Concrete is a wonderful building material; it's durable, versatile, and relatively inexpensive. Concrete's biggest drawback is appearance. Let's face it, plain grey concrete is not generally the most attractive look. However, thanks to the availability of acrylic concrete stains, you can now change your concrete from plain grey to a variety of different colours. You can apply a faux finish to create a natural flagstone look.
Prepare the surface of the concrete to accept the stain. First sweep and hose off the concrete to remove any surface contaminants. Then use a concrete etching product to create a porous, rough texture. After you've etched, the surface of your concrete should have a look and feel similar to that of 120-grit sandpaper. It should also absorb water readily.
Wash the etched concrete with concrete cleaner. This will neutralise the concrete etching product and remove any concrete dust created by the etching process. Let the concrete dry for 24 hours.
Tape off your flagstone pattern. Painter's blue masking tape works well. What you are doing is masking off the space that will take on the appearance of the mortar joints in between the flagstones. Take a look at natural flagstone patios to get some ideas. The tape lines should be organic and asymmetrical.
You can also create the look of a natural stone tile patio by taping off symmetrical joints.
Use your pump-up sprayer to apply the concrete stain.
Adjust the nozzle on your sprayer so that it produces as wide a spray pattern as possible. Start in one corner of the patio and work your way out. Spray the product down with a flowing, circular motion. Be careful not to work in straight rows; you run the risk of seeing lap lines in the finished product.
Keep in mind that the stain goes down as a milky clear solution; you will not see the colour emerge until the stain begins to dry.
Use multiple colours. Natural flagstone has a wide range of colours within it. In order to really achieve a natural look, use two or three different natural stone colours. One colour will serve as your base, and the others as accents to give the finished faux flagstones depth and drama.
Allow 24 hours for the stain to dry before removing your masking tape. You'll notice that the taped-off concrete now appears to be the mortar joints between the flagstones.
Apply a clear sealer over the entire patio to add additional protection. A gloss sealer will also add shine to your patio.
Allow 24 hours for the stain and sealer to dry before walking over it, and 72 hours before you move furniture back onto the patio.
Stained concrete can get slick. There are additives available that will add texture and grip to the finished product. Make sure anything you use is compatible with the stain and sealer you're using.