Which concrete should be used for concrete furniture, concrete decorations, etc.?

Which concrete should be used for concrete furniture, concrete decorations, etc.?

Concrete furniture sounds very unusual at first. Concrete is used to connect load-bearing, highly resilient components that are functional but not very aesthetic. On its own, however, the gray texture of concrete isn’t all that unattractive. Ground, polished and sealed, a smooth concrete surface looks very noble and sovereign. However, so that the concrete furniture remains usable and mobile, the construction should be carefully planned. This also applies to the type of concrete used. 

Why concrete furniture?

Concrete furniture and decorative elements made of concrete are particularly popular in horticulture. The main advantage of a concrete bench is its durability. Concrete furniture can be left outside all year round. With a little care, concrete furniture will last indefinitely. And if a damaged area needs to be repaired, this is done quickly.

The main disadvantage of concrete furniture is its weight. A concrete bench can easily weigh well over two hundred kilograms. Then it is no longer so easy to move. The manufacture of concrete furniture such as benches and tables therefore always requires precise planning of where the furniture will be placed. It is best to always set them up directly at their place of installation. That is why the top priority when building concrete furniture is: Build as thin as possible. But that’s not that easy, especially with concrete.

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Concrete: firm on pressure, weak on tension

Concrete is an excellent material when it comes to absorbing pressure loads. However, it is weak in all types of tensile and shear loads. Whether with concrete furniture or buildings, the trick to make concrete strong on tension is always the same: reinforcement.

In the case of concrete furniture, it depends on what type of stress is to be expected. Structural elements that protrude or are only supported at two points must be reinforced more strongly than parts that are not subject to loads. Tabletops and benches, therefore, need a real reinforcement mat in order to be usable over the long term. For less stressed components, however, rabbit wire mesh is sufficient. The reinforcement needs a cover of at least 1.5 cm on both sides. This results in minimum width of 3 cm for each element on concrete furniture.

Process concrete by hand

Free design with plastic concrete

The rabbit wire mesh has the advantage that the rough shape of the end product can be pre-designed. The plastically mixed concrete can then be spread over it. This is best done with a trowel and with your bare hands. To do this, however, it is very important to wear rubber gloves! Concrete is strongly alkaline and causes severe burns if it comes into contact with the skin. Kitchen washing-up gloves and disposable gloves are too thin. Rubberized work gloves are ideal. They cost 1.50 – 3 euros for the pair. Eye protection is also very important when working with concrete. The slightest splash of cement slurry in the eyes threatens blindness! It is therefore essential to use protective goggles for 3-5 euros.

Mix concrete

Concrete for concrete furniture: the finer, the better

Conventional concrete is usually a fairly coarse material. Pebbles up to 12 millimeters in size hardly allow filigree structures. However, cement is just as effective with fine aggregates. There are offers for creative design with concrete, but they are extremely expensive. A 5 kg bucket with creative cast concrete costs 25 euros. However, it is also very easy to produce usable concrete yourself. You need:

  • 1 mixing bucket 10 l (approx. 5 euros)
  • 1 bag of Portland cement (2.50 per 25 kg)
  • 4 sacks of quartz sand 0.4 – 0.8 grain size (approx. 5 euros per 25 kg)

Concrete is always mixed in a ratio of cement to a surcharge of 1: 4. From the specified ingredients, 125 kilograms of fine concrete for garden furniture can be produced at the same price as the finished concrete should cost. You can also mix the concrete a little thicker, this results in a smoother surface and increases the weather resistance. A ratio of 1: 3 can give slightly better results. The concrete produced in this way is so fine that even filigree structures can be produced with it.

Smooth or structured?

You can easily create smooth structures yourself using the appropriate formwork. The contact side of the formwork must be as smooth as possible. Even the “Betoplan” used in construction is too coarse for high demands in the construction of concrete furniture. Painted surfaces, such as chipboard, are ideal. The formwork itself should be made of sturdy plywood at least 3 cm thick. Additional battens prevent sagging. Corners should always be broken with chamfers. A sharp 90 ° angle does not have a long shelf life. For example, silicone can be used to create a corner joint or fillet if a semicircular broken edge is preferred.

Before casting, the formwork must always be well oiled. At 35 euros per 5L canister, formwork oil is quite expensive, but it is very economical. It is optimal for this purpose as it does not leave any discoloration on the concrete. Tests with the machine or cooking oil are therefore not advisable.

Structural formwork is made of silicone. A large selection of these can be found in specialist shops. With the appropriate skill, you can also make them yourself. To do this, you build a small formwork, place a sample piece in it and cover it with normal bathtub silicone. When it has hardened, you remove the sample and can now make as many duplicates in concrete as you want. You should always give yourself plenty of time when stripping. A resting period of 3-4 days can prevent the edges from cracking when stripping.

To seal

So that the concrete furniture is weatherproof, it still has to be sealed. Colorless sealing is recommended so that the concrete retains its character. A 2.5 L canister with a concrete/stone seal costs around 25 euros. The clear coat of paint reinforces the color and makes for a particular aesthetic look.

Tips for readers in a hurry

  • Make concrete for furniture and decorative elements yourself
  • Always oil concrete formwork
  • Always seal concrete furniture
  • Always build as thin as possible
  • Always chamfer or fillet the edges