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Discussion Starter #1
So I had a thread a while back here:
http://www.woodworkingtalk.com/f8/trouble-polyurethane-57061/

And I'm working on the rest of the actual cabinet (that thread was just a door in the back) and I"m going along the same process last time:

  1. coat of polyurethane
  2. sand with 220
  3. coat with polyurethane
  4. sand with 220
  5. etc.

The whole point of all the coating/sanding is to make the surface level. When I sand I can see sanded parts and then other parts that are still reflective because they're lower than the surface getting sanded. So I repeat this whole process till the hills are flattened down and the valleys are filled up so the whole surface is level.

Awesome in theory and it works....but it is so ridiculously slow. I am still working on the same project and it's been almost 4 months. I put a coat on in the morning and wait for it to cure then sand and put on a new coat.

It's very frustrating because all the sanding to make it level has messed with the stain underneath and lightened the color a lot from what the original dark stain was. It's very disappointing to put literally weeks of work in to sand it to make it level to get the finish right and all the work is now pretty much worthless because the color is now off and lighter/darker in places.

Is there a better/faster way to do this?

The wood underneath is 3/4" plywood with a red oak veneer. Is this wood naturally really uneven?

Any help would be most appreciated, because I'm only about 1/3 the way done with the cabinet..so that means about 3 more months on this project.
 

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What you have found is pretty normal, considering how slow varnish is to cure. Using a polyurethane formula may be making it just a tad harder (versus a non-poly varnish) because the urethane resins are scratch resistant (their calling in life) so they may be a little slower to sand down. Something I've done a lot with oak that works well is slurry-sand it. This works if you aren't otherwise staining the wood: use either BLO or danish oil ( my preference, 1/3 each BLO/MS/varnish) and wet/dry sandpaper. Apply the finish to the bare wood, and then sand it. This creates a fine slurry of the finish and the dust, which does fill the grain. There are all kinds of versions of the next steps: what I usually do iswork up a good slurry, then take a piece of plastic like an old credit cad, and work the slurry across the grain, cleaning a lot of it off. This is similar to what you would do with a grain filler (which is what I use on stained oak), The process still has to be repeated several times (once a day)to fill the grain, but eventually it gets there, and more quickly than if using just varnish. If the wood is stained, then I color a grain filler with gel stain and work it in. You might consider getting a copy of Bob Flexner's book and checking his methods on grain filling as well. The approach I described above was published in Wood (Nov., 2003. Issue 152, titled Fill 'er Up) if you can get a copy of the back issue.

Edit in: you can also fill the grain with other finishes, like shellac, but to me it's a lot harder to sand and the thin nature of it makes it more work; at least in my attempts.
 

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You didn't say how you are applying the finish. I will assume it is sprayed. If wiped or brushed it will take more coats and sanding. For a mirror finish on oak I would start with a grain filler. Normally the grain isn't filled on oak but a mirror finish would call for it. Then I would seal the wood with a sanding sealer, sand it with 220 grit paper and put another coat of sanding sealer on it. If it is already starting to look good you could sand it again with 220 grit paper and start the polyurethane. Then when it is dry wet sand it with 320 grit paper and apply another coat of polyurethane. When thoroughly dry if it looks real close to what you want I would wet sand it with 1500 grit or finer sandpaper and buff the finish with rubbing compound. If it doesn't look quite right you could wet sand it with 400 grit sandpaper and apply another coat before going to the 1500 grit.
 

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Discussion Starter #4
You didn't say how you are applying the finish. I will assume it is sprayed. If wiped or brushed it will take more coats and sanding. For a mirror finish on oak I would start with a grain filler. Normally the grain isn't filled on oak but a mirror finish would call for it. Then I would seal the wood with a sanding sealer, sand it with 220 grit paper and put another coat of sanding sealer on it. If it is already starting to look good you could sand it again with 220 grit paper and start the polyurethane. Then when it is dry wet sand it with 320 grit paper and apply another coat of polyurethane. When thoroughly dry if it looks real close to what you want I would wet sand it with 1500 grit or finer sandpaper and buff the finish with rubbing compound. If it doesn't look quite right you could wet sand it with 400 grit sandpaper and apply another coat before going to the 1500 grit.
I started by putting on two coats of Zinsser Seal coat since on the original piece (the door) took forever to fill the pores. I did notice that it took a lot less time to get all the pores to become filled and "under the surface" after putting on the sanding sealer.

The poly is being brushed on.

And it looks alright when everything dries and looks level to the eye, but when you go to sand it, the high/low spots stick out like night and day. It literally takes 18-25 repetitions of sanding/coating of poly for the surface to become completely level and sanded smooth. Then I can begin the process of wet sanding up to 2,000 grit and using the abralon pads.

Here's a good description:
Leveling - Once the high spots, drips and other defects are removed, switch to the leveling step. The goal here is to establish a consistent scratch pattern across the entire surface of the wood.
From: http://www.homesteadfinishingproducts.com/htdocs/rubbingout.htm

It says to use 600 grit, but even using 320, it's taking an hour or so to make any progress of leveling things out. The 220 is certainly faster but even still I feel like I'm doing something wrong because it just shouldn't take this many repetitions to get a level surface.

My common sense tells me the poly should level itself because it's a liquid. I've tried using straight poly and mixing it with mineral spirits to make it less viscous and flow better but it just isn't creating a perfectly level surface.

I feel like spraying wouldn't accelerate the process because it's just going to put a nice coat on all of hills/valleys. The unevenness isn't brush strokes that are left in the wood or drips and stuff, it's the actual contour of the wood it seems. I could be wrong because I'm new at this, but my gut tells me brushing/spraying wouldn't make a difference here.
 

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The problem leveling a finish with poly is it is so hard there is not much material coming off for all the elbow grease you are putting into it. When you do that kind of finish it's best to do that kind of leveling with the sealer. It is a softer material better suited for sanding. I normally stick with sealer until it would make a fine looking finish before I start with the topcoat. Filling oak grain with the finish is especially difficult but since you are already into the polyurethane you either have to continue or strip it off and start over. I would keep going. Another option is if you are sure there is a good amount of finish on you can use a orbital sander with 220 grit paper between coats for leveling. It's risky though and don't stay at it too long. You just have to build up the finish and sand most of it off until you get it level. Spraying the finish would make life a lot easier but they were making furniture with the mirror finish before the civil war so there is no reason you can't do it. You just have to build up enough finish you can hand rub the brush marks off when you are done. The brush you use can make a big difference too. Use as soft of a brush as you can find and apply the poly as thin as you can with as little strokes as possible. The more you brush it the more the brush marks show.
 

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Rick Mosher
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I spray polyester on one side on Monday, the other side on Tuesday (same day if I'm in a hurry), flat sand and top coat with 2K Polyurethane on Wednesday let it cure for a couple days (probably over the weekend if there is time) Then wet sand and buff out on Monday.

It is VERY time consuming to do this finish with oil based coatings. If I HAD to I would start with this finish schedule. You don't say but I believe in the original post the wood was oak? That is the most difficult wood to pick to fill the grain with.

1. Stain
2. Seal with 1 lb cut of De-Waxed Shellac
3. Oil Based Paste filler tinted to whatever color you want the pores of the wood to be. Push into grain and when the filler turns dull take off as much as possible with a squeegee. (I like Sherwin Williams paste filler D70T1 If you follow the directions it will be dry in 4 hours, wait until the next day anyway and fill it again if you are using Oak.
4. After another day seal the filler with the same shellac mix
5. When dry scuff sand with 320 grit Tri-Mite FreCut sandpaper
6. Apply your first coat of clear finish (Poly, Varnish, etc) Use ONLY gloss for your build coats I would use a foam roller to apply and tip off with a foam brush if you can't spray, let dry 24 hours between coats and sand with the 320 between each coat dry (If it doesn't powder up, let it dry longer.) You only need to wet sand your final coat if you are polishing or rubbing out the finish. If you wet sand too fine between coats of finish it may not adhere.

Do a sample and see what you think. :thumbsup:
 

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bzguy
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I've used 2 part catalytic urethane that dries quicker than laquer.
This makes what you're trying to do 100 times easier.
It has kind of a "surface tension?" that flattens out quickly, fills small voids, freezes runs in their tracks, etc.
 

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Discussion Starter #8 (Edited)
Well the general consensus at this point is to keep sanding/coating with poly for this part of the project.

The rest of the cabinet has two coats of Zinsser Sealcoat on it to seal the wood so I can change my method on the rest.

So Steve Neul's thought was to keep adding the sealcoat and sand between coats to level that out and then add the poly for the top coat after it's level. This seems a much better way to go since you only have to wait an hour before you can sand and recoat. Should I continue to use sealcoat or should I just cut my own shellac? If so, how many pounds?

Rick Mosher:
So it seems that you have a similar process of using the shellac to seal everything mostly, use a wood grain filler, then put another coat of shellac on. At this point it should be somewhat level so then you start the whole process of applying the poly then waiting a day, sand/recoat, wait a day, etc. Is the shellac the same as the sealcoat? Do you have to use the grain filler if you just use additional coats of the shellac to seal it?

bzguy:
I tried googling two part catalytic urethane and didn't come up with anything on google. Do you have a specific brand or any additional information you can post so I can do some research into it?
 

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Yes, the rest of the cabinet I would level the surface with shellac but you need to watch and not build a really thick layer of shellac in the process. Most of it is sanded off in the process. The extra shellac is to fill the grain.
 

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Discussion Starter #10 (Edited)
Yes, the rest of the cabinet I would level the surface with shellac but you need to watch and not build a really thick layer of shellac in the process. Most of it is sanded off in the process. The extra shellac is to fill the grain.
Just so I can learn, why do you say to watch to not build a really thick layer of shellac in the process? Are there any issues that can arise?

Also, since shellac is softer than polyurethane, will using shellac underneath the poly cause any issues? Or since it's only filling the pores to make a level surface, it won't make much of an issue?

What grit sandpaper do you recommend between coats of shellac to level? I am just so nervous to go through and ruin the stain underneath. For some reason everytime I sand, even though I don't think I'm going through, over time the color of the stain lightens significantly. Is this because I am breaking through and starting to wear down the stain? It's getting pretty frustrating working on the project trying to get the surface level and I sanded through just a little too much this morning and now the color lightened significantly in one spot so the whole project is now amateur looking since the stain (which already wasn't even) now looks a lot lighter in one area.
 

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Just so I can learn, why do you say to watch to not build a really thick layer of shellac in the process? Are there any issues that can arise?

Also, since shellac is softer than polyurethane, will using shellac underneath the poly cause any issues? Or since it's only filling the pores to make a level surface, it won't make much of an issue?

What grit sandpaper do you recommend between coats of shellac to level? I am just so nervous to go through and ruin the stain underneath. For some reason everytime I sand, even though I don't think I'm going through, over time the color of the stain lightens significantly. Is this because I am breaking through and starting to wear down the stain?
The entire finish won't completely dry for months after you get done and since the shellac is softer it will shrink at a different rate than the poly and has the potential of making the poly crack. Anyway the finish you end up with is the poly and if you put a thick coat of shellac on and a thin coat of poly your final finish won't have the hardness it should and will tend to scratch and mar more than it otherwise. Yes it's a scarry thing trying to fill the grain with any sealer. That is why it would have been best to use grain filler. The next time you won't skip that step. I've refinished table tops where the grain filler didn't do it's job and made the decision to fill the grain with sealer only to sand through to the wood after a couple of days work. It just happens. All you can do is try. Sometimes a job goes awry and you end up having to start over. Sometimes though if you watch when you sand between coats you see yourself cutting into the stain and stop. You can also watch the color of the dust. If it is white then you are sanding sealer. When the dust changes color you are likely into the stain. If the sand through is minor you can touch up the color and move on. It's when you use an electric sander with between the coats sanding it gets especially risky. You can take off too much too fast.
When sanding sealer I sand with 220 grit paper. When sanding the poly between coats I change to a finer paper. Sometimes you can see the scratches from 220 grit paper in polyurethane
 

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Discussion Starter #12
The entire finish won't completely dry for months after you get done and since the shellac is softer it will shrink at a different rate than the poly and has the potential of making the poly crack. Anyway the finish you end up with is the poly and if you put a thick coat of shellac on and a thin coat of poly your final finish won't have the hardness it should and will tend to scratch and mar more than it otherwise. Yes it's a scarry thing trying to fill the grain with any sealer. That is why it would have been best to use grain filler. The next time you won't skip that step. I've refinished table tops where the grain filler didn't do it's job and made the decision to fill the grain with sealer only to sand through to the wood after a couple of days work. It just happens. All you can do is try. Sometimes a job goes awry and you end up having to start over. Sometimes though if you watch when you sand between coats you see yourself cutting into the stain and stop. You can also watch the color of the dust. If it is white then you are sanding sealer. When the dust changes color you are likely into the stain. If the sand through is minor you can touch up the color and move on. It's when you use an electric sander with between the coats sanding it gets especially risky. You can take off too much too fast.
When sanding sealer I sand with 220 grit paper. When sanding the poly between coats I change to a finer paper. Sometimes you can see the scratches from 220 grit paper in polyurethane
So in future should I use grain filler before or after staining? After a bunch of research and charles neil's recommendation, I think I'll use aquacoat grain filler:
http://aquacoat.com/collections/frontpage/products/clear-grain-filler

So is wood naturally level except for the grain? So grain filler essentially does most of the levelling and you use the shellac/sealcoat to do the last of the levelling. Then you use your polyurethane to build a hard finish that you can rub out and buff to get your mirror finish?

Thanks for all your help, this is definitely a learning process.

Also, is it worth it to buy shellac flakes and cut my own or just continue to use the sealcoat?
 

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So in future should I use grain filler before or after staining? After a bunch of research and charles neil's recommendation, I think I'll use aquacoat grain filler:
http://aquacoat.com/collections/frontpage/products/clear-grain-filler

So is wood naturally level except for the grain? So grain filler essentially does most of the levelling and you use the shellac/sealcoat to do the last of the levelling. Then you use your polyurethane to build a hard finish that you can rub out and buff to get your mirror finish?

Thanks for all your help, this is definitely a learning process.

Also, is it worth it to buy shellac flakes and cut my own or just continue to use the sealcoat?
The wood should be pretty level except for the grain. If you are having the wood uneven there is something going wrong with the sanding of the wood. I normally use a random orbital sander to sand the wood. It tends to sand the wood flat since the pad is more ridgid. Some folks use a finish sander that has a soft felt pad. These type sander do little to sand the wood flat.

If you were to look at wood through a microscope it would look like a cluster of drinking straws glued together. Picture this and slice the straws off at a angle. There would be a bunch of open crevaces where it was cut. This is the grain showing on oak. Then if you put a finish over it some of the finish would go into the straws but it would take a bunch of coats to fill them completely. Then grain filler is like a thin wood putty you can paint on. It's much thicker than a finish and would fill the straws. You would rub the excess across the grain and let dry. Then what little void is left the finish can easily fill and level.

Not every wood needs grain filler. Most of the time oak isn't finished with a mirror finish and the grain is allowed to show. The mirror finish is usually held for more formal woods like walnut and mahogany. Both of these woods would need grain filler for this type of finish. Then there is woods like maple or alder that have a tight grain you could put a mirror finish on completely without the grain filler.

I've never used the aquacoat so I couldn't advise on that product. I really have only used one grain filler. I started using a oil based grain filler made by Star Finishing Products. Some years ago Mohawk Finishing Products bought out Star and I started using theirs. It worked so I stayed with it. I apply it first to the raw wood rubbing or squeegeeing it out and let it dry overnight. Then I lightly sand what residue is left on the surface. Then I apply the stain and finish. On the filler I use you have to let the first few coats of finish dry really well because it can cause the grain filler to swell out of the grain. If you sand it too soon when it dries it shrinks below the surface of the wood and makes the wood grainy again and you end up having to fill the grain again with sealer.

As far as sealers I use different types of sealers depending on the finish I'm using. There are sanding sealers and Sealcoat which works fine for poly. If I finish with lacquer I normally use a lacquer sanding sealer and if using a pre-catalyzed lacquer I use a vinyl sealer. There are too many different finishes to list them all but each has a approiate sealer that works best for that finish.

You are correct that once you have enough poly on that the only problem is the brush marks it can be rubbed out and polished. That is assuming the brush marks are minor. In the long run you would be much happier if you got the means of spraying the finish. It would get you there much faster than brushing. Not only are you fighting having to fill the grain you have the brush marks to contend with creating more sanding between coats then if it was sprayed.
 

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Discussion Starter #14
So I went out and sanded with 320x just to be really careful of not ruining the stain further and took some pictures of what it looks like:




First off, you can see where the stain looks really weird (almost whitish compared to the rest) and this happened as a result of sanding. It doesn't appear that I've gone through the poly, but it has definitely lightened the stain in parts. Is this normal? Does this mean I've gone all the way through the poly? It blows my mind to think that I have since this thing has 15+ coats on it.

The concept I'm going with here is that where it's white it's sanded and where it's still the dark semi-gloss, is where it's lower than the surface (not level). The process has been sanding the whole surface until it has that "uniform scratch pattern" across the whole surface.

I figured after reading all the helpful posts that the low parts would pretty much be the grain but it seems about 60% of the time to be the grain, the rest of it is other random patches. Is there something else that I'm doing wrong? It just seems like a never ending process of poly/sanding to get the whole surface level.

I'm about to say screw it and throw a coat on and be done since I'm 5 months into finishing this thing and I want to be done.
 

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Old School
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The wood underneath is 3/4" plywood with a red oak veneer. Is this wood naturally really uneven?
If your Oak ply is from the box store it's likely rotary cut faces. It's a wide variegated type grain that's very uneven. It isn't easy to get a glass like finish. If you're using a stain/dye, you could get the color first. I don't sand that. You could use a tinted grain filler, and apply that as directed.

If you use an oil base stain, I would use the grain filler first. The oil stain could seal some of the grain where the filler may not adhere too well. When that is done and ready to sand, use a block sander. It may take more than one application.

If you use an NGR (non grain raising) stain/dye (alcohol based) you could apply first. It doesn't seal the grain. When the surface is ready for a finish, You could use a vinyl sealer and a CAB lacquer. Or, you could use a waterbase polyurethane as a topcoat and sealer. I wouldn't sand the first application or two. It will take several to get enough build, to wet sand and polish. After the second or third spray application of topcoat, sand with a block sander with 320x. Sand with the grain.

I wouldn't use shellac as a sealer. IMO it's too soft of a finish, to topcoat with a film finish like lacquer or WB poly.





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bzguy
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I used Polyform 5000, it's a Mexican product probably not available in the US.
I assumed that they would have a counterpart there.
 

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Don't concern yourself with the white. You are correct it is from the sanding and is normal. The darker spots is low spots not sanded. For what you are doing it would have been great if it was 100% white however it may not be necessary to get it all level. It's just the tiniest fraction of a inch difference and is hard to see once rubbed out. What is more disturbing is the dark scratches. It appears to be in the wood rather than the finish. These marks would show in the finish and are more important to level than the grain. It just means more finish and more sanding.
 

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Discussion Starter #18
Well thanks everyone for all the helpful comments and posts, I truly appreciate it and I learned a lot for what to do next time to get the desired result.

I've learned that I need to use grain filler to level the surface and fill the pores instead of using tons of coats of polyurethane to fix it.

I've also learned that the red oak veneered plywood from home depot isn't the best to try and get a mirror finish with.

Is it mostly due to it being a veneer, or because it's oak which is very porous?

But at this point, since the surface is about 85% level and the stain has already been messed up in places the care-level has plumeted, so I'm just going to finish the rest of the project with a few coats of poly to get it mostly level, then wet sand it since it's close enough to level. It won't have the same level of mirror finish, but in a year or so I'll reattempt this project and I'll use different woods/methods for that.

What wood would be recommended to use for this? Mirror finishes are typically achieved on what kinds of wood?
 

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Plywood in recent years has gotten pretty crummy regardless of where you buy it. You may experience the same problems anyway. Probably the reason it has become acceptable to show the grain on oak is that it is labor intensive to level the finish. Oak also has large patches of open grain where some other grainy woods like walnut and mahogany don't. Even though grainy it is easier to fill and level. Another wood to avoid is ash. It often is more grainy than oak. There are many different kinds of wood you could use that would not need the grain filler. Some common ones would be pine, alder, maple,cherry, birch and poplar.
 

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Old School
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I've also learned that the red oak veneered plywood from home depot isn't the best to try and get a mirror finish with.

Is it mostly due to it being a veneer, or because it's oak which is very porous?
Hardwood plywood can be made with different faces (front and back). It doesn't matter much what the core is made of (layers of plies between the faces). There are different ways of cutting the veneer that makes up the faces. IOW, how the log is sliced up.

The Red Oak plywood at HD has rotary cut faces. It's the most efficient and cost effective method. It's one where the log is pinned at the ends (like in a big lathe), and a long knife peels a thin layer of wood while the log rotates. So, the veneer comes off in a long continuous sheet. That method produces a wild type grain, which is difficult to fill and level out.

Red Oak plywood can be bought with plain sliced type faces, which to keep the explanation simple, is where the log is cut along it's length in segments. The veneer from this kind of cut is very uniform and tight. It looks like a piece of Red Oak lumber with all long grain. Since the pieces taken this way aren't usually wide enough to cover a 4'x8' sheet, longitudinal sections called "flitches" of veneer are applied to the sheet, which will appear as a very thin line where they join from one end to another. There could be several flitches across the sheet.

This type of face takes filler well, and flattens out without much trouble. When filled, sealed and topcoated, with the sanding regimen to ultimately polish it out to a high gloss, makes for a very slick glossy finish.

If you have good finishing skills, and use a filler, and a sealer, and do in between application sanding, your topcoat could be applied that may not need the build up and wet sanding and polishing. A finish like that I call "off the gun", and done well looks very nice. It has a very smooth finish, and retains the look and feel of wood, but without the clear plastic appearance of a rubbed out finish.

There are many species of decorative hardwood plywood that have a tight smooth grain, that take finishing very well. Mainstays for cabinets can be Red Oak, White Oak, Maple, Birch, Mahogany, Walnut, Cherry, and Ash to name a few. The HPVA (Hardwood Plywood and Veneer Association) grading for the faces of decorative plywood is an alpha character (A-C) for the front face, and a number for the back face (1-4). IOW if you want a first rate quality sheet of hardwood plywood, the grading for that sheet would be A-1.






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