How many ducks do you have? It doesn't matter if the concrete is smooth or not it's not good for them and is very bad for there feet. 10x10 and 6x7 are extremely small I wouldn't even think about putting a pair of muscovys in that.they go up at night, I'm not stupid enough to leave them in all day in a muddy pen. Thats unhealthy first of all and just down right stupid, i don't know anyone who is that inhumane to their ducks. i have two pens 10 feet by 10 feet and the other is 6 feet by 7feet. and no because the concrete is not natural exactly right, its also more clean than just bedding on a dirt floor, so...