Step 4: Staining and Finishing
Now, you've finished the edges of your shelves, and you're happy with your results.
However, you're not done sanding yet. MDF needs to be roughed up a little so it will take the stain well. See Fig. 1.
Pull out your sanding block yet again, and sand the entire shelf - top, bottom, edges, corners. I started with 180 grit, and then use 220 to get a finer finish. You don't need to kill yourself sanding, just get a nice surface before you stain. The stain is quite forgiving.
Once you've finished sanding and gotten most of the sanding dust off (you WERE wearing your dust mask, right?), get some mineral spirits, some lint-free rags, and your nitrile gloves.
Wet the rag with the mineral spirits and wipe them down. Get all the dirt, crud, etc. off the shelves. You want them as clean as possible. See Fig. 2.
If you want to test your skills, get some of that scrap MDF from Step 2, and follow the staining process below. It's actually quite easy to do, but practicing will let you screw up before you go on to staining the shelves themselves. See Fig. 3.
Now, on to the stain! MDF does not stain like regular wood does. Normal liquid stain will soak in and give you a strange finish.
I used Minwax Gel Stain in Brazilian Rosewood, and a cheap 4" chip brush. The trick to this is simple. If you've ever stained anything, forget about what you did then. The best way I can explain it is to treat the stain like paint.
Use long strokes, but do it unevenly. Lay the stain on thick in some areas, thin in others - you want to approximate real wood as much as possible, which means: be uneven! See Fig. 4 for a general idea of what you will get as you stain.
I did the shelf tops and edges first. Since the 1.5" holes for the cables are not finished, I just took a small brush and smeared them with stain to they'd have coloration similar to the rest of the shelf. Now let the tops dry.
One important note: this will take time to dry. A long time. I'm in a tropical climate, with average temperature of about 80 degrees, and I let the tops of the shelves dry for at least a day. See Fig. 5.
Next, I repeated the same process for the bottom of the shelves. If you ding or scrape some stain off, don't worry. Touch-ups are very easy with a small brush.
One good trick is to use one of your all-thread rods as a hanger to let the stain dry without anything touching the stained parts.
I have to repeat: let the shelves dry for at least a full day. This will get you the best results in order to put on the polyurethane finish.
Now it's on to spraying the polyurethane. I used spray cans of Minwax Fast Drying Polyurethane in Clear Satin.
The biggest problem with the polyurethane is dust and dirt getting into the finish as it dries. I solved my problem by converting one of my bathrooms into a spray booth. If you have a significant other or roommate, don't do this without getting consent first!
"Spray Booth" Prep:
I lined my bathroom and the tub with plastic drop sheets. They're cheap, and indispensable, unless you want to get polyurethane everywhere. Tape them up, cover everything, and you're good to go. Oh, and get yourself a respirator. You don't want to breathe in polyurethane fumes. They can kill you.
Use a couple of your all thread rods as hangers - I hooked them on to the shower curtain rod (which is screwed into the wall) and to the window. Check out Fig. 6. Follow the directions on the can regarding spraying. You don't want to lay on too thick a coat, or it will run.
Spray on 2-3 coats, depending on your preference. The fast-drying polyurethane requires no sanding between coats, and I didn't do it. Let the shelves dry for at least a day, or you might get some ugly fingerprints on them.