A concrete driveway must be installed on solid, stable soil, otherwise it will eventually fail reducing the life span. Excavating and adding base material or any other type of structural base to unstable sub-grade can stabilize the soil and in turn, will lengthen the life expectancy of the concrete driveway. However, whether base should be installed or should not be is a difficult question to answer. It really depends on what the soil is like in the region you live in and more particularly the area where the concrete driveway is to be installed. You must be prudent when getting bids because there are two things to look out for:
1) Contractors who don’t include base in their estimate when it really should be installed
2) Contractors who try to sell us base where it just isn't necessary.
Let me give you an example.
Here in Denver, there are two types of soil we install concrete on. The first, which is along the front range far east of the mountains. The soil in some areas can be considered to be expansive soils that tend to be a bit unstable and move a lot. It's hit or miss. Some contractors will include 3 to 6 inches of base in their bids to stabilize the sub-grade and minimize any cracking that may occur in the concrete. On the other hand, the soil just west right into the foothills and into the mountains is completely different. It’s mostly made up of decomposed granite which is almost identical to that of base. You couldn't ask for a better, more stable sub-grade material. So most contractors will not include the installation of base in their estimates.
Now, I say most contractors because again, there are some contractors who will include base in their bids and oversell the importance of it to increase their profits. But there are also contractors who will not include base in their bids so they can, "Get in, get paid and get out" fast!
So, how do you know whether base should or shouldn't be included in your bids?
The best way to determine whether the region you live in requires base or not is one of two ways. The first and least expensive way is to get 3 estimates from 3 different contractors. If all of the estimates have base installation on their proposals, then it’s more than likely needed. On the other hand, if 1 or 2 out of 3 have base installation on their proposals, then we’ll need to do a little investigation to find out why. Start with the contractor that doesn't include base installation on their proposal and ask them for 3 references near your home. Request that each reference is 2 to 3 years older than the next. What we’re looking for is longevity. If the driveways have an excessive amount of cracking, failed areas or low spots, that's probably a sign the soil is unstable and base should be installed. I would eliminate that contractor from the choices and then investigate the other 2 contractors work. If those driveways are in great shape then that should be a good sign base is a standard practice in your area. On the other hand, if the 1st contractors driveways look great, then the other two may be overselling it. Either way, it may take some thorough investigation on your part.
The only sure fire way to determine if the area you live in requires base is to hire a soils engineer. But that can cost hundreds if not thousands of dollars. But even then, there’s not a 100% guarantee that the concrete will not fail unless the soils engineer is willing to guarantee it in writing, which in most cases... they won't.
Base can be very important. Before you hire any contractor... avoid concrete installation scams and see our report on “The Most Common Ways Concrete Installation Contractors Rip Us Off and How To Avoid Them”.
Or make it easy and request a concrete installation estimate from one of our Trusted Contractors!