When thinking about using porcelain tiles design outdoors there are a number of important considerations to take into account. Firstly, and very importantly, porcelain tiles have different grades and you will need to check that your chosen tiles are Grade 5 i.e. suitable for outdoor use. Check with the supplier or manufacturer if you are unsure and double check that they are suitable for extremes of weather if that is relevant to where you live.
Use a bonded cement/sand screed to level the concrete substrate if necessary. To avoid problems with the screed shrinking (and causing the spots tiles to crack), allow it to dry out for 1 to 2 weeks. For minor surface irregularities simply use a levelling compound.
Ensure the surface that you are laying the porcelain tiles on is as level as possible, clean and dry, and remove any loose particles. Select a “thin bed” adhesive for very flat surfaces with level differences of no more than 6mm. Otherwise select a “thick bed” adhesive. Always press the porcelain tiles firmly in place to avoid any air pockets forming underneath.
Remove any excess adhesive from the wall tiles design surface immediately as it is difficult to clean off once dry. Allow the adhesive to dry for at least a day (longer in very cold weather) and protect from rain during the drying period if necessary.
Once the adhesive is dry you can then apply the grout between the wood tiles; the type you choose is important because some grouts are only suitable for narrow joints but others for wide joints up to 20mm. Press the grouting well down into the joints so that no air pockets are created and remove the excess with a damp cloth. Again, leave to dry for at least a day, covering if it starts to rain.