I want to create a soaking tub in the wetroom I am building in my house, and I want the finished product to be, of course, waterproof and watertight, but I also want to keep the look of concrete, i.e., no tile, sort of like the tub in the above image. I figure I'd fill all the cores of the cinder blocks with rebar and concrete (of course on a solid foundation), but then what? should I take the pool plastering approach? I mean, swimming pools with it layers of gunite, and pool plaster are durable and water tight, so why not treat the building of this soaking tub like building a swimming pool with its concrete and steel reinforced walls as the gunite layer, and then apply a couple of coats of plaster inside and out using a grey portland cement pool plastering mixture . . . ? Is there a waterproofing product that will make the tub watertight, that looks like concrete?