CONCRETE FINISHING AND ESTIMATES BASIC INFORMATION


All exposed concrete surfaces require some type of finishing. Basically, finishing consists of the patch up work after the removal of forms and the dressing up of the surface by troweling, sandblasting, and other methods.

Patch-up work may include patching voids and stone pockets, removing fins, and patching chips. Except for some floor slabs (on grade), there is always a certain amount of this type of work on exposed surfaces.

It varies considerably from job to job and can be kept to a minimum with good quality concrete, with the use of forms that are tight and in good repair, and with careful workmanship, especially in stripping the forms.

This may be included with the form stripping costs, or it may be a separate item. As a separate item, it is much easier to get cost figures and keep a cost control on the particular item rather than “bury” it with stripping costs.

Small patches are usually made with a cement-sand grout mix of 1:2; be certain that the type of cement (even the brand name) is the same used in the pour because different cements are varying shades of gray. The labor hours required will depend on the type of surface, the number of blemishes, and the quality of the patch job required. Scaffolding will be required for work above 6 feet.

The finishes required on the concrete surfaces will vary throughout the project. The finishes are included in the specifications and finish schedules; sections and details should also be checked.

Finishes commonly required for floors include hand or machine troweled, carborundum rubbing (machine or hand), wood float, broom, floor hardeners, and sealers. Walls and ceilings may also be troweled, but they often receive decorative surfaces such as bush hammered, exposed aggregate, rubbed, sandblasted, ground, and lightly sanded.

Finishes such as troweled, ground, sanded, wood float, broom finishes, and bush hammered require no materials to get the desired finish, but require only labor and equipment. Exposed aggregate finishes may be of two types. In the first type, a retarder is used on the form liner, and then the retarder is sprayed off and the surface is cleaned.

This finish requires the purchase of a retarding agent, spray equipment to coat the liner, and a hose with water and brushes to clean the surface. (These must be added to materials costs.) The second method is to spray or trowel an exposed aggregate finish on the concrete; it may be a two- or three-coat process, and both materials and equipment are required.

For best results, it is recommended that only experienced technicians place this finish. Subcontractors should price this application by the square foot. Rubbed finishes, either with burlap and grout or with float, require both materials and labor hours plus a few hand tools. The burlap and grout rubbed finish requires less material and more labor than the float finish. A mixer may be required to mix the grout.

Sandblasting requires equipment, labor, and the grit to sandblast the surface. It may be a light, medium, or heavy sandblasting job, with best results usually occurring with green to partially cured concrete.

Bush hammering, a surface finish technique, is done to expose portions of the aggregates and concrete. It may be done by hand, with chisel and hammer, or with pneumatic hammers. The hammers are commonly used, but hand chiseling is not uncommon. Obviously, hand chiseling will raise the cost of finishing considerably.

Other surface finishes may also be encountered. For each finish, analyze thoroughly the operations involved,material and equipment required, and labor hours needed to do the work.

The finishing of concrete surfaces is estimated by the square foot, except bases, curbs, and sills, which are estimated by the linear foot. Since various finishes will be required throughout, keep the takeoff for each one separately.

Materials for most operations (except exposed aggregate or other coating) will cost only 10 to 20 percent of labor. The equipment required will depend on the type of finishing done. Trowels (hand and machine), floats, burlap, sandblasting equipment, sprayers, small mixers, scaffolding, and small hand tools must be included with the costs of their respective items of finishing.

Estimating Concrete Finishing.
Areas to be finished may be taken from other concrete calculations, either for the actual concrete required or for the square footage of forms required.

Roof and floor slabs, and slabs on grade, pavements, and sidewalk areas can most easily be taken from the actual concrete required. Be careful to separate each area requiring a different finish. Footing, column, walls, beam, and girder areas are most commonly found in the form calculations.

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