Manual coating allows the operator to have a permanent eye on the quality of the fabric. The various stages of gluing, sanding and coating make it possible to correct the defects of the fabric and to reduce by more than 90% the imperfections present on the fabric. Conversely, the mechanical "robot" coated without asking questions...
When you stretch a canvas in a humid environment, there is a risk that it will relax in a dry environment. This is why it is always necessary to stretch a canvas with a low level of ambient humidity. You can also stretch the canvas temporarily and let it dry before fixing it definitively. As the fibers are of natural origin, the canvas reacts to weather conditions and paint.

We recommend the traditional frames, with wooden keys (and not aluminum) in order to be able to easily tighten your canvas and above all to preserve it from the worries of traces that the metal can cause due to oxidation and hygrometry. We obviously recommend the Châssis France chassis (www.chassisfrance.fr)
Wrinkles are bad for any canvas. Stretch the fabric with care and always properly roll the fabrics that you are not using. Any surface creases disappear when you stretch the canvas. It is almost impossible to remove the deeper creases.
Old oil canvases may have small cracks at the edge of the stretcher. These are very superficial and inherent to aging. There is no reason to worry. They have no effect on the paint. At most, there is greater absorption in these places, but the fiber remains well protected thanks to the double layer of glue.

It is strongly discouraged and even frankly harmful for the painting if the canvas has already been painted. You can easily tighten a slack canvas by tightening the keys a little in the corners. If that does not work, you can always consider detaching the canvas and re-tensioning it according to the rules of the art. So do not use water, but on the contrary tighten it in a dry environment.
The one and only time you can use a little water is if the canvas is made from linen and if it is slightly relaxed before you start your work.