Tips for specifying exterior concrete surfaces

March 30, 2015

IMG_7463
Brooming large-area placements is a much more difficult task than brooming sidewalks or driveways. Controlling the depth of broom marks is just one of the problems faced by finishers. Photo courtesy CECO Concrete Construction

by Ward R. Malisch, PE, PhD, Bruce A. Suprenant, PE, 
and Frank Salzano, PE, PhD

Based on the information presented in the article, “Specifying Broomed Exterior Concrete Surfaces”[1] by Ward R. Malisch, PE, PhD, Bruce A. Suprenant, PE, and Frank Salzano, PE, PhD in the April issue of The Construction Specifier, the following are recommendations for specifying exterior concrete surfaces.

Appearance (broom finish)
The broom finish should be specified to match the appearance in an existing slab or pavement of comparable size. For instance, one should not specify a sidewalk appearance for a parking structure. Also, a mockup or reference sample should be specified for appearance consistent with the placement size. The limitations of a mockup should be understood; when one is used, there should always be a repair portion so the contractor’s means and methods using the specified repair materials and procedures can be evaluated when repair is necessary.

Texture
A limited-range broom finish—such as light, medium, or heavy—should be avoided because it is hard to distinguish between textures to that degree. One should specify a broom finish as light-to-medium or medium-to-heavy. Further, texture depth should not be specified unless a procedure for measuring depth is included in the specifications.

Flatness
For parking lots and other site paving, a 13-mm (½-in.) gap under a 3-m (10-ft) straightedge can be specified. Use ACI 117-10, Standard Specifications for Tolerances for Concrete Materials and Construction, methodology for measuring with a straightedge. For parking structures, one should specify an overall floor flatness (FF) of 17 and a minimum local floor levelness (FL) of 11. (ASTM E1155, Standard Test Method for Determining FF Floor Flatness and FL Floor Levelness Numbers, can be used for its methodology for measuring F-numbers.)

Drainage
Whenever possible, a top-surface one-way slope or a one-way top and bottom surface slope should be specified, with two-way slopes and warps avoided. A two percent slope for water drainage of suspended slabs should be specified. The structural engineer should check short-term and long-term deflections to determine their effect on drainage.

Endnotes:
  1. “Specifying Broomed Exterior Concrete Surfaces”: http://www.constructionspecifier.com/specifying-broomed-exterior-concrete-surfaces/

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