Will the pond liner float?

If used in a normal situation where the liner is containing the water, the water will push the liner down into the ground below, making it impossible for the liner to float. However, if there is a large fold in the liner, or if you place a loose piece of liner in the water as a secondary protective layer, the fold or loose piece may float or move around. In those cases, we recommend placing some ballast over the folds or loose material.

In unusual situations, groundwater below the liner, caused by high water tables or underground springs, can create pressure that begins to push the liner upward. In these cases, you can place ballast on top of the liner to counter the groundwater forces. Consult a geotechnical engineer for more information in these situations.

For ballast material, we typically say gravel less than 1" in size doesn't require a protective layer over top of the liner.  The larger the aggregate size,  the more likely it is to damage the liner when spreading out the material, so if using 1" ballast, spread the material out carefully.  If using ballast over 1" in size that has sharp corners and edges (like crushed gravel), we recommend a protective geotextile fabric to help prevent damage to the liner.