Mixing Drywall Compound for Flat Box Finishing

Author: LEVEL5 Tools

Publish Date: November 15, 2023

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A flat box enables you to smoothly apply drywall compound (“mud”) over taped flat seams on walls and ceilings. To ensure your flat box is functioning correctly, you need to use the correct type of compound and also thin it down with water to an optimal consistency.  This article provides some guidance to get you started.

The Best Types of Mud for Flat Boxes

For most automatic tools, including flat boxes, it is best to avoid setting compounds or “hot muds” such as Durabond, SheetRock, EZ Sand, and LiteSand.  Why? These products use chemicals that react and provide a set drying time, such as 20 minutes, 60 minutes, 90 minutes, etc.  If you don’t clean the tool before the mud starts to set, cleaning can become a nightmare. 

Our recommendation is that you use standard general purpose or lightweight general purpose mud for outstanding results and easy cleanup.  Yes, this means there is more drying time versus a hot mud, but the auto tools increase your efficiency so much that it more than compensates for this downtime. 

Advice from the Pros

Watch this video from Drywall Nation where Brian Kitchen explains the pros and cons of varying levels of mud consistency.

Mud Consistency for Best Results

Fortunately, you won’t be breaking any rules when it comes to mud consistency, as this part is mainly a matter of personal preference.  As a general suggestion, add your box of mud to a 5 gallon bucket with about 28oz to 30oz of water to start.  Then, mix the mud thoroughly (for incredibly smooth consistency with the least amount of effort, we recommend you use the patented LEVEL5 mud mixer #5-292).  You can then continue to add water to your mix using a sponge until it reaches your preferred consistency.

Also, here are some considerations regarding thinner versus thicker consistencies:

Thinner Mud Consistency

Thinner mud means lighter mud that flows easily through the tool. This is especially advantageous for finishing flat seams on ceilings with minimal exertion.  On the flip side, thinner mud can lead to the “Christmas Tree” effect, where  the mud tends to create drag marks at the beginning of each run, especially when working on ceilings. This effect is produced when the mud rolls over the flat box trowel bar the moment you apply pressure.  Thinner mud also shrinks more during drying.

When do you know that your mud is too thin?  The crown of the mud should feather out nicely towards the edges of the flat box blade.  If your mud is too thin, the mud will flow past the edges and create a pronounced ridge during the pass.   If you are doing ceilings, it will also tend to drip on you, which is highly annoying.

Thicker Mud Consistency

When you use thicker mud, you will get a smoother, more predictable finish with your flat box, but you will also notice a weight increase, and you will be required to put more physical effort into getting the mud to dispense from the box evenly.  Many pro finishers will use a slightly thicker mud for walls, because they have more leverage and are able to apply heavier, more consistent pressure to the flat box as they run along the seam.

When do you know your mud is too thick?  To answer this, let’s refer to advice provided by one of our professional finishers.  He often finishes seams on high ceilings with flat boxes on a fully extended, extendable handle.  He says although there is very little leverage to apply pressure to the pressure plate on the flat box, he is able to get great results and stay off the stilts.  His comments are “if you are having to lean into the flat box with your shoulder to get the mud to flow out of the box, think to yourself… could I do this on a fully extended handle on a 10 or 12 foot high ceiling? If not, your mud is too thick and you are over-exerting yourself unnecessarily.

If you can achieve a mix that is thin enough for easy flow and thick enough that it holds its structure, almost like “Greek yogurt”, you should be good to go for your first few passes.  Then, as you operate flat boxes with regularity, you will develop a sixth sense of the mud feel that works best for you in a variety of circumstances.

Learn More

LEVEL5 offers some of the highest quality, most advanced flat boxes available on the market. They are available in a variety of lengths and mud capacities.  You can purchase them from this website or Amazon and eBay.  You can also call us at 800.227.7713 if you have any additional questions about the flat boxes, or you would like to purchase them from one of our friendly sales representatives.

A flat box enables you to smoothly apply drywall compound (“mud”) over taped flat seams on walls and ceilings. To ensure your flat box is functioning correctly, you need to use the correct type of compound and also thin it down with water to an optimal consistency.  This article provides some guidance to get you started.

The Best Types of Mud for Flat Boxes

For most automatic tools, including flat boxes, it is best to avoid setting compounds or “hot muds” such as Durabond, SheetRock, EZ Sand, and LiteSand.  Why? These products use chemicals that react and provide a set drying time, such as 20 minutes, 60 minutes, 90 minutes, etc.  If you don’t clean the tool before the mud starts to set, cleaning can become a nightmare. 

Our recommendation is that you use standard general purpose or lightweight general purpose mud for outstanding results and easy cleanup.  Yes, this means there is more drying time versus a hot mud, but the auto tools increase your efficiency so much that it more than compensates for this downtime. 

Advice from the Pros

Watch this video from Drywall Nation where Brian Kitchen explains the pros and cons of varying levels of mud consistency.

Mud Consistency for Best Results

Fortunately, you won’t be breaking any rules when it comes to mud consistency, as this part is mainly a matter of personal preference.  As a general suggestion, add your box of mud to a 5 gallon bucket with about 28oz to 30oz of water to start.  Then, mix the mud thoroughly (for incredibly smooth consistency with the least amount of effort, we recommend you use the patented LEVEL5 mud mixer #5-292).  You can then continue to add water to your mix using a sponge until it reaches your preferred consistency.

Also, here are some considerations regarding thinner versus thicker consistencies:

Thinner Mud Consistency

Thinner mud means lighter mud that flows easily through the tool. This is especially advantageous for finishing flat seams on ceilings with minimal exertion.  On the flip side, thinner mud can lead to the “Christmas Tree” effect, where  the mud tends to create drag marks at the beginning of each run, especially when working on ceilings. This effect is produced when the mud rolls over the flat box trowel bar the moment you apply pressure.  Thinner mud also shrinks more during drying.

When do you know that your mud is too thin?  The crown of the mud should feather out nicely towards the edges of the flat box blade.  If your mud is too thin, the mud will flow past the edges and create a pronounced ridge during the pass.   If you are doing ceilings, it will also tend to drip on you, which is highly annoying.

Thicker Mud Consistency

When you use thicker mud, you will get a smoother, more predictable finish with your flat box, but you will also notice a weight increase, and you will be required to put more physical effort into getting the mud to dispense from the box evenly.  Many pro finishers will use a slightly thicker mud for walls, because they have more leverage and are able to apply heavier, more consistent pressure to the flat box as they run along the seam.

When do you know your mud is too thick?  To answer this, let’s refer to advice provided by one of our professional finishers.  He often finishes seams on high ceilings with flat boxes on a fully extended, extendable handle.  He says although there is very little leverage to apply pressure to the pressure plate on the flat box, he is able to get great results and stay off the stilts.  His comments are “if you are having to lean into the flat box with your shoulder to get the mud to flow out of the box, think to yourself… could I do this on a fully extended handle on a 10 or 12 foot high ceiling? If not, your mud is too thick and you are over-exerting yourself unnecessarily.

If you can achieve a mix that is thin enough for easy flow and thick enough that it holds its structure, almost like “Greek yogurt”, you should be good to go for your first few passes.  Then, as you operate flat boxes with regularity, you will develop a sixth sense of the mud feel that works best for you in a variety of circumstances.

Learn More

LEVEL5 offers some of the highest quality, most advanced flat boxes available on the market. They are available in a variety of lengths and mud capacities.  You can purchase them from this website or Amazon and eBay.  You can also call us at 800.227.7713 if you have any additional questions about the flat boxes, or you would like to purchase them from one of our friendly sales representatives.

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