DIY Polished Concrete Outdoor Countertop and Base

Step 1: Build the Blockwork Base

Level, plumb U-shaped concrete block base ready for the countertop mold.

Watch this step (2:24)

You'll need: Drill with Paddle Mixer, Mixing Bucket, Trowel, Spirit Level, Concrete Blocks, Cement, Building Sand, Washing-up Liquid

1. 1.1 Mix the Mortar
   • Put building sand, cement, and water in the mixing bucket.
   • This guide does not state the mix ratio; general practice is 4:1 sand to cement.
   • Add a few drops of washing-up liquid as a mortar plasticizer.
   • Blend the batch to a workable consistency using the drill with paddle mixer.
2. 1.2 Lay the Concrete Blocks
   • Lay concrete blocks in a U-shaped footprint shorter than the 1.67 m countertop, leaving room at each end for the batten, the cladding and the overhang.
   • Trowel mortar onto horizontal and vertical joints.
   • Check every course is plumb and level with the spirit level.

Key measurements

• Countertop and formwork length: 1.67 m; build the block base shorter by batten + cladding + overhang at each end
• Barbecue side clearance: about 150 mm of countertop each side of the grill

• Tip: A few drops of washing-up liquid make mortar smoother and easier to spread.

Before you move on: Level the top block course both ways with the spirit level before formwork.

Step 2: Construct the Countertop Formwork

Insulation base and outer timber side forms clamped tight with even overhang.

Watch this step (3:08)

Parts in this step: (B) Insulation board (Kingspan / Celotex ), (C) Timber formwork strips

You'll need: Hammer Drill, Hammer, Clamps, Spirit Level, Insulation Board, Timber/Plywood, Masonry Screws

1. 2.1 Create the Form Base
   • Cut insulation board (B) to fit the U-shaped block opening.
   • Set the board flush with the block tops as the mold floor.
2. 2.2 Build and Attach the Side Forms
   • Pre-drill and screw a spacer strip of batten plus cladding thickness to the blocks.
   • Add a second spacer strip outside the first to set the concrete overhang.
   • Fix the 1.67 m timber formwork strips (C) against the outer spacer with clamps.
   • Unscrew the inner spacer strips so the formwork overhangs the future cladding.
   • Patch timber joint gaps so wet concrete cannot leak.

Key measurements

• Formwork length: 1.67 m along the front face
• Overhang offset: batten plus tongue and groove thickness plus desired slab overhang

• Tip: Tap masonry screws in with a hammer before tightening the last threads.
• Heads up: Unsealed gaps or weak clamps let shuttering give way under wet concrete weight.

Before you move on: Check inner spacer strips are unscrewed and formwork joints sealed tight.

Step 3: Pour and Level the Concrete Countertop

Formwork filled with reinforced, vibrated concrete screeded flat to the top edge.

Watch this step (6:10)

Parts in this step: (D) Steel reinforcement mesh

You'll need: Drill with Paddle Mixer, Mixing Bucket, Shovel, Hammer, Oscillating Multi-Tool, Trowel, Spirit Level, Cement, Building Sand, Washing-up Liquid, Steel Reinforcement Mesh

1. 3.1 Mix and Pour Concrete
   • Mix building sand, cement, water and a few drops of washing-up liquid.
   • Shovel wet concrete into the formwork until the mold is half full.
2. 3.2 Add Reinforcement and Vibrate
   • Lay steel reinforcement mesh (D) flat on the half-filled concrete.
   • Tap around the outer formwork with a hammer to release air bubbles.
   • Or press an oscillating multi-tool to the timber sides to vibrate the mix.
3. 3.3 Top Off and Level the Concrete
   • Fill the formwork to the top rim with a final concrete skim.
   • Draw the spirit level across the forms to screed the surface flat.
   • Trowel the wet top smooth and cover if rain starts.

Key measurements

• First concrete lift: 50% of formwork depth before placing steel mesh

• Tip: Vibrating the outer formwork settles the mix and prevents edge air pockets.
• Heads up: Omitting the steel reinforcement mesh lets the concrete slab crack over time.

Before you move on: Check the screeded surface is level and flush with the formwork top.

Step 4: Remove the Formwork (Demold)

Cured concrete slab stripped of its wooden mold with clean perimeter edges.

Watch this step (9:21)

You'll need: Hammer, Clamps

1. 4.1 Unscrew and Remove Forms
   • Wait 1 week for the slab to cure before touching the mold.
   • Remove clamps and unscrew the fasteners holding the timber formwork strips (C).
   • Pry the timber sides off the concrete edges without chipping the corners.

Key measurements

• Concrete cure time: 1 week minimum before removing formwork

• Heads up: Stripping formwork before 1 week risks cracking or chipping green concrete edges.

Step 5: Initial Grinding and Polishing

Top cement paste ground off to expose stone aggregate and smoothed to 200 grit.

Watch this step (10:21)

You'll need: Angle Grinder, Variable Speed Angle Grinder, Diamond Polishing Pads

1. 5.1 Grind the Surface
   • Fit a coarse grinding pad to the angle grinder.
   • Dry-grind the top to strip surface paste and expose stone aggregate.
   • Run the grinder along the vertical perimeter edges to match the top.
2. 5.2 Polish with Coarse Diamond Pads
   • Fit the 50 grit diamond polishing pad to the variable speed angle grinder.
   • Set speed to setting 3, around 5,000 RPM, and smooth the slab.
   • Repeat on the top and vertical edges with the 100 and 200 grit pads.

Key measurements

• Grinder speed setting: setting 3 (around 5,000 RPM out of 11,000 RPM)
• Initial pad progression: coarse grinding disc, then 50, 100, and 200 grit diamond pads

• Tip: Grind only when dry so dust clears and reveals high spots.
• Heads up: Running polishing pads at 11,000 RPM flings pads off the backing plate at high speed.

Before you move on: Check for even aggregate exposure on the top and vertical edges before hardening.

Step 6: Apply Concrete Hardener

Saturate ground concrete pores with chemical hardener and cure overnight.

Watch this step (14:38)

You'll need: Paintbrush, Concrete Hardener & Dustproofer

1. 6.1 Brush on the Hardener
   • Liberally pour concrete hardener and dustproofer on the dry ground slab.
   • Coat the top and vertical edges with the paintbrush.
   • Add a second liberal splash once the first sinks in.
   • Let hardener soak in and cure overnight to harden the concrete matrix.

Key measurements

• Hardener cure time: overnight soak before final polishing

• Tip: Saturating with hardener stops surface dusting during finer polishing.

Before you move on: Test that water or tea beads up without soaking into the concrete.

Step 7: Final Polishing Stages

Level and polish the hardened countertop to a glass-like sheen.

Watch this step (15:38)

You'll need: Variable Speed Angle Grinder, Diamond Polishing Pads, Paintbrush, Concrete Hardener & Dustproofer

1. 7.1 Polish with Mid-Grit Pads
   • Circle high spots on the dry top with a crayon.
   • Brush on a fresh splash of concrete hardener and let dry.
   • Grind down the marked high spots until flat.
   • Polish top and vertical edges at low speed with 400 and 800 grit pads.
2. 7.2 Final Polish with Fine-Grit Pads
   • Stop at 800 grit if dark brown spots appear.
   • Otherwise, make a final pass on top and edges with the 1500 grit pad.
   • Grind out dark patches with the 800 grit pad for a uniform sheen.

Key measurements

• Final pad progression: 400, 800, and 1500 grit diamond polishing pads
• Stopping grit to avoid dark spots: 800 grit

• Tip: Over-polishing with a 1500 grit pad can bring up dark brown patches.

Before you move on: Sight the dry slab against the light for a uniform, glass-smooth glare.

Step 8: Clad the Base

Wrap the concrete block base in horizontal grey tongue and groove cladding with corner trim.

Watch this step (21:21)

Parts in this step: (E) Wooden battens, (A) Tongue and groove cladding, (F) Corner pieces

You'll need: Hammer Drill, Hammer, Paintbrush, Wooden Battens, Masonry Screws, Tongue and Groove Cladding, Grey Paint

1. 8.1 Attach Wooden Battens
   • Set four vertical 900 mm wooden battens (E) across the front block wall.
   • Set one batten at each end and two across the middle to stop flexing.
   • Set three vertical battens across the side wall the same way.
   • Drill through battens into blocks with the hammer drill; fix with masonry screws.
2. 8.2 Install Cladding
   • Cut pre-painted grey tongue and groove cladding (A) to span the walls.
   • Fix boards horizontally to the vertical battens from bottom to top.
   • Fit vertical corner pieces (F) over outside corners to cover board ends.

Key measurements

• Vertical batten length: 900 mm
• Front wall batten count: 4 battens (1 at each end, 2 in the middle)
• Side wall batten count: 3 battens

• Tip: Two front middle battens keep the cladding from bending or snapping.

Step 9: Seal the Countertop

Two brushed coats of paving seal lock and weatherproof the polished top.

Watch this step (25:40)

You'll need: Paintbrush, Paving Seal

1. 9.1 Apply First Coat of Sealer
   • Pour paving seal onto the clean, dry polished concrete top.
   • Coat the top and vertical edges evenly with a clean paintbrush.
   • Let the first coat dry until slightly tacky.
2. 9.2 Apply Second Coat of Sealer
   • Brush on a second coat of paving seal while the first is still tacky.
   • Cover the top and vertical edges without leaving puddles.
   • Let the sealed top dry and cure for a couple of days.

Key measurements

• Sealer application count: 2 brushed coats
• Recoat window: first coat slightly tacky
• Final color cure time: 2 days

• Tip: Applying the second coat while the first is tacky bonds the two coats.

Before you move on: Inspect wet edges; brush drips flat before the second coat sets.