The Best Way to Mortar Boulders on the Sides of Rubber-Lined Koi Ponds

Rubber pond liners, such as EPDM rubber, effectively maintain water in ponds, but the black lining is not particularly appealing when viewed up close. Small boulders mortared into the sides of a rubber pond liner provides you the advantages of a rubber pond liner with the aesthetic appeal of a natural water feature. If you have a built-in shelf at the pond, add the boulders down as the shelf, or towards the top 12 inches of this pond. Thin, flat boulders are encouraged most easily with mortar.

Drain the water from the pond into a few inches below the desired level for the boulders. Scrub the rubber liner free of debris and dirt. Alternatively, use the boulders to a different pond before filling it with water, however you still must wash it blank. Remove koi fish into a large tub with filter until you use the stones and leach the lime from the mortar.

Mix mortar to reach a consistency very similar to pancake batter. It has to be thick enough to maintain its shape when remaining spreadable. An 80-pound bag of mortar is enough to apply boulders to about 5 feet of distance. Mix the mortar just 1 bag at one time so that it doesn’t setup before you can apply it into the pond sides.

Spread a layer of mortar about 3/8-inch thick on the side of pond liner with a mason’s trowel. Apply the mortar into a little space at one time so that it will not set too quickly.

Line up the first boulder on the liner and press it firmly into the mortar. Hold it for a minimum of 30 seconds to ensure it’s firmly embedded and put into the mortar. If you have a pond shelf, simply line up the bottom border of this stone on the shelf. With no pond dish, draw a line with chalk or line up the stones by sight.

Line up a second boulder with the very first rock, putting it as near the first stone as possible. Push it into the mortar. Fill in the rest of the gaps in the mortared place with added boulders, fitting them together like puzzle pieces.

Apply mortar to another section of this liner. Fill in the place with boulders. Repeat this process until the sides have been coated with boulders.

Scrape or brush off any excess mortar that squeezes from the cracks between boulders, utilizing either a mason’s trowel or a wire brush.

Allow the mortar to place 24 hours until it becomes dry and hardened. Spray the boulders and mortar joints with a light mist of water every couple of hours to keep it moist. This prolongs drying so the mortar cures as powerful as possible.

Scrub the mortar joints with white vinegar and a scrub brush to help neutralize the alkalinity from the lime content. Mortar mix includes dry cement mix and walnut, which makes pond water too alkaline for koi fish to thrive. Furthermore, fill out the pond with a mixture of water and white vinegar, which makes it for about 10 days so the lime leaches from the mortar. Pump the water out and add fresh water before you can add or return fish into the pond.

Examine the water with a pH testing kit before adding fish into the pond. Testing kits change, but generally require you to swirl the test rod in the water and wait for a few minutes to the color of the rod to change. The testing kit usually includes a color panel that you compare the rod and ascertain the pH. The pH should range between 6.8 and 7.8 before adding fish. Refill the pond with water, wait for a couple of days and drain it again if the water is too alkaline.

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