Casework - Brush-on Poly Finishing Technique Question

My bookcase construction is done and I've got a coat of stain on it. I'm planning to brush on several coats of Polyurethane. I've heard, and it makes sense to me, that I should only apply brush-on finish to horizontal surfaces. In other words, finish one side, let it dry, turn the piece to the next side, and repeat. That way, I'll avoid runs and the finish will flow flat. That sounds great but what happens where the outside or inside edges meet. I doubt that I can finish the inside sides without getting at least some finish on the back or front (unless I used an artists brush and even then, I'm not that steady). The finish that I get on the other surfaces would create ridges that I would think would be visible and too hard to sand off without sanding through the stain. I'm sure spraying lacquer would be ideal but I like the durability of Poly although I'm not about to buy 100 cans of Poly spray either.
I'd be interested in hearing how any of you finish casework with brush-on Poly. What is your technique? Have you solved this problem?
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Well, for each shelf I would do the back, then the top, the sides and finish with the bottom. Several thin coats are going to flow together well as long as you don't apply it too thick. You shouldn't get runs with light coats. Using a spray bomb in an enclosed bookshelf would be messy. I have use poly for a bookcase however I do remember a not too distant thread where in someone said they were having a problem of having books sticking to the shelves months after application. Might be worth a google of this group. Cheers, JG

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I have never gone to that much trouble and I doubt that you would notice any problems with my finishes. That said, typically the best way to avoid runs is to put on several and very light coats with a rag. Ok, you want to use a brush. Typically the better the brush, the better the results.
Several years ago I started using a brush to apply my finish and in as few as 2 coats. Specifically, I use General Finishes Oil based Arm-R-Seal varnish. I start by wiping on the first coat with a rag followed with a light rub with 0000 steel wool. Final coat with a "Name Brand" FOAM brush. Yeah, a foam brush. The foam rush holds a lot of varnish and lets you complete as much as one to two square feet of area without having to reload. I prefer the brand brushes that are sold singley and made by Wooster or Lisdser. Start at the top and work down. On the sides start at the top of one side and work down completing that side and moving across after that run starting at the top and working down again. As always do a little practice on scrap but I think you will be pleasantly surprised.
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Vertical surfaces should not be a problem if you use a relatively dry brush and THIN the poly. It seems counter intuitive but a thin finish will sag less than a thick one. As far as foam brushes are concerned, they have limited carrying capacity. The best finishes are put on with a roller (of all things) followed by tipping off with a foam brush. Dave
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I had apprehension just before doing the inside of some drawers. In actuality if you don't own spraying equipment you're probably gonna run up to the project and nobodys method wil be better than yours. I used Helmsnman Spar and a newPurdy brush, three coats I think, and it worked fine, for all purposes I would say, all things considered. You're not gonna leave sides out for any sequential pattern. However I went to look a thtem and I now remember a side-effect of something I did or didn't do. I got what looked to be bits of sand or grit, air bubbles, or non-adherance spots, tiny, in the finish. I am sure pretty I would have dipped/saturated the brush in whatever thinner before applying the poly. I now remember looking at the spots with a magnifying glass loupe and they were air bubbles. It was not possible to snad them out to get rid of them completetly. Other than that I saw no runs just now; nothing to prevent me from saying I would do all again. But I cannot tell you why I got the bubbles. I could not brush them out, it probably'd make em worse. I could knock the top off, and some were worse than others. The gal. can was 6 mos old, and had been used from the can before, but I have to say it was air, nothing else. A perfect finish, otherwise. . You may want to research this specific bubble problem to find out the exact procedure and follow it. It may have been the quantity of thinner on the brush, or lack of maybe 1% added to the product. May want to do a test run or two.
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Why not use wipe on poly? No runs, no brush marks. It dries fast - multiple coats in a day.

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I'll second that. I've been using Minwax Wipe-On Poly[1] and it's been wonderful to work with. I've used some of the other stuff, and ran into difficulties ranging from runs, to dust and long dry times. This stuff is easy to work with, and produces a nice finish. And if you're a fan of New Yankee Workshop, this is something Norm seems to use on a number of his projects.
[1]: http://www.minwax.com/products/protective/wipe-on.cfm
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wrote:

I've applied poly to some existing built-ins where applying only to a horizontal surface is impossible- and they turned out fine. I'd suggest disposable foam brushes, and multiple thin coats. When you sand, don't go overboard- 220 or 320 should be coarse enough sandpaper for the application. Usually what I do is start at the top, then work down on the sides, and do the bottom last- keep looking back at what you've finished to make sure it isn't pooling in the corners. If it is, squeeze out your brush a little on the side of the can, and give the area a quick once-over to remove the excess poly.
And remember not to shake the can up, or it'll be full of bubbles.
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klklimes wrote: <snip>

I'll second the recommendation for wipe-on poly. I've never had very good results brushing on poly - probably because of my technique. WIping it on with a rag makes the application very easy - foolproof.
BTW, if you already have regular poly, just thin it down a bit to make a wipe-on poly.
Mike
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Mike wrote:

Make it three.
Remember that you'll need about twice as many coats as with a brush, and you should still knock any dust off with 400 grit before the final coat.
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B A R R Y wrote:

I have not tried this with oil-based poly, but with water-based I've found that using a foam brush works really well.
I do like wipe-on poly a lot also.
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Better still to do that before *every* coat -- and make sure to remove the dust from sanding, too. A microfiber cloth works great as a tack cloth, and can be reused over and over and over -- just rinse and allow to dry, or blow clean with compressed air.
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you can buy a big piece of cheesecloth, and make your own tack rags as you need them, just cut a square and add some drops of poly - thats all they are. Keep it in a ziplock. Whatever you have around - shellac, poly, varnish. you might be able to use an alternative if necc, like a J-cloth, if needed but its probably pretty cheap, and worth a trip. Insurance.
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klklimes wrote:

I just finished up a pair of built-in bookcases; I was planning to use spray-on poly all along but at the last minute I wound up going with Zinser amber shellac, wiped on. Came out very nice, and was easy to apply as long as you work fast and have plenty of lint-free rags. I love that stuff now - looking for excuses to put it on anything. There must be a saying, "once you shellac you'll never go back"...
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What do you consider to be a lint-free rag? An old t-shirt?

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klklimes wrote:

I've just been using the Finish Factor brand bag of wiping cloths from Lowes - claims to be 'all cotton, t-shirt material, lint-free'. They do a decent enough job. A friend of mine always has a roll of real lint-free cloth that he uses to clean his gun barrels - not sure where he gets them, but that's probably the real McCoy - the texture is different, sort of pitted like a cloth paper towel. He's pretty fussy about those firearms, more so than I am about my weekend warrior wood projects.
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klklimes wrote:

Cut it 50% with mineral spirits, wipe on with a rag, keeping the surface wet with finish for 5 - 10 minutes. Wipe off until the surface feels dry to the touch. Scuff with grey Scotchbrite. Repeat for 3 - 4 coats. A dash of linseed or tung oil added to the varnish / thinner mix helps to keep the rag from sticking to partially dried finish.
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