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Nothing says strong quite like concrete. So if you want a really durable, knock-over proof bench for your garden then a concrete one is the answer! This DIY concrete garden bench would be a great addition to any yard for its simplicity.
It’s quite a big concrete project, but it’s easy even to those who have never built anything using concrete!
When finished, this garden bench will weigh around 250 kg. It’s really heavy and will almost be impossible to move on your own. So make sure to do this project very near the site where it would be placed!
However you can also do this project a little differently if you want to get rid of some of the weight. You could use polystyrene or PVC pipes as fillers. You can also go for lightweight concrete that’s readily available in most hardware stores. This would make your bench 25% lighter. Or you can build a ‘thinner’ version of it if you want to make it look lightweight.
But ultimately you need to determine the maximum load that you want your bench to support. This is so that you will know what materials can and cannot be used in your DIY project. If you’re unsure, you can do some research or consult a knowledgeable friend! ;)
Do you want a concrete garden bench for your outdoor area?
Learn how to build one now through the step-by-step tutorial below!
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You’ll need these materials:
- Melamine Board / Shuttering Plywood
- Silicon Sealant
- Release Agent (Silicone Spray, Petroleum Jelly, WD40)
- Masking tape
- Scrap Wood
- Concrete Coloring (optional)
And these tools:
- Power Drill
- Caulking Gun
- Old Orbital Sander
- Mixing Bucket
1. Melamine Board or Shuttering Plywood
To make your mold, you’ll need a waterproof plywood with a smooth surface. Shuttering plywood is a material that’s designed to make molds. It’s got a very smooth surface and is water resistant. It’s also very expensive. When you are planning on reusing the mold I will recommend shuttering plywood. Otherwise melamine board is a cheap alternative.
A melamine board has a smooth surface, but it’s not water resistant at the sides. I found an old closet in the dumpster and reused its boards to construct my mold.
I used 10 premixed concrete bags (25kg each) as they are easy to use. When you want to make your own concrete you have to put the cement, sand and gravel together. 1 part cement, 2 parts sand and 3 parts gravel. When you change the size of the bench you have to calculate the amount of concrete you need. A 25kg bag of concrete is good for 12 liters.
Making the mold: The cutting of the pieces was done by my local hardware store. When everything fits correctly it’s really easy to screw together.
The cutout was made with a circular saw. Place the two sidepieces on top of each other and clamp them down before cutting. Doing this you will get two identical pieces.
You can now screw everything together. Be sure to use a lot of screws because it has to be able to withstand the weight of the concrete.
Adding rebar: I used a piece of an old fence to function as rebar. I cut it down to the correct size with an angle grinder. You can also buy rebars at your local hardware store.
While making and placing the rebar you have to consider two things:
- You have to place the rebar with an offset of at least 4 cm from the concrete surface. If you don’t do this, the rebar can rust and you can get spalled concrete. When you want to place your rebar closer to the surface you can use a coated rebar or stainless steel.
- You have to place the rebar as far down in the seat as possible. When you sit on the bench it creates tensile forces in the bottom of the seat. This is the place you want your rebar to be.
I doubt if rebar is really necessary for this particular bench. The seat is 15 cm thick so it should withstand a lot by its own. But it’s better to be safe than sorry.
Applying silicone sealant: When using melamine board you have to apply silicone sealant at the joints because the melamine board isn’t waterproof at the joints. The silicone seal also creates a nice round edge. I used masking tape to create a tight seal.
NOTE: Before you seal the inside of the legs you have to place your rebar in!
Placing rebar: I placed the rebar with some scrap pieces of wood and some string.
The rebar is placed as shown in the drawing.
Mixing the concrete: Follow the instruction on the bag to mix your concrete. I used a big plastic tub and mixed the concrete and water with a shovel. A good tip is to first calculate the water you need and than add 2/3 of this in the tub. Add your concrete little by little while mixing it. At the end add the other 1/3 of the water.
I used black pigment powder to give the concrete a darker color. I did a shitty job mixing the pigment with the concrete. This is why the concrete has a patchy appearance. But in the end I really liked this.
NOTE: Be sure to wear gloves when mixing concrete. I did not know this and made the mistake of touching the concrete, scooping it in the mold and even mixing the concrete with my bare hands! The cement in the concrete is hydrophillic and will get your hands as dry as dessert sand. My hands were a disaster for three days! Always use gloves folks!
Filling the mold: Before you fill the mold you have to be sure the mold is placed level.
To make the mold easy to come off you have to use a release agent. There are special release agents on the market but it’s not worth the money. I used silicone spray as a release agent. You can also use olive oil, WD40, petroleum jelly, almost anything that’s greasy.
To get a smooth surface you have to get the air bubbles out of the concrete. To do this you have to vibrate the mold, I used two different techniques for this:
– Tap the mold rapidly with a hammer. This is used to get the bottom of the mold smooth (seat part)
– Use an old orbital sander to press against the mold. This is a good method to get the air bubbles out of the legs and sides.
You can also use a drill hammer to vibrate the mold.
Knowing this you can now fill the mold with concrete. Be sure to spread the concrete and press it into the base of the mold. Fill small batches of concrete and tap the mold frequently between the batches. This is really important! Also use the orbital sander on the sides of the bench.
When you have filled the seat of the bench you have to put the piece of board in place before you can fill up the legs. When you’re finished filling up the legs, you have to cover the legs with a plastic foil. This is done to prevent the water in the concrete from evaporating.
NOTE: I made extra bracing pieces to strengthen the sides of the mold although this wasn’t necessary at all.
Demolding: When you’ve waited for five days you can start demolding. Unscrew the boards and use a joint knife as a wedge between the wood and the concrete.
Final product: You’ve made yourself a nice looking concrete bench that will last forever and ever and ever… Good luck with moving the bench. This 250 kg beast is a real back breaker.
Thanks to rubenrijst for this great project!