Hot vs. Cold Fluid-Applied Waterproofing for Commercial Work

For horizontal waterproofing in new construction or renovation projects, liquid membranes are a sounder solution than sheet-based products. They’re also a go-to when surface conformity is the #1 priority of the project.

That much you probably knew already, but what about the debates of hot vs. cold fluid-applied waterproofing?

The differences in products aren’t quite as stark as they once were. Nonetheless, you can still save precious time and energy by picking the right method for your job site.

What Is Hot Fluid-Applied Waterproofing?

Hot fluid-applied waterproofing usually refers to a specific product – hot rubberized asphalt (HRA). This waterproofing material consists of asphalt, synthetic rubber polymers, and mineral stabilizers.

HRA installation involves using a jacketed, gas-fired kettle. The user heats the membrane inside and moves it to the working area by bucket or pump.

What Is Cold Fluid-Applied Waterproofing?

In the past 30+ years, cold liquid-applied waterproofing has increased in popularity as a convenient way to address older roofs. The product’s qualities allow contractors to restore, rather than replace, the roof, reducing costs and environmental impact. 

As the name implies, cold-applied fluids are usable at ambient temperatures. Also unlike hot liquid-applied waterproofing, cold-applied systems in a much wider range of membrane materials:

• Polyurethane
• PMMA (polymethyl methacrylate)
• PUMA (polyurethane methacrylate)
• Asphalt emulsions

You can apply these systems by spraying or by hand. With the spray-on type, you’ll simply mix and apply the fluid. With the by-hand version, you’ll pour the fluid onto the substrate and spread it with a squeegee.

As you work, these systems will cure by chemical reaction or exposure to moisture.

6 Factors in Choosing Hot vs. Cold Fluid-Applied Waterproofing

Picking a fluid-applied waterproof membrane most often comes down to:

1. Time
2. Cost
3. Installation difficulty
4. Safety
5. Environment
6. Strength & adhesion

1. Curing & Lead Time

Fitting a construction product into your work schedule involves more than just 

the time it takes for a membrane to cure. You must also consider:

• Substrate prep
• Material prep
• Application
• Cleanup
• The financial impact of all of the above

Think of a high-traffic plaza deck atop an office building in bustling downtown Boston. If this deck allows water into the occupied space below, the repair timeline is … 4 hours if you’re lucky? The second you arrive on-site, the race is on to keep revenue-driving spaces open, prevent damage to merchandise and decor, and protect structural integrity. And before you cross the finish line and let people and vehicles back into the work zone, all waterproofing products must be fully cured.

Hot fluid-applied product use is laborious and not very efficient. Detailing is an entirely separate step from cleaning and priming, as it requires its own setup and material (polyester fabric).

During this time, you’ll heat the asphalt to 350-425°F – this alone can take 3-4 hours. In fact, just about every step of hot fluid-based waterproofing takes longer than its chilly competitor:

Cold fluid-applied membrane installation is up to 4x faster. The reason is simple: There are fewer steps to it.

After priming, the crew needs only to mix the membrane and get started. Spraying is faster than working by hand, allowing you to apply a single membrane immediately.

No matter how you do it, the numbers show that cold liquid-applied installation can cover more area in less time. Some industry experts have reported saving up to 2 weeks on large projects.

2. Cost

Liquid-based waterproofing is a rare case of the newer, more advanced technology being cheaper than the old standard.

As you can see, hot rubberized asphalt treatment is more expensive in every way possible. 

Cold-applied liquid products go on quickly and easily, minimizing the building downtime your work creates. Because they last an average of 10 to 30 years, you're also gaining long-term value. Reapplication is simply a matter of adding a new top coat over the existing system, meaning there's even more value for the owner further down the road.

3. Installation Challenges

The application process is vastly different between hot and cold waterproofing products.

Hot fluid-applied waterproofing requires a roller or squeegee for application, depending on the membrane product. The work necessitates a team of 3-5 people to go efficiently.

If there's one advantage to it all, it's this: HRA waterproofing is feasible in conditions as low as 0°F. As long as the surface is free of snow and ice, a hot-applied solution can help you avoid waiting days or weeks until the cold weather breaks. 

Unfortunately, the benefits don’t extend to hot-weather use. If you apply HRA at high temperatures, air will escape and moisture will evaporate through any defects in the primer, resulting in pinholes and blistering.

In fact, outside of low-temp use, HRA membrane installation is more intensive and a much bigger hassle than cold fluid-applied waterproofing. For starters, it often requires several more layers to form a full coat:

Is your job site sitting pretty on solid ground or perched up high? This will also affect how much of a haul HRA installation is.

If it's at ground level, bringing in the necessary gear and materials is straightforward. But if you're dealing with a plaza deck or a rooftop scenario, opting for a hot fluid-applied system can run up your bill and eat into your schedule. You’ll need a crane or lift to hoist those huge, heavy kettles or melters to the application site. Also, note that the unused product will need to remain hot throughout the process.  

Cold fluid-applied waterproofing forms a successful barrier in just 1-2 layers (excluding the primer). You can even skip the reinforcement layer, as the membrane is self-leveling. 

You can do the job with a crew of three competent installers. The toolkit will include sprayers or rollers – easy and simple to use. Most cold fluid-applied systems come in 5-gallon pails, making them easy to move with a service elevator.

Applying the product is also low-intensity work. There’s minimal chance of water evaporation or air expansion causing the concrete to weaken.

The one major limitation of cold fluid systems is, ironically, cold weather. Manufacturers don’t recommend you apply them when the weather is 40°F or below.

4. Safety

Hot fluid-applied waterproofing involves high heat and heavy weights. There’s a much higher chance for error – and injury.

The dangerous duo of heat and an open flame makes combustion a looming threat. Because of this, there are several potential hurdles to using hot asphalt:

• Many local building codes restrict HRA use or ban on-site kettle presence.
• Urban places like New York City often limit the height at which you can use HRA kettles.
• The local fire marshal might require you to get a special permit for the work.

If you or the property owner is eco-conscious, environmental safety may also affect your choice of membrane. The VOC (volatile organic compound) levels of hot fluid-applied membranes sit firmly in the middle – not great, but not awful. Hot-applied products are usually bitumen in nature and used in a molten state, so they don’t include dangerous solvents. There may still be modest emissions from other additives as you heat the asphalt.

Cold fluid-applied work doesn’t require a super-heavy vessel, nor will you need a flame or propane to heat it. Cold-applied waterproofing is a more reliable option that’s free of fire and burn hazards.

Solvent-based cold-applied membranes do present more of a VOC hazard. These products require solvents to keep them in a liquid state; the solvents evaporate into the air as the membrane cures.

Water-based cold fluid-applied membranes, however, contain fewer VOCs than both hot-applied and solvent-based cold products. Water-based membranes use good ol’ H²O as the primary carrier, which results in far fewer emissions.

5. Environment

What about the well-being of the product itself?

Durability is, naturally, a huge factor in considering any construction product. The building’s local climate and intended use have a huge influence on the success rate of waterproofing products.

Temperature swings, seismic activity, and even the natural settling and shifting of a building can fatigue waterproofing systems. If your job site is prone to one of the first two, elongation and elasticity are especially relevant traits in your choice of membrane. Cold liquid-applied membranes often include advanced materials such as polyurethane, acrylic, or silicone, which have excellent flexibility and recovery ability. These traits enable them to cover cracks effectively as the substrate moves or settles.

Note that not all cold fluid-applied membranes are created equal. Each popular material is best for meeting unique goals:

• Silicone – resisting low temps, ponding water, & chemicals
• Polyurethane – resisting foot & vehicle traffic
• Acrylic – UV protection on a tight budget

6. Strength & Adhesion

This may have sounded like a hit piece so far, but the “hot vs. cold” discussion isn’t entirely one-sided.

Hot fluid-applied waterproofing is excellent at adhering to construction surfaces due to its molten state at the time of application. The mixture seeps into the substrate slightly, creating an interlocked bond as it solidifies.

Scenarios that demand a high-adhesion membrane like HRA include:

• Below-grade – to resist hydrostatic pressure and soil movement
• Bridges – to cope with vibration and heavy traffic
• Terraces – to prevent leaks into living spaces
• Roofs – to deter water accumulation and wind uplift

The bitumen-based formula may also include modifiers that add to the product’s general strength (which is already impressive). Using HRA results in a thick, sturdy, uninterrupted layer across the substrate.

Cold fluid-applied waterproofing membranes offer competitive strength – with the right material. Stick to silicone or polyurethane if strength is a key consideration in your construction specs. 

As for adhesion, many cold-applied products make it happen without the need for a primer. The bond is usually inferior to hot-applied waterproofing, but ultimate performance depends on the specific product formula and application thickness.

Other Tricks for Commercial Waterproofing

Today, both cold and hot fluid-applied coatings can form a seamless shield for plaza decks, terraces, balconies, planters, and more. In many large-scale use cases, though, the more modern waterproofing technology (cold-applied) outpaces traditional hot rubberized asphalt.

If there’s an urgency to the situation, use cold-applied waterproofing to minimize disruption of the building’s operations and ability to drive revenue. If the owner’s mindset is “low cost at all costs,” cold fluid-applied is once again the logical solution.

HRA installation is still valuable if the job site is currently below ~40°, or if the application requires super-strong adhesion. Choose thoughtfully, and the results you want will follow.

Of course, there are other products that influence the outcome of your waterproofing and weatherproofing efforts. To learn about expansion joints’ massive role in building envelope protection, get our free guide below: