Before You Start: Planning Your Concrete Slab

A well-poured concrete slab can last 50+ years. A poorly poured one can crack within months. This guide covers the essential steps to get it right the first time.

When to DIY vs. Hire a Pro

DIY-friendly projects:

Slabs under 100 sq ft
4” thick or less
Level ground
Non-structural (patios, walkways, shed pads)

Hire a professional for:

Garage floors or structural slabs
Sloped sites requiring grading
Areas with drainage issues
Anything requiring permits

Tools and Materials Needed

Tools

Shovel and rake
Wheelbarrow
String line and stakes
4-foot level
Tamper or plate compactor (rental)
Bull float
Magnesium hand float
Edger and groover
Broom for texture
Concrete mixer or ready-mix truck

Materials

Gravel or crushed stone (4-6” base)
2×4 or 2×6 lumber for forms
Stakes (wood or metal)
6x6 welded wire mesh or rebar
Concrete (calculate using our Concrete Calculator)
Plastic sheeting (for curing)
Form release oil

Step 1: Site Preparation

Excavation

Mark the slab outline with stakes and string
Dig 8-10 inches below final slab height
- 4” for gravel base
- 4” for concrete
- 2” for final grade above ground
Extend excavation 6” beyond slab edges for forms

Grading

Slope away from buildings: 1/8” per foot minimum
Use a string line to check levels
Compact soil with a tamper or plate compactor

Critical: Remove all organic material (roots, grass, debris). Decomposition causes settling and cracks.

Step 2: Install Gravel Base

Why You Need a Base

Provides drainage under slab
Prevents frost heave
Creates stable, level surface
Allows wire mesh/rebar placement

Installation

Add 4-6 inches of crushed gravel
Spread evenly with rake
Compact in 2-3” lifts
Check level with string line
Final surface should be 4” below finished slab height

Step 3: Build the Forms

Material Selection

2×4 lumber for 4” slabs
2×6 for 6” slabs
Use straight, un-warped boards

Installation Steps

Set corner stakes - Drive stakes 1” below form top
Attach forms - Screw boards to inside of stakes
Check for square - Measure diagonals (should be equal)
Check for level - Use 4-foot level, adjust as needed
Add support stakes - Every 3-4 feet
Apply form release - Oil or diesel prevents sticking

Slope for Drainage

For outdoor slabs, create a 1/8” per foot slope:

10-foot slab = 1.25” lower on drain side
Adjust one form board lower than the other

Step 4: Install Reinforcement

Wire Mesh vs. Rebar

Feature	Wire Mesh (6×6)	Rebar (#3 or #4)
Best for	Patios, walkways	Driveways, structural
Grid	6” squares	12-18” on center
Placement	Mid-slab	Bottom third
Cost	Lower	Higher

Installation Tips

Support mesh on chairs or rocks (2” above base)
Overlap mesh sheets 6” minimum
Tie rebar intersections with wire
Keep reinforcement at least 2” from edges

Step 5: Calculate and Order Concrete

The Concrete Formula

Length (ft) × Width (ft) × Thickness (ft) ÷ 27 = Cubic Yards

Example: 12’ × 12’ × 0.33’ (4”) ÷ 27 = 1.76 cubic yards

Add 10% extra for waste and uneven excavation.

Ordering Ready-Mix

Minimum order usually 1 cubic yard
Specify PSI strength (3000-4000 for residential)
Request fiber mesh for crack resistance
Schedule delivery with adequate help on-site

Use our Concrete Calculator for accurate estimates.

Step 6: Pour the Concrete

Preparation

Dampen gravel base (not soaking wet)
Have all tools ready
Plan your pouring direction
Work towards your exit point

Pouring Process

Start in far corner - Work towards access point
Fill to form tops - Slightly overfill
Spread with shovel - Move concrete to low spots
Work in sections - Don’t pour more than you can finish

Consolidation

Use a 2×4 screed board across forms
Pull towards you in sawing motion
Fill low spots, re-screed
Remove excess concrete

Step 7: Finishing

Bull Floating (Immediately)

Push float away, lift, pull back
Overlap strokes by half
Creates initial smooth surface
Pushes aggregate down

Waiting Period

Wait until bleed water evaporates:

Surface sheen disappears
Footprint leaves 1/4” impression
Usually 30-60 minutes (varies by weather)

Hand Floating

Use magnesium float in circular motion
Work edges first, then interior
Creates smooth, dense surface

Edging and Grooving

Edger: Run along forms for rounded edges
Groover: Cut control joints every 8-10 feet
Control joints should be 1/4 slab thickness deep

Final Texture

Broom finish: Drag broom perpendicular to traffic direction

Provides grip for outdoor slabs
Hide imperfections

Trowel finish: For garage floors, covered patios

Requires more skill
Very smooth surface

Step 8: Curing

Proper curing is crucial for strength. Concrete reaches:

50% strength in 3 days
70% strength in 7 days
100% design strength in 28 days

Curing Methods

Plastic sheeting:

Cover entire slab
Weigh down edges
Keep in place 7 days

Curing compound:

Spray on after finishing
Forms moisture barrier
One application sufficient

Water curing:

Keep surface damp for 7 days
Best results but labor intensive

Weather Precautions

Hot weather (above 85°F):

Pour early morning
Dampen forms and base
Use evaporation retarder
Cure immediately

Cold weather (below 50°F):

Avoid if possible
Use accelerated mix
Insulate with blankets
Extend curing time

Step 9: Form Removal and Sealing

Form Removal

Wait minimum 24-48 hours
Remove stakes first
Pry forms gently
Don’t walk on slab for 3 days

Sealing (Optional but Recommended)

Wait 28 days for full cure
Clean surface thoroughly
Apply penetrating sealer
Reapply every 2-3 years

Common Mistakes and How to Avoid Them

Mistake	Consequence	Prevention
No gravel base	Settling, cracks	Always use 4-6” compacted gravel
Mesh on ground	No reinforcement effect	Use chairs to lift 2”
Over-watering	Weak surface, dusting	Don’t add water to mix
Early finishing	Surface defects	Wait for bleed water
No control joints	Random cracking	Cut every 8-10 feet
Skipping curing	Weak, dusty concrete	Cure 7 days minimum

Cost Breakdown

For a typical 12×12 foot (144 sq ft) slab:

Item	Estimated Cost
Gravel (1 ton)	$30-50
Concrete (2 yards)	$250-350
Lumber for forms	$30-50
Wire mesh	$40-60
Tools/rentals	$50-100
DIY Total	$400-610
Pro Install	$800-1,500

Ready to Calculate Your Project?

Use our free Concrete Calculator to determine exactly how much concrete you need, along with cost estimates for your specific project.

Pro Tip: For first-time DIYers, start with a small slab (under 50 sq ft) to practice techniques before tackling larger projects. Consider asking an experienced friend to help on pour day - you can’t pause once the concrete is in the forms.