How to Use a Drywall Flat Box on Walls

Need some tips for running your flat box on walls? Look no further. Read on or watch the video below and you'll be running your flat box like a pro in no time.

How to Fill and Carry Your Drywall Flat Box

When pumping a drywall flat box, make sure to move it side to side to ensure you get a nice even fill. This will help with mud distribution as you're running your box along the surface. When carrying your flat box, make sure to carry it right under the head of the box itself where the handle meets the flat box. You don't want to carry it by the brake because it's really top-heavy which creates unnecessary wear and tear on the break's mechanisms.

If you're familiar with Drywall Nation you'll have noticed they use Butt Boards on all their jobs. That's why their butt joints aren't staggered; they use recessed floating joints to help with structural integrity.

Drywall Nation showing how to carry red LEVEL5 drywall flat box and short extension handle.

Running a Flat Box on Vertical Wall Joints

When finishing vertical seams, it's generally best to begin by running your flat box from the bottom-up. It's easier to pull your box off when coming from the top-down. This will leave a nice, small lap mark that's easily smoothed out and concealed.

Often you will notice small bubbles and indentations after your first flat box run. This is why it's always advised to run your flat box twice over all seams (usually referred to as "chasing" or "tracing"). Running your finishing box a second time along the seam should eliminate most of those imperfections and leave a nice, smooth finish.

When running your box top to bottom, a little trick when using LEVEL5 drywall flat boxes is to align the nut seen in the center of the box with the seam; this will help ensure your box is centered along the tape that you're coating.

Drywall nation showing how to use a drywall flat box on vertical wall joints.

Running a Flat Box on Horizontal Wall Joints

Begin at the butt joint and run your drywall flat box along the wall. Finish off the seam and then go over it again to remove imperfections left in the mud from your first run. Pull your brake and lift your box off to leave a lap mark right against and into the butt joint.

Remember to apply your flat box break right before you pull the box off the wall for the best results (ideally when you reach a butt joint, corner or window). Ending your run in the middle of a wall will often result in an unnecessary lap mark which means more work later.

Drywall Nation showing how to use a drywall flat box on horizontal wall joints.

How to Run a Flat Box Over Unfinished Wall Plugs

When working around plugs, make sure not to run right through/over a plug with your flat box - it doesn't look good and, more importantly, it's inconsiderate for the electrician. Instead, start on either edge of plug and run your flat box in either direction, using the plug as your starting point. Then, run your box again from the opposite direction towards the plug, apply your break right as you get to the plug and lift your flat box off. The goal is to leave a lap mark right in the middle of the plug hole (but not to cover or get mud into the plug itself!).

Drywall Nation showing how to use a drywall flat box when finishing wall plugs.

Pro Tip: Keep Your Drywall Flat Box Blade Clean

If you've been using your flat box for a while, it's not uncommon for small pieces of paper or debris to get caught in the blades. If not removed, you'll start to notice grooves, lines or imperfections in your joint compound. This is even more of a problem once the compound on your box starts to dry up.

To keep things clean, you can periodically use a sponge or a cheap brush to remove pieces of debris from your drywall flat box blades. A cheap dollar store brush will do the trick. Don't forget to also give the sides of your box a quick brush to remove any dried up pieces of mud.

Drywall Nation showing how to keep a drywall flat box clean when finishing wall joints.

Final Thoughts

  • As you get more practice with your flat box, you'll be able to finish your seams faster and faster. It takes a bit of time to get up to speed but once you do you'll never look back!
  • Remember to periodically check your flat box blades and sides for bits of debris and dried mud. Use a sponge or brush to remove these pieces.
  • You're most likely to pick up small pieces of debris around windows, plugs and other receptacles so keep an eye out for those.
  • When coating walls, typically a short flat box handle is best; you don't need a long handle unless you're using your flat box to finish ceilings.
  • Experiment with your box's settings to achieve the exact results you want. Everybody has a slightly different technique or approach.
  • To use a drywall flat box, it's highly recommended to also have a drywall mud pump.
  • LEVEL5 offers a wide selection of drywall taping tools for every possible finishing job.