Whether you’re installing a concrete driveway for your new home, or ripping up your old one to upgrade to a shiny new exposed aggregate one, there are a number of items on the installation check list that you should make sure your contractor ticks off, to guarantee a quality, long lasting product.
You can choose a skilled concreter as far as finishing goes, who will make your concrete driveway surface look great, but the differences between a Quality Project, an Acceptable Job and OMG What Has Happened often comes down to the little things within the concrete layers.
Excavation & Subgrading
Lets begin with the dig out of your site. As a general rule of thumb when excavating, if you’re digging out good fill, sand or rock, then it’s perfectly fine for that to be excavated and sub-graded ready for the new concrete. On the other hand, if your contractor is encountering clay seams throughout the area, then a bit of further work needs to be carried out.
It is a good idea to remove these clay seam areas and replace them with good, solid fill. What will typically happen, is when the concrete is placed over the clay seam, it will sink from the concrete’s weight, causing the concrete itself to move and at best find a point to crack along, at worst….fail and lift/drop in that section completely.
From here we start working on the steel and expansion material installations that form the backbone of your concrete driveway.
Firstly, N12 starter dowels should at least be drilled into all cold joint trip points where the new concrete is meeting old concrete in a walk through area. These dowels are drilled into the existing concrete, then will be in the middle of the new concrete while it is installed, this will create a strengthening point which will not allow the new concrete to either drop or lift above or below the existing concrete level.
Next, Abel Flex expansion foam should be installed at all cold joints where new concrete meets old concrete. This material allows the concrete to shrink during the curing stage without pulling away from the adjoining hard surface, as well as, if the concrete does move at some stage in the future, it has a cushioning barrier where the tension can’t get too high causing the concrete to lift above the joint.
Then we move onto the slab mesh installation. Slab mesh should be installed throughout the entire area approximately 50mm from the edge of your new concrete, then chaired to a minimum depth of 50% of your new concrete.
We push onto the final necessity which are re-entry bars. These are made typically from N12 deformed bar and placed at all internal corners of your new concrete, which are usually a high percentage point of failure for cracking.
During your concrete installation, assuming that you have hired a skilled person on the screed and trowel, there is only one thing that you need to keep an eye on, water content.
The water acts as a separator for the the materials within and reduces strength throughout the concrete as a whole, as well as separating the matrix on the surface which is to be finished. Apart from not wanting to weaken your concrete for obvious reasons, if the surface matrix (mixture of sand and cement on the surface), is watered down and separated, it can a lot of the time cause your concrete to start dusting up and eroding. If this happens with plain grey concrete, it’s not the end of the world, as a simple clean and seal will fix the problem, however, if it happens with your exposed aggregate concrete, you may find yourself having stones start to let go and not be held in properly, leaving a terrible looking result over a short period of time.
Control joints need to be installed on all concrete driveways. These control joints act to weaken a certain high percentage cracking line, which allows the concrete to find that weakened point and (hopefully), crack within the control joint that has been installed. Control joints can be installed either during the pour by tooling them into the concrete, or saw cut into the concrete after the setting process (typically 2 days after pouring).
It is also advised that you seal your new concrete, then continue to maintain the sealer every 12 months after installation. Sealer acts as a vapor barrier, stopping water from penetrating into the surface matrix of the concrete. Whilst also making it easier to clean, it stops the concrete surface from eroding away.
I hope you found some of this information informative. Have a chat with your contractor during the quotation process to make sure all these areas are not only included in your pricing, but are 100% to be installed.
It’s always better to pay a little more for a quality installation, rather than saving some money upfront, only to end up paying double down the track when things start to fail.