• Produced specifically for dam construction, pond bottom, and lake bottom sealing.
• Highest swell = Max Sealing Capacity per Pound  learn more

Help me calculate how much bentonite I need.

Not all clay is created equal.  Sodium Bentonite Clay has the highest swell & soil sealing capacity of all naturally occuring clays. This natural material has been used for hundreds of years to seal water bodies and preserve water.

The USDA Web Soil Survey is an excellent resource for learning about the soi types at your pond site. We often use it to select the best site to the build a pond. This DIY tool is free to use and gives access to a wealth of pond soil data. You can watch a short tutorial video that shows how to get the right soil data for a clay lined pond.  You will also learn how to interpret the data.

We recommend that you test application rates with your particular soils by treating a small area at the anticipated bentonite clay application rate. Drive a 12" or larger diameter smooth wall pipe at least 8" into the soil column. Manually compact the soil-bentonite mix within the pipe and fill with 18" or more of water. Measure the rate of decline in the pipe and adjust application rate for your soils as needed. 45 lb bags of sodium bentonite are available for testing application rates or treating small areas.

Another simple bentonite sealing test can be completed using a 5 gallon bucket.

The bentonite bucket test is completed as follows:

1. Drill 15 - 1/4" to 3/8" holes in the bottom of a 5 gallon bucket
2. Place 6-8 inches of soil from the pond to be sealed in the bottom of the bucket
3. From the application rate table, select the bentonite application rate for the soil that matches the pond soils
4. Mix soil with bentonite at that rate in lbs/square foot
5. Thoroughly blend the soil and dry granular bentonite until the mixture is uniform
6. Add 3 cups of water to the soil bentonite mixture and mix again until moisture is evenly distributed
7. Firmly tamp the soil/bentonite mixture into the bottom of the bucket
8. Using a permanent marker or paint stick mark a fill line roughly 2 inches from the top of the bucket
9. Gently (so that the soil isn't disturbed) add water to the fill line
10. Monitor water loss over a minimum 48 hour period
11. If seepage continues, repeat at an increased bentonite application rate until desired results are achieved
12. Calculate the bentonite required for your pond area as follows. Multiply the number of pounds of bentonite used in the successful bucket test by 1.75 to determine the application rate in pounds per square foot. (If using our 5 gallon pail for the test. The area of the bottom of our standard 5 gallon bucket is 0.57 square feet) If using a different bucket, determine the bottom area by the radius of the bottom (in inches) squared times 3.14 and divide by 144 to convert the answer to square feet.

Order a complete Bentonite Bucket Test Kit including preweighed bentonite packets

For more precise analysis, use our Pond Soil Testing to determine the hydraulic conductivity of the pond bottom soil on your site. This laboratory measurement can be incorporated into the water budget to determine 1) whether additional clay liner material is needed and 2) if clay is needed, the application rate necessary to construct the impermeable clay liner.