Make sure the existing patio surface is clean and level. Clean the surface using a concrete cleaner, such as Trisodium Phosphate (TSP), and either a pressure washer or a stiff scrub brush. This will help you to see any cracks, pits or uneven parts of your patio. It also ensures optimal adhesion for the tile mortar. A flat, level surface will also keep your decorative tiles from cracking under foot traffic. If the slab is finished with paint or another sealer, or if your patio is excessively rough, you'll need to grind the surface with a scarifier.
TSP can be corrosive. Make sure you wear protective clothing, gloves and eyewear before working with TSP.
If you have wider-than-hairline cracks in the concrete, you'll have to fill them to keep the tile from cracking after it's laid. Use a liquid-applied crack isolation membrane to fill any cracks. With a paint brush or roller applicator, apply the liquid before applying the reinforcing membrane. Finish with another coat of liquid and allow it to dry. Using a good concrete patch or leveler, smooth the surface and let it dry thoroughly. Next, apply a concrete sealer with a small paint brush. This will allow better mortar adhesion.
Always wear kneepads when kneeling on hard surfaces.
Check the weather forecast. If there is a possibility for rain during your project, set up a temporary tarp cover to keep water away from your work.