Summary

Just a quick but effective 40 mm aeration grid i needed (twice), for my bath tub side tiled cover. i drilled the tiles with 40mm circular bell bit.
The purpose is double :
-allow the ventilate under the bathtub,
-being removable, i can use the holes to handle (remove and placing) the cover itself, as it needs to be pushed firmly under the bath tub border

I guess this can be used as plaster panel aerations too.