DIY Polished Concrete Outdoor Countertop and Base
Step-by-step guide made from Tidybricks patio restore's YouTube video.
This project guides you through building a sturdy outdoor countertop station from concrete blocks, casting a concrete slab top, and then grinding, polishing, and sealing it for a durable, high-end terrazzo-style finish. The base is also clad with painted tongue and groove boards for a complete look.
- Difficulty: intermediate
- Finished size: 1.67m long
Safety
- Always wear a dust mask or respirator, safety glasses, and hearing protection when grinding concrete, as it creates a large amount of fine silica dust.
- Be cautious when using angle grinders, as the polishing pads can fly off at high speeds if not properly secured or if the speed is too high.
Must know before you build
- Use a variable speed angle grinder for polishing; high speeds burn pads and damage concrete.
- Embed steel reinforcement mesh in the slab to prevent cracking over time.
- Meticulously seal formwork to prevent leaks, ensuring an even countertop and clean pour.
- Add a few drops of washing-up liquid to concrete mix as a plasticizer for workability.
- Vibrate the concrete formwork after pouring to eliminate air bubbles for a denser slab.
- Polish concrete dry to clearly see progress and avoid obscuring the finish with slurry.
Tools
- Variable Speed Angle Grinder (Angle Grinder, Bosch, GWS 9-125 S, 900W)
- Angle Grinder (Makita, GA5030, 720W)
- Diamond Polishing Pads (Various grits (50, 100, 200, 400, 800, 1500))
- Drill with Paddle Mixer (Power Mixer, Titan)
- Mixing Bucket
- Trowel (Pointing Trowel)
- Spirit Level
- Oscillating Multi-Tool (Makita) (optional)
- Hammer Drill (SDS Drill)
- Hammer
- Clamps
- Shovel
- Paintbrush
Materials
- Concrete Blocks
- Cement
- Building Sand (Multiple bags, Travis Perkins)
- Washing-up Liquid (A few drops, Fairy)
- Timber/Plywood
- Insulation Board (Celotex)
- Steel Reinforcement Mesh (1 piece)
- Masonry Screws
- Wooden Battens
- Tongue and Groove Cladding
- Grey Paint
- Concrete Hardener & Dustproofer (5 Litre, Alphachem)
- Paving Seal (Thompson's, One Coat)
Step by step
Step 1: Build the Blockwork Base
Mix mortar using a drill and paddle mixer, then lay the concrete blocks to construct the U-shaped base for the countertop.
- Mix the Mortar. In a large bucket, mix cement and sand with water. Add a few drops of washing-up liquid to act as a plasticizer, making the mortar more workable. Use a drill with a paddle mixer attachment to combine everything thoroughly.
- Tip: A few drops of dish soap (like Fairy liquid) can act as a plasticizer, making the mortar easier to work with.
- Lay the Concrete Blocks. Lay the concrete blocks in a U-shape to form the base. Apply mortar to the joints and use a spirit level to ensure each course is level and plumb as you build it up.
Step 2: Construct the Countertop Formwork
Build a wooden form on top of the block base to create the mold for the concrete countertop, using insulation board as the base and plywood for the sides.
- Create the Form Base. Place a piece of insulation board (like Celotex) inside the U-shaped block base. This will form the bottom of your mold.
- Build and Attach the Side Forms. Cut pieces of plywood or timber to create the side walls of the form. Assemble the frame around the insulation board base and secure it tightly with screws and clamps to prevent any concrete from leaking out.
Step 3: Pour and Level the Concrete Countertop
Mix and pour the concrete into the formwork, embedding steel reinforcement for strength. Vibrate the form to remove air bubbles and then level and float the surface.
- Mix and Pour Concrete. Mix your concrete to a workable consistency and pour it into the prepared formwork, filling it about halfway.
- Add Reinforcement and Vibrate. Place the steel reinforcement mesh into the partially filled form. Use an oscillating tool or tap the sides of the form with a hammer to vibrate the concrete, which helps release trapped air bubbles.
- Top Off and Level the Concrete. Pour the remaining concrete to fill the form completely. Use a trowel and a spirit level as a screed to level the surface, ensuring it's flat and smooth.
Step 4: Remove the Formwork (Demold)
After letting the concrete cure for a week, carefully remove the screws and pry off the wooden formwork to reveal the cast countertop slab.
- Unscrew and Remove Forms. After allowing the concrete to cure for at least a week, remove the clamps and screws holding the formwork together. Carefully pry the wooden sides away from the concrete slab.
- Tip: Let the concrete cure for at least a week before attempting to remove the formwork.
Step 5: Initial Grinding and Polishing
Begin the finishing process by grinding the surface of the concrete slab with coarse diamond pads to remove the top layer and expose the aggregate, creating a terrazzo effect.
- Grind the Surface. Using an angle grinder with a coarse grinding disc (like a flap disc), begin grinding down the top layer of the concrete to expose the aggregate underneath.
- Polish with Coarse Diamond Pads. Switch to a diamond polishing pad, starting with a low grit like 50. Work your way across the entire surface, then move up to the next grits (100, 200), ensuring an even polish.
Step 6: Apply Concrete Hardener
After the initial grinding, apply a liberal coat of concrete hardener and dustproofer to the surface. This strengthens the concrete for the final polishing stages.
- Brush on the Hardener. Pour the concrete hardener and dustproofer onto the ground surface. Use a paintbrush to spread it evenly, ensuring the entire countertop is saturated. Allow it to soak in and cure overnight.
Step 7: Final Polishing Stages
Using a variable speed grinder, continue polishing the hardened concrete with progressively finer diamond pads (400, 800, 1500 grit) to achieve a smooth, glass-like finish.
- Polish with Mid-Grit Pads. Using a variable speed grinder set to a low speed, continue polishing the surface. Work through the 400 and 800 grit diamond pads, covering the entire top and edges.
- Final Polish with Fine-Grit Pads. Complete the polishing process by using the finest grit pads, such as 1500. Go over the entire surface one last time to bring it to a high sheen. The surface should feel as smooth as glass.
- Tip: Inspect the surface for high spots and perform a final leveling before continuing to the next step.
- Tip: After polishing, apply additional concrete hardener to the surface and allow it to absorb before continuing.
Step 8: Clad the Base
Finish the base by attaching wooden battens to the blockwork and then fixing pre-painted tongue and groove cladding to the battens for a clean, finished look.
- Attach Wooden Battens. Drill into the concrete block base and attach vertical wooden battens using masonry screws. These will provide a mounting surface for the cladding.
- Install Cladding. Cut the pre-painted tongue and groove boards to size and attach them horizontally to the battens, covering the front and sides of the blockwork base.
Step 9: Seal the Countertop
Apply two coats of a one-coat paving sealer to the polished concrete surface to protect it from the elements and enhance its color and shine.
- Apply First Coat of Sealer. Pour a generous amount of paving sealer onto the polished countertop. Use a clean paintbrush to spread it evenly across the entire surface, including the edges.
- Apply Second Coat of Sealer. Once the first coat is tacky, apply a second coat of the sealer in the same manner to ensure a durable, long-lasting protective finish.