To help you get the most satisfaction from your project, we recommend several steps before you get started:
Plan Ahead
• Thickness 4 inches is generally sufficient but more depth may be beneficial to areas that have higher traffic and heavy loads.
• Base Compacted rock is recommended in all application of concrete placement. Base rock is usually ¾” minus or 1” minus crushed.
• Slope The finished slab should have a slope of at least 1/8 inch per foot away from structures for drainage, and 1/4 inch per foot is preferable.


Preparation
• Depth Remove all organic matter and sludge, but don’t excavate deeper than necessary.
• Base Place base rock of a minimum 2”.
• Compaction Uniform compaction provides even settling and consistent thickness of your concrete slab.
• Concrete Forms Standard 2” x 4” can be used to achieve a 4” slab. Remove any loose materials from the edges to insure full thickness around the perimeter of your pour.
• Joint Material A barrier separating existing concrete from new concrete is necessary, and must extend to the bottom of the slab to insure complete separation. Pre-molded material can be used, and should be placed against existing buildings, slabs, steps, walls, et. al.


Concrete Specifications
• Strength A 5 sack mix (3000 psi) should suffice for most projects. The higher the concentration of cement (reflected in the sack mix and psi – pound per square inch), the greater the curing strength. Regardless of the mix, complete curing will take about 28 days.
• Slump A slump of about 5” is normally sufficient. A slump greater than 4” will extend the time needed for finishing, especially in cool weather. Higher slumps will also increase the potential for shrinkage and cracking.
• Admixtures Various products are available to accelerate or retard setting, reduce water content and increase the plasticity of the concrete.


Placement
• Filling forms Place the concrete in its final position rather than dumping it in piles and then pushing or raking it to the desired location.
• Leveling Screed the concrete to level the surface (or strike off) with a board then use a magnesium bull float to level out the high and low spots. Do not do anything more to the surface until the water sheen disappears.


Finishing
• Timing After the water sheen is gone (the water is done bleeding to the top), joint, edge and texture as desired.
• Final finish A broom finish is the most common finish, particularly for driveways, sidewalks and other exterior areas. We do not recommend machine floating or steel troweling for exterior surfaces.
• Joints Control joints can be added with a hand tool or a saw, and must be cut at least ¼ of the thickness of the slab. Joints must be straight and continuous; not staggered or offset. The spacing is 10 ft max, and square sections are preferable. Control joints should be made after all finishing and curing applications are done, and as soon as the concrete has sufficiently hardened to allow sawing without raveling.
• Over-finishing Too much finishing is the single biggest contributor to surface deterioration. Over-finishing pulls too many of the fine materials to the top, thus weakening the surface strength. Also, do not use a steel trowel on concrete that will be exposed to the weather.
• Cure Newly cured concrete should have a period of uninhibited exposure to the air before being sealed. A surface cure can be applied after final texturing is complete, and should not mar the concrete surface.


Curing
• Need Curing is one of the most important steps in concrete construction. Effective curing is essential to good surface durability. Uncured concrete has a weak surface that could deteriorate when exposed to freezing and thawing. Fresh concrete must be kept warm and moist until the water and cement hydrate (combine chemically). That's what hardens the concrete and gives it its strength.
• Warm weather The most common method of curing is to spray or roll the slab surface after finishing to prevent premature drying. The rate of application should be consistent with the manufacturer’s instructions, e.g. 200 square feet per gallon. Water can be used in place of a cure if the surface can be kept wet for three days.
• Cold weather Newly poured concrete cannot freeze for at least a week. Some sort of heating or insulation must be used to maintain proper curing temperatures during freezing weather.
• Caution Do not use a curing method that will allow the surface to dry in a short time. Concrete that dries too quickly is more likely to show surface cracking. Membrane curing is not sufficient, nor does the use of accelerants prevent concrete from freezing.

Timely Tips
• First Winter Do not use salt or other deicers during the first winter. To improve traction, use sand instead. Even a small amount of salt can cause scaling on newly placed concrete. Fertilizer is not acceptable as a deicer at any time.
• Drainage Proper drainage will help avoid saturating the concrete.
• Sealing Sealing is different from curing. Water repellant coatings or sealers inhibit water from getting into surface pores and help prevent damage from freezing, thawing and salt.


Salem Mobile Mix
503-371-8084