Revisiting Grouting of Water Wells

Published On: December 7, 2020By Categories: Drawing from the Well, Drilling

The columnist looks back on the history of grouting domestic water wells.

By Gary Shawver, MGWC

I wrote a series of columns on the grouting of domestic water wells some years ago.

From those, I continue to get emails and calls from readers of Water Well Journal. Grouting of any kind can generate a lot of interest from water well contractors and regulators, so I feel it is again time to write about the things I am continuing to get questions on. I plan to author several columns on grout this year.

In this one, I will give the background of grouting domestic water wells from my perspective and how I’ve used bentonite-based grouts.

The 1970s

Grouting of domestic water wells was just beginning to make its way into the industry when I began working in the mid-1970s. Much of the early grouting requirements were token and many required only the top 20 feet of the casing be grouted. In many instances this was adequate, especially if the aquifers were overlain by heavier clays. However, in areas where bedrock (and especially fractured limestones) was shallow, this was less than adequate.

Over time, both regulators and contractors saw the necessity of full-length grouting of casing become more and more of a necessity as well as a standard practice in the construction of a new well. Early on, grouts consisted primarily of neat cement grout, which is a slurry of Portland cement mixed to a maximum of 6 gallons of water per 94-pound bag of Portland cement.

Neat cement grout had been used in the construction of public water supply wells for years. In many instances, the placement of the neat cement consisted of dumping it down the outside of the casing, especially if the regulations only required a 20-foot grouting depth. Other early grouts consisted of a high-solids bentonite grout, which in reality was often heavy drilling mud.

As PVC casing entered the market, neat cement grout wasn’t considered an option because the potential heat of curing could cause distortion of the PVC casing. Early PVC casings were not as thick as many of the PVC casings today, so often heavy drilling fluids were utilized as grout.

There was really no specification to that grout other than the generally accepted phrase, “heavy drilling fluid.” The heavy drilling fluid grout was whatever solids were in the contractor’s mud at the time the casing was set. Often this heavy drilling fluid didn’t set sufficiently to form a consistent seal to the casing, and it was not uncommon to have this seal fail regardless if the casing was steel or PVC.

Checking your water pH is just as important in the grouting phase as it is in the drilling phase of mixing bentonite.

The 1990s

As the 1990s rolled around, bentonite producers were introducing sack grouts that contractors could mix on site and tremie along the outside of the annulus to seal the casing. Many of these early grouts continued to evolve as time progressed, as did methods of mixing and placing to make truly high-solids bentonite grouts become the success they are recognized as today.

The use of high-solids bentonite grouts revolutionized the grouting side of water well construction and made it a necessity for all contractors to make it a regular part of their routine construction in the domestic water well market. Regulators also continually pushed for grouting of domestic water wells and contractors followed suit in meeting the challenge.

The introduction of bentonite-based sack grouts also ushered in the era of designing grouters that would help contractors with the mixing and placing of the grout. As time progressed, grouters continued to evolve and today the industry is blessed with an array of grouters that are well designed. Most contractors have one or multiple types of grouters at their company.

The firm I owned and operated for the latter part of the 20th century and the early part of the 21st century used both high-solids bentonite grouts and neat cement grouts and continues to do so to this day.

Lessons Learned

One of the things I learned is that both grouts, high-solids bentonite (20% by weight) and neat cement (a maximum of 6 gallons of water per 94-pound bag of Portland cement), have their place in the domestic water well market.

I’m going to outline where we used each grout and why. Given the amount of space for this column, I’ll focus on the high-solids bentonite. In my next column, I’ll focus on neat cement.

First, I want to outline which type of wells we constructed so you have a better understanding of why we used the different grouts. Most of our wells were finished in either an open bottom limestone or a sandstone formation. About 5% of our wells were sand and gravel wells utilizing a well screen.

We operated in a diverse geological setting. Parts of our area had a heavy glacial clay that typically overlaid a limestone aquifer. This heavy clay area could find limestone as shallow as 60 feet or as deep as 450 feet.

In another part of our area, we often encountered limestone that was shallow to the surface, say less than 40 feet, and the wells were finished in either an underlying limestone or sandstone aquifer. When a well was finished in a sandstone aquifer, it was often required by regulation to case and grout to the top of the sandstone. Some of these casing depths were often 500 feet or deeper. In these types of wells, we would select neat cement grout.

Drilling Through Heavy Glacial and Finished in Deep Limestone Aquifer

In these settings, we typically drilled a 3-inch larger hole than the casing size to the top of the limestone, set casing approximately 5 feet into the limestone, and then grouted the annulus. In these areas, we most often selected a high-solids (20% by weight content) bentonite grout.

Typically, we placed the grout using a tremie placed down the outside of the casing. However, in really deep casing settings, we sometimes used a packer set at the bottom of the casing to install the initial batch or batches of grout. The packer was sometimes selected as it was difficult to get a tremie down 400-plus feet in a fluid-drilled hole through clay.

We used the high-solids bentonite type of grout for primarily three reasons:

  1. First, the grout was compatible with the surrounding glacial clay geology. Mixing and placing a bentonite clay grout with a dense blue clay overburden simply made sense.
  2. Since a high-solids grout hydrates (absorbs water) when mixed with water, it was essential the grout be able to maintain the moisture content of the grout in order to remain hydrated, thus maintaining the long-term integrity of the grout and the grout seal.
  3. And last, it allowed us to mix the grout on site with a grouter that facilitated mixing a high-solids bentonite grout. Typically, we could usually drill a uniform hole through the clay with no washouts. By doing so, we could easily calculate the sacks of grout that it should take to seal the annulus and haul them to the site. Given that the bags were 50-pound bags (in lieu of 94-pound bags of Portland), it was much easier for the crews to mix and handle.

Rarely did we ever have an issue with using the high-solids bentonite grout in this geological setting. The only issue we had was staying focused on deep grouting projects (more than 300 feet) and using procedures that would prevent the premature setting of the grout prior to getting it placed in the annulus. Plugging your tremie with a high-solids bentonite grout is not fun!

Tips on Deep Groutings with High-Solids Bentonite Grouts

  1. Maintain your pH near a 7 so as not to have water that was compatible with easily mixing the grout. Checking your water pH is just as important in the grouting phase as it is in the drilling phase of mixing bentonite. Adding soda ash as necessary is vital for good grout.
  2. Be sure that your polymer—used to help keep the grout suspended while in the mixing tank and to prevent premature setting of the grout—is fresh and in proper mixing ratio to the water in the mixing tank. Keeping polymer fresh is important, especially the deeper you are planning on pumping the grout.
  3. We also focused on the temperature of the water. A high-solids bentonite grout will set sooner with warmer water than it will with colder water. This could be a problem on a hot day, so we always wanted a cool tank of water to mix from.
  4. We also tried not to place more than 40 to 60 feet of grout in one pumping before we pulled 40 to 60 feet of tremie. The caution here was we always wanted our crews to know the approximate depth the grout would fill with a given number of bags pumped. This meant we didn’t want to pull too much tremie and leave a gap in the grout in the annulus where no grout was physically placed.

If this happens, the grout above it will settle through the water, thus reducing the solids content per gallon of water and diluting the grout. In any grouting situation where tremie is being pulled during different phases of grouting, this is a focus that needs to be in the forefront of all crews. You have one chance to grout a well right, and it’s important to focus on this important issue.

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Realize there are a lot of other details to be taken into consideration when grouting or preparing to grout to make sure your job is successful. While space didn’t allow me to outline all of these, I’d be more than happy to discuss any details or questions you may have. You can contact me at
grs@shawverwell.com, and I will reply as soon as possible. Please include your telephone number and best time to call (and time zone) if you drop me an email.

In my next column, I’ll focus on grouting wells with neat cement grout with deep casing settings and through deep layers of limestone, and the reasons why we selected neat cement.


Gary Shawver, MGWC, is vice president of Shawver Well Co. Inc. in Fredericksburg, Iowa. He has been in the water well industry for more than 40 years and is a Master Groundwater Contractor. He served on the NGWA Board of Directors. Shawver is semi-retired, having sold his business to his employees. He can be reached at grs@shawverwell.com.

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