Office build-along, pt. 9

Progress on my office bookshelves has slowed, but not stopped. I'm keeping at it. Part of the problem is the season. Despite the relative lack of winter weather, at the stage I'm in it is often too cold or too wet or too windy to work outdoors, and the staining and varnishing produces too many fumes to safely breath whilst working in the garage. So progress is slow.

That said, today I'm going to talk about a major milestone and genuine headache for woodworkers in general: Polyurethane. When I built my bookshelves at the old house, I didn't use polyurethane. Instead, I applied sanding sealer, which builds up quickly after just a couple coats to form a smooth, shiny surface. The downside to sanding sealer is that it is soft and scratches easily. It's not terribly durable. I didn't know that then--my main concern was getting a polished, smooth finish on my shelves. Polyurethane, on the other hand, is harder, more durable and comes in a wider variety of finishes. I used polyurethane on my workbench for its durable properties, so I thought I should stick with it for the bookshelves.

For the record, I went with a satin finish. I though full gloss coat would look cheap, but I'd put too much effort into this to settle for a dull matte finish. Satin was a comfortable compromise.

The thing is, polyurethane (and spar urethane for outside projects) comes with its own set of challenges. Go online and the most common complaint focuses on bubbles. Tiny bubbles like to form in polyurathane, and if they dry that way, the surface is marred and uneven. Smooth and glassy is what we're going for here, remember? In fact, people are so paranoid about bubbles forming that the can carries a warning not to shake it to mix contents, because that will induce bubble-forming. Well, I'm here to tell you that you shouldn't shake a can of polyurethane to mix it, but not out of fear of bubbles. It separates after sitting a long time into an oily liquid and thicker, resinous goo that will not willingly mix together no matter how much you shake a can. They can only be mixed by stirring, and stirring, and stirring. Shaking, and even stirring, will create largish bubbles, but these aren't stable and pop easily. No, the bubbles that bedevil woodworkers are those that form when actually applying the varnish to the wood. Unlike stain, polyurethane is something of a prima donna when it comes to application and requires a decent-quality brush. Cheap bristle brushes and foam brushes apply it unevenly and are very frustrating to try and use. I know, because I tried. The polyurethane should be applied slowly in long, straight strokes. That show part is key. The slower applied, the fewer tiny bubbles form, but at some point you get diminishing returns. You have to figure what trade-off you're comfortable with. For me, I apply to the entire board/section at a moderate speed. The polyurethane begins curing almost immediately, so usually by the time I've finished the initial coat on a board, it's gone from liquid to tacky. At this point I give it another brush-over with more vigorous back-and-forth strokes, and this seems sufficient to eliminate most remaining bubbles. At least, that's what seems to work for me. Some people can be borderline superstitious with polyurethane, so they might give completely different advice.

Another thing I can't recommend highly enough is to have back lighting. That is, a strong light source opposite you that can reflect off the wet, freshly-varnished surface. If a fixed light's not available, a flashlight will do. That reflection is the most effective means of locating areas that the brush missed. The last thing you want is to spend 20 minutes on a shelf only to discover later that there's a big, bare spot along the left edge. There are always bare spots. The bare spots kill the reflection and show up easily, showing exactly where another few brush strokes are needed.

Another thing I can't stress enough: Less is more. Apply the polyurethane in thin coats. Resist the temptation to glop it on. If memory serves, sanding sealer was very forgiving on this count. Not polyurethane. Thickly applied, it doesn't cure properly and remains soft, which defeats the purpose of using polyurethane. With this, you apply a thin coat, and once it dries, sand lightly with a fine grit sandpaper (I use 400) and then apply another thin coat. The idea is to just remove the surface imperfections, bubbles, etc. with the sanding. You don't want to sand hard enough to remove the coating and get down to the actual wood. Repeat this process until the buildup is sufficiently smooth. To be honest, this is a serious time sink, because polyurethane doesn't contain the filler additives of sanding sealer, and therefore doesn't build up nearly as quickly as sanding sealer. Whereas two coats of sanding sealer was more than enough to give me a smooth, glossy surface on the old bookshelves, the polyurethane demands three or more coats to match that level of finish. It's not a fast process, so that extra work adds up. The temptation to cut corners and say "Good enough" is very strong, and I'll admit I've done so on the undersides of shelves, where one coat is sufficient to seal the wood but not enough to give it that smooth texture. I justify this by saying, "Who looks at the undersides of shelves, anyway?"

Despite all that, the 2"x12" upright shelf supports are all finished. Stained, coated and sanded, ready for installation. So here I'm installing the end board on the far wall. Firstly, I need to use a stud finder to locate where anchor spots may be lurking behind the sheetrock. Fortunately, there are horizontal framing boards near the top of the wall that come down 2.5" below the ceiling.

I mark the bottom edge of the framing boards, just to be on the safe side. Relying on my memory is a good way to make a lot of avoidable mistakes.

Next, I repeat the process for the lower part of the wall.

On the upright shelf support, I mark where the framing boards would be, then mark the spot for a pilot hole about an inch from the edge of the board.

I use a large drill bit--I can't recall the exact size, but it's diameter is slightly larger than the screws I'm using--to make a shallow, pseudo-pocket hole. I say pseudo, because true pocket holes are normally drilled as shallow angles. This one's right at 90 degrees.

Then I take a smaller bit--again, not sure the size but it's slightly smaller than the thread width of my screws--to drill the pilot hold directly in the middle of the pocket hole. Drilling a pilot hole serves two purposes: 1) it eliminates the chance of the wood splitting while drilling in a screw, and 2) it makes the drilling of said screw much easier.

This is what the pocket/pilot combination looks like on the unstained end of the upright, the part that will be covered by the base cabinet.

For comparison's sake, this is what the pocket/pilot looks like on the stained and finished end. Once all is said and done, I'll fill the shallow pocket hole with wood putty and stain it to match the surrounding wood. It should be mostly invisible, if I manage to use the proper stain color.

I set the upright against the wall where it meets the floor, and push it up into position. It's looking more and more likely that I'll end up replacing both the baseboards and crown molding in my office. I'd hoped to avoid that because of the expense, but I'm not seeing any way around it as this project progresses.

Now I drill 3" wood screws through the pilot hole to anchor the upright to the wall. Those are long screws and not super-easy to work with, but necessary when going through 2" of pine and another 1/2" of sheetrock. You've got to find solid wood to anchor the shelf.

The top didn't quite want to fit into position. I'd tested it before, and it was tight then. Storage outside must've caused some swelling in the wood from the absorption of moisture from the air. It's been humid lately. So I pull out one of my newer purchases, a rubber mallet. A few solid whacks and the upright is neatly in place. What's really nice is that the rubber doesn't damage the wood or leave any marks on the finish. I expect I'll be repeating this in the near future.

With the upright firmly in place, I can take the next step and attach the end cabinet. The process is essentially the same--drill pilot holes through both the cabinet and upright, then insert screw. I didn't bother with the pocket holes this time, because a shelf will be covering the hollow where the screws reside.

And there you have it! One end of my built-in bookshelf has taken shape, with more to come!

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