The National Kitchen and Bath Association recommends 132" (330 cm) or 11' (3.3 m) of usable counter frontage for kitchens under 150 square feet (13.5 square meters) and 198" (495 cm) or 16.5' (4.95 m) of counter frontage for kitchens over 150 square feet [source: Farris]. Countertops are typically 24 to 26" (60 to 65 cm) deep, and if you plan to integrate functional features like a sloping drain board into your concrete countertop, it will need to be 2.5" (6.25 cm) thick. Concrete of that thickness weighs around 30 pounds per square foot (150 kg per sq. m) [source: Cheng]. In a small kitchen, you'll have over 650 lbs (300 kg) of countertop sitting on your cabinets; it'll be almost 1,000 lbs (450 kg) for large kitchens.
The weight of concrete is a critical physical consideration. Countertops made of concrete are heavier than countertops of any other material, including granite. You'll need to assess the condition of your cabinets and floor to determine if they're strong enough to carry the weight of a concrete countertop. Factors include age, strength and condition. Location also comes into play for cabinets; are they against a wall or freestanding?
You can reinforce cabinets with 1/2" (1.25 cm) plywood glued and screwed to their sides and backs. To distribute the weight over the widest possible area, put 3/4" (1.875 cm) plywood over the cabinet tops. Keep in mind, though, that reinforcement changes the dimensions and possibly the appearance of your cabinets and raises your countertop height.
Beyond weight, you should also consider whether a concrete countertop is suitable to your lifestyle. Like all countertop materials, concrete has strengths and weaknesses.
Hard and durable as it is, concrete requires more frequent maintenance than granite. It must be stripped and resealed with wax every three months. Even with care, concrete changes in appearance with age. It accrues hairline cracks as it expands and contracts with temperature changes. It won't melt if you put a hot pot on it, but it might chip if you put the pot down too hard. And none of the available sealants provides perfect protection from stains and scratches.
Concrete is not the best countertop material if you live in a seismically active area. Its strength is compressive, which is why it can take the weight of tractor-trailers and skyscrapers without shattering. But it's not good on a twist. If the supporting structures shift from level, concrete cracks.
While the materials to make concrete are not costly, the expertise of a concrete artisan is. Expect to pay around $70 per square foot of countertop for a simple professional manufacture and installation. If you want to incorporate special features, plan to fork over $200 or more per square foot. You can do the work yourself, but it may cost you in other areas. Read on to see what we mean.