Laura's Backyard Renovation: How to Lay a Concrete Slab

Laura's Backyard Renovation: How to Lay a Concrete Slab

Jun 10, 2014

Name: Laura Watson
Type of Project: Outdoor renovation
Location: Adelaide, South Australia
Type of building: Semi-detached shop front/cottage with 1200 sq. ft. backyard

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We had quite a big job to tackle this week: to concrete the floor of the garage. Both Tommaso and Dad have done this before and seemed pretty confident that with a couple of extra hands it wouldn’t be a problem. We picked up the equipment needed a few days earlier from the local hardware store, and they kindly provided us will a free trailer for transporting the bulky rio reinforcing mesh home.

Luckily the local hardware store provides free trailer hire, which was useful when we needed to transport the reinforcing mesh for the concrete floor of the garage.

Firstly, the prep work, which started with a similar process to preparing the area for pavement at the back door: checking and pegging string lines to level and levelling any high/low areas of ground. We boxed the sides of the garage area by using wall sheeting off-cuts which we attached to the outside of the garage. This allowed the concrete to set with the same profile as the garage wall, which is beneficial as the lack of any concrete lip means rain can run straight off!

We used wall sheet cut-offs to create an external finish which matches the silhouette of the garage walls.

We also boxed a decent sized area at the entrance to the garage with a run off slope where the downpipes from the garage are. This will provide a good surface for water runoff and also help prevent excess gravel and dirt making its way into the garage.

Laying the moisture barrier.

We covered the area with a moisture barrier to prevent any water leaching out of the concrete mix into the soil and vice versa. Then we laid the rio reinforcing mesh, ensuring it all overlapped for extra support, and used plastic ‘reinforcing bar chairs’ (yes that’s what they’re called!) to hold the mesh up off the ground and in the centre of the concrete floor space. Two metal guides were installed, dividing the garage longways into quarters; these acted as a reference to set the top level of the concrete and also were used to run the screeders along to help ensure a consistently level floor. The area of concrete at the front of the garage was set at a slightly lower level than the level of the floor inside the garage. This recess creates a water barrier for the roller door to close into and prevents any water entering the garage under the roller door.

Everything was ready to go, including two very helpful volunteers (which made four in total) when the truck arrived. We had calculated how much concrete we would need ourselves, so the truck simply dropped the load and left. They boys used some homemade screeders to screed the concrete level, but as they worked their way to the entrance of the garage they realised that they were short on concrete! We made a quick call to the truck, which wasn’t too far away, and luckily the provider had some spare concrete, but unfortunately that meant another delivery fee for us, which will eat into the money we thought we were saving by DIYing this part of the work. We will never know, but we suspect that we were not delivered the correct volume of concrete at the first drop, as when we were chatting with the concrete delivery guy, he seemed to think that what we had calculated would have been too much when in fact we were short.

The concrete was levelled with homemade screeders.
These metal guides were used to ensure an even level of concrete.
Removing the metal guides then required some filling in of the gaps.

When the floor was screeded level and the two metal guides were removed and the gaps filled in, the boys stopped for lunch to let the concrete begin to cure. After lunch they attempted to ‘float’ the concrete for a smooth finish on the surface, but the concrete had already become too solid to achieve a super smooth finish. Still, the end result is pretty impressive, and the extra texture on the surface will simply act as traction!

We set the level of the floor outside the garage slightly lower than inside. This creates a recess for the garage door to close into and will prevent water entering the garage from outside.
The finished product (escuse the dirt on the roller door!).

One helpful tip for anyone considering concreting: make sure you are all wearing rubber boots; there were some issues with sneakers getting stuck in the wet concrete!

Estimated time for project: 8 weeks
Time remaining: 0 weeks (but there is still a little more work to be done, so we will go over.)

Check out the full series (so far) and be sure to check back tomorrow for installment #12 of Laura's Backyard Renovation.

(Images and diary text: Laura Watson)

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