Is 20mm deep enough for a recessed shower? I'd rather not have to build a hob if it can be avoided, The shower would be recessed 20 mm and the floor of the shower graded with a 1:50 slope giving me a minimum screed thickness of 10mm at the shower grate which is in the middle of the shower. The shower waste pipe is 100mm so it should carry the shower water away fast enough so the recess does not over flow. Am I right ? any help is appreciated.

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