Thickness: 4”-6” is standard for residential.
Base: Sand and other granular material assists in providing uniformity and drainage.
Drainage: Always slope outside for positive drainage. Make sure no water runs towards the house, unless special drains have been incorporated. The surface of the base should parallel the final slab. A minimum slope for a slab should be 1/8” drop per foot.
Excavating: Be sure to take out all organic material. Sub grade must be compacted evenly so the slab won’t settle or vary in thickness.
Forms: Stake securely. Make sure you scrap base away from form edges so edges will be at least full thickness.
Isolation: Install pre-molded joint material wherever flatwork comes against buildings, steps, walls, existing slabs etc. Joint material must extend through full depth of the slab.
Moistening: Shortly before placing concrete, wet the forms and the sub grade. Don’t over wet and create a muddy condition.
SPECIFICATIONS FOR CONCRETE
Strength: A high quality mix should be used. Water reducers, set retarders in hot weather, accelerators in cold weather and other adaptations for your particular application should be discussed between your contractor and a representative from MULLINAX CONCRETE.
Slump & Water Content: A controlled water-cement ratio is more important than slump. A 4-5 inch slump is usually desired by the finisher. A water-to-cementitious content of 0.5 is recommended, for outside slabs 0.45 is recommended.
Air: Total amount of entrained air for outside concrete should be 4%-7%. . Concrete that will never be subject to freeze/thaw conditions may be mixed with air or non-air at the contractor’s option.
Addition of water: Water should not be added at the job site, unless absolutely necessary. Water can reduce strength by diluting the cement content
Filling the Forms: Chute, wheel, pump or shovel the concrete directly into it final position. Don’t dump in piles then drag or rake the rest of the way.
Leveling: Screed (strike off) twice to level the surface. Immediately use wood or magnesium bull float to take small high and low spots. Then, stop everything on that portion of the slab until bleed water (water sheen) disappears from the surface.
When to Finish: Immediately after all the bleed water is gone is the proper time to (1) Broom OR float surface once. (2) If hand tooled, cut control joints while concrete is still plastic. (3) Edge final finish. A broom is recommended for driveways walks etc. Where a smooth finish is desired a wood hand float is recommended.
Joints: Control joints may be hand tooled, sawed or formed by use of inserts. It is recommended that control joints not exceed 8’ on 4” slabs, 10’ on 5” slabs and 12’ on 6” slabs. On sidewalks every 5’ is recommended.
Need for Curing: Curing is one of the most important steps in quality concrete construction and one of the most neglected. Effective curing is absolutely essential for surface durability. Fresh concrete must be kept warm and moist until the water combines chemically with the Portland cement, this is called hydration, Without proper curing the strength of your concrete can be cut by up to a half. A 4000 PSI can become a 2000 PSI mix at the surface with improper curing.
Curing in Warm Weather: Curing can be accomplished in a number of ways. But the simplest, most economical way and widely used method is a liquid membrane* which is sprayed on the surface of the slab as soon as possible after finish.
*( There are different choices in curing and sealing compounds depending on your application and intended use. Check with your contractor or MULLINAX Construction Supply for the many options and products available at the store.)
Curing in Cold Weather: It is absolutely essential that fresh concrete be kept from freezing. Usually for more than 7 days. To assist in curing and protection from freezing, it is desirable to cover slabs with insulated blankets. (Link to insulated blankets)
What not to use: Avoid any curing compound that lets the surface dry in a short time. Quick drying stops the hardening process making the surface week and likely to scale.
Sealers: Water repellant coatings and sealers* can help protect concrete. Newly cured concrete should have a period of air drying before being sealed.
* There are different choices in curing and sealing compounds depending on your application and intended use. Check out our Link for more information
Safe Use of Deicers: Deicers containing salt and or calcium should, be safe AFTER THE FIRST YEAR.However use sparingly, never let it stay on concrete for an extended period of time. After snow or ive have melted or softened remove deicer with shovel or broom. Never use any deicer that contains ammonium sulphate or ammonium nitrate. Make sure you read the deicer label to see what it contains.
Fertilizers: Certain lawn fertilizers will chemically attack concrete. Care should be taken to avoid contact with concrete. Fertilizers should be swept off concrete before they dissolve. NEVER use fertilizer for deicing.