How do I make a polished concrete hearth for our new fire place?

[PaulaD]

 

 

 

We have just purchased a wood fire place and we need a hearth. Does anyone have some guidance with how to make a polished concrete hearth for this one. I have attached the pic and dimension etc.

could someone also confirm the size of the hearth I need to build.

[MitchellMc]

Hi @PaulaD,

Be advised that polished concrete is typically something done by professionals with specialised equipment. You could potentially get an adequate result following the method below.

You'll need to start by preparing the area where you plan to create the hearth. Remove any existing flooring if necessary to expose the subfloor. Cover the surrounding walls, floors and any nearby furniture with plastic sheets to protect them from concrete splatter.

Measure and mark the dimensions of the hearth on the floor. Use painter's tape to create straight lines. Build a formwork using plywood or melamine boards. Cut the boards to the desired dimensions and assemble them to create a rectangular box that matches the marked area. Use screws or clamps to hold the formwork securely. Caulk a bead of silicone around the outside of the formwork to stop the concrete from creeping under it.

Concrete tends to crack over time, so adding reinforcement will help strengthen the hearth. Place a steel mesh or rebar inside the formwork to provide structural support. Make sure the reinforcement is elevated from the bottom of the formwork by using bar chairs.

Prepare the concrete mix according to the manufacturer's instructions. Slowly pour the concrete into the formwork, ensuring it fills all the corners and edges. Use a trowel to level the surface of the concrete. Remove any air bubbles by tapping the sides of the formwork with a rubber mallet. Cover the newly poured concrete with plastic sheets to retain moisture and promote proper curing. Leave it undisturbed for a few days to allow the concrete to dry and gain strength. Follow the curing instructions provided by the concrete manufacturer.

Once the concrete is fully cured and dry, remove the formwork carefully. Use an orbital sander to begin the smoothing process. Begin with coarse-grit pads to remove any imperfections and achieve a smooth surface. Gradually progress to finer-grit pads for a fine finish.  With a sander, the finest grit you'll likely be able to use is 240-grit, which isn't really fine enough to begin the polishing process. Professionally this process would be done with a dedicated machine and diamond-impregnated discs. Applying a wet-look concrete sealer will enhance its appearance and potentially give it more of a polished look. 

Remember your PPE, including a respirator, gloves and eye protection.

As far as I can tell, the size of the required hearth is not specified in your instructions. In order to work it out, you'd need to know the depth of your heater. The width of the hearth will either be 900 or 1000mm, depending on your model, but the other dimension would be B (300 or 400mm) + X (125 or 175mm) + the depth of your heater (marked with blue arrows).

Please let me know if you have any questions.

Mitchell