The Foundational Science Backing SlabTECK
At Hygrothermix, science comes first. Before creating our first product, we spent two years in dedicated R&D, focusing on the physics of heat and moisture transport in and around concrete slabs. We started out intending to create a best-in-class, premium-priced vapor retarder offering. The science didn't support it. The project turned into a value engineering exercise and we're excited to share what we discovered and created.
After two years of delving into the underslab hygrothermal science, we found the industry to be:
1) Surprisingly disconnected from the underlying science governining heat and moisture transport,
2) Heavily over engineered in terms of membranes, and
3) Underengineered in terms of assembly design and installation accessories
Combining our industry experience and product development & manufacturing knowhow with this newfound knowledge, we designed and developed the SlabTECK system from the ground up. Most under-slab specifications are written around membrane properties. We engineer toward the only performance metric that ultimately matters: the slab's long-term internal relative humidity.
We built a value-engineered ASTM-compliant membrane and custom accessories chemistry-matched to our films coupled with design and support services to provide the industry with science-backed and proven slab RH results.
We don’t rely on buzzwords or repurpose existing technology — we engineer purpose-built solutions based on measurable, real-world outcomes. Most manufacturers compete by matching and advertising "me too"membrane properties. We engineer slab moisture performance outcomes.
We aren’t marketers. We are building scientists, engineers, product developers, manufacturers, and installation experts with decades of hands-on experience. We used this experience and research to bring you the best possible system of value-engineered products and services. Let's dig into the assembly design...
What Matters in Slab Design
A successful slab moisture control system depends on many interrelated factors, including:
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Soil type
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Subbase material and depth
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Stone capillary break
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Insulation used or not
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Vapor retarder properties, including permeance, toughness, and installation quality
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Concrete mix design
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Drying of the concrete slab prior to flooring placement
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Flooring adhesive sensitivity
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Floor covering permeance
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Indoor operating conditions
We consider all of these factors alongside the complex, coupled heat and moisture transport mechanisms that govern slab performance. Through thousands of validated hygrothermal simulations using WUFI®, the internationally recognized software used by building scientists to model coupled heat and moisture transport, we’ve identified the variables that truly impact long-term results — and we provide this insight through our design assistance, products, installation support, and verification services.
Our Support Includes:
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Design assistance
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Pre-slab planning meetings
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Real-time project guidance
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CAD drawings, instructional videos, and step-by-step instructions
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In-person or virtual installation reviews
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As-built models of your slab’s future performance, predicting heat and moisture profiles for decades of operation
Whether you want detailed modeling from the start or basic guidance based on our modeling R&D and literature findings, we can provide:
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Comparisons of the moisture condititions resulting from your specified options versus SlabTECK solutions
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Value-based insights based on predicted slab performance, not guesswork
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Custom-designed moisture control systems for your specific building assembly
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As-built after-the-fact moisture report detailing your slab's RH profile for decades to come.
See our full hygrothermal consulting design and support options HERE
Proper Science:
The physics behind heat and moisture transport are complex and coupled. That is, the heat transport
depends on the moisture condition and the moisture transport depends on the heat condition. (See
the WUFI description of the calculations in the figure below.) To solve the equations requires
hundreds of iterative calculations per timestep at each finite layer of the construction. This results
in hundreds of millions of calculations over a decades-long simulation.
Why temperature matters:
Most below-slab vapor analyses don't pay enough attention to temperature beyond it's effect on the assumed vapor pressure above and below the assemblies. But it's the heat and the media it transfers through that really define the moisture conditions and transport expecially when a temperature gradient exists.
First, when the sub-slab soils exhibit capillarity, a stone break should not be considered an optional design feature. Protecting your slab and building envelope from liquid water should be mission 1. The capillary break will do two very important things:
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Prevent the capillaries from sucking liquid moisture close or into your slab from the temporary or permanent water tables below, and
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Create a permeable region where the negative temperature gradient can work its magic. (Preventing 100% RH from existing below your vapor retarder.)
The importance of the moisture conditions in and around the slab is fairly obvious. The temperature’s affect is less obvious, but arguably as or more important. The key is #2 above and the overall temperature gradient from around 70F in the building to about 55F below the slab.
When capillarity and convective flow (vapor movement with bulk airflow) is shut off, vapor's only means of travel is diffusive flux. Diffusion is driven by the H20 partial pressure difference between adjacent locations. Relative Humidity, RH, is a measure of the amount of moisture in the air divided by the maximum amount of moisture in the air (also known as saturation). RH also equals the actual pressure divided by the saturation vapor pressure.
Relative Humidity = Actual Pressure / Saturation Pressure - (eq. 1)
The saturation vapor pressure, in the clausian clayperon zone (where vapor and liquid coexist- between 0 and 100 C), has an exponential relationship with temperature. Explicitly, as the temperature increases, the saturation vapor pressure increases exponentially while the actual pressure only increases linearly based on the ideal gas law. Since the saturation vapor pressure is in the denominator of the RH equation (1), as temperature goes up, and all else is equal, RH goes down. In standard building construction and operation, the temperature gradient fights the moisture gradient in terms of partial vapor pressures and the resuting diffusive vapor drive… usually slowing inward vapor drive and even sometimes reversing it!
When we take all of these project and climate-specific factors into consideration and we do the math and physics analyses, we typically result in a minute difference between the results from using a high-quality vapor retarder and using what other manufacturers have coined as "barriers". In most scenarios the difference ends up being a single percent or two RH difference over a 100-year building life. This is less than the error involved in measuring these values!
This is why we advise you to consider engineering your solution (per ASTM E1643) instead of specifying the most expensive products and systems without any signifiant or measurable gain in performance. Contact us to learn more about our consulting services or to schedule a meeting.
We can help design an economical slab moisture protection system utilizing value-engineered quality membranes, accessories that bond, and support that will last the life of your building.
Want to learn more?
Call or submit the form below to learn more. 303-305-3802