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Concrete Driveways- dos and don'ts
Concrete driveways should last you many years if they are properly installed and spec'd. Here are some recommendations about what to put in the contract and what to avoid. The existing driveway was about 50 years old and had some huge cracks in it. Last summer we installed a new 24-foot wide x 44-foot long driveway in the Washington DC area. We hired a concrete contractor to do the job. Our driveway also slopes down sharply from the street. During heavy rains, their is water in the garage. So we also wanted to install a 4-inch wide drain in front of the garage door to take of the problem. We decided not to replace the concrete driveway apron. In our area, concrete driveways are not reviewed by building inspectors, although concrete driveway aprons are. The concrete driveway you end up with really depends on specifying what you want in the contract and then holding the concrete contractor to it. What do Concrete Experts Recommend? We did our home work and visited various websites of concrete trade groups such as the Concrete Network. Armed with this knowledge, we talked to many concrete contractors and some who professed to be. The Concrete Network specified the following for driveways: a) A concrete mix of 4,000 psi (pounds per square inch) .50 water to cement ratio for driveway construction. According to them, this provides better wearability and a "denser" concrete than the typical 2500-psi mix, b) The sub grade should be compacted and have an even thickness. A standard driveway is 4" thick you want 4" thick continuously, not a 3" to 4" varying thickness. In the west it's even more important to pay attention to this since soils expand, c) Reinforcement with either wire mesh, or steel bars (1/2 inch rebar) placed in a grid pattern. In either case blocks should be used to keep the reinforcement in the center of the concrete, d) Joints should be at least 25% of the thickness of the concrete- so a 1" deep joint should be used in a 4" thick concrete driveway. Joints should also be spaced 2-3 times in feet the thickness of the concrete: so a 4" thick driveway should have joints no farther than 8- 12 feet, and e) A simple broom finish for sufficient traction We also found out that concrete can now be made to match any almost any color desired. It also can be stamped to make it look nicer. We opted for the plain vanilla color and just a broom swept surface for traction. What most Washington DC metro area Concrete Contractors say We were very concerned and amused that most of the concrete contractors don't follow the above recommendations. Even the contractors that have been in business over 20 years. We purposefully showed our ignorance to see what concrete contractors would tell us. Most said that: 1) The standard 2,500 psi mix was fine. Some contractors said they would use 3,500 psi, but only when we asked about the mixture. When we asked why a 2,500 psi mixture was OK, they just said it's typically used in our area. That's not a good enough reason in our opinion, 2) When we insisted on a 4,000 psi concrete mix, they went along stating that it would cost a little more. All they have to do is request it and it costs only a $100 to $300 more, 3) Most contractors said a 4-inch thick driveway was needed. The concrete thickness should be 4-5 Inches, we went with the 5 inches thick driveway, 4) When it came to reinforcing with rebar, most contractors balked at doing it. They preferred wire mess, because it is very easy to work with. Rebar will take time to install. We ended up using heavy gage wire mesh, 5) Most contractors were knowledgeable about where to install pressure joints and when to make cuts to prevent cracks from being seen, and 6) No one we talked to had a problems with installing a 4 inch drain across the driveway, We'll be writing a separate article on that soon] So, we contracted for the above and work began. Because this is a big job we decided to keep an eye on things. We are glad we did. Lessons learned Constructing a concrete driveway involves preparing the surface adequately with crushed stone, assembling forms, and reinforcing mesh or rebar. That part of the project goes slowly. The actual concrete pour goes very quickly and everyone is a bit nervous because the concrete can't stay in the concrete mixer too long. Processing the concrete as it is poured is hard work work that can be compounded by hot weather. Make sure that your contractor has plenty of people on hand so when the concrete is poured they can distribute it and start to smooth it immediately. Here are the lessons learned from our experience 1) You must be on top of the contractor or have someone who is to make sure that the concrete you ordered is the proper mix, in our case it was 4,000 psi. We asked the cement truck driver for the slip. If it had said 2,500 psi, we would have sent the driver home, 2) No problems with the grading or compacting rocks, 3) We opted for heavy wire mesh. The concrete contractor said that there was no need of blocks to keep the wire mesh in the middle of the concrete. They usually pick it up right after they pour. This was a mistake on ourpart. It is impossible to pull it up consistently and half the time we hadto insist that they do it. We should have just used the rebar, 4) Make sure they install pressure joints between the new concrete and any solid surface (a stone wall, other concrete, or brick). If they don't that where the concrete is going to crack, 5) You need more than 5 people when you pour 4,000 psi concrete. Why?Because it is harder to work with then the standard 2,500 psi mix anddries faster. My heart went out to our crew who were really understaffedin very high temperatures, 6) Don't pour concrete when the temperature is nearing 90 degrees F. Its hard on the crew and the concrete as well. If you have to, schedule an early pour early in the morning. It's best though to choose a nice day in the Fall instead. 7) Make sure that the contractor cuts the lines in the concrete the very next day to prevent cracking from showing. All concrete cracks, but at the bottom of the cuts where you can't see them, and 8) Bring a copy of the contract with you. Many times, what you specify in the contract is not always adhered to or communicated to the people who actually do the work. Given that, you must speak up and point this out to the contractor and there staff. You can expect to meet some resistance at this point, but you should hold your ground. We found that being able to speak a little Spanish and providing refreshments especially if it is hot, will go a long way in getting the work done the way you ant it.