Fully set and cured in 24 hours helps eliminate downtime.
By Gary Shawver, MGWC
Most neat cement grout mix is a Type I Portland Cement, but I became aware of Type III Portland Cement in the early 1990s.
The difference between the two is that Type III Portland is a finer ground cement than Type I. Because of this, Type III mixes quicker and sets quicker. Because the powder is a finer grind, the water surrounds the particles easier, thus allowing it to mix quickly.
The finer grind also enhances the set time. Type I neat cement is fully set and cured in 72 hours while Type III is fully set and cured in 24 hours.
In my last column (March 2021, “Grouting PVC Casing with Neat Cement Grout“), I outlined how we use neat cement grout with PVC casing.
I pointed out in many parts of our trade area we had to often set strings of 300 feet to 500 feet of casing and grout the entire length of the casing. Setting casing that deep was due to local regulations enacted to prevent upper to middle aquifer waters that may be of lower quality from intermingling with the deeper aquifers and potentially contaminating them.
I also shared that the deeper formation we set casing to was a sandstone formation often poorly cemented in the top portion, but typically firmer the deeper one drilled into it.
When we used steel casing in these wells, it was imperative to set the casing into the top of the formation, which again was soft and prone to running. Therefore, this casing always needed to be grouted to prevent the casing from following down the hole as the underlying, water-producing sandstone was drilled, which we always drilled with high pressure air.
Type III Use
To minimize downtime from grouting the entire length of casing and waiting for the grout to set, we started using Type III cement and grouted the bottom 20-feet plus-or-minus of casing.
To do this, we installed a ¾-inch steel tremie the entire length of the casing and then hand mixed four to five sacks of Type III neat cement grout and pumped it down the annulus through the ¾-inch steel tremie after the casing was set (typically a 5-inch ID × 59/16-inch OD in an 8.75-inch borehole). When we were done, we removed the tremie and let it set overnight.
We always focused on getting the grout installed at the end of the day, regardless of how late we had to work. We then allowed the grout to set overnight. When returning to the job the next morning, we always did a tug on the casing with the casing line to ensure the grout was in fact set and the casing was grouted at the bottom.
We then finished drilling the underlying sandstone with a roller bit, which typically ran from 40 feet to 60 feet in thickness. We developed the well with high pressure air after that.
Upon completion of the drilling, we removed the drilling tools and re-installed the ¾-inch tremie to the top of the previously set grout. We then ordered the appropriate amount of neat cement grout from a ready-mix company, brought it to the site, and finished grouting the annulus. The cement that was brought from the ready-mix company was always Type I as that is what all ready-mix companies in our area had on hand.
Type III Benefits
The use of the Type III enhanced our ability to get the base of the casing grouted and then set up during our off time (overnight). The next day then allowed us to finish drilling the well and complete the final grouting. No time was lost due to having to allow the grout to set for several days.
We also used Type III in other parts of our trade area. Some of our wells required we drill through 100 feet to 350 feet of overburden before encountering the underlying limestone formations, which was the ultimate water-bearing formation for many of our wells.
In many of these wells as we fluid drilled through the overburden and into the top of the limestone, we often encountered soft and sometimes broken limestone at the interface of the overburden and the limestone. Often this area of broken limestone at the interface of the overburden tended to produce a fair amount of water. Our goal was to set the casing into firm limestone and grout the casing and then drill the underlying limestone.
If the limestone was firm and not broken or we did not start to lose circulation, we would then use a high-solids bentonite grout. However, if we encountered the broken limestone or started to lose circulation, we would then set the casing and subsequently pump four to six sacks of Type III neat cement grout.
Depending on the degree of brokenness or loss of fluid, we may pump more Type III neat cement. We did this to ensure that we had the loss circulation zone or the broken rock zone well sealed.
And again, if we used Type III for this situation, we would allow the grout to set overnight and tug on it the next morning with the casing line to be sure the grout took and the casing was sealed.
The neat cement grout being placed at the base of the casing has a higher set strength than does a high-solids bentonite grout. Therefore, one doesn’t have to worry that the grout would wash out during the completion of the drilling of the limestone and thus undermine the rest of the grout in the annular space.
However, we would then typically finish grouting the annulus with a high-solids bentonite grout in these types of formations before drilling the underlying limestone/waterbearing formation.
It’s important to remember that if you use both neat cement grout and a high-solids bentonite grout in the same annulus, you first allow the neat cement to set prior to installing the high solids.
Neat cement grout dehydrates when it sets and a high-solids bentonite grout hydrates as it sets—the opposite of each other. So, if the grouts have an interface and the neat cement has not set, they will work against one another and you don’t have a competent grout for a certain portion of the annulus.
Using this method of grouting in this geologic setting worked well for us. It ensured we didn’t have a compromised grout job. Prior to using neat cement, Type III in this situation, we had times where the grout would wash out when we were drilling the underlying limestone. We then had a mess to deal with. When this did occur, we typically backfilled the drilled borehole with a finer sand up to within about 2 feet of the base of the casing.
We then installed a hydraulic packer in the casing about 2 feet from the bottom of the casing and pumped 6-10 sacks of neat cement grout to reseal the base of the casing. This typically solved the problem, but it led us to figure out a way to prevent this in the future—and thus, the method of grouting the base with Type III Portland Cement that I have just outlined.
Some Closing Thoughts
- One might ask where can you purchase Type III Portland Cement? We had a local lumber yard order it for us. Most of the time we were required to order a pallet. Early on we did this, but as we started using more and more, we would order two or three pallets at a time. It became less expensive, and we were then never out of stock.
- If you do order any type of Portland cement to have on hand in your inventory, it’s well advised to store it in a dry cool place and to keep the inventory moved. Otherwise, the Portland powder can and will draw moisture, thus prematurely giving you partially set bags.
- All grouts have their places of strength and benefit. It is simply a matter of knowing the strengths and weaknesses of each.
- There are many different methods of placing grouts. Again, the differing methods can enhance your grout placement and facilitate a well-constructed well.
Grouting is an extremely important part of any well. Knowing how deep to case and grout is important to water quality.
One can have the best equipment and tooling to drill a well and use quality casing in the construction of their wells, but if you have a poor grout job, you simply have a poor well that will most likely be compromised for the entire life of the well.
That’s not in your best interest or that of your customer!
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 email@example.com.