210 slump is more than four inches , and no more than three feet when the slump is less than four inches .
6 . Strike-off concrete immediately after placing with a straight edge to level concrete to the top of the forms . Ensure that all screeding has been performed before bleed water rises to the surface .
Finishing Concrete :
1 . Bullfloating the surface immediately after screeding will avoid surface bleeding and eliminates high and low spots on the surface .
2 . Wait for bleed water to disappear before continuing finishing . Finishing concrete surface with bleed water present can lower concrete ’ s surface strength and lead to blistering , dusting and scaling . 3 . 1 / 8-inch edging at all slab edges will reduce chipping . 4 . Jointing includes hand tooling or sawcutting contraction joints in slab . 5 . Never spray water on the surface during the finishing process . Water is used only after finishing is completed .
6 . Depending on finish , float the surface with either wood or magnesium floats . Floating imbeds larger aggregates beneath the surface , produces a level surface and consolidates the surface in preparation for troweling .
7 . Trowel the surface only after floating to produce a hard , smooth surface that will be easy to clean and maintain .
8 . Sawcut contraction joints if jointing was not performed during plastic stage . See Rule # 9 for more description .
9 . Cure slab .
RULE 8
ARCHITECTURAL CONCRETE FINISHES
Finishes should match the mock-up panels approved by the owner and architect , and consistency should be strictly adhered to in visual appearance when viewed from 20 feet away , as recognized by American Concrete Institute ( ACI ). ( Shaw & Sons has its own in-house lab for generating six-inch by six-inch by one-inch samples for color and finish that can be made with the exact materials for any specific project .)
The most popular architectural finishes are :
1 . Lithocrete , Shaw & Sons ’ specified proprietary paving is structural concrete with an extremely durable surface with imbedded materials that expand the design parameters with colors , durability and exotic materials .
2 . Acid-etch finish reveals the fine aggregate sand by removing the cementatious paste without fracturing the sand particles . Provides a suitable non-slip exterior surface .
3 . Light sandblast finish reveals the fine aggregate sand , but fractures or frosts the integral sand and cement paste .
4 . Medium and heavy sandblast reveals both the fine and coarse aggregates and cement paste , but also fractures or frosts the matrix .
5 . Blasting with copper slag and / or silica carbide reduces the fracturing and is recommended and practiced by Shaw & Sons .
6 . Exposed aggregate retarder finish retards the surface setting time only of the cement , enabling the concrete matrix to set up enough for the top surface to be pressure washed the same day , or up to 24 hours after finishing . ( Note : After concrete has leached free lime and other mineral deposit , surface must be acid and pressure washed clean approx . three weeks after project completion .) Depth of retarders can be adjusted to light , medium , and heavy etch degrees .
7 . Hard trowel finish is not recommended for exterior hardscape due to a less than adequate slip co-efficient . However , hard troweling can develop a deeper contrast on walls if forms are stripped and “ faced .” This is also applicable to wall tops , fountains , etc .