How do I enlarge a patio in my back yard that was put in when the house was built?

Lyle W EXPERT March 13, 2009

Enlarging your patio should not be a problem as long as you prepare the work area properly. As far as matching the existing concrete, that poses a larger problem. More than likely you will never get the same texture or color to match. Over time, wear and use, the color of the existing patio faded. But there are ways of resurfacing the whole patio without removing the old concrete. That would be very expensive and unnecessary. The following is a fundamental process to enlarge your patio, along with alternatives to resurfacing your existing patio and the new portion to look as one:

• Based on a 4 inch slab you should dig out approximately 6 to 7 inches of soil. This will allow for 2 to 3 inches of gravel to be laid down first for drainage under the slab. The first image below shows the basic steps in expanding your concrete patio.
• To eliminate standing water on your patio, it should be sloped toward the street and away from existing structures (such as your house and garage) a minimum of 1/8 inch per foot is recommend. If proper drainage is prevented because the concrete slab is wedged between two structures, you may need to install a drain that will collect the water at a low point in the concrete and divert it away.
• Control joints help concrete crack where you want it to. The joints should be of the depth of the slab and no more than 2-3 times (in feet) of the thickness of the concrete (in inches). So 4"concrete should have joints 8-12' apart
• Shrinkage is a main cause of cracking. As concrete hardens and dries it shrinks. This is due to the evaporation of excess mixing water. The wetter or soupier the concrete mix, the greater the shrinkage will be. Concrete slabs can shrink as much as 1/2 inch per 100 feet. This shrinkage causes forces in the concrete which literally pull the slab apart. Cracks are the end result of these forces.
• Know the allowable water for the mix the contractor is pouring- or be very sure you have chosen a reputable contractor who will make sure the proper mix is poured. It is more expensive to do it right- it simply takes more manpower to pour stiffer mixes.
• Also, rapid drying of the slab will significantly increase the possibility of cracking. The chemical reaction, which causes concrete to go from the liquid or plastic state to a solid state, requires water. This chemical reaction, or hydration, continues to occur for days and weeks after you pour the concrete. You can make sure that the necessary water is available for this reaction by adequately curing the slab. This means that over the course of 3 to 7 days you should water the pour to help with the curing process.
• The use of wire mesh is the most common procedure that is used to strengthen concrete. In order to further strengthen the pour is to put fiberglass in to the concrete as it is being mixed, this can be purchased by the bag when you order the concrete.
• Concrete does not require much water to achieve maximum strength. But a wide majority of concrete used in residential work has too much water added to the concrete on the job site. This water is added to make the concrete easier to install. This excess water also greatly reduces the strength of the concrete.
• The second image below provides a chart for the amount of concrete that you will need based on the size and thickness of the slab.

Stamped concrete, commonly referred to as patterned concrete or imprinted concrete, is concrete that is designed to resemble brick, slate, flagstone, stone, tile and even wood. Due to the wide array of options when it comes to concrete pattern, concrete colors, and the cost of stamped, or imprinted concrete in relation to the materials it is a substitute for, the choice of stamped concrete is becoming more popular and frequent. This appears to be the type of patio that you already have. If you are able to match this pattern and color yourself using the finishing steps in the first image below, you may be able to complete this project yourself. If you are not able to match the pattern or color, then you may need to overlay the existing patio. Here are some considerations regarding an overlay:

• Does the concrete have a lot of cracks or pitting? Is the surface out of level? If so, choose a higher-build material, such as an under lament or self-leveling overlay, that can be applied at a thickness of 1/4 inch or greater.
• The average cost of an overlay ranges from about $3 to $7 per square foot, depending on the type of system installed. However, the total cost can run considerably higher if you choose elaborate decorative treatments to pattern the surface or use more than one coloring method (such as integral color accented by stains or dyes). Be sure to ask the installer how much these decorative options will boost the final price tag.
• Using stamped concrete or a coating over the patio as a whole will make the final result of the project look as though the patio is one solid pour with no breaks in color or texture and will make your yard look beautiful. The third image below shows some finished patios.