Whether you’re just thinking about a new concrete garage floor or ready to start planning one, you likely have many questions. Calling a concrete contractor might seem like a good idea, but calling several can lead to different ideas and cost estimates. Do Your Research. It pays to do a little research before starting a home remodeling project. Understanding as much as possible is important whether you plan to do the work yourself or hire someone.
When searching for contractors, ask good questions and be able to recognize when answers don’t add up. Lousy concrete slabs are common, with cracks being a major issue. Some contractors might say ‘concrete is always going to crack’, but don’t believe it. Good concrete slabs in garages can hold weight, withstand hot and cold weather, and last for many years with little to no cracks. If you have cracks, they can be repaired. But to know what differentiates good from not-so-good slabs, here are some things to know. Floor Level. Old building codes used to require the floor of an attached garage to be four inches lower than the house floor to prevent spilled gasoline, vapors, and carbon monoxide from entering. Today’s codes don’t have this requirement, but some contractors and inspectors still insist on it. If you encounter this, question their wisdom and ask for evidence of legal necessity. It might still be required by local codes, but not in the International Residential Code. Ground Preparation. The biggest threat to a garage concrete slab is not what’s on top, but what might move below. If the soil or base shifts or settles, the slab can crack. Good ground preparation starts with removing topsoil and adding a minimum four-inch layer of gravel or stone if the soil hasn’t been previously disturbed.Soil that has been dug up before should be compacted. The gravel or stone also needs to be compacted.
Vapor Barrier: Vapor barriers (essentially, thick sheets of plastic) are often not required, but you really should insist on one. It’s an inexpensive bit of insurance against water moving up through the porous concrete, condensing on the surface and damaging items placed on the slab. Vapor barrier products manufactured specifically for use under concrete are the best choice. Vapor barriers also help keep moisture in the curing concrete, slowing the curing process, which strengthens the concrete because slow-cured concrete is stronger than fast-cured. The Right Mix: The concrete slab should be at least four inches thick; it needs to be thicker if heavy equipment will rest on it. Building codes offer requirements for the concrete mix, which vary by region. The standards are expressed in terms of ‘compressive strength,’ which boils down to the amount of water used in the mix. More water makes for easier pouring, which is why some contractors try to water down the mix that arrives in the truck. The problem is that adding water can also make for a weaker slab. Contractors can add plasticizers to the mix that create an easier flowing mix without compromising the compressive strength. If you live in a cold climate, your concrete mix should probably include air-entraining agents, which limit damage to the slab through seasonal freeze-thaw cycles. Fiber reinforcement is another inexpensive product that you should insist on. The fibers are mixed in with the concrete and produce a stronger slab. Reinforcement: Wire mesh or thick reinforcement bars (‘rebar’) has long been a component of concrete slabs. However, with proper ground preparation, a good concrete mix, and sufficient expansion joints, it really isn’t necessary. Still, many contractors continue to add the cheap insurance offered by reinforcement. If the reinforcement is to do its intended job, it needs to rest in the middle of the slab, not on the bottom. That means that it needs to be anchored in the ground well enough to stay put when the concrete is poured. Expansion Joints: Many people understand that wood shrinks and expands as temperature and humidity ebb and flow through the year. But the same thing happens with concrete. That’s why it is necessary to include expansion joints along the edges of the concrete garage floor as well as around posts or other protrusions in the slab. The resilient material used in expansion joints absorbs any expansion, thus reducing stress, yet fills that joint when it contracts. Finishing and Curing: Once the concrete has been poured, it needs to be leveled and smoothed. Expansion grooves should be cut into the wet concrete to provide additional crack resistance. Then, the new slab needs to be left alone. Concrete doesn’t dry out; it undergoes a chemical curing process that creates a dry, solid mass. The top surface needs to remain wet while the curing process takes place. Contractors often spray curing compound on top of the slab or cover it with sheeting to reduce evaporation.Maintaining the moisture of a slab during the curing process is crucial for its structural integrity. One effective method is to spray a small amount of water on the slab daily. This practice helps to keep the slab hydrated, which is essential for the proper hardening and setting of the material.
By offering to perform this task, you ensure that the slab remains in optimal condition throughout the curing period.