The Ultimate Guide to Using a Drywall Flat Finishing Box

The Ultimate Guide to Flat Boxes

Drywall has been around for over 100 years, and today we are looking at one of the profound mudding and taping tools that changed drywall taping tools for the better. Out of all the automatic mud and tape tools, finishing flat boxes are the most popular. In this ultimate guide to using drywall flat finishing boxes, here is what we’ll discuss.

  1. What a flat finishing box is
  2. Prepping your drywall flat box
  3. Using a flat finishing box on walls
  4. Using a flat finishing box on ceilings
  5. Answer frequently asked questions

What is a drywall flat finishing box?

This drywall mudding machine is used to cover drywall tape applied in the first level of drywall finishing. Drywall finishing boxes are most commonly used during the third, fourth, and fifth levels of drywall. Before we start applying our coats of mud we will examine how to prep your drywall box.

Prepping your drywall flat box

The first thing you will want to do before filling the flat box is to make sure the box itself is clean. Make sure your drywall box does not have caked-on mud from previous jobs. Ensuring your box is fully cleaned before ending your current job will ensure a faster start-up process for the next job. Make sure that the trowel bar is flexible. The flexibility gives your wall or ceiling joint an even crown. When you adjust your flat box blade, you want to make sure that you have at least a fingernail width of the blade. If you need to adjust the blade, you can use a screwdriver to lower or raise the blade.

How to fill a drywall flat box

After you are done mixing your drywall mud, submerge your pump into the bucket of mud. Prime the pump by pumping it a few times until nothing but the drywall compound comes out. This eliminates any kind of air or debris that may be caught in the pump. 

Once your pump is ready, insert the nozzle attached to your pump into your flat box. As you pump the compound into the mud box, move the box side to side to ensure an even fill. Fill your flat box until it is completely full. Once you fill the drywall flat box, attach your handle to the box. Now you are ready to start running your drywall flat box.

How to use a drywall finishing box on a wall

Using a drywall flat finishing box along butt joints

First, we will go over verticals then move on to horizontals. Place your box on the wall starting from the bottom and stop partway through. Next, start at the top and lap over the bottom run. Ideally, you will want to have your lap marks run into butt joint intersections. Sometimes the first run will create bubbles and pits in the mud. You will want to go over the mud again to cover any imperfections in the first run.

Using a drywall finishing box along windows

When using a drywall finishing box near a window, you will want to start the run from the wall and move towards the window. You will want to pull your brake on the handle as you get to the edge of the window and pull off. This technique does not leave lap marks.

Using a drywall finishing box around wall boxes.

Boxes such as electrical boxes can be tricky to work around as you have to take into consideration not mudding the entire length of the wall. Start from the opposite end of the receptacle and as you get closer to the receptacle, brake and lift off. Make sure you do not get any mud into the receptacle. Finish the rest of the area around the box with a taping knife.

Cleaning your flat box between laps

As you use your flat finishing box, you may notice that the mud will start to harden. This is why you will want to use a sponge or brush to clean off the mud every few joints you tape. Sometimes you may also notice that your mud box will catch paper or other imperfections under the blade. In this case, use your finger to wipe it clean.

How to use a drywall finishing box on a ceiling

Start from the edge of the wall and run it straight across. To avoid lap marks, you want to run your lap marks into the closest joint and feather it in, which cuts down on the sanding process in the end.

Frequently asked questions for flat boxes

If you have any questions about flat boxes feel free to contact us and we will answer and questions you may have. 

Should I carry my mud box by the handle?

Ideally, you want to carry the box by the head. Carrying your flat box by the handle can damage the joint between the handle and head since the head is heavier than the rest of the tool.

Is a longer handle better?

A longer handle isn’t always better. However, it depends on how tall your ceilings may be. For rooms with an eight-foot ceiling, a small extendable handle is all you need. You want the handle to be shorter when you run the box along the wall so you can apply more pressure and have more control over the taping box for drywall as you run it. The only time you would want to extend the handle is when you are working ceilings.

What are the advantages of using a bigger mud box?

Using a bigger box is ideal for larger jobs. The box may weigh more when you carry it, but you will hold more mud and require fewer trips to the pump to fill the mud box.

How long will a finishing flat box last?

Level 5 has a 7-year guarantee warranty on their drywall flat boxes.

Are the parts replaceable?

Yes, many parts are replaceable on drywall flat boxes. You can see some of our repair kits here.

How thick should the compound be?

The mud you want to use while running flat mud boxes is all-purpose or lightweight. Using taper’s mud may result in having pinholes as you apply the coat. There are two ways to prepare your mud, both with their own advantages. 

The first method is using thinner mud. Using thinner mud will make the box weigh less but may leave streaks or drag marks for the first few inches. Another negative is that the watered-down mud will cause it to shrink more. The second method, using thick mud, will cause the box to weigh more, but the drywall compound shrinks less.

Can I use a flat box to cover nail spots?

While nothing stops you from using a finishing flat box to cover nail spots, it is highly not recommended. The reason for this is that you’ll be applying too much mud in one spot, which is a waste of your materials. Another issue is that you will be causing problems in the sanding phase of the drywall mudding process. You should use a nail spotter instead.

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