Expert: Roger Zona - 1/6/2011

Question
Mr. Zona,

         First thank you for your time. I think you can help me and if not point me in the right direction. I am building a large pond, approximately 29,000 sq ft in floor area. My soil is sandy loam to sandy and does not hold water at all.
         When cement trucks come back to the yard if they have any leftover it is unloaded and separated and the washed out concrete is left in powder form. They sell this concrete powder  for a very reasonable price. Could this powder be mixed into my soil and compacted,in sufficient quantity to seal the water from leaking through.

Answer
Hey Chip,

A pond is a great feature.  My son has one at his home and it is stocked with Koi.  

I don't mean to correct you but - cement is the raw product that must be mixed with water and an aggregate to make concrete.  What they are selling is like a boxed cake mix - just add water and you will have concrete.

Mixing the ready-mixed concrete with your loamy soil will slow down the absorption of the water into the ground but will not stop it unless you use the concrete to make a lining for the pond.  You can also buy a slurry mixture of concrete which has a very small aggregate and, when poured and leveled to about 2" thick should hold the pond water for extended periods.  If you are in a cold climate with freezing temperatures, the slurry mix will crack and allow the pond water to soak into the soil.  

Another solution is to compact the soil as much as possible.  Use a rented "sheeps foot" mechanical compactor for best results.  Then line the pool with "visqueen" plastic sheeting. Buy the largest dimensioned pieces and, using a contact glue, join the seams with an interlocking fold.  Wrap the entire pool area and cover the top edge with a layer of soil which will define the limits of water level.  If you intend stocking the pond with fish you will want to grow some water plants.  Before you fill the pond, add 6" or 8" of soil to the bottom over the liner.

Don't forget to provide an overflow pipe to direct surplus water away from buildings and will keep the pond at a desired level.  This can be a piece of 4" pvc piping.

I hope this has been helpful.

Roger
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