Learn how to build an outdoor garden bench
To make this project easier, you can have your timber pre-cut to size at your local Bunnings. Here's our cut list.
90mm x 90mm Merbau
90mm x 19mm Merbau
70mm x 19mm Merbau
35mm x 70mm treated pine
Measure and mark the 19mm form ply panel to make the concrete mould. For the sides we measured 2 lengths of 1240mm x 75mm and 2 lengths of 640mm x 75mm. For the base of the mould, we measured out 1240mm x 600mm.
Start by making the rip cuts on the form ply with the circular saw. Then cut the ply to size with a drop saw. Note that the width of the form ply will be the same as the width of the concrete tabletop.
Once the ply is cut, pre-drill with a countersink bit and then screw together the frame with 50mm timber screws.
To give the concrete slab a nicer finish, measure, mark and mitre cut the tri-quad trim to fit the internal corners. Fix it into place with a nail gun. You can also place tri-quad vertically in each corner to remove any sharp edges. Then trim the tri-quad in each corner to size with a hacksaw.
Wipe away any dust from the mould. Then to prevent the concrete sticking to the mould, give the frame and base a spray with silicon spray.
To make sure the concrete stays strong, you'll need to use reinforcing mesh. Measure, mark and cut the reinforcing bar with bolt cutters to fit into your concrete form. When putting the mesh in the frame make sure it is centralised in depth, length and width. You can use a timber block to help you hold the mesh in place, but it'll need to be removed before the concrete sets.
Place 450mm reo bars diagonally across each corner. Then tie the reinforcing mesh to these with the reo wire to help suspend it during the pour. Make sure the mould is level before you start.
To make the concrete slab we used 4 bags of ready-mix concrete and half a bag of ready-mix cement. We also added BondCrete for added strength. To mix it, we used a concrete mixer, but you could also mix it in a wheelbarrow. Add water slowly until you have a thickish slurry.
Once the concrete is ready, shovel it into the mould. If the concrete looks too firm and isn't spreading like pancake mixture, add some water and keep mixing. Level it off and use a trowel to remove any air bubbles along the side of the concrete. Tapping the sides of the frame with a rubber mallet can help with this. Leave the concrete to settle.
While the concrete is drying, you can build the wooden frame. Take the 2 pieces of 1130mm timber for the sides and 2 pieces of 545mm timber for the ends. Set the mitre saw to 45-degrees and cut one mitre on each length, then measure, mark and make the second cut on the other end of each length.
Lay out the frame, making sure the mitre joins are perfectly aligned, then join it together with the fixing gun. Add two of the treated 35mm x 70mm pine supports to the frame for extra stability. To secure, pre-drill using the combination drill and 4.5mm countersink bit before screwing the frame together. Use two 50mm timber screws in each treated pine support.
Lay out 4 lengths of Merbau for the legs and use a 505mm pine support as a brace at the top. Then measure and mark further down the leg to attach the other 505mm pine length for the shelf on the inside of the legs. You can place the shelf wherever you like, but ours measured 300mm up from the base.
To make sure the shelf is positioned evenly on the legs, use a Merbau offcut as a 70mm spacer. When the leg frame is square, countersink with 4.5mm bit, drill pilot holes and then screw into place with 75mm bugle screws. Repeat this process for the other set of legs.
Position the legs inside the frame and make sure they are square. Then countersink, pre-drill and fix the legs to the frame with the 4.5mm countersink bit, 5mm drill bit and 50mm bugle screws. You should use 2 screws on each side of the legs to secure.
Next you'll need to lay out the timber for the rectangular shelf frame. Use 2 Merbau side pieces and attach 3 treated pine supports, 2 at the ends and another in the centre. Just make sure you allow 70mm for the outer Merbau shelf.
Attach the shelf frame together by countersinking, making a pilot hole with the 4mm drill bit before screwing into place with 50mm decking screws.
Once the shelf frame is made, fit it into place. To make it easier, turn the island frame onto its side the screw the shelf to the legs with some 50mm decking screws.
Once the shelf frame is fixed into position, fix the shelf slats into place. Pin the first slat into place with the fixing gun, then use a 12mm spacer to evenly space the rest. You'll need to countersink, pre-drill and screw into place with 50mm decking screws. You should use two screws for each slat into the centre of each support.
Once the concrete has settled, you'll need to cut the wire and remove the reo bars. Next you'll need to screed the slab to remove any excess concrete and ensure the surface is smooth. This will be the underside of the table so it needs to be flat. Use the edging tool around the edges and then trowel the slab. Let the concrete set.
Remove the concrete from the mould by undoing the screws that hold the form ply mould together. Then you'll need some friends to help you flip the concrete benchtop onto the timber frame. Give it a light sand to remove any sharp edges, or for a more polished finish, you can use a grinder.
To finish off the island bench you can paint, varnish or stain it. We used a natural stain to protect the timber and bring out the natural grain. Apply as many coats as necessary.
You'll also need some help to put your wooden and concrete island bench in place once you're finished. Whether it goes indoors or outdoors it's going to look fantastic and come in very handy when you're entertaining family and friends.