THE
BASE AND THE FORMS:
To build the form, position two parallel boards in the excavation
so that their inside edges form the sidewalk sides. Drive stakes
in place next to the ends of the form boards. Starting at the ground
level's highest point, raise the ends of the boards up wit their
top edges about 2 inches above ground level. Check
for level with a carpenter's level across the tops of the two form
boards. Fasten the boards to the stakes with scaffolding (double-headed)
nails. If the stakes are not flush with or slightly below the tops
of the form, saw them off when the form is completed.
Raise
the opposite ends of the boards up to suit, either following the
contour of the ground, or raising them to match the desired pitch.
Then drive stakes, spaced every 3 feet along the form boards and
nail the stakes to the form boards. Use double-headed nails throughout,
nailing from the outside of the forms.
Install
a stake at any location where two form boards join together. Nail
the stake to both form boards. Butt the two boards tightly. If the
ends of the boards are angled or uneven, square them off with a
saw before nailing them into position.
Oiling
The Forms-
Oil the form boards by painting on crankcase oil with an old paint
brush. With the oil treatment, the boards will not stick to the
concrete or absorb water from the pour and weaken the concrete.
Nail the end form boards to the side forms and drive stakes against
the ends to hold them securely in position.
Tamping-
To check the level and depth of the excavation, cut a board equal
to the thickness of the base and the slab. Center this on a 2X4
that is at least 12 inches longer than the form and nail the two
boards together. This combination is called a dragboard or a strikeboard.
Slide the dragboard along the forms. Fill in all low spots; excavate
all high spots. Tamp to assure a solid subgrade.
Adding
base material-
Install a base of crushed stone and gravel and tamp them in place,
if your specifications call for base materials. Be sure that the
gravel is level by creating another dragboard, this one equal in
height to the thickness of a 2 inch layer of sand plus the thickness
of the slab.
Now add
sand. At first it will sift down to fill the openings between the
gravel. Keep adding and tamping until there is a 2 in. layer with
a dragboard equal to the thickness of the concrete slab.
Reinforcing
Mesh-
When set on soil that may heave or shift, the wall- will require
reinforcing mesh. This also is the case with a subgrade of very
wet or sandy soil. The mesh won't stop the cracking, but it will
hold the cracks tightly closed. The mesh is called size 6/6 and
10/10, which means it is made of welded 10-gauge wire having 6 inch
square openings.
The mesh
is available in rolls and can be cut with fencing pliers or bolt
cutters. Take care to fatten the mesh thoroughly so it won't be
near the top or bottom surface on the pour. Before placing the mesh,
set small stones or half bricks on the base to raise the mesh up
about 2 inches below the top of the form-or the approximate center
of the concrete slab. Position the mesh on top of the rocks. Do
not allow the mesh to come into contact with the form, or you will
have a piece of metal sticking out the side of the concrete. This
will later rust and discolor.
