Pond Sealing

GEO Gel (Bentonite), in its dry state, is similar in appearance to any inert, natural clay material. It is when wetted that GEO Gel shows its unique ability to swell 12 to 15 times its normal dry size. It is this swelling capability that makes GEO Gel the ideal low cost, low maintenance way to effectively stop water seepage from ponds and reservoirs and through dams and other earthen structures.

The conditions existing in any given situation will generally dictate the best method to be followed for sealing earthworks with Bentonite. Basically, there are four main methods of application. The one most suitable to your own particular problem can be easily determined by reading the descriptions below.


Use of this method requires that the entire area be drained. Surface rocks and all vegetable growth should be removed. Make sure that any large rock outcroppings, holes or crevices are filled or covered with a GEO Gel/earth mixture of 5 parts soil to 1 part GEO Gel. Cultivate the area and level out any deep furrows or surface irregularities with a drag. If wet, let the surface dry before proceeding further.

To treat small areas use twine or stakes, marking off the area into ten foot squares. Allow for one 100 pound bag of GEO Gel per square - if original leakage was not too great and water depth will not exceed six feet. For deeper water, or for severe leakage conditions, use 150 pounds per square. Two 100 pound bags per square is required when both conditions prevail. As these amounts are only typical rules of thumb, to be sure, make the percolation tests described on Page 3. The Bentonite should then be raked or otherwise spread evenly over the entire area.

Next, mix the Bentonite into the top 3 to 5 inches of soil using a disc, spike tooth harrow or hand rake. Roll or tamp to restore original or required soil density. The addition of extra moisture may be helpful. Finally, fill with fresh water. Proper application in prescribed amounts of GEO Gel using the Mixed Blanket Method should reduce water seepage by as much as 90 percent.

Please note that in utilization of the Mixed Blanket Method, the type of soil is an important factor in determining the amount of Bentonite needed. See the application chart on the next page. Bentonite being a clay, does not mix well with other high clay content soils, and under these soil conditions the Pure Blanket Method should be followed.


This method is generally used in areas where extreme water loss conditions exist. While it is the most efficient method it requires the most care and expense in construction.

Using a blade or bulldozer, remove three to four inches of dirt from the bottom of the pond and pile the dirt up on the banks for later use. Smooth the surface with a roller or drag. Lay a pure blanket of GEO Gel (although one pound per square foot of GEO Gel will cover most conditions, it is advisable to perform a “Percolation Pretest) - roll it - and re-cover with the original soil from the bottom of the pond. Tamp the surface to the desired consistency, then refill the pond with water. Satisfied users report 95% seepage reduction through the use of the GEO Gel Pure Blanket Method.

Note: The soil cover coat over the GEO Gel “Pure Blanket” should be thicker than four inches if waders or cattle are expected to use the pond.


When a pond cannot be drained, or when only portions of it need treatment, seepage can easily be halted by sprinkling GEO Gel over the surface of the water. Using a rope or twine grids, mark off the surface area into 10 foot squares, then scatter GEO Gel at the rate of 100 pounds per square.

The Bentonite will sink to the bottom and the resultant gel is drawn into the porous openings, closing them up. Any residual gel remains in a protective layer which is not disturbed by a mild current.

The Sprinkle Method will cause slight and temporary cloudiness in the water which does not affect its drinking properties. 75% to 80% average reduction in water loss can be expected from this method.

Note: Since the efficiency of all three sealing methods depends on GEO Gel’s ability to swell when mixed with water, and since GEO Gel will not swell in water containing large amounts of salt or acid, when used in industrial waste lagoons it is recommended that the pond be filled with fresh water and allowed to stand for one week to allow the Bentonite to swell and the seal to become effective before introducing any salts or acids.

An alternate method for salt water pits is the use of two parts GEO Sea Mud with one part GEO Gel.


If the leak can be identified as coming from a particular area, a simple paste may be used as a sealant. Mix 3 to 3 ½ pounds of GEO Gel in a 5 gallon bucket of water. Stir until all the Gel is moistened. Apply this mixture to the leak with cement tools or by hand, working it into any cracks and crevices. A two inch thick layer is almost impervious to water. This material is easily disturbed by waders or cows. A protective layer of 6 to 8 inches of earth should be added if there is a risk of disturbance.


The more porous the soil the more GEO Gel will be required to shut off water leakage. For a more accurate determinations of the amount to add perform the following test:

  1. Perforate the bottom of a large pail, washtub or 5 gallon can that can be covered to prevent evaporation.
  2. Put in 6 to 8 inches of pond bottom soil, tamping it lightly.
  3. Fill the container with water and cover.
  4. Measure the rate at which water flows through the soil.
  5. Repeat the experiment, mixing ½ pound of GEO Gel for each nine pounds of dry soil as a top layer. If seepage is not stopped, increase the amount of GEO Gel in ½ pound increments until water flow is stopped completely.
  6. Add 25% to 50% more GEO Gel to the above determined proportion as a safety factor. This allows for increased water pressure at the actual pond depth as well as for inconsistencies inherent in large scale mixing. In addition, soil type may vary and the treatment must be sufficient to seal the worst (most porous) soil.


Soil Application pounds per square foot Area covered by one 100 pound bag Tons of GEO Gel
per acre
Coarse sand, rock or gravel (add extra soil) 2 1/2 lbs. 6 1/4' x 6 1/4'  53
 Sand or silt 2 lbs. 7' x 7' 42
Loamy sand, sandy loam or silty loam 1 1/2 lbs. 8 1/4‘ x 8 1/4‘ 32
Loam, sandy clay loam, silty clay loam or clay loam 1 lb. 10' x 10' 21
Sandy clay, silty clay or clay 1/2 lb.  14 1/2' x 14 1/2' 11

Most types of porous soils can be successfully sealed with the addition of one pound of GEO Gel per square foot.
Lake or pond beds should be well pulverized, cultivated or otherwise tilled. If the soil material is cloddy, twice the recommended rate may be required.