10 Tips for Working With Concrete

Concrete is one of the most versatile and widely used construction materials. Learning how to properly work with and finish concrete opens up endless possibilities for projects and improvements around your home. Follow these 10 essential tips to get the most out of working with concrete.

1. Choose the Right Concrete Mix

There are many different types of concrete mixes available, each suited to specific applications and conditions. Here are some of the most common types of concrete mix:

General Purpose Mix – This basic concrete mix works for most general applications like pouring slabs, footings, and foundations. It uses standard Portland cement and aggregates.

High-Strength Mix – This concrete mix contains a lower water to cement ratio and is designed to achieve greater strength and durability. It’s suitable for driveways, garage floors, and structural elements.

Fast-Setting Mix – As the name suggests, this concrete mix allows you to remove forms quicker and complete finishing faster. It uses finer aggregates and achieves high early strength.

Fiber Reinforced Mix – This mix includes synthetic reinforcing fibers which increase flexural strength and resistance to cracks. It’s useful for driveways and slabs.

High-Performance Mix – This specialized mix uses pozzolanic materials like fly ash to provide increased strength, lower permeability, and greater resistance to chemical attack.

Always choose the appropriate concrete mix for your specific project and intended application. Consider strength needs, curing conditions, exposure elements like freeze-thaw cycles, and finish requirements.

2. Calculate Concrete Quantities Correctly

Figuring out exactly how much concrete you will need for your project is crucial to avoid wastage or having too little mix. Here is a simple process to estimate concrete quantities:

Calculate the volume needed in cubic feet – length x width x thickness of the area to be poured.
Subtract the volume of any objects that will displace concrete like forms, rocks or pipes.
Divide the net volume by 27 to calculate how many cubic yards (CY) of concrete is required.
Add 5-10% extra to account for waste, over excavation and truck vibration during transport.
Order concrete by CY from your local supplier. Make sure to order it at least 1 day in advance.

Having some extra concrete is better than running short, so err on the side of excess when in doubt. Make sure you have adequate help for quick pouring and finishing.

3. Prepare the Site and Forms Properly

Proper site and formwork preparation is key to achieving finish grade and avoiding flaws in the concrete:

Ensure the base layer is well compacted before pouring concrete over it.
Layout and assemble wooden formwork to serve as the mold for pouring. Seal forms with caulk or foam backer rod.
Install reinforcement steel rebar or mesh before pouring concrete if required for structural strength.
Apply a concrete release agent or motor oil to the forms to prevent sticking and ease removal.
Layout control joints to guide crack development using joint formers or saw cuts after pouring.
Arrange water drainage away from the pour site to prevent washing out of fresh concrete.

Adequate preparation minimizes issues like surface honeycombing, edge slumping, and improper curing that can ruin the concrete finish.

4. Pour and Consolidate Concrete Correctly

Careful pouring and consolidation of the concrete ensures there are no weak spots due to air bubbles or segregation:

Before pouring, spray the forms and base layer with water to prevent premature drying.
Start pouring concrete from the lowest elevation to avoid splashing forms.
Maintain a relatively low height when pouring off a concrete bucket.
Spread and consolidate concrete immediately after pouring using come-alongs or vibrators.
Insert vibrators methodically, allowing the vibrating head to penetrate the layer below. Pull out slowly to avoid air pockets.
Avoid over-vibrating, as it can cause segregation of the aggregates and cement.
Pour concrete continuously in each section to prevent cold joints from forming.

Proper pouring and consolidation results in dense, strong, and durable concrete.

5. Strike Off and Screed Concrete

Once poured, the excess concrete must be leveled using a process called striking off and screeding:

Use a straight 2 x 4 board to roughly strike off poured concrete immediately after placement.
Next, tamp and screed the concrete by moving a long straightedge board back and forth across guides to achieve the desired grade.
Account for the desired thickness by adjusting the screed guides or rails.
Add concrete to low spots and remove excess from high points as you screed.
Repeat screeding in perpendicular directions to get a flat level surface.
Check the surface with a level or straightedge to identify any high or low areas.

Proper screeding produces a flat concrete surface ready for finishing.

6. Apply a Float or Trowel Finish

Floating and troweling are essential steps to achieve the desired concrete finish texture:

Floating is done after bleed water absorbs using wood, magnesium or rubber floats. This levels the surface and prepares it for troweling.
Troweling compact and densifies the concrete surface while imparting a smooth texture. Use hand trowels or walk-behind power trowels.
Avoid starting the finish work while the concrete surface is still bleeding. Allow time for absorption.
Begin finishing edges and corners first before moving to the interior surface. Trowel in circular motions.
Minimize trowel passes to avoid excessive fines accumulation which causes blistering and delamination.
Take care to trowel consistently and avoid cold joints. Overlapping high and low areas becomes permanent.
Apply a light broom finish as the last step to create slip resistance in outdoor flatwork.

Proper floating, troweling, and finishing results in a smooth, durable, and attractive concrete surface.

7. Apply Curing Compound or Moisture

Curing is extremely important to achieve the full designed strength of concrete:

Cover the surface with damp burlap and keep moist for 3-7 days, or use a garden sprayer to frequently fog the surface.
Ponding the slab and weighted tarps help provide water for a good cure.
Spray-on membrane-forming curing compounds can also effectively retain moisture during the curing process.
Avoid excessive heat, wind or cold weather that can cause concrete to cure improperly. Maintain caution for the first 7 days.
The use of a concrete sealer after curing provides additional protection from the elements.

Effective curing allows concrete to properly hydrate and strengthen over time.

8. Control Cracks with Joints

While cracking cannot be completely prevented, proper joint detailing helps control crack location and development:

Construct contraction joints using weakened planes or saw cuts to allow shrinkage cracks to occur in a straight line.
Install control joints to isolate slabs into rectangular sections to guide cracking. Optimal spacing is about 2 times the slab thickness.
Use isolation joints to allow movement where concrete abuts other materials like a driveway against the house.
Arrange joints to be aesthetically pleasing and unobtrusive. Hide them along design lines and patterns.
Seal control joints with backer rods and flexible sealants to prevent debris accumulation and reinforce the joint.
Repair isolated random cracks due to plastic shrinkage or settlement as soon as possible.

Proper joint design and detailing minimize random unsightly cracking of concrete.

9. Avoid Common Concrete Problems

Being aware of common concrete problems helps avoid them through proper inspection, placement and curing:

Prevent weak surfaces and honeycombing by adequately consolidating concrete after pouring.
Ensure sufficient curing, protect surface from rapid drying to avoid plastic shrinkage cracks.
Avoid adding extra water which lowers strength and causes scaling and efflorescence problems.
Prevent segregation by avoiding over-vibration or excess water addition during placement.
Verify formwork is square and suitably braced to avoid edge slumping or surface defects.
Maintain minimum slab thickness and proper reinforcement to prevent curling or cracking.
Repair isolated surface defects like blisters, delamination, or spalling as soon as possible.

Careful pour, consolidation, finishing and curing minimizes mistakes and prevents common concrete problems.

10. Enhance Appearance With Stamping or Staining

Adding decorative treatments like stamping, etching, or staining can enhance the appearance of cured concrete:

Stamp concrete with textured mats at various intervals to mimic stone, brick, tile or wood patterns.
Create exposed aggregate finish by washing off surface cement to reveal pebbles.
Etch decorative designs into concrete using masonry or carbide-tipped saw blades.
Apply penetrative stains in different colors to create a more visually appealing surface.
Ornament concrete borders by embedding various decorative stones, shells or bricks when pouring.
Consider polished or dyed concrete flooring for an ultra-modern look.

Decorative concrete stamping, staining or etching opens up exciting design possibilities.

FAQ about Working with Concrete

What is the best way to get a smooth finish on concrete?

The best way is to properly screed the surface first, then float to remove ridges and fill voids. Follow up with consistent hand troweling in a circular motion when the surface can adequately hold a trowel edge without slumping. Power troweling also helps achieve smoothness.

How long does poured concrete take to cure?

Most concrete gains sufficient strength within the first 7 days to be put into service. However full design strength takes 4 weeks or longer to properly hydrate and cure, so control loading and impacts accordingly.

Can concrete be poured in hot weather?

Yes, concrete can be poured in hot weather but extra precautions are needed to prevent premature drying which causes plastic shrinkage cracking. Erect sun shades, use cooled mix, mist forms, and start curing immediately. Avoid pouring on extremely hot days.

What causes surface dusting of concrete?

Dusting is caused due to a weak top layer with excess fines. This is often from improper finishing while the concrete is still bleeding, overworking the surface, inadequate vibration, or insufficient curing. Sealing helps but damaged areas may need repairs.

How thick should a concrete garage floor be poured?

Typical garage and driveway slab thickness is 4-5 inches. Minimum thickness is 3 1/2 inches for light vehicle use. Heavier duty floors are 6 inches thick or more depending on the loads. Rebar is often used to reinforce garage slabs.

Can concrete be poured over existing concrete?

Yes, new concrete can be poured over existing cured slabs after proper surface preparation. The key is to ensure adequate bonding by cleaning and roughening the existing surface before pouring fresh concrete over it. Proper reinforcement is also recommended.

Conclusion

With the right mix, proper site prep, skillful pouring and finishing, and effective curing, even first-timers can achieve beautiful, durable concrete results. Pay close attention to concrete consolidation and moisture retention for strength development. Decorative treatments open up endless possibilities to make your concrete surfaces uniquely eye catching. Remember to control cracking through proper joint detailing and sawing. With practice and care, anyone can maximize the versatility of concrete to build amazing landscapes, structures and flatwork.

10 Tips for Working With Concrete

Concrete is an incredibly versatile material that can be used for a wide range of construction and home improvement projects. However, proper techniques need to be followed to achieve successful results. This comprehensive article provides 10 essential tips for working with concrete:

Select the right concrete mix – Many options exist for strength, setting time, workability.
Accurately estimate quantity needed – Consider volume, waste, delivery. Order 1 extra yard.
Prepare site and forms thoroughly – Compact base, seal forms to avoid flaws.
Pour and consolidate correctly – Avoid segregation, cold joints. Vibrate carefully.
Level and smooth with screeds – Strike off excess, screed guides for grade.
Float and trowel for finish texture – Delay till bleeding stops, minimize trowel passes.
Cure properly with moisture – Prevent drying, use fogging, ponding, curing compounds.
Control cracking with joints – Contraction joints, isolation joints, sealants.
Prevent common problems – Consolidate fully, protect curing, avoid extra water.
Enhance appearance – Stamping, exposed aggregate, stains, polished.

Proper site prep, pouring, finishing, curing and joint detailing are key to success with concrete. Follow these tips to achieve professional quality results.