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5. Use of different source materials often meet the same per
formance and design strength criteria. Therefore, a readymix batch plant may use and batch several different sand,
rock and cement sources in the course of one day. This is
why it’s important to check and verify that the Statement of
Mix Design uses the sole source materials throughout the
duration of the project.
RULE 4
FORMWORK
Precise formwork leads to precise concrete work, and since concrete is fluid when poured, it will conform to its confining formwork. Precise formwork will result in concrete having crisp and
precise edges, smooth grades and even transitions.
1. Form lumber should be S4S (surfaced four sides) #2 grade
Douglas fir or better.
2. Form lumber should be handpicked to be free of crooks,
RULE 3
SUBGRADE PREPARATION
hooks, warps, wanes and/or knots.
3. Layout should be performed with digital transits for precise
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Without a well-graded and compacted subgrade, the best architec-
alignment. (Wind blowing on a tight string commonly used
tural concrete may fail. This is often the most overlooked step in
for layout can deviate more than 2 inches in a 150-foot run.)
creating a quality concrete installation. Key factors to ensure quali-
4. New material should be used for each new project.
ty subgrade are:
5. Straight wall forms should be 3/4-inch M.D.O. plywood.
6. Radius forms should be 2 laminations of plywood with the
1. Subgrade should consist of semi-permeable, non-expansive
soils.
2. Materials must be graded and compacted in accordance with
the soils report.
3. Pipes and conduits must be placed in the subgrade and
appropriately backfilled and compacted prior to commenc-
second lamination being M.D.O (facing concrete side).
7. For radius forms, 2 top plates pre scribed and laminated and
2 bottom plates pre scribed and laminated over 2 by 4-inch
framing with studs at 16-inch o.c., with horizontal plates no
greater than 4 feet o.c.
8. Straight wall plywood joints can be sealed with foam tape,
ing with concrete installation. On- structure concrete must
or covered with reveals to prevent bleed water occurrence.
be covered with drain board prior to placing topping slabs.
Lamination of radius wall forms prevents bleed water leakage.
4. Architectural concrete should always be placed over a minimum of 2 inches of damp, screeded and washed concrete
sand. Sand creates a proper slip plane, retains moisture, and
provides an avenue for migration of bleed water. This
reduces surface cracking, prevents soil-to-concrete surface
contamination, and controls bleed water.
5. Use Mirafi 500x or 600x in natural compacted fill conditions
or expansive soil.
6. For on-structure concrete, always place concrete topping on
drain board material.