Restoring a Concrete Pond :: Repairing Cracks, Parging and Sealing with Epoxy

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Right, so I had this, well, pit in my backyard. I can only assume – an old concrete pond. It never held water, even after it rained. It sat there just off a beautifully updated wrap-around patio. A giant unfinished hole in the ground.

And, of course, as the time approached to list this house, we knew it had to be addressed. So I researched – How to Restore a Concrete Pond.

What Do You Do with an Old Concrete Pond?

To start, I posted this pic to the popular social home site – Hometalk. I’ve written about, and well, for them before (See). And anyhow, here is that picture.

I got back a slew of very excellent ideas. (Of course, I welcome you to read the comments on that post by clicking through.) With those suggestions, a pretty wide range of potential effort and cost is represented. Some of those ideas follow.

* Ideas for my Old Concrete Pond

• Fire Pit – Turn it into a Fire Pit (or a BBQ pit or a grill and/or an outdoor stove). Most commenters pointed out that it already had seating.
• Fountain – Add a Fountain – concrete or other “pondless” water feature.
• Bird Bath – Sanitize it and make it a Bird Bath. hmmm.
• Planter – Fill it in with dirt and Plant a.) trees and shrubs b.) flowers. Basically making it a giant planter.
• Remove it – Jackhammer it out, haul it away and fill it in with dirt. Plant a.) trees and shrubs b.) flowers. c.) grass.
• Replace it – Jackhammer it out, haul it away and install a pre-formed pond shell (or design some other water feature).
• Finish it with Tile – Repair Cracks and Finish it with Tile.
• Seal it – Repair it and Seal it with Flex Seal or equivalent.
• Install a Liner – Install a rubber or other Flexible Pond Liner.

Pretty good, right?

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We were in the process of getting to sell this house. And while time to execute was of high importance, Cost, instead, was my biggest hinging consideration.

While some of the ideas above were good or, well, at least entertaining, I’ll say, only two of those options ever really made it to the table. A.) Repair & Seal the Pond. and B.) Install a New Pond Liner. Both would have amounted to Restoring this Concrete Pond.

While a number of the posters called out – “Add a Liner”, I was a little more intrigued by one single comment. It went like this:

This comment came from a Facebook friend, another “Hometalker” – a pond pro, Lannie Hagan. (More from her in a bit.)

* A Plan of Attack for my Concrete Pond

To eliminate any further suspense, in the end, this is what I did. I Repaired existing Cracks, Parged the entire Surface of the Concrete, and I Sealed the Pond using Pond Shield from Pond Armor.

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Like a Liquid Pond Liner :: Pond Shield

Pond Shield is an epoxy coating made by a company called Pond Armor. From their site – Pond Shield® is a specialized non-toxic epoxy liner system. Basically a liquid pond liner. Their three steps to success: Prepare the Pond, Apply the Coating, & Enjoy the Pond.

Application FAQs include instructions for not only concrete, but also wood, stone, brick/block, metal, plastic, Fiberglas, and tile.

After some calculations and, well, a little thought, I purchased (3) 1.5 quart kits. It is also available in 1.5 gallon as well as larger kits. The 1.5 quart kit is said to yield 60 square feet at 10 mils thickness on a smooth surface.

In also checking their General FAQs – it appears that 10 mil is both the minimum and maximum – the ideal thickness at which a single coat can be applied. To put 10 mils into context, the internet says a standard coat of interior paint is generally between four and five millimeters thick. So basically, Pond Shield needs to be applied twice as thick as a single coat of interior paint.

We selected a light gray – which honestly wasn’t our first choice. But this color was on sale (it seems Pond Armor frequently has sales), and it would match very well with our newly installed paver stones.

A Note on Color: Lannie, from above, pointed out, “A light color highlights dark elements (plants and fish and the pump) while a dark color would highlight light elements.” Makes sense.

Exploring the Pond Liner Option :: Cost & Effort Considerations

They say there are two types of Concrete: “Concrete that is cracked, and Concrete that is going to crack!”

I mean – as it were, there was already a large fissure – at the “top” of this pond. It was likely a half-inch wide. There were also a few dime size holes in the base of the pond – presumably where a stone or other aggregate worked itself free. In my part of the country, Maryland, the freeze and thaw cycle certainly comes into play. It can wreak havoc on concrete that comes into contact with water. (And that’s most concrete.)

Because of this, some say the only way to effectively fix a concrete pond is by installing a liner. And I did explore that for a bit. But first …

*(Rough) Sizing the Pond for a Liner

My pond was oval – just short of 10 feet long by 8 feet wide. The shelves set about 12″-14″ deep. It also had a 4′ x 5′ rectangular recess that itself was about 2 ½ feet deep.

Using this link (now just for demonstration), I could calculate the area of my oval. To make life simple, I used this formula: Area = π R1 R2. My radials were 10/2 = 5 & 8/2 = 4 or 3.14 x 5 x 4 = 62.5 sf. This, however, only gives me my horizontal surfaces. (In calculating pond dimensions, it seems that we sometimes work in averages.)

While the total depth of the pond was around 3 ½ feet, its footprint changes. So I tugged and pulled, estimated and guesstimated to come about with 62.5 sf (by a factor of 2.5) = around 156 sf. (Looking back now, I really have no idea how I came up with it.) But this was roughly how I figured what I would need to order from Pond Armor. (That, and I emailed their customer support staff. Ha! They do actually respond.)

Turning my attention back to a flexible liner, though, I can find this site now. (How scientific or accurate it is – who knows.) But I plug in some numbers and it gives me both A.) What Size Liner and B.) Water Volume of my Pond. (We’ll need to know volume later for sizing a Pond Pump.)

* Ballpark Pricing on EPDM Pond Liners

19 x 21 – Now remember my pond was actually smaller than this. And perhaps slightly more complicated. In searching only for ballpark pricing, I targeted a 20 x 20 liner. Clicking through on this site (for example) and with others, an aquatic plant and fish-safe liner. Here, Firestone‘s PondGard EPDM Pond Liner = $250.00.

As it were, I was looking at a hard cost of $275 including shipping on (3) 1.5 quarts of the Pond Shield. Meaning – at first glance, pretty equivalent, actually cheaper. But I had to also consider “soft costs”. (With the Pond Shield, too, I mean – What other supplies and/or tools do I have or would I need?)

A cap, a sorta “edge” detail, was already installed. Installing a Liner would have meant looking at either filling in or removing that existing edge and likely installing a new one. (Ironically, I probably had nearly enough flat “cap” stones lying around on the property.) Another idea – instead of removing this edge, cut a groove or a channel just below the rock ledge. And tuck the liner in there.

With installing one, plan to tuck, fold and trim a flexible pond liner. That is – without potentially tearing it.

Prep for the liner (as with the Pond Shield) would have required me to address high or rough spots in the substrate, as well as, still fixing to some degree that nasty crack.

While I originally envisioned setting my still hypothetical liner in a bed of sand. Mark Russo, Lannie’s boss at Rocky Mountain WaterScape corrected me. He said, “You would probably be better served to install a felt underlayment instead of the sand. This will protect the entire liner instead of just the bottom, which is where the sand would settle.”

A quick search yields a 20 x 20 felt underlayment for $100 on Amazon.

Summing Up: In looking at the costs between installing a new liner vs. coating with an epoxy coating, surprisingly they seem pretty much the same. Effort, too, would have probably been roughly equivalent. I’d suggest that the time to install would have perhaps actually been slimmer with the flexible liner. And I might go so far as to say – in any other situation, and/or for you, it’d be hard not going the flexible liner route.

That said, though, for me still, the refinishing option just felt like the path of least resistance. And please read on, in any case, for tons more useful information.

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Restoring a Concrete Pond

This refinishing process was executed across several months. While I repaired the concrete and applied my epoxy coating in the Fall, I didn’t actually run electric and install the pond pump until the following Spring.

Actual Working Time: One day to clean, and a few hours over two days to execute crack repair. Two days to parge – an hour or so on one day for the base of the pond and another part of one day for the walls. Follow that with a week for cure. Etching and epoxy application occurred in a single weekend. And finally, the installation of a new electrical circuit, plus setting up the pond pump took a part of two days (mainly because of the trenching).

* Cleaning Out and Power Washing the Pond

First, I cleared the pond of debris. I did this through a combination of sweeping and shoveling. Using a quality biodegradable outdoor cleaner, I then thoroughly pressure washed its surface. While I didn’t grab any images here, you can read our article on the Basics of Pressure Washing if you need tips.

As it were, this pond was heavily stained. So as I pressure washed, I scrubbed the entire surface. A stiff bristle scrub brush attached to a wooden extension pole worked great on the tenacious stains. (It is used later, too, with etching below.) Because I was working in an area that is meant to hold water, I cleared waste water using both a trusty portable submersible pump (love this tool!) and a wet and dry vac.

I let everything dry overnight.

* Repairing Cracks in the Concrete Surface

I mentioned the large crack at the “top” of the pond. Repairing this was a multi-part operation. I started by squaring off the already large crack. For this part of the task, I used my angle grinder fitted with a 1/4″ diamond-coated Tuck Pointing Blade (designed for repointing brick and stone joints.)

To begin the build-up on this crack, I started by filling it about 75% full with an epoxy filler. In my case, I used an Archoring Expoy. While perhaps not the most ideal choice here, I had some hanging around from the work on my Downspout Leader Inlets during my Half Round Gutter Install. Applied from a standard caulk gun, I generally achieved what I was looking for.

Anchoring Epoxy is pretty quick drying, but I did allow it to cure overnight. I filled the balance of the crack with a kneadable two-part repair epoxy. I actually found this product at a local pool store. From Atlas Minerals, I used it also on other small cracks throughout the pond surface. The great thing about this product, though – it is sculptable with a damp (tile) sponge.

While probably not required, I finished with a waterproof hydraulic cement. I found this product at a different pool shop. This product was mixed and was used to fill both the holes in the base of the pond, and was also used on minor imperfections throughout the pond surface.

* Parging the Pond Surface

Once cracks were addressed, I parged the entire surface. While I considered for sure, and though pictured, I don’t recall ultimately pre-treating with a bonding agent. As with repairs above, I circumvented a bonding agent by wetting the surface prior to and intermittently throughout application of the parge coat.

I used an all-purpose repair product found at the Home Depot called Cement All. It’s in the Rapid Set line of products made by CTS Cement Manufacturing. (On Amazon, here.)

I mixed using a Low-Speed Mixer, fitted with a cement/mortar mixing paddle. Recycled 5-gallon tubs (from the polymeric sand used in our patio install) worked great as the containers for both mixing and applying.

I integrated Rapid Set’s specified Flow Control additive to make my mix more fluid. Set Control, too, was used to extend cure time.

* Applying the Parge Coat

Using these additives made my mix incredibly workable. I poured out and used a screed to get a rough level on the pond’s bottom first. This did occur on a separate day.

With the walls, and in some cases, I troweled the mix on with a finishing trowel. In other places, I just poured my blend out and worked it into the surface using a 6″ masonry brush. Misting either directly from a hose and/or with a spray bottle, I keep things wet throughout.

With this mix working so well, I even began forgoing the trowel and just started brushing my slurry on. I ultimately brushed all the pond’s vertical surfaces. Starting at the bottom and working my way up – I made sure to give myself an escape plan.

Like my epoxy patch above, I used a grout sponge for isolated fine tuning in the parge coat. At the pond’s cap, I used an old 3″ polyester paint brush to get in between rocks. I used just over a 55 lb bag for my job. (For other Rapid Set Products, on Amazon – here.)

* Water Curing the Parge Coat

The final step of any concrete job is perhaps the most important – water curing. Directly from CTS‘s specs: “The objective of water curing is to maintain a wet surface until the Cement All has achieved sufficient strength. Begin curing as soon as the surface has lost its moist sheen and continue for a minimum of 1 hour.”

As things began to cure for me, I could see spots of dryness (a lighter gray in the repaired surface). I misted the entire surface with my garden hose. With my hose nozzle set to, well, mist, I wetted and rewetted everything several times throughout the day.

Then taking two 10 x 12 sheets of 2 mil plastic, I draped these (as I would a pond liner, ha!) over the pond. I peeled back the plastic and re-wetted the pond a couple of times over the week after installation. I removed the plastic and exposed it to the air, one day prior to moving on to the epoxy coat.

Applying Pond Shield Epoxy Coating

The steps in this next part were dictated by the pairing of the two products I was using.  The Cement All and the Pond Shield.

First, from Cement All’s FAQs, “Rapid Set reduces the waiting time prior to coating. Under dry conditions, water based coatings such as latex paint can be applied after the product is hardened and dry. This usually takes 1 to 4 hours. Solvent based and impermeable coatings such as oil based paint and epoxy can be applied in 16 hours.”

As mentioned above, I extended water curing and gave the repair a full week to set up. (This did in part have to do with convenience.)

Now turning my attention to Pond Shield. From Pond Shield’s General FAQs, “Concrete surfaces whether newly poured or older need to be etched prior to coating. Etching will remove any residual calcium sulphate that can be found on the surface of the concrete. If it is not removed, it will likely fall off later with the new coating attached.”

In regards to prepping for epoxy coating, “Surface Tooth – A properly prepared concrete surface will feel like 60-grit sandpaper. Concrete that has been etched properly will feel this way because the calcium sulphate has been removed from the surface pores.”

Therefore, I applied a mild etcher and cleaner before applying my epoxy coat.

* Etching my recently Parged Concrete Pond

Because of the nature of my repair, I chose a mild etcher over say a more aggressive Prep & Etch. Much like using any outdoor cleaner, I mixed the etcher to instructions. In this case though, I applied it with a pump sprayer. As I did with initial cleaning, I scrubbed everything down, but this time I let the etcher linger according to instructions. I washed everything clean with a garden hose and removed standing water with my wet and dry vac.

* Mixing the Epoxy Coating – Pond Shield

For the Pond Shield, I mixed according to the recipe. Equal parts of Part A & Part B were measured in an old measuring cup and poured into a 1-Gallon drywall bucket. I blended the two parts with a long sturdy paint stirrer. In general, I worked in batches of about half of the 1.5 quart kit at a time.

On mixing, Pond Shield’s General FAQs say: “Start with the smallest recipe in the instructions regardless of the kit size. This means that you’d probably start out mixing one half of a 1.5 quart kit worth of material. There are a couple of reasons for this. First the outside temperature, the humidity, the surface type, the tools and even your skillset will play a big part in how easy it is to get the material on in 30 minutes.”

Mixing in a small batch allows you to judge how far material will spread and how exactly it goes on.

* Applying the Epoxy Coating – Pond Shield

When asked about Pond Shield, Mark from Rocky Mountain WaterScape said, “Although we don’t work with it every day, we have used it in various applications for years.” When asked about adding plants and fish, he continues, “Yes, you could add plants and fish. Pond Shield is perfectly safe for both once it dries.”

While Pond Shield included a plastic gauge in their kit (presumably for laying out flat), my coating thickness was hard to gauge. This related, I’m sure, to roughness of my pond’s surface. In the end, I simply tried instead to cover everything – hoping my estimates and their coverage info were accurate. I did work to leave about a 1/4 of that final quart and half in the cans for possible future touch ups. (More on this below.)

I knew going in I would be stretching my three 1.5 quart purchase – again because of that rough surface. While the company provided instructions for thinning – “{Use} Denatured Alcohol or 99% Isopropyl Alcohol ONLY.” I don’t believe I ended up thinning my mix at all. Denatured Alcohol, however, was effective at cleaning tools after use.

I found myself most of the time, just pouring out this product. Brushing it out with a 4” synthetic paint brush and then finishing by rolling out with a semi-rough roller (¾” nap).

* Touching Up Pond Shield

Again on their General FAQs, Pond Shield says of the topic – CAN I JUST SPOT COAT A CRACK IN MY POND? “That is not advisable. The problem is that concrete is porous. Water will eventually leak out by finding a way around the repair. The crack should be repaired properly and then Pond Shield should be used over the entire submerged surface.”

However, they also go onto say on the question: CAN I APPLY A SECOND COAT OF POND SHIELD OVER THE FIRST? “Yes, but it is not necessary if the coating is already at the minimum thickness of 10 mils. Pond Shield is designed to perform properly at a finished thickness of 10mils. Applying it thicker will not hurt, but will cost more in regards to materials. The coating can be touched up over the top of itself with no extra surface preparation within 12 hours of the original application. After that 12 hour period, you should scuff the area with 60-grit sandpaper to give it the surface tooth.”

For disclosure: I’ll note that my pond did develop a small hairline crack appear in my installation after the first Winter. I don’t necessary fault Pond Shield here, but rather my slight coating might have been a factor. That, paired with, well, the nature of concrete. I scuffed up the surface, pressed in some pool repair epoxy noted above and touched up the Pond Shield using a 3-inch foam roller. (Stoked that I thought again.)

Adding a Wet Location Outlet & Installing the Pond Pump – What I Did

* Setting the Pond Pump (Selecting a Pond Pump)

I have searched my pictures and notes and I can’t seem to find any of/on the pond pump I installed. I do know it was a Beckett Pump (here  on Amazon). It was submersible-style pond pump (perhaps with a direct drive impeller). It had an integrated synthetic filter. A waterfall fountainhead shot up from the front of the motor. It was a gift from one of Mrs. Moxie’s clients, an extra pump actually. I had absolutely no part in sizing it.

If I were sizing it, though, I would’ve needed to know the volume of the water the pond holds. (One calculation I have seen – Pond volume (gallons) = 7.5 x average width (ft.) x average length (ft.) x average depth (ft.)).

Of the pump I installed, again Mark at Rocky Mountain said, “This pump looks a little small to actually do much filtering. Probably around 500 gph would be better.” At the time frankly, I wasn’t much concerned with it’s size. Remember one of my biggest considerations – COST. And I’m sorry, a free pump fit in very nicely with my plan.

As a rule of thumb, the pump should be placed at the low point of a pond. Further, you want to choose a pump that has a flow rate equal to one half the total volume of water found in the pond. This means that half the water in the pond re-circulates, and is filtered within one hour. Judging from quick calculations on my water volume (as depicted above), and considering that fountainheads factor into flow rate – 500 gph seems close to exactly right.

* Plant Life Helps with Filtration

Mark noted that there were no plantings present in this setup. When asked about this, Mark said, “Plants can make a huge difference in both water quality and algae control. We recommend plants in all of our water features.” On asking him whether I needed a bigger pump, he responded, “I would try the plants first.”

My fountain pump came with about two-foot of tubing. Detailed specs told me how to calculate something called “head height”. (A little beyond me honestly, and nothing I feel we have time to cover here.) The spray pattern, as well as the flow rate, on my pump were adjustable. It had a little, idk, cup at its head. Pulling this cup in and out allowed me to produce the perfect simple bell pattern with its spray.

I placed this pump, which had built-in suction cups, on a platform of interwoven bricks. (I had many left over from the removal of the original patio.) In the end, the pump was then elevated by some nine or so inches. While elevating it did allow me to overcome the issue of having “an undersized pump”, and over-taxing perhaps the fountain, I think it will hurt in the long run. I wonder how the pump will do with filtering the floor of the pond.

More Moxie: A nice Overview on Pumps from the Home Depot. Choosing the Right Filter from Aquascape, Inc. (They authored our post: Tips for Designing a Backyard Pond). Mark, too, points me to the Pond Owner”s Handbook again by Aquascape.

* Electrical – Installing a Dedicated Pond Circuit (Waterproof GFCI Outlet)

This pond pump had about an six-foot power cord. But as it were, it had nowhere to go. Fortunately, when we installed our patio, I thought far enough ahead to pull a new circuit stub over with / to the location of my post lamp. (And this is something that I have written about previously – opportunistic remodeling.) See also my post on installing In Patio Lighting for more context.

* My Remaining Steps with Installing Electrical:

• Trench to a location near the pond.
• Pull Wire over.
• Install a Waterproof GFCI.
• Add a breaker back at my breaker panel.

If I were doing more than a very utilitarian set up, I probably would have worked harder to conceal this outlet. But for me, here, all I really needed was a power source. While I’ve seen specifications calling for a 6-foot distance from the water feature, the length of the pump’s cord hobbled me. (Admittedly, I am not sure of code specifically here. It might be wise to check with an electrician in your area.)

Using my trusty post hole digger, I sunk a five-foot scrap 4×4 post just off the edge of the pond, honestly only about 6″. (You might notice in pictures that I painted this post with foundation paint and gave it a more finished look with a spare fence post cap.)

While evaluating my underground wiring options, which I laid out in that post lamp post (jump to it), I chose to run UF (underground feeder). Since I selected gray pvc for the outlet box being installing on said 4×4, I chose to run the UF also through ¾” gray pvc tubing. I did this especially because my wire would be passing through and near gardens. I felt these locations were at risk to growing roots, digging and planting (now and in the future).

For trenching, I had to navigate down the yard some six or so feet before bringing things over. I was passing below a large and mature holly tree. While I tried to get as deep as possible with my trench, in reality, I could only get a depth of about 12″. (For more info on what to expect in trenching plus tools used for trenching, please again see my article on Installing a Post Lamp.)

* Installing the Exterior GFCI

While there’s not space to discuss the exact steps for installing my waterproof, exterior GFCI, I do provide some coverage here – Installing Wet Location Outlets. Optionally, I could have placed the GFCI at the breaker in the Breaker Box, but I did not. Call me superstitious, but I like the protection near the location that, well, needs to be protected.

I finished my electrical outlet with an Expandable In-Use GFCI Cover. This worked out great considering there’d be an appliance always plugged into it. While I did consider finishing by attaching the pond pump cable to the pond, ground or post, I decided against it. As I learned with weekly cleanings, it was very nice having the ability to unplug my pump so I could more easily access the pump and its filter.

Enjoying the Pond

I think my friend Lannie summed it up pretty perfectly. At the outset of this project, she said:

Pond Armor is an excellent product, however, as with any product you must follow the instructions. Prep work is of the utmost importance. You must have a clean surface, you must fill the cracks.

It is also important to understand that by filling a crack you are not adding any strength to the crack you are only filling the crack. If the ground moves again (this is what caused the crack to begin with) the crack may or may not reopen and may or may not cause a crack in the Pond Armor.

This is not the fault of the Pond Armor. If you prep your surface correctly the Pond Armor will stick for many years. And, yes it is safe for the fish.

In the context of discussing my pond, she went on to tell me about Rocky Mountain‘s design philosophies, as well as her own pond:

I love a gravel substrate so I can take them out of the pots and plants right into the pond. Looks so much more natural that way. AND they grow better when their roots are not confined to a pot! Can’t do that with concrete. Fish do better in a natural environment, also. The ponds we build are ecosystem ponds and provide, food, water, shelter and space for the inhabitants.

I built my pond for my turtles.

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Again, because we have now sold this house and have moved, I no longer have access this pond. I can’t grab missed photos and/or tell you how it held up through its now second Winter. I will say, it was a fun project … that I was able to share with folks in my extended network. From living with the pond for one full Spring/Summer, without a doubt, I want to add a pond at our new house! (More on that maybe one day.)

Fixing this hole in our yard was like fixing a hole in my life. The soft sounds from our new patio were straight up soothing. And I hope the new owners love it just as much as I did.

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This article is part of a year-long dumping on the final months/years of the restoration of our 1880’s Victorian Farmhouse. Already covered, Repairing Dutch Lap Wood Siding. Up Next: Refinishing & Hanging Antique Exterior Wood Shutters. Thanks for sticking with me. Be well. ~jb