112 Section 2 Construction Materials
Forms for concrete should be leveled and well braced, Figure 6-8. Forms
for footings, concrete floors, and sidewalks are often made from boards
standing on edge. They are held in place by stakes driven in the ground
along the outside of the board, Figure 6-9. Forms for concrete walls consist of
panels on each side of the wall that are joined by form ties. Form ties
maintain the correct thickness of the wall, Figure 6-10.
Forms should be clean and joints should be tight to contain the liquid
concrete. Form oil is sprayed on the form surfaces that will be in contact
with concrete to facilitate removal and cleaning. Reinforcement for footings,
floors, and other concrete placed directly on the ground should be in place
and off the subgrade the correct distance. Rebar in walls is tied in place
before the inside form panels are put in place.
form ties:
Component that
attaches to a wall
form to maintain
the correct wall
thickness and
prevent wall forms
from separating
when filled with
concrete.
Nails
Stake
Subgrade
2 × 4 board
Figure 6-8. You can see a firm subgrade, some reinforcing mesh, and part of
a form. The black expansion joint along the wall allows the concrete to expand
during hot weather without buckling.
Figure 6-9. Stakes nailed to 2 × 4s hold these sidewalk forms in place.