Concrete is an excellent choice for a subfloor because it is strong, cost-effective, and durable. It is favored due to its ease of installation and maintenance. The specific requirements of your subfloor should be taken into account before choosing concrete.
This article discusses the benefits of concrete as a subfloor and some considerations to keep in mind before installing it.
Is Concrete a Good Subfloor Choice?
Concrete is one of the common subfloor materials since they are versatile, easily available, and provide a smooth and even surface for the installation of stone and tile flooring.
Additionally, they require minimal upkeep and are easy to clean.
However, there are certain situations when a concrete subfloor would be a poor choice.
For instance, if you reside in an area that is prone to flooding, concrete may not be the most suitable choice as it is not waterproof.
Similarly, if your home is situated in an earthquake-prone region, concrete may not be the best option as it can crack and cause damage.
Pros and Cons of Concrete Subfloor for Your Home
To make an informed decision on whether to opt for a concrete subfloor as a construction option, it is important to consider both its advantages and disadvantages.
| Pros of Concrete Subfloor | Cons of Concrete Subfloor |
|---|---|
| Durable | Cold, and uncomfortable |
| Cost-effective | Cracks can occur |
| Easy to maintain | Not waterproof |
| Fireproof | Flaws are difficult to fix |
| Eco-friendly | Creates mess during installation |
Pros of Concrete as a Subfloor
Concrete is quite popular as a subfloor due to its durability and cost-effectiveness, in addition to being mildew and mold-resistant.
Furthermore, it is easy to maintain and can be painted to match your visual preferences.
In areas with heavy foot traffic, concrete is an ideal option as it is resistant to wear and tear.
Additionally, it is fireproof and can help to minimize sound transmission.
Another advantage of concrete is that it does not contain any harmful VOCs like some subfloor panels, making it a safer choice.
Cons of Concrete as a Subfloor
One of the main disadvantages of concrete as a subfloor is that it can be cold and uncomfortable.
Additionally, concrete will deteriorate over time, leading to cracks.
Another disadvantage is that concrete is not inherently waterproof, meaning the area must be appropriately sealed and waterproofed before installation.
Any flaws or damage to the concrete subfloor can also be cumbersome to repair.
Furthermore, the installation process of concrete subfloors can be noisy and disruptive.
Guidelines for Concrete Subfloor Preparation
Laying a concrete subfloor is relatively easy, but it is crucial to follow some important guidelines.
The first step is to prepare the area before pouring concrete and to use the correct concrete mix.
A flat subfloor is also essential.
As per NWFA guidelines, flatness tolerance must not exceed 1/8” to 3/16” in 10’radius.
Additionally, the concrete must meet the ASTM F710(Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring)requirements.
It is also important to waterproof and seal the concrete appropriately to prevent moisture from penetrating it.
The maximum relative humidity requirement is 100% testing, in accordance with ASTM F2170((Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes).
Finally, it is crucial to properly cure the concrete before installing any flooring on top of it.
WBDG(Whole Building Design Code) also provides some additional guidelines for subfloor preparation that are worth considering.
| Property | Test | Value |
|---|---|---|
| Tensile Strength | ASTM D638 | 4,400 psi |
| Bond Strength | ASTM D7234 | 100% bond to concrete failure |
| Tensile Modulus | ASTM D638 | 1.9 X 10 5 psi |
| Percent Elongation | ASTM D638 | 12 % |
| Volatile Organic Compound Limits(V.O.C) | SCAMD Rule 1113 | 25 grams per liter |
| Permeance | ASTM E96 | 0.1 perms |
| Cure Rate | Per the manufacturer’s data | 4-hour tack free with 24-hour recoat window |
Concrete Subfloor Moisture Testing
When laying a concrete subfloor, you should properly test the area for moisture.
A moisture meter can be used to determine the moisture content of the concrete and the surrounding region.
If the area is too moist, it is important to reduce the moisture before installing the flooring.
Various methods to determine the moisture content of concrete are
- In situ probe test
- Plastic Sheet Method
- Calcium carbide testing
- Anhydrous calcium chloride testing
A relative humidity value greater than 75% indicates high moisture content, and if calcium chloride readings exceed 3, a vapor retarder must be used.
How Thick Should a Concrete Subfloor Be?
The thickness of a concrete subfloor depends on the flooring you plan to install.
Floor slabs in residential construction are typically four inches thick.
However, if the concrete will be subjected to heavy loads, a thickness of five to six inches is recommended.
Installing Floors Over Concrete Subfloor
Once the concrete subfloor has been laid, the next step is to install the flooring of your choice.
Concrete is a versatile subfloor material that can support any flooring.
When selecting the appropriate flooring, it is important to consider your personal preference and the level of foot traffic in the area.
Both hardwood and laminate flooring are common options.
However, it is crucial to ensure that the flooring is specifically designed for use on concrete subfloors.
Concrete Subfloor Preparation for Hardwood or Laminate Floor
To properly prepare for the installation of hardwood or laminate flooring on a concrete subfloor, it is essential to follow specific steps.
Begin by checking the concrete for debris, cracks, and crumbling.
Check that the concrete is level, with a flatness tolerance of no more than 3/16 inches in a 10-foot radius.
Use a self-leveling compound to level the concrete, if necessary.
The next important consideration with a concrete subfloor is moisture.
For laminate flooring installation, use a vapor barrier underlayment between the subfloor and flooring.
Foam and fiber are used as an underlayment between your subfloor and flooring, and it also helps to insulate your room.
For hardwood floors, floor muffler or aquabar underlayment can be used, and glued-down hardwoods do not require underlayment.
After surface preparation, allow the concrete to cure for 28 days before installing any flooring.
Avoid installing flooring over concrete subfloor drains or sump pumps.
Finally, once the subfloor is inspected and approved, begin the floor installation.
Plywood vs Concrete Subfloor
| Plywood Subfloor | Concrete Subfloor |
|---|---|
| Inexpensive | Expensive |
| Easy to install | Hard to install |
| Prone to warp and rot | Durable |
| Can be nailed | Difficult to nail into |
Plywood is an affordable and easy-to-install option for subflooring, but it can be susceptible to warping and rot and is not as strong as concrete.
High-quality plywood will remain stable and flat if it stays dry.
In contrast, concrete is more durable and resistant to damage and is easy to maintain.
Additionally, concrete is fireproof and soundproof.
However, installing flooring directly to concrete is more time-consuming and costly.
Gluing plywood to the floor joists can prevent creaking.
But when gluing directly to concrete, it is essential to use the appropriate adhesive and carefully follow the instructions, taking into account the application method, coverage rate, dry time, and trowel size.
Even minor deviations from the instructions can negatively impact the performance of the flooring.
Concrete is also colder and harder than plywood and is difficult to nail into.
Inspection of Concrete Subfloors
To maintain a concrete subfloor, it is important to conduct regular inspections.
Monitor the moisture content to prevent damage, and ensure the area is properly sealed and waterproofed.
Regular cleaning is also essential.
While inspecting a concrete subfloor, also keep the following factors in mind.
Cracks
Shrinkage and poorly constructed concrete can cause cracks in concrete.
So, inspect the subfloor regularly for crack-related damage.
Contaminants
Contaminants include primer, oil, grease, spray paint, lumber crayon, and grease pencils.
Most of them have significant staining potential.
Determine the most effective removal technique based on the depth of penetration.
Curing Compounds
Curing compounds help to prevent shrinkage cracking by reducing water evaporation from concrete.
However, they have an impact on bonding efficiency.
The use of emulsifiers or concrete blasting can help to remove them.
Spalling
Concrete spalling occurs due to natural weathering and/or chemical reactions, resulting in cement chipping away from the main body.
Before treating spalling, first determine what caused it and seek immediate advice from a specialist.
Laitance
Concrete laitance is a weak cement and fine aggregate layer.
To remove laitance, use light abrasion with a suitable sanding machine.
Cost of a Concrete Subfloor
Installation of a concrete subfloor can vary in cost depending on its size and the type of concrete used.
The cost per square foot varies from $4 to $10.
It is also essential to consider the expenses associated with the installation, including the cost of tools and materials needed.
Frequently Asked Questions(FAQ)
What is the Best Subflooring Material to Use?
Depending on your unique requirements and the kind of flooring you’re installing, the optimal subflooring material will vary.
Plywood is popular for subflooring because it is affordable and easy to install.
Concrete is also a good choice for a subfloor because it is durable and cost-effective.
Which Flooring is the Warmest Over Concrete?
Rubber flooring is a suitable choice over concrete to make the floor feel warm and comfortable.
Carpets can also keep the area warmer for longer periods.
What is the Lifespan of a Subfloor?
A subfloor’s lifespan depends on the kind of material used and maintenance practices.
Under normal circumstances, the subfloor can last up to 20 to 30 years.
