De qualquer tipo, moldado no local ou pré-fabricado. Pode ser piso (caso mais geral) ou parede. Veja e visite estes dois exemplos, especialmente o primeiro:

Coalition for Quality Concrete Flatwork
Craft training for concrete apprentices and concrete workers who finish concrete flatwork such as concrete floors and slabs.
www.flatwork.org/

Flatwork forms :: dee Concrete Accessories
... dee's metal flatwork forms are used in concrete flatwork placement such as
... dee's concrete's flatwork forms are perfect for most edge forming, ...
http://deeconcrete.com/flatworkforms.html