Abstract: There is disclosed concrete form apparatus comprising three elongated panels with sides hingedly connected and a method of using such apparatus to enable one to repair reinforced concrete slats in the floor of an animal pen by breaking away the concrete of a damaged slat while leaving any reinforcing bars within such slat and arranging the foldable three-part form apparatus to create a trapezoidal concrete form into which one pours a concrete mix and allows it to become firmly self-supporting before removing the form by lowering it to an unfolded position and drawing it up between two slat positions. In the event one wishes to proceed to replace most or all of the slats of an animal pen floor slab, it is accomplished by breaking out and reforming alternate ones of said slats in a first forming and pouring operation and subsequently, after those slats have become firm, performing the same procedure on the remaining set of alternate slats.