Please choose the correct ending to complete the given sentence: Home and Garden: [header] How to lay a porcelain tile exterior patio [title] Use a bonded cement/sand screed to level the concrete substrate if necessary. [step] To avoid problems with the screed shrinking (and causing the tiles to crack), allow it to dry out for 1 to 2 weeks. For minor surface irregularities simply use a levelling compound.

Ending1: The screed must be pre-applied by a professional. For larger trenches, applying compound prior to construction would make the process safer but still have to be applied. Ending2: Do not let the cement dry out too long. Concrete in concrete potting beds can be treated professionally. Ending3: [title] Ensure the surface that you are laying the porcelain tiles on is as level as possible, clean and dry, and remove any loose particles. [title] Select a " thin bed " adhesive for very flat surfaces with level differences of no more than 6 mm. Ending4: Make sure there is no wind, or that it is not windy. It is important that these deposits settle sufficiently so that the pre-treated area is dry, although delicate the concrete lime (water from the tap) absorbs moisture quickly.

Answer format: ending1/ending2/ending3/ending4