Tips for pairing the right tooling and mud mixtures

Updated August 22, 2023

If you’ve heard it once, you’ve heard it a thousand times — tooling and mud mixture should be adjusted for the ground conditions you’re working in. Often, that’s where the advice stops, though. That’s because it seems impossible to develop a guide that outlines all possible combinations with so many different types of soil conditions, tooling options and drilling fluid additives. But, by following a few tips for pairing the right tooling and mud mixtures to soil conditions, it is possible to dial in your drilling operations for more efficient horizontal directional drilling (HDD) performance.

An excellent place to start is to look at the broad categories of soil conditions, tooling characteristics and the mud mixtures that perform well in them. From there, you can make adjustments based on the unique challenges of the project your crew is working on. 


Conditions: Sand, sandy loam or any soil where sand is a major component can be a punishing soil makeup, as sand is abrasive and can be hard on tooling. But choosing the right combination of bits and fluid can help you maximize the life of your tooling. 

Drill bit characteristics: When drilling exclusively in sand, you should consider a drill bit with a broad front profile to enhance steerability. As a layer of sand is often followed by more difficult material (coral), some contractors prefer a balanced, semi-tapered bit shape.

Vermeer bit options to consider: 

Drilling fluid mixture: In sandy soils, maintaining the bore path integrity and cooling tooling are two important factors to consider when choosing the drilling fluid additives. 

Additive to consider: 

  • Bentonite as the primary filtration control (filter cake)
  • PAC polymer for secondary filtration control 
  • A large molecular weight polymer to act as a suspension aid  


Conditions: There is a wide range of clay and loam soil conditions — from soft to medium compaction levels. Also, not all clays react the same way to added moisture, so choosing the right drilling fluid mix is important.

Drill bit characteristics: In softer conditions like clay and loam, selecting a bit with a broad front profile will optimize steerability. Adding features like hardfacing and carbide buttons will help protect the bit as more difficult material is encountered. 

Vermeer bit options to consider: 

  • Maximized wear life
    • Ace™ Standard bit
    • Gladiator Mallet bit
    • Gladiator Club bit
  • Standard wear life
    • Standard hardfaced bit

Drilling fluid mixture: Without the proper tooling and drilling fluid combination, some clays will ball up around the drill bit or reamer instead of flush cleanly from the hole. The first step to determining which additives you need for clay is to decide if the clay is reactive (swells when moisture is added) or nonreactive (doesn’t expand with extra moisture).  

Reactive clay additives to consider: 

  • Bentonite for primary filtration control (optional for small drills but mandatory for mid to maxi rig jobs that require fluid reclamation)
  • PHPA polymer to help prevent clay swelling 
  • Thinner to regulate if you’re running a higher excessive drilling fluid viscosity or thickness
  • Soap/detergent to keep your tooling clean

Non-reactive clay additives to consider:

  • Bentonite for primary filtration control
  • Soap/detergent to keep your tooling clean

Cobble/broken formation

Conditions: Cobble, gravel, glacial till, chunk rock and any non-consistent type of rock requires more of a scooping action to push material out of the way. With this chunkier material, you will also need a higher-viscosity mud mixture to help suspend and flush the heavier material from the drill path.   

Drill bit characteristics: By selecting an aggressively tapered bit, you can needle through cobble sections or break up larger chunks to complete the pilot bore efficiently. For extreme cobble or cemented cobble ground conditions, you should utilize a more robust bit with a tapered design and increased carbide coverage to help improve penetration rates, as well as overall bit wear.

Vermeer bit options to consider:

Drilling fluid mixture: You will want your mud to be mixed thick enough to efficiently carry shavings from the bore path. Thick drilling fluid will also help suspend chunky material and help maintain the integrity of the bore path. 

Additives to consider:

  • Bentonite for primary filtration control
  • Large molecular weight polymer as a suspension aid
  • A loss-of-circulation material (LCM) to disperse within the base fluid, creating a lattice network of fibers across broken formation zones to keep bore walls intact without excessive fluid loss


Conditions: Rock is typically categorized by its pounds per square inch. Soft rocks fall below a 4,500 psi (31 MPa) threshold and include sandstone, shale, soft limestone, caliche and some coral. Medium rock ranges from 5,000 psi to 9,500 psi (34.5 MPa to 65.5 MPa) and includes some limestone, shale and coral. Everything above that falls into the hard rock category, which includes hard limestone, granite and skirt.   

Drill bit characteristics:

The Armor and Ultra X3 drill systems are both designed to be versatile options for a variety of ground conditions, but especially soft to medium rock, cobble and hard-packed soil. Utilizing bits from either of these lineups can be key when working in abrasive ground conditions as they can be rebuilt multiple times. Depending on the wear, the bits can be rebuilt and ready for your next jobsite — it’s as simple as sending in your worn-down bits back to Vermeer to be analyzed by drilling experts. There is a massive range of HDD drill bits designed to work in rocky grounds, making selecting the right one for the conditions a topic unto itself. Learn more about choosing the right bit for drilling in rock.

Vermeer bit options to consider:

Drilling fluid mixture: The drilling fluid you should use in rock will depend on the tooling and drill setup you choose. You want to go with a mix that is thick enough to float cutting from the drill path while providing adequate cooling and lubrication to the drill bit. 

Additives to consider: 

  • Bentonite for primary filtration control
  • Large molecular weight polymer as a suspension aid if needed

There are many tooling and drilling fluid additives on the market you can consider for your next challenging job. With this quick overview of the different drill bit and drilling fluid combinations based on the soil conditions, you can now make more informed choices — starting on your next project.

The team at your local Vermeer dealership is up to speed on all those details. Give them a call for additional help or visit to learn more about Vermeer HDD tooling options

Vermeer Corporation reserves the right to make changes in engineering, design and specifications; add improvements; or discontinue manufacturing at any time without notice or obligation.

Equipment shown is for illustrative purposes only and may display optional accessories or components specific to their global region. Please contact your local Vermeer dealer for more information on machine specifications. Vermeer, the Vermeer logo and Ace are trademarks of Vermeer Manufacturing Company in the U.S. and/or other countries.

© 2023 Vermeer Corporation. All Rights Reserved.

A yellow Vermeer horizontal directional drill tooling piece.


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