Actually I could not understand your question. You are talking about slab or you are talking about countertop of the modular kitchen. If you are talking about concerete slab then it is not necessary but we do need countertop. It can be of any material like granite, quartz, concerete, stainless steel, artifical marble, marble etc. If you are willing to make modular kitchen showroom then you can even use wooden countertop with laminate but not at your home. At home you need rough and tough countertop.