Pond liners are pieces of flexible and thin plastic that are laid on the bottom of the pond in order to prevent the leakage of water into the ground below which in turn prevents the pond water from getting murky. But as they are thin, they are susceptible to tear and damage due to various reasons.
You can strengthen the liners by adding layers of things like concrete, mortar, and of course, cement on top of the liner. This will protect the liner from external damage and keep the pond clean and healthy.
Now, let’s take a look down below at how you can cement on top of pond liners and what its benefits are.
Why is placing cement on top of the liner necessary?
Before finding out how can you cement on top of pond liners you have to know the reasons to do so. As stated earlier, pond liners are pieces of thin plastic. If you place them in your pond without any sort of protection, they are bound to get damaged for various reasons. Falling branches may tear them instantly.
Even if they don’t damage them instantly, once there is a storm and the water is churned by the wind, so will the branches underwater. With the added force of the wind, they will most certainly tear the thin liners.
Another way your pond liner may get damaged is because of animal movement. No matter what animal you have in your pond, they will move underwater and they will come in contact with the pond liner. The bigger the animal, the heavier the contact will be.
This will leave a mark on the liners. You can even inadvertently damage your liner when you step into the pond. So, adding a layer of cement will prevent it from happening.
Another reason to place cement on top of pond liners is, although they serve the purpose of protecting the pond’s bottom, the liners themselves are not very eye-pleasing, especially from up close. Adding cement on top of it will make it more aesthetic.
Last but not the least, layers of cement on top of pond liners guarantee you durability. If the layer is applied properly, these ponds will still function perfectly even long after you are gone.
Additional Read: How to fix pond liner to wood
7 Easy Steps to Place Cement on top of a pond liner
Now that you have known why you should place cement on top of pond liners, let’s get to the ‘how’ part of the question. There are a few steps you have to follow to perfectly place a layer of cement
1. Preparing the liner
Before adding or mixing or doing anything with the cement, first prepare the liner and the ground at the bottom of your pond. Cement will add a considerable amount of pressure to the liner. Add this with the pressure of water, this will result in the liner being under a significant amount of pressure.
So if there are any irregularities in the ground below or small rocks, debris, or anything of that sort on it, the liner will be the victim of tears. In order to prevent this from happening, smooth out the ground below and remove every little thing that may cause any damage to the liner
2. Mixing the cement
After laying the groundwork, literally, it is time to mix the cement. Ideally, the sand and cement should be mixed in a ratio of 3:1. When mixing the cement, make sure to do it in a large container. Add sufficient water to it so that you get a muddy texture.
3. Laying the cement
After you are done mixing the cement, lay the mixture on top of the liner. The layer should be smooth and flat. In order to achieve the desired flatness, use either a mason trowel or a flat trowel. Make sure to keep the thickness of the layer between 1 and 2 inches. Any less than that and the layer will not be able to do its job properly.
On the other hand, a layer of over 2 inches of thickness will put immense pressure on the liners, which will be impossible to handle for even RPE liners.
4. Making shelves for fish
You need to make shelves for fish or places for plants to grow. In order to do that, press rocks on top of the applied layer. Press them in such a way that they are set firmly at the bottom. To make sure that the rocks stick to the bottom, put some more cement around them. This will create a seal that is water-tight.
5. Keeping the layer wet
The layer has to stay moist throughout the whole curing process. In order to keep it that way, water it every hour. If the layer becomes dry before the curing process is finished,it will crack.
6. Sealing the cement
Now it is time to seal the cement. Use a paintbrush to apply the cement sealer on the layer. After sealing the cement, wait for 24 hours to allow it to dry.
7. Pouring water into the pond
There are conflicting opinions regarding when the water should be poured. One group of owners think that you need to wait one week or even a couple of weeks before pouring the water. According to them, it provides the best chance of strengthening the cement.
On the other hand, others say that you have to pour water into the pond as soon as the cement dries. You can consult an expert on this matter.
Putting cement on the edges of the liner
Just putting a cement layer on the top of the liner is not enough. If you leave the edges of the liner out of the layer, then it will look even weirder than before. One way to cover the edges is to put gravel on them. But they won’t provide a permanent solution as rain will wash them away. So you will have to depend on old friend cement for this as well.
Use them with rocks to cover the edges for a permanent/ durable solution. There are a few steps you can follow here as well. They are :
1. Preparing the pond
Drain the water from the pond up to a few inches below the level you want to put rocks in. Then clean the liner by scrubbing with your hands. Make sure that no dirt or debris is present on it.
You can also put the rocks on a new pond without water, but you must scrub the line nonetheless. This process is better if you plan on rearing fish because if you have fish present in the pond, you have to go through the extra pain of removing them from water.
If you have fish in your water and don’t remove them before the start of the procedure, there is every chance that they will be harmed by either the debris or the rocks.
2. Cement mixing
After you are done cleaning, mix the cement and water. Don’t make it too thick or too liquid-ish. Imagine a pancake batter, that’s what the texture of the mixture should be.
There isn’t any specific ratio to mix cement and water, just make sure it can hold its shape while it is being applied. To apply cement on a space of 5 feet, you will need a bag of 80 pounds cement.
3. Applying the mixture
Apply the mixture along the edges. If you do it all at once, chances are it will dry off quickly. To avoid this, apply the cement in sections. You have more freedom in choosing the thickness of the layer than you had during laying cement on liners. The thickness can be anywhere between 3 and 8 inches. Spread it with a mason’s trowel so that it is flat when applied.
4. Placing rocks
Now take the first rock and push it on the layer. Make sure to place it firmly so that it does not fall off. In order to do so, it is better if you keep holding it for about half a minute into the cement. If the pond has a pond shelf, you only need to line the bottom edge of the rock with the shelf.
If there is no shelf, there is no need to worry as you can also mark the outlines of the rocks with chalk. Even that isn’t necessary if you can just line them up by seeing only.
Take the second rock and put it as close to the first one as possible. Place it in the same manner as before. Then gradually place all the rocks as you have placed the first two rocks.
5. Cleaning up
When you push the rocks firmly onto the cement, some of them will come out through the gaps of the rocks. When they do, use a mason’s trowel or a wire brush to brush them off.
6. Keeping the cement moist
Wait at least 24 hours for the cement to dry. To prevent the cement from cracking, spray it with water hourly.
7. Getting rid of alkali
The mixture of cement contains a high concentration of alkali. If it mixes with the water, it will bring the pH value of water up, which will result in the fish in your pond dying off quickly. To avoid this, use a scrub brush to apply white vinegar to the cement.
Make sure the vinegar is distilled before applying. You should also add this vinegar to the water in order to remove whatever lime seeps out into the water. Leave it for 10 days or so, then drain the water and pour fresh, new water and then release the fish.
8. Re-checking the pH levels
Even after waiting for 10 days, you can not be too sure of the pH levels of the water. So, bring a pH scale to test the alkalinity of the water. The ideal pH levels of the water should be between 6.8 and 7.8.
If the levels are satisfactory, then the pond is ready for the fish to be released. If the pH value is over 7.8, drain the pond, refill it and drain it again after some days. That should get rid of any alkali still left.
Drawbacks of cementing on top of a liner
There is one drawback of applying cement layers on your liners. As the cement mixture is kind of slippery, putting them on vertical or steep surfaces may prove to be somewhat difficult as they will tend to slip downwards due to gravity. To overcome this problem, extensive formwork should be done when applying cement mixture on steeper slopes.
Alternatives to using cement on a pond liner
Applying a layer of cement isn’t the only way to strengthen your pond liners. There are a few other options you can choose from as well. Some of them are :
Rocks or gravel are not only useful but eye-pleasing as well. You can even put them without cement. One thing that rocks provide which the cement layer doesn’t is that it creates small spaces where the bacteria that are useful to the pond are able to grow.
Just because the previous liners are old, doesn’t mean they are obsolete. As you have already prepared the ground before you had put the old liner in place, it saves you the time and effort of preparing the ground from zero.
If there are big holes, just patch them up and you are good to go. They provide excellent padding while also protecting the new liners from tears caused from within the pond.
Geotextile is exactly as the name suggests. It is a piece of fabric that has been put into the soil. It prevents soil erosion by stabilizing it. When applied over the pond liner, it can provide much needed protection from damage.
Putting cement on liner is a process that needs to be done with care and precision. It’s important to know how can you cement on top of a pond liner properly and I’m confident I’ve given you all the necessary info about it. If you need further help while doing this, a few searches on the internet should provide you with some diagrams about how to go about it.