Mixing decorative gravel with cement and sand helps to create a topping for a colourful concrete slab. The decorative gravel takes nothing away from the strength of the slab, but adds a smooth exposed pebble texture to the surface in a wide variety of colours, depending on the gravel type used. To use, you simply toss the gravel onto a poured slab, allowing the cement in the concrete slab to hold the gravel in place. After placement, use an additional cement mix to pour over loose gravel to bind it further. When cured, the decorative gravel remains in place for decades, deeply embedded in the concrete slab beneath.
Measure out the amounts of materials that you're using to create your concrete, depending on your use for the slab.
Use a weight-based mixing ratio when measuring the amounts of each material to use. Create a strong slab for vehicle use by combining one part cement, two parts sand and three parts gravel by weight. Decrease the sand for a less strong concrete for paths or patios, consisting of one part cement, three parts sand and three parts gravel.
Pour each of the dry materials into a cement mixer.
Turn on the mixer to combine the materials and then add water with the mixer still going, to bind them together. Keep adding water until the mix is about the same consistency as oatmeal.
Add desired admixtures to the cement mixer after adding the water to modify the concrete, such as integral powder colour.
Mix the admixture in thoroughly.
Pour the concrete into your prepared slab form, filling the form to the top with the mix.
Fill a wheelbarrow with the concrete if you require transport from the mixer to the slab area, then transfer the concrete from wheelbarrow to form using a spade.
Drag a wood screed in a sawing motion across the placed concrete to level the surface.
The screed pushes the concrete before it, filling voids in the surface while smoothing down high points.
Drag a bull float across the concrete after the wood screed to disperse the gravel throughout the slab and pull moisture towards the top to aid in curing.
Wait about an hour for the slab to reabsorb the moisture. Smooth the surface a second time by running the flat of a steel trowel over it.
Add the decorative gravel by tossing it onto the concrete slab with a sweeping motion of your hands.
Cover the slab with an even layer of the gravel, and then level the gravel out and fill any small gaps in the gravel surface by brushing over the gravel with a broom.
Mix one part cement with three parts sand and enough water to create a thin batter-like slurry.
Pour this batter mix over any sections of the gravel not held in place by the concrete.
Run the bull float over the decorative gravel to help press the gravel deeper into the concrete.
Pour additional gravel on any bald spots in the coverage, and then go over the spots with the float a second time.
Allow the slab to cure for an hour, and then test it for firmness using the ball of your thumb.
If you can push down on the concrete and move away without leaving an impression then the slab is ready for rolling. Roll a lawn roller over the gravel to press it even deeper into the concrete beneath. If the roller creates ridges as it goes, remove it from the surface and allow an additional 30 minutes curing time for the concrete to gain firmness. Roll the firmer surface, and then remove any ridge lines by pressing them into flatness with a 2 by 4 plank.
Go over the slab with a broom to remove the top layer of concrete between the decorative gravel, revealing the shapes of individual gravel pieces without dislodging them from the concrete.
Spray the surface with a water hose, aiming the light spray at the surface using a low angle to remove concrete from the top of the stones. Brush with the broom a second time to clean the tops of the gravel, and then wait two or three weeks for the concrete to cure before using.
Things you need
- Portland cement
- Cement builder's sand
- Cement mixer
- Concrete admixtures (optional)
- Wood screed
- Bull float
- Steel trowel
- Decorative gravel
- Lawn roller
- 2 by 4 plank
- Water hose