How to Repair a Crack in a Concrete Pond

About 18 months ago I noticed a crack in a concrete Koi pond I had built in 1981. Although this pond had survived the Northridge earthquake of 1994, it had now developed a crack next to where a large “Umbrella tree” (Schefflera actinophylla) was growing. Update: I now believe that the Northridge earthquake started the crack. I decided to put off repairing the crack until I had some time off during the summer of 2000. Because of some unforeseen surgery and recovery, the project got put off another year. I did have a chance to remove the Umbrella tree, but by then the crack had “grown” and it was now much more noticeable that the pond was losing water. With the tree stump gone, I reinforced the concrete edge of the pond where the crack started with more reinforced concrete and waited until the summer of 2001.

As summer approached, I disconnected the pond filtering system and added some Simazine (Aquazine 80) to kill all the algae growing on the sides of the pond. Then in June I emptied the pond of water. I already knew by then that the crack was worst than originally expected. Although the crack appeared to go completely across and up the other side, after the pond was empty, I could see that the crack did not run all the way across the bottom of the pond.

My plan for repairing the crack was to “chisel” the crack to open it up. Then to use concrete adhesive and some concrete crack repair product to patch the crack. I did not have total confidence that a new crack would not develop along the edge of the repair. I was even considering a costlier backup plan that would involve hiring some laborers to remove the old pond and dig a deeper hole to accept a W. Lim prefab pond.

I was searching the web for articles on repairing cracked concrete ponds when I stumbled across an article by Valiant Technologies on repairing a crack in a pond. After reading the article, I decided to give the product a try. Although the article talks about fixing a crack under water, I figured it should be better on a dry exposed surface.

Valiant Technologies Inc. advertises RayCrete as the “Ultimate patch, fill, glue for strong long lasting repairs (can even be applied underwater).” RayCrete comes in two cans and appears to be a “epoxy” like product. Valiant says it is “polymer based” and RayCrete is different from normal epoxy in that it is odorless, nonflammable, and can be cleaned up (before cured) with “lemon juice” (although I used acetone).

Repairing the crack was easy because of the preparation I did. I took the time to clean the cracked area and obtain various putty knives, small trowels, mixing tools, etc. Because of the short 20 minutes curing time, I applied the RayCrete in two sessions. The product “covered” more area than I expected and waste was minimal. The first application pretty much did the trick. The next day the second application allowed me to go back and cover some areas I missed.

When applying RayCrete it has the consistency of epoxy or “bondo.” After the RayCrete adhesive/filler has had a chance to set up it appears like it may remain a little flexible. But by the next day it was as hard as a rock. I was very confident that it would hold up and not leak.

Although RayCrete may appear to be a little expensive; $29.95. for 420 ml kit (BTW: I ordered the 850 ml kit), I have no regrets considering what my other options were. I feel the RayCrete did a better job than any of the more readily available concrete patch products at big box stores. My one advice to the manufacture would be to try and make RayCrete available in a more cement gray color. The appearence of the repaired crack does not bother me. I know in time a carpet of dark algae will again cover the sides of the pond.

[Update from the manufacture]

"The color of concrete can be duplicated with some black or gray powered colorant (concrete power color or just use some pastel chalk and some sandpaper to make some filings)."

"The best technique for coloring is to pour your dry powder colorant into the light weight material (Part A) and mix it until it becomes about the color you want, then when you mix an equal share of the Part B with your colored Part A you will have colored RayCrete. It is a good idea to experiment with the colors before you use it on a big job, but when you are confident that your Part A is the color you want then mix enough colored Part A to do the full job. Mix small portions of the colored Part A with an equal portion of Part B and apply it in small areas. Because you have a consistent Part A color you can be sure that each small batch you make will have the same color when mixed together with the Part B."

"RayCrete is sandable and that you can sand down the surface of the RayCrete repair area. Then with some colorized RayCrete you can make a thin layer application over the previous repair area and make the repair disappear."

"Remember that the timeline to take advantage of RayCrete's most liquid state is only within the first five minutes, so if you want to use it in this state, mix small quantities so you can cover the area within this short period of time."

Jack Mattson
Valiant Technologies Inc.

[More information on How to Repair a Crack in a Concrete Pond pt. 2]