I love working with concrete because it's tough and versatile and relatively cost effective.
In this instructable I'll be jazzing up a new footpath by exposing the aggregate.
There are a few ways to do this, and many commercial operators use a high pressure spray to blast off the top surface of cement.
The method I will show you doesn't require any special tools other than what you would use when mixing and laying concrete...it doesn't use any surface disruptors or acid, nor does it use a water blaster.
So if you can lay concrete, you can do this.
If you're concerned about committing to a large project, you may want to do a test run of the method by making some pavers or tiles on a small scale. Then when you're comfortable with the process you can create your large project.
Aggregate (pebbles) around 12-22 mm in diameter.
Screed (board or straight edged box aluminium)
Bucket (for pebbles)
Garden hose and water supply
Brush or broom - medium firm bristles
Helpers (the more the better, especially about an hour in...you'll be pleased you had them!)
Edging tool (optional but nice)
Step 1: Box; Mix; Pour; Lay; Screed; Trowel
We mixed our own concrete onsite but this method will work with premix concrete that has a normal cure time. A rapid set concrete should not be used.
I won't go through the specifics of the above steps, but so you know...
- box the area
- mix the concrete
- pour the concrete
- lay and screed the concrete
- trowel the concrete smooth
Curve your path...it's much nicer to the eye and can be easier to create than a straight edge.
Step 2: Seed the Pebbles
The pebbles are scattered or sprinkled onto the surface of the concrete. Do this by the handful, and have a good supply of pebbles on hand.
The concrete needs to be firm enough so the pebbles do not sink out of sight, but not so firm as to be difficult to push the pebbles into the concrete. You'll have to make a judgement call on this but I was able to seed the pebbles soon after trowelling the concrete smooth.
Pro tip: Wash the pebbles to remove any twigs etc.
Step 3: Push the Pebbles Into the Concrete
When you have a good covering of pebbles, begin to push them into the concrete with a trowel. You can see in the video that the concrete is still quite pliable. Take care not to push dents into your concrete...keep your tapping pressure consistent and trowel it smooth keeping the surface flat.
Finish the process by trowelling the concrete to a smooth finish. You'll know this is done when you see only a faint outline of the pebbles as shown in the last photo. A thin cement slurry will have covered all of the pebbles.
Step 4: Continue Seeding and Trowelling
It pays to have help! There is a point in this process where concrete has been laid and seeded, while at the other end, concrete is still being made and laid. Then it becomes apparent that the concrete is beginning to firm up and it needs to be seeded...while elsewhere the seeded stones need to be pushed down. It can be hectic!
So, have a few pairs of hands available...I had my family all working on this project and I was thankful for their effort!
Continue to trowel-in the seeded pebbles while someone else is seeding the new concrete further along the path. It will be a moving front of lay-screed-trowel-seed-trowel, lay-screed-trowel-seed-trowel, interspersed with cries of help as you realize the concrete is going off somewhere! See below for definition of 'going off'.
The last photo shows the concurrent stages of seeding concrete...empty boxing; fresh concrete; screed concrete; trowelled concrete; seeded concrete; trowelled seeded concrete. Whew!
Use an edging tool to create a nice edge to your path, using the tool while the concrete is still easy to work.
'going off' in this instance is Kiwi slang for the concrete setting or firming up.
In different circumstances it can mean:
"Streuth mate, you better get that 3 week old lasagna out of the fridge 'cos it's going off big time."
"I'd stay away from the neighbor for an hour or two. Someone egged his house and he's royally going off."
Step 5: Last of the Seeding
We made it! Nice work everyone.
Finishing off the path, the final pebbles are being pushed into the concrete and trowelled off.
Now you have time to go and eat the cold toasted sandwich that was made for you an hour ago.
The next step takes place when the concrete has firmed up.
Step 6: Wait for the Concrete to Firm Up
It was about 8 hours on a warm day until I was ready to expose the aggregate.
Setting time will depend on many factors so you'll need to use your judgement, but as a guide the concrete won't stick to your finger when touched, and you can scratch your fingernail into the surface of the cement. You can also gently walk on the concrete...but don't twist your foot as you may loosen or tear out your precious pebbles!
Step 7: Time to Expose Your Aggregate
This is the best part!
Using a brush and light spray of water, begin to gently brush and wash away the top layer of cement to expose your pebbles. Keep your brushing light and water to a minimum...but you'll get a feel for it and can increase both as you continue.
Take your time and don't brush out too much cement as you risk the pebble coming out. Constant watering will reveal your progress.
Step 8: Your Path Is Complete
If it's all gone to plan, you should have a beautiful exposed aggregate path. You've never appreciated a footpath like the one you've just finished!
One final optional step is to apply a concrete finish coating to the path. You'll need to leave your path for 28 days or more to cure, but the coating will add luster to your path as well as seeping into the concrete and 'locking in' the pebbles.
I used a brush and roller to apply the coating to the path. It looks magnificent!
I hope you have success with your exposed aggregate projects.
This is an entry in the
Stone Concrete and Cement Contest