Replacing A Concrete Garage Floor: 15 Important Steps To Focus On!

Replacing a concrete garage floor is not a small project. You’ll have to find the best professional for the job. The contractor must have expertise, experience & equipment to successfully complete the project.
 
Remember you have only one chance to get it right. So do not take any risks. Pay a little extra if required, but certainly get the best!
 
Another point to keep in mind at this stage is that you will require a permit from your local building authority. Usually the contractor will arrange this as part of the deal. It is much easier for the contractor to get the permit as they are knowledgeable about all the rules & regulations.

Replacing the concrete garage floor requires that everything within the garage has to be  moved out. You need to store all that stuff in another location for 6 to 8 weeks. In other words, you need temporary storage.
 
NOTE: Use this opportunity to declutter your garage. Get rid of stuff that you don’t really need.
 
Maybe a family member or a friendly neighbor can help you out! If you have way too much stuff, consider splitting it up and storing it in multiple locations.

You must clear out the garage before the contractor’s crew arrives. Move as much as you can using your own vehicles. If that is not enough request a family member or friend to help out
 
Alternatively you may have to rent transport for the movement.

Your job is mostly done. Now the contractor will take over. Assuming that your garage  structure is in good shape, they will suggest lifting up the garage structure by a foot or two.
 
If the garage structure is quite dilapidated, they may recommend demolishing that as well.

Once the garage structure has been raised, the work on the demolition of the garage floor can start. Be aware that this will create a tremendous amount of noise, dust and debris.
 
The debris has to be dealt with on a day-to-day basis. You don’t want it lying around in your driveway or backyard. A good contractor should take care of the debris. In fact they should use some of the crushed concrete from the old floor as aggregates for the new concrete slab base.

Do not stop at just breaking up the concrete slab. The problem with the original concrete garage floor probably came from the poor quality base or damaged footing & foundation. 
 
The contractor must dig deep to excavate the old base. This also gives him access to the foundation & footings.

The contractor will then examine the condition of the garage foundation & footngs. It is possible that there may be structural cracks there. The contractor will need to repair the cracks and reinforce the foundation & footings.
 
If the foundation and footings are heavily damaged then the contractor will need to remove them and install new ones.

Geotextile fabric is absolutely necessary when preparing the base for a concrete slab-on-grade foundation. Geotextile fabric prevents the aggregates from getting dissipated and lost in the subgrade below.
 
Geotextile fabric also helps in better drainage and reducing the risk of soil subsidence.

NOTE: If not done now it can never be done! 

To prevent groundwater from washing away the subgrade below the concrete slab, you need to install a sub-slab drainage system.
 
Perimeter Drains (aka French Drains or Weeping Tiles) is a sub-slab drainage system that runs around the proposed concrete slab-on-grade foundation.

The subgrade should be tamped tight before placing the geotextile fabric on it. The base itself should be at least 4 inches thick and made up of a combination of coarse and fine aggregates.
 
The coarse aggregates should be sharp angular gravel, crushed stone or recycled concrete. The fine aggregates should be stone dust or sand.
 
Make sure that the aggregates are compacted at every stage. A well prepared base will reduce the risk of ground settlement and ensure that sub-slab drainage is effective.

Vapor barrier is a material that prevents the movement of vapor or moisture from one area of concentration to another. Vapor barrier between the base and the concrete slab will prevent moisture from wicking up from the grade below into the concrete slab above.
 
Ingress of water in a concrete slab is extremely damaging and the main reason for concrete degradation and reinforcement corrosion. Ensure that a vapor barrier between the base and the concrete slab is installed.
 
NOTE: If not done now it can never be done! 

Some kind of reinforcement within the concrete slab is necessary to prevent the concrete from cracking under stress. Concrete has very high compressive strength but relatively low tensile and flexural strength. Reinforcement compensates this weakness.
 
Concrete garage floors that are 4” thick or less, should not have rebars. But they must be reinforced either with a wire mesh or polymer fibers incorporated in the concrete mix.
 
Though a 4” thick concrete slab is strong enough for a standard garage, you may want to go for a 6” – 8” thick slab. You certainly need to use steel rebars in that case.
 
NOTE: Rebars, as well as wire mesh, should always be placed on 2” high chairs. Reinforcement at the absolute bottom of a concrete slab is not effective.

Once the reinforcements are in place you are ready to pour the concrete mix. The strength of the concrete depends a lot on the quality of the concrete mix ingredients as well as certain ratios. 
 
The water cement ratio is the most critical and should be kept at 0.5 or less for optimal strength. Water reducing admixtures can reduce water cement ratio without compromising on the plasticity of the concrete mix.

Once the concrete mix has been poured and troweled to get the desired finish you have to let the concrete cure. Concrete takes 28 days to cure fully and develop maximum strength. 

However there are several factors that affect the curing process and ultimate strength. Concrete cures when water reacts with cement to form a crystalline structure. The rate of water evaporation plays a vital role in this reaction. 
 
The water evaporation rate depends on the ambient humidity & temperature, wind speed, concrete temperature, etc. Control the water evaporation rate by ponding or covering the concrete slab in wet blankets if it is very hot outside.

More often than not, the last step of sealing the concrete floor is missed. This step is as crucial as any other. Sealing a concrete garage floor will prevent the ingress of moisture and water into the concrete. 
 
Penetrating sealers permeate into the capillaries of the concrete and form hydrophobic barriers. This is the best way of preventing concrete degradation from within. Application of a couple of coats of a penetrating sealer is a must!
 
Topical sealers prevent water from entering a concrete slab by forming a clear, water impermeable layer on the surface. Topical sealers also make the concrete garage floor stain resistant, less dusty and easy to clean.
 
NOTE: Do not apply topical sealer if you plan to use epoxy, polyaspartic or polycuramine coatings. They will not bond with the concrete.