How to cast a retaining wall

Whether you are going to cast a retaining wall, plinth, staircase or worktop, concrete is an excellent material for both indoor and outdoor use. A retaining wall separates two surfaces and gives you a nice and stable finish at, for example, a driveway or a slope. In this guide, we show how a retaining wall is cast, but you can also apply much of the information to other casting projects.


It is important to use the right type of concrete for the purpose when you are going to cast. There are very many different varieties, but the most common concrete is aerated concrete. If casting takes place in minus degrees, you can add antifreeze to the concrete when it is mixed. Always read on the packaging what the concrete is suitable for and how it should be mixed.

You can also choose to mix concrete from the ground up with cement, sand and aggregate (single) and clean water. This can be a good option if you are going to cast larger quantities as it is slightly cheaper per unit volume. If you are going to cast larger quantities, a raffle (concrete mixer) is good to buy or rent, regardless of whether you use concrete or cement. If your own ballast is used, it is important that it is clean to prevent dirt and contaminants from mixing with the concrete, as this can cause corrosion (rust) in the reinforcement.

Reinforce with rebar

Reinforcement is an important element in casting to prevent cracking, absorb loads and stresses. Reinforcing bars are easily cut with an angle grinder and should always be placed in the mold so that they are completely cast in so that they do not rust. When you cast a retaining wall, a lot of rebars will need to be bent and then rebar is an invaluable tool.

Build a stable mold of the right material

The preparations before casting are at least as important as the casting itself, where a good preparatory work will be reflected in the finished construction. A mold is usually built of molded plywood or wood of various kinds. The molded plywood can be used for simpler castings, while wood is better suited for demanding castings. If a material other than mold plywood is used, it is important that the material is treated with mold oil or plenty of water so that the mold can easily release after casting. Depending on the material used for the mold, the concrete will have different appearances when the mold is removed.

Building a stable shape is important and the higher the shape, the more stable it needs to be to absorb the increased loads. When a retaining wall is backfilled from one side, build that side of the mold last. Since it is built backward, the work is made more difficult and any shortcomings will then not be visible.

To consider when casting against the ground

Whenever concrete is poured against the ground, a well-packed macadam base of about 10 cm is important to counteract settling and frostbite. Macadam prevents water from coming into direct contact with the casting and thus creates expansion space for the water due to the macadam’s draining and capillary-breaking properties. If the ground is muddy or otherwise in poor condition, you may need to dig deeper. Here you can advantageously use a rock crusher to compensate for the deeper excavation. The ground cloth should always be placed between the ground and macadam or rock crusher to prevent the different materials from mixing and collapsing.

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A concrete structure normally does not need maintenance, but it is good to keep track of whether any microbial growth has occurred, such as mold, rot, bluish fungus or soil bacteria.

Follow our step-by-step guide to help you succeed with the project casting retaining wall.

Step 1

Excavate the surface where the mold is to be built down to the stable ground. Make the excavation wide enough to prevent landslides and make room for mold construction.

step 2

Cut out and place a ground cloth against the shaft bottom.

Step 3

If the shaft bottom is deeper than 10 cm, first fill with a rock crusher which is then compacted with a vibrator plate.   

Step 4

Layout a 10 cm thick layer of macadam which is then compacted with a vibrator plate.

Step 5

Use a masonry cord to mark where the top of the retaining wall should end.

Step 6

Build the side of the shape that will be visible. Use at least 45×120 mm rule when building the frame. Start with the lower part of the frame and then put upright bars at the beginning and end of the mold and mount the upper part of the frame about 5 centimeters below the masonry cord.

Step 7

Stabilize the shape by building triangle support with a center distance of 120 cm.

Step 8

Nail the standing boards to the inside of the mold. Cut the boards so that they go about 5 cm above the masonry string.

Step 9

Stead the shape with more horizontal bars between the lower and upper bars.

Use a lace-up to mark on the standing boards where they should be cut. Use a circular saw and cut the top of the boards.

Step 10

Screw in reinforcement spacers at the bottom and top of the standing boards at the inside of the mold. Use a center distance of about 60 cm.

Step 11

Cut and bend the rebar to an L-shape and place the rebar in the spacers. Also, place ground distances on the reinforcement against the macadam. The length of the reinforcement at the ground surface must be at least 2/3 of the height of the retaining wall.

Step 12

Continue to reinforce and form a grid pattern that is approximately 15×15 cm. Well, the reinforcement at all places where it meets another reinforcement.

Step 13

Cut and bend the reinforcement to form a 10 cm distance where the next layer of reinforcement is to be mounted. Reinforce and sew a 15×15 cm grid pattern along with the height of the retaining wall.

Step 14

Cut and bend L-shaped reinforcing bars to the angle of the retaining wall. Reinforce and naja layer two to a grid pattern at the ground surface of the reinforcing bars that contribute to 10 cm distance.

Step 15

Drill holes in the standing boards at the bottom and top with a center distance of about 120 cm.

Step 16

Cut as many pieces of a threaded rod as drilled holes insufficient length to get on both double nuts and washer at both ends.

Step 17

Also cut up 16 mm electrical cable pipes, or so-called VP pipes to the same length as the inside width of the mold. These should be used as spacers and determine the width of the mold.

Step 18

Place the cut threaded rods in the holes and mount the pipe pieces on the threaded rods at the inside of the mold.

Step 19

Place blocks on the reinforcement on which the inside of the mold is to rest.

Step 20

Build the inner frame of the mold in the same way as the outer one. When you start assembling the standing boards, a cut is cut out where the tie rod reinforcement runs.

Step 21

Cut and place upright bars on each side of the tie rod reinforcement.

Step 22

Then lock the mold with square washers and nuts on both sides of the threaded rod and tighten tight enough. Then lock the nuts by fitting one more nut per side and tightening.

Step 23

Place a stop bar in the foot of the mold about 5 cm from the ends of the reinforcement.

Step 24

If more durable corners are desired on the retaining wall, a triangular strip can be mounted in the upper part of the mold.

Step 25

Water the mold abundantly before casting so that the mold can easily release later.

Step 26

Mix the concrete according to the instructions on the package and fill the mold as quickly as possible to get a homogeneous casting.

Step 27

Vibrate the concrete with a vibrator rod during casting and let the concrete flow out so that it reaches the stop rule. Do not vibrate in the same place for too long so that the ballast sinks to the bottom.

Step 28

Remove the bricks on which the inner form rests and smooth to the surface with when the concrete has begun to settle a little.

Step 29

Cover the casting with plastic and let the concrete harden according to the manufacturer’s instructions before removing the mold. Keep the casting moist for at least three days, but preferably for a week.

Step 30

The mold can usually be torn down after only three days, but wait at least a week before refilling against the wall.