added which thin it a bit. My floor guys use gloss for the frist two coats, then go to satin for top coat or buff the gloss off.
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I'm with Idaho and bill on this. Spar will hold up ok, but it is a softer finish. For the degree of water the bench is going to get, a harder poly should do fine and give you a longer lasting more durable finish. I would go with a Floor poly as mentioned. Spar was developed for marine use, for UV rays, and lots of rain, good on doors and outside stuff. If what you're making is going to be inside but has a lot of contact, better to go with the harder poly. Do as Piffin says, and make it in 3-4 very well dried coats, sanding in between.
As far as the shellac goes, again Piffin said it (thank you sir), always use dewaxed if used as a sealer, and shellac will not hold up to certain things like amonia or alcohol.
Pretty much what Idaho, Bill, and Jer said: go with the regular Minwax Poly not the Spar-Poly. As others have said, the Spar-Poly is for exterior use and is softer so it can flex a bit to cope with weather extremes. You want the durability of regular Poly. Gloss will give you best resistance to abrasion. Your last coat can be satin or semi-gloss if you prefer a softer look than the gloss or you can finish up by putting a coat of wax on the piece. Wax (a hard wax like old-fashioned Simonize or Johnson Paste Wax) will also take some of the gloss of the piece.
Sanding in between coats is not a big deal. A once-over with a sanding block and 220 paper should largely do it. That will show you any bits of dust or hair that you may need to lightly sand a second time.
Chip Tam
This is a reply to all the excellent replies to my original query. Let me first answer a few questions and clarfy the present situaton.The bench surface is 1 1/8" x 18" laminated pine board. The vertical panels are 1/2" hardwod (oak) plywood. Both are stained with two coats of Minwax oil stain. After assembly I have "painted" all surfaces with the Minwax "spar" poly. It has now cured for 3 days and is not yet sanded.I now see where a gloss finish will be harder. Can I apply a gloss (not spar) poly over the first spar coat after sanding and tacking? By the way, the client does not like high gloss finish.How long should I wait between coats?Thanks to all for your excellent advicepoppi
you can switch back and forth between the various kinds of poly staying within the same brand name, yes.Three days should be plenty. A lot depends on temperature and humidity wheere the piece is. If you do not feel any gummyness touching it and cannot easily mark it with your thumbnail it is probably fine for the next coat
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I usually go 24 hrs or so between coats of poly, light sanding in between starting with 220 grit paper. The sanding is just light pressure on the paper enough to make a white dust and thats it.
Wipe the dust off and reapply another coat, let dry then sand with 300 grit paper.
Keep repeating this step until you are happy with the results, I up the grit of the paper in between each coat. You are taking away scratches with finer ones.
After 400 grit paper I start wet sanding, working up the grits as well 600-800-1000 this puts a finish on that is indestructable, and looks like a piece of glass is sitting on the bench.
Do not shake the cans of polyurethane, stir them gently. Shaking puts air bubbles in the finish.