Stamped concrete is sometimes called pattern concrete, but the two processes are actually separate things. Both can create a decorative concrete surface that imitates the appearance of stone or other textures. A stamped concrete overlay involves two layers of concrete; a thin layer of concrete is poured over older, hardened concrete, and then a texture is stamped into the thin layer. Pattern concrete, meanwhile, involves a single layer of concrete; the stamp is applied directly to the original concrete layer while it is setting up (curing).
While researching your options to create a decorative stamped concrete surface, you have a choice of whether to tear out your existing concrete and repour it with a pattern concrete pattern or simply apply a stamped overlay to the floor. Generally, going the pattern concrete way will be more expensive than the stamped overlay and takes longer. However, if you are having serious issues with your concrete, i.e., very large cracks with one side higher than the other, severe drainage problems, etc., then it may be better to tear out and start again with a pattern concrete floor.
The biggest difference between the two processes is that you can only apply a pattern concrete when the concrete has been freshly poured and not yet hardened. A stamped concrete overlay, meanwhile, can be laid on top of either new or an old concrete, so long as it has had at least fourteen days to cure (dry). If you don't have any concrete, then pattern concrete is the best option for that stone like look, if you already have concrete or are planning to do an extension and want it all to look the same, then a stamped concrete overlay does the job very well for less money.
Here's a good example: at this Prosper, Texas home, another contractor had added an extension to a concrete patio. The problem was that concrete used in the extension didn't match the color of the older section of concrete. The homeowner wanted us to cover up both patio sections with an overlay of stamped concrete. They wanted the stamp to resemble a random stone pattern stained a variegated mix of red, black and white. If the entire patio had just been freshly poured, the homeowner could have used a pattern concrete process to create the stone pattern and texture. But, because part of the patio was much older, a stamped concrete overlay was needed to cover both sections.
Our homeowner wanted us to get started on the stamped overlay as soon as possible. However, the patio extension was so new that it hadn't completely hardened and cured yet, and it would need to do so before we poured the overlay. We insisted on waiting a few weeks before getting to work. The patio extension needed time to cure; if we poured the overlay too soon, the new concrete layer could crack or peel off.
Why did we need to wait so long for the patio extension to cure? Concrete is a mixture of ingredients blended with water. It hardens during a process called hydration, which creates a chemical reaction that pushes salts and other minerals to the top of the concrete layer, leaving behind pores in the concrete. Before anything is placed on top of the concrete, the concrete needs time to push out these minerals. If we had applied the overlay too soon, the overlay would have adhered to those minerals instead of the concrete.
The water mixed into the original concrete also needs time to evaporate. As the water evaporates, the concrete hardens (and it shrinks a little too). In general, concrete gains about 75% of its strength seven days after it is poured, and it obtains close to 100% of its strength at twenty-eight days. As long as we have gone past the initial cure and set of the concrete we should not have any problems applying any type of overlay, whether it be skim or stamped, etc. The absolute minimum "curing period" that we will wait is fourteen days after the original concrete is poured and that depends on the weather, if it is cold, it needs to be longer; regardless, unless temperatures have been hovering around the freezing mark, by twenty eight days we are good to go.
The homeowner in Prosper agreed to wait, so we came by a few weeks later and applied the overlay, stamped it, scored it into a stone pattern, then wrapped it up with a multicolor stain followed by a sealer coat. Red stain can sometimes by a little overwhelming so we try to be judicious in its application but our homeowner wanted a heavy does and in the end he loved it, and that's what counts. In our next project we'll take a look at what we can do to fix a concrete surface damaged by some severe Texas weather.