You can “seal” a garage floor, you can “coat it,” and you can apply a “moisture barrier” to it, but are any of these really waterproofing the garage floor?
You cannot waterproof a residential garage floor, but you can come close using a membrane barrier under the floor and an epoxy coating on top. Polyurethane and acrylic coatings are the next most effective, and penetrating sealers are the least able to block moisture.
In this article, you will learn how to come as close as possible to waterproofing a garage. The thing is, you don't need to waterproof a garage to protect it from excess moisture. Even the least effective penetrating sealer offers plenty of moisture blockage for a typical garage.
How to Waterproof a Garage Floor
A combination of a membrane barrier and an epoxy coating offers the most protection from excess garage ground water
The fact is that you can't “waterproof” a garage floor, so we need to stop using that word.
Manufacturers need to stop referring to their garage coatings and sealants as “waterproofers,” because their products do not block all moisture at all times.
When we apply a membrane barrier, a coating, or a sealant to the problem, we are blocking moisture, not completely preventing it.
A Membrane Barrier Plus an Epoxy Coating is Nearly Waterproof
A combination of a moisture membrane barrier and an epoxy floor coating is the most waterproof solution for a garage floor. It's not completely waterproof, but it's the closest you will get in a residential garage.
An epoxy coating on a garage floor that is supported by a moisture barrier membrane can create a highly water-resistant surface, but it may not be considered truly “waterproof” in the absolute sense.
“Waterproof” implies that no water can penetrate or pass through the surface under any circumstances.
However, no floor covering or moisture barrier system can completely eliminate the possibility of moisture transmission or penetration.
An epoxy coating on a garage floor with a moisture barrier membrane can provide a high degree of protection against moisture and water ingress from above, such as spills, leaks, or surface water.
The membrane beneath the concrete slab effectively blocks ground moisture from entering the concrete, reducing the risk of moisture-related issues.
This combination can create a highly water-resistant floor that effectively manages moisture and protects the garage floor and any materials or items stored on it.
Even with these measures in place, some level of moisture transmission or penetration may still occur under extreme conditions, over an extended period, or in the event of material failure.
If a garage is in a deeply wet environment that needs maximum water protection, a membrane and epoxy might be in order.
But if a garage has some “moisture issues,” a sealant might be the answer.
The first thing is to understand the types of garage floor moisture barrier, so you know your options.
What is a Garage Floor Moisture Barrier?
A moisture barrier is a membrane under the garage floor slab or any coating or sealant on the garage floor that blocks water passage to some degree.
A Moisture Barrier Under the Slab is a Membrane
A membrane moisture barrier is a sheet of plastic that is installed when the garage floor is installed. The membrane sits between the ground and the slab, protecting the floor from the groundwater underneath.
A moisture barrier is so effective that having it might mean not needing a sealant or coating for moisture protection. You might still apply a topical solution to protect the floor from grease and chemicals, but a membrane might be sufficient to protect the floor from excess water.
In extremely wet environments, a membrane and epoxy combination is the strongest protection from water damage to the garage floor.
In a normal environment, a moisture membrane block might be sufficient.
Since you cannot add a membrane after the garage floor is poured, you probably need to understand your topical sealant and coating options better.
A Moisture Barrier on the Slab is a Coating or a Sealant
Once we're done pouring the slab, the water protection choices are a coating or a sealant.
Coatings are made of acrylic, epoxy, or polyurethane. They coat the floor in a mostly-impervious film.
Sealants are silica-based chemicals that change the structure of the concrete to block moisture movement.
A Penetrating Sealant Changes the Floor's Molecular Structure
A sealant moisture barrier is also known as a “penetrating sealer” because it seeps into the floor surface.
A sealant chemically alters the concrete to block moisture. It creates molecules that are larger than water and so tend to get in its way.
Just as water can pass around a rock, the sealant method has low protection.
But don't let that bother you, as sealants are often the best choice to block moisture in the garage. They offer enough protection for low-level moisture problems.
Penetrating sealers come in water-based and solvent-based varieties. There are several variations of each type based on their chemical makeup and effects. Solvent-based sealants are a bit better at water blockage but they put off fumes during application.
A Floor Coating Forms a Film that Blocks Water Movement
A moisture barrier coating sits atop the concrete where it seals the surface under a rubbery-plastic-plasma shield of epoxy, polyurethane, or acrylic.
Coatings are “film-based” because they form a hard film that prevents water from passing through.
The coating choices for the garage are water- and solvent-based acrylic; epoxy; and water- and solvent-based polyurethane. They have varying levels of water blocking capacities and fume issues.
Why Does a Coating Seal and a Seal Penetrate?
If a coating can seal the water into the floor, then why do we call it a “coating”? Why don't we refer to it as a “sealant”?
If a penetrating sealant doesn't seal the floor but creates blockages to the water, then why do we refer to it as a “sealant”? Why don't we call it a “molecular blocker”?
These questions remind of when I asked my Disney-obsessed boss about the difference between Disney's Pluto and Goofy.
She loved Disney's dogs, and I loved real dogs, so this was something we sort of had in common.
I could not tell the difference between Pluto and Goofy.
One talked, and one was Mickey's pet dog.
Which was which?
My boss explained, “Pluto is the dog that acts all goofy. Goofy is the dog that acts like a real dog.”
I thought about this for a minute, because it made my head spin.
“So… Pluto is goofy? And Goofy is not?”
She says, “Yup, you got it.”
And that is why sealing block water movement in the floor, and coatings seal moisture inside the concrete.
Sealants block, and coatings seal.
Pluto is goofy. Goofy is not.
How do Sealants and Coatings Rank for Water Protection?
From most to least protective, here are the rankings for the sealants and coatings you can apply to your garage floor.
The most effective water protection is the membrane under the slab and epoxy atop the floor. This combination offers enough water protection for a Louisiana swamp. Since most houses are not sitting in alligator water, we need to lower our expectations of moisture barrier solutions.
Any of these products will provide decent water protection in a “normal” garage.
In a garage with wind-driven rain and de-icing agents ruining the floor, you could go high-end, or you could fix those hazards and do a normal sealant or coating.
If you put down epoxy in a wind-driven rainy garage, you will still have water on your epoxy, as well as the walls, doors, windows, and ceiling. Fix the excess moisture that does not belong inside, and then pick the sealant or coating moisture barrier based on the result.
Whether the membrane is there or not, the sealants and coatings you can apply will add water protection to your garage floor.
From best to least protection, this is how the sealants and coatings rank. Note that these are general rankings, because individual product formations can offer more or less than average results.
| Moisture Block Rankings of Garage Floor Sealants and Coatings | |
|---|---|
| Sealant and Coatings | Moisture Block Ranking |
| Water-based Penetrating | Low |
| Solvent-based Penetrating | Low |
| Water-based Acrylic | Moderate |
| Solvent-based Acrylic | Moderate to High |
| Epoxy | High |
| Water-based Polyurethane | Moderate to High |
| Solvent-based Polyurethane | High |
The sealants offer the least amount of protection, but at a rate that is still more than adequate for many garage floors.
The water-based acrylic blocks more water than penetrating sealers, but less than the rest of the coatings.
Solvent based acrylic and water based polyurethane are tied in 2nd place.
Epoxy and solvent based polyurethane offer the highest amount of garage floor water protection.
Now, did that make things better or worse for your confusion?
This article explains the relative moisture blocking capacity of these products, but not how to choose which product to buy.
What if You Need to Truly “Waterproof” the Garage Floor?
You cannot truly waterproof a residential garage floor, but some solutions provide better protection than others.
But if you were creating an underground bunker, wouldn't you have to make a truly waterproof concrete moisture barrier?
You could envelop your waterproofed concrete inside multiple membranes and outer concrete structures to create a truly waterproof floor.
If you were planning something like that, you would not be reading this article about moisture in your garage. You'd be working with architects to encapsulate the inner living area with waterproofing protection.
For a residential garage, you are limited to a membrane barrier installed during construction, and sealants and coatings you apply after construction.
The Downsides of the Nearly Waterproof Garage Floor
Creating a moisture barrier membrane under the garage floor and applying an epoxy coating atop the floor provides significant benefits in terms of moisture control and protection.
However, there can be a few potential downsides to consider, including installation cost, installation complexity, consequences of material failure, and the epoxy maintenance requirements.
Cost of a Moisture Barrier Plus Epoxy
Installing a moisture barrier membrane during construction and applying an epoxy coating on the garage floor can add to the overall project cost. Both materials and labor costs for proper installation should be factored into the budget.
Installation Complexity of a Moisture Barrier Plus Epoxy
Installing a moisture barrier membrane requires careful attention during the construction process. If not installed correctly, it may not provide the desired level of moisture protection.
Similarly, epoxy coatings require proper surface preparation, including cleaning, crack repair, and potentially etching or grinding, to ensure proper adhesion and performance.
Epoxy is notoriously hard to apply without making a curse-filled spectacle of your shouting abilities.
Risk of Failure with a Moisture Barrier Plus Epoxy
A failure in the moisture barrier can lead to floor mold, delamination, and efflorescence (salt migration to the surface).
The failure can occur if the moisture barrier membrane is installed incorrectly or breaks after the concrete pouring to make the floor.
The failure allows groundwater to rise through the concrete where it can become trapped between the membrane and the epoxy coating.
This can potentially lead to issues such as mold growth, delamination, or efflorescence.
The Maintenance Requires of an Epoxy Floor
While epoxy coatings are durable and long-lasting, they may periodic maintenance. An epoxy floor eventually will require a re-coating to address chipping, peeling, or wear. This can add to the long-term maintenance cost of the garage floor.
Why Install a Membrane Barrier During Garage Construction
Installing a garage floor moisture barrier during garage floor construction can add years to the floor's lifetime. Moisture control reduces the risk of mold, delamination, and more.
The Moisture Barrier Controls Destructive Water Accumulation
Groundwater that rises up through the floor slab can cause mold growth, and floor delamination (when the top of the concrete peels off). Installing a membrane under the concrete slab effectively prevents ground moisture from entering the concrete slab. The membrane is a waterproofing measure that can stop the processes of mold growth and floor deconstruction.
The Moisture Barrier Improves Garage Air Quality
By blocking ground moisture from entering the concrete slab, a membrane moisture barrier reduces the amount of moisture vapor that can rise up through the slab into the interior space, helping to protect floor coverings and improve indoor air quality.
The Moisture Barrier Enhances the Sealant or Coating Performance
By controlling moisture and vapor transmission, a membrane moisture barrier helps to ensure the long-term performance and durability the sealant or coating applied into or atop the floor.
The Moisture Barrier Protects the Concrete Material Itself
Moisture can cause damage to the concrete over time, leading to issues such as cracking, spalling, or efflorescence. Installing a membrane moisture barrier during construction helps to protect the concrete slab from moisture-related damage and extends its lifespan.
The Moisture Barrier Can Eliminate the Need for Surface Protection
Installing a membrane moisture barrier during construction can reduce the need for additional moisture mitigation measures later on when installing floor coverings. This can simplify the floor preparation process and save time and resources.
What's Involved in Installing the Membrane Moisture Barrier
If you're on the verge of installing a garage floor, now is the time to consider the membrane moisture barrier.
Do you put a sheet-based water blocker under your garage floor slab?
The installation process usually involves the following steps mentioned here to give you an idea of what you're getting into:
- The construction site is excavated, and the soil is prepared for the concrete slab
- The soil is graded and compacted to provide a stable and level base for the membrane and the concrete slab
- The moisture barrier membrane is rolled out over the prepared soil, with the seams overlapped and sealed to create a continuous barrier. It is essential to ensure that the membrane is free from punctures, tears, or other damage that could compromise its effectiveness.
- In some cases, the membrane may also be installed around the perimeter of the slab, extending up the foundation walls to further protect against moisture intrusion
- Once the membrane is in place and properly secured, the concrete slab can be poured on top of it.
What's Involved in Applying the Sealant or Coating Moisture Barrier?
A sealant penetrates into the concrete, and provides an adequate but the lowest level of moisture barrier.
A coating sits atop the floor and provides the best level of moisture protection.
Sealants are made of various silicate compounds, each having its own affect on the concrete.
Coatings are made of acrylic, epoxy, and polyurethane, which is why they are able to film over the concrete to seal out moisture penetration.
You'll get much more detail on how to decide which moisture barrier to use in our other articles. To give you a quick idea, though, here is what's involved in applying a sealant or a coating moisture barrier in the garage.
| Preparation Tasks Before Sealing the Garage Floor | ||||||
|---|---|---|---|---|---|---|
| Concrete Sealer Type | Surface Cleaning | Repairing Cracks and Damage | Ensuring Concrete is Dry | Surface Etching | Surface Grinding | Priming |
| Water-based Penetrating | Yes | Yes | Yes | No | – | – |
| Solvent-based Penetrating | Yes | Yes | Yes | No | – | – |
| Water-based Acrylic | Yes | Yes | Yes | If needed | – | – |
| Solvent-based Acrylic | Yes | Yes | Yes | If needed | – | – |
| Epoxy | Yes | Yes | Yes | Yes | If needed (alternative to etching) | If required |
| Water-based Polyurethane | Yes | Yes | Yes | If needed | – | – |
| Solvent-based Polyurethane | Yes | Yes | Yes | If needed | – | – |
The Many Names of the Moisture Barrier
While researching this article, I discovered there were terms for the moisture barrier that I thought referred to something else.
It turns out that all these terms mean “moisture barrier,” which might help you in your research.
Terms that mean “moisture barrier”:
- Vapor barrier
- Moisture control system
- Moisture protection layer
- Vapor retarder
- Moisture mitigation system
- Moisture-resistant coating
- Moisture-blocking sealant
- Vapor-blocking membrane
- Waterproofing layer
- Moisture prevention barrier
So as you're doing research, any of these terms mean the method of keeping moisture from rising up through the floor's concrete slab.
