I’m making up some coasters from red oak with epoxy inlays and i’m just curious what you guys would recommend as a nice waterproof finish? I was thinking of just using a spray polyurthane to keep things simple. I applied a couple of coats of shellac prior to pouring the epoxy to help prevent color bleed if that makes any difference.
The shellac does make a difference. I use Zinsser Universal Sanding Sealer (dewaxed shellac. Zinsser also makes a traditional finish shellac whick is not dewaxed. Dewaxed can cause other top coats to not adhere properly.
The Minwax wipe on poly is easy. The spray works but is easy to get orange peel. The sprayon dries quickly so give light multiple coats and not a heavy coat which pools and runs.
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Polyurethane spray also works well over epoxy. They are both really plastic, so adhesion has really been good for me, as long as the surface being finished is clean, which is also true for shellac.
Sometimes in this area, shellac is more difficult to find in stock, especially de-waxed.
Thanks for the advice. I ended up going for a can of minwax spray polyurethane. I’ve done 2 light coats sanding with 400 grit in between. Overall im really liking the finishing however i am noticing liitle of the orange peel effect Guy was mentioning. Any way to deal with that?
You’ll probably need to do a light sanding and spray again with lighter coats and allow more drying time in between. I’ve struggled with that too at times.
I may try Guy’s wipe-on poly suggestion next time.
Spraying a finish takes some practice and there is a bit of art to it. Light coats work great for the first few coats, but the material starts to dry in the air before it hits the stock. Much of this action cause the orange peel effect. Slightly heavier coats (called wet coats) flow out nicer and reduce the bumpy effect. But its a balancing act between wetter coats and keeping it from running. For a coaster, where most of the surface is flat and parallel to the table top you are working on, you can spray pretty heavy and let it flow out.
Follow the directions for Poly finishes because some products require coats or sanding every 30min to an hour. If you wait too long, you may need to wait 24-48 between coats. This is because Poly does not melt into the previous coats like lacquer or other solvent based finishes.
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People seem to like my unfinished coasters made of eastern Red Cedar (Juniper). If they leave an icy glass on it for hours it will seep through, and I tell them that. But most folks don’t do that and the wood drys just fine and leaves no marks.
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I’ve also just done a clear coat of table top epoxy resin and that works pretty well (although takes more time and cost to produce than coating with poly).
For the bottom I’ll brush on a light coat and be careful to not let it run down (up) the sides. After it cures, tape around the bottom edges with thermal silicone tape, flip them over and pour or brush the top side coat that’s somewhat heavy and clean up the edges so they are even all around. Best to have them elevated with a ‘bench cookie’ (I use small pieces of scrap) so they don’t stick to your work surface or the ponds of resin around them. You may also want to cover your ‘cookies’ with the silicone tape, so if there’s some stray resin they don’t become part of your coaster.
Your work surface and ‘cookies’ will need to be level otherwise it’ll run off or pond on one side.
These tend to look better than they function as coasters. Unlike the functional ones Charles described, condensation builds up and creates a vacuum, causing the party-foul of your glass and coaster staying connected.
I really appreciate everyone’s input. I’m working on a few coaster ideas I’m hoping to sell so I’d like to find a finish that’s relatively inexpensive and easy to apply. I’ll use up the can of spray poly i bought but i think i’ll go with the wipe on poly next. I really like the look of epoxy flood coat finishes but i think that would add a little too much work for the sale prices i’m thinking of. . One other issue: I’m finding it rather tricky getting a nice smooth surface on the side with cuts going against the grain. Do those areas just need extra attention or is there any tips or tricks for getting uniformly smooth sides?
end grain is tricky and requires more sanding. But without going down a rabbit hole, normally you have to seal and grain fill the end grain to get a smooth finish. This becomes a whole new step in the finish process. Some wood has smaller grain/pores then others and not only machines smoother, has less issues with finishes on the ends. Others have large pores and require lots of work.
As @Ensalaco said end grain can be somewhat tricky. If you sand the face grain to 220 then go to 320 for the end grain. As @Ensalaco you can use grain filler and then a sanding sealer and then the finish. The cheapest thing to use is wipe on poly. They do make a water based one but I have not seen it in wipe on form. The wipe on is simply regular poly that is thinned. It usually takes 2-3 layers with a sealer. Without a sealer 3-4 coats. So the sealer helps for less coats.
I paint and coat many CNC carved signs in my shop. I have used shellac (non-dewaxed) in a previous life and now with my signs to soak in some initial sealing. Perhaps your coasters would benefit from this. There has long been a legend that you should not coat over wood that has shellac’d (with the typical waxed version) because of adherence. I’m still waiting for the shoe to drop. I paint over and spray several different types of clear coat on wood products.
Spraying takes practice but worth the effort. I’ve never used rattle can products but I’m sure the aerosol version of clear polyurethane would work well. I spray a ton of it and it flows out nicely. Seldom do I sand between coats. If I was building furniture and cabinets again I would be sanding. If you want to apply shellac and don’t want to worry about adhesion by all means get a small amount to dewaxed.
Can you post some pics of your coasters? tnx
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For sure. I’ve cut out a bunch from red oak but thought i should start with finishing just a couple untill i get the hang of epoxy, finishing etc. These were the 2 i was working on yesterday. Not too bad for a first attempt. I used opaque dye, the black turned out nice but the white came out kinda milky and translucent. I suspect i didnt shake the dye bottle enough, lesson learned for next time. They are smooth to the touch but you can still see the orange peel effect, mosty with the one on the right. I think i goofed with application of the spray poly. The can said recoats can be done in 1-2 hrs, but the websie says 4-6 with light sanding using 220 grit in between. I used 400.
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Late to the party here.
My favorite for projects like coasters is Mohawk Pre Cat lacquer rattle cans. Outstanding durability, easy application, re-coat in 20-30 minutes (or less 
).
I’m not sure how widely available it is. I get mine from my local hardwood suppler. Comes in flat, matte, semi gloss or gloss.
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With clear polyurethane and many paints its challenging to see the difference between orange peel and lack of material. Test pieces will be your best friend. Be sure you have plenty of light on your work when you spray and your coatings and shop air are north of 60 degrees. Test pieces will take the pressure off and you can be liberal with your spray passes and hold back to see the difference between lack of spray and to much where it “runs”.
I have only used lacquer a few times and do not know the difference between pre and catalized lacquer. I thought lacquer turned white when someone set a sweaty glass on a table top with lacquer. Does lacquer turn white with water left on it.
What I remember is a hot beverage cup on shellac with damage the appearance. Many moons ago wood workers encouraged each other to apply lacquer on top of older shellac’d pieces to extend the life of the finish. Traditional lacquer’d finishes would however suffer from trapped moisture after application. Don’t remember heat or sweaty cups hurting a lacquer finish. Lacquer was actually developed to surpass shellac and it’s properties. It’s also a brave new world with anti VOC rules and regulations. I gave up trying to keep track. Even paint thinner is on the endangered species list.
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Thanks for the tip. We dont get many of the brands i see mentioned here in Canada but ill definitely check it out. Thats the other thing that may be affecting my finish. My garage this time of year isn’t the warmest place in the world.
RE: Orange peel, meant to ask you about the temperature. The polyurethane will orange peel if it’s too cold in the shop. Been there, done that!
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I’m no expert on finishes by any means, just personal experience.
These guys know a bit:
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