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How to build a designer bench

Combine concrete with hardwood timber for an edgy outdoor piece.

Every backyard is different, so it’s a good idea to make individual furniture instead of buying something off the shelf. Creating a garden bench with real personality isn’t just for the pros, and this modern design is well within the reach of every DIYer. It has a solid appearance but with a few pairs of hands, it can be easily located and relocated as you need.

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Gather your supplies

  • Formwork sides (2) 434 x 467 x 17mm formply
  • Formwork back 400 x 467 x 17mm formply
  • Formwork base 400 x 400 x 17mm formply
  • Formwork front 400 x 377 x 17mm formply
  • Shutter 90 x 45 x 400mm pine
  • Concrete (six or seven 20kg bags per block, depending on size of polystyrene blocks, if used)
  • Seat pieces (2) 200 x 100 x 2400mm hardwood timber
  • Cleats 50 x 50 x 1800mm hardwood timber

You’ll also need Wheelbarrow; waste polystyrene blocks (optional); 45 and 74mm wood screws; steel finishing trowel or float; power saw; belt sander; electric planer; cordless drill; tape measure; spirit level; 10mm blue metal; exterior furniture oil; safety gear; selection of plants (we used agave)

Notes

1. To cast a solid concrete block of a certain size, you need to build formwork with an internal size that is the same as the required block size. Here, we created blocks that are 400 x 400mm square with a height of 450mm and a 140 x 90mm rebate across the top to support the hardwood seat.

2. To make multiple blocks, you simply re-use the same formwork, but you will only be able to make 1 block a day. You will also need to clean the formwork after each use, so it is smooth.

3. All screws must be driven from the outside of the formwork, otherwise you will not be able to strip it from the cement without destroying it. Then, you can keep using it many times until it wears out.

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Here’s how

Before (Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)
(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 1

Predrill, then, using 45mm wood screws, attach formwork sides to formwork back and base with joints flush. Attach formwork front so top edge is 90mm down from top of sides. Predrill, then screw shutter between sides with back edge 140mm from front edge (this creates the rebate in block).

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)
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Step 2

Pour contents of 3 bags of concrete into wheelbarrow and slowly Photography Brent Wilson add water to make a workable mix. You do not want it too stiff as it will not flow into corners of formwork. To lessen final weight of blocks, you can add waste polystyrene blocks to sit inside concrete. Just make sure there is at least 50mm of concrete all around polystyrene. Continue mixing and adding concrete to fill up to level of bottom of rebate. Using a spade or a short length of timber, tap formwork to vibrate concrete so it settles properly and to eliminate excess air bubbles.

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 3

Finish filling formwork to top. Use steel finishing trowel or float to smooth surface of rebate and top of block. Make sure concrete rebate finishes flush with underside of shutter. Let concrete set overnight, leaving formwork in place as long as possible after concrete has set and keeping block moist by hosing gently.

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)
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Step 4

Remove all screws from formwork and gently tap with a hammer to release it from block. Carefully remove formwork piece by piece (you will need to tip block over to remove base).

Step 5

Repeat Steps 1-4 to make a second concrete block.

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 6

Find desired positions for concrete blocks, allowing for desired length of timber sleepers (here, ours measured 2100mm after they were cut), then spread a bed of 10mm blue metal for each block.

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(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 7

Position both concrete blocks on blue metal, then check level.

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 8

Using power saw, cut both seat pieces to desired length (here, 2100mm). Using electric planer, smooth upper surfaces of sleepers and chamfer edges to prevent splinters forming. Using belt sander, smooth all surfaces, starting with a coarse-grade sandpaper and finishing with a medium grade.

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(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 9

Using power saw, cut three 50 x 50 x 360mm cleats with a 45° angle at each end.

(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 10

Put seat pieces together and position 1 cleat at each end and 1 in centre. Predrill, then, using 75mm wood screws, attach cleats to seat pieces. Finish with a coat of exterior furniture oil

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(Credit: Better Homes and Gardens) (Credit: Better Homes and Gardens)

Step 11

Position finished seat on rebates of concrete blocks.

Step 12

Add plants, then cover area around and under bench with blue metal.

Looking to make more outdoor furniture? Give these DIY’s a go: 

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How to create an outdoor table and benches 

How to build a planter box and bench seat

Charlie and Adam make a fire pit

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