Is Hempcrete Waterproof?

Published Categorized as Sustainability
Mixing Hempcrete

When it comes to building materials, manufacturing companies have come up with more environmentally friendly materials with variations that are quite notable. Hempcrete provides excellent thermal insulation, prevents condensation, and has a low environmental impact, but is it waterproof?

Hempcrete is waterproof. It is highly versatile and features desirable structural and moisture-handling properties. Depending on the mix variables, hempcrete makes an ideal choice for insulation, flooring, drywall, and roofing. Hempcrete is also fireproof and rot-proof.

This guide will help you determine whether hempcrete is a versatile building material to withstand water and moisture without rotting or getting damaged. So read on.

Hampcrete’s Moisture Handling Resistance

Hempcrete features a multi-scale porous structure with plant-fiber insulation materials that give it the ability to maintain integrity in humid conditions. The product utilizes hemp shives – the inner stem of the plant and a limestone base. The vegetal aggregates resulting from the pulping of the hemp stalks can store a great deal of moisture due to their porous structure.

The hemp hurds absorbs moisture on the large internal surface of the plant fibers into the cellular structure. Hemp can rapidly absorb large amounts of water during material preparation, but the underlying mechanisms of liquid water amalgamation are not well understood.

Unlike Portland cement that needs water to hydrate, hempcrete takes on moisture when it exists and releases it when the conditions allow. Research indicates that hempcrete blocks fabricated and stored in different weather conditions – without any coating – for a few months showed water vapor pressure between 1000 Pa for the drier block and 1600 Pa for the moister one.

The discrepancy in the blocks shows that hempcrete can remain moist once installed as long as it is not heated. However, it is possible to accelerate the drying process if necessary, emphasizing the importance of good initial conditioning of blocks during the manufacturing process.

Hemp hurds are massively porous and can absorb a large volume of water than generally required for a hempcrete mixture. Too much water can have considerable effects on the results, even when hurds and lime variables are mixed.

Too much water can increase the length of drying the hempcrete and affect the setting of the lime binder.

Studies also indicate that the Physico-chemical incompatibility between the binder and vegetal hemp aggregates can lead to inadequate mechanical hydration. Therefore, liquid water absorption has a more significant influence than vapor diffusion resistance on the blocks’ moisture and heat transfer.

Besides, hempcrete cannot be overwhelmed when it comes to adsorbing of moisture thanks to the vast storage capacity with a sustained elevated humidity of 93 percent. Therefore, high levels of moisture don’t propagate deeply into the hempcrete.

The advantage of hempcrete over other plant fiber materials is in the properties of the lime binder. Lime binder helps to stabilize the internal humidity of the building by absorbing and releasing moisture.

Lime features a high pH and includes antimicrobial and antifungal properties. Conversely, it has excellent workability that allows you to achieve full joints with superior bonding to other materials that enhances performance and aesthetic value.

The lime coating in each hemp block creates a surface that resists the development of mold, even when the conditions cause decay. The resilience to tackle humidity and liquid moisture makes it a desirable choice and a unique insulation material in hot and cold climates.

Benefits of Hempcrete

There are many benefits associated with hempcrete that make it a popular building construction material. Let’s dive in and have a look at the most common pros.

Environmentally Friendly

Hemp hurd is a by-product of the hemp plant, which is typically grown for its seed or strong fiber. According to a 2003 study, the environmental performance of hemp-based natural fiber mat thermoplastic (NMT) shows that it isolates carbon in its cellulose structure. Therefore the carbon inside the hemp hurds does not release carbon back into the atmosphere and can save 207,345 lbs of carbon.

For every 200,000 homes built, the carbon footprint after sequestration is about 897,764 tons that makes the carbon net savings for the planet significant. Conversely, hempcrete is useful material. The hemp plant takes 14 weeks to mature, and the farming process uses fewer pesticides and herbicides than other grain or fiber crops.

There is a lot of dust when mixing hemp hurds and lime binder, which is highly caustic. Adequate protection is necessary when handling dry ingredients. However, once fully cured and dried, hempcrete does not release any toxins in the indoor environment.

Moisture Handling and Resistance

Hempcrete is a unique plant-fiber insulation material that can absorb up to 3.6 gallons per square meter of water. The hemp hurds can store a large volume of moisture due to the porous structure feature.

Furthermore, the moisture is then absorbed into the considerable internal surface area of the plant fibers and adsorbed into the cellular structure. It’s also resistant against mold since it contains lime, which is antimicrobial and antifungal, making it an ideal choice for roofing and flooring.

Good Carbon Sequestration

Hempcrete has a small carbon footprint. One hectare of the industrial hemp plant can absorb 22 tons of CO2 and other climate change gas. Hemp acts as a carbon store, sequestering (absorbing) atmospheric CO2, and releases it when the material is burnt or composted.

Additionally, hemp produces more robust and more versatile fiber than cotton or other fiber plants. Therefore hempcrete acts as a high performing building envelope and protects it against external weather.

Excellent Structural Qualities

Hemp hurds is porous while the lime-based binder sticks together and protects the hemp. When the two materials are combined, they offer a building material that is resistant to fire and decay.

Besides, hempcrete insulation cast around conventional wall framing or double-stud framing can restrain the stud from bending and increase the load that can be carried by each framing member.

The rigidity of hempcrete insulation paired with the textured surface makes an ideal substrate for plaster finishes without a need for other bonding agents. 


As with any construction material, the cost of hempcrete can vary depending on the complexity of the design, specification, and several other factors. Hempcrete provides a definite advantage and can allow considerable savings when building. 

Additionally, hempcrete allows you to avoid incurring the extra cost of thermal insulation and cuts down fuel bills. Hempcrete features loads of thermal mass and little insulation, which gives it extraordinary thermal performance.

Hempcrete helps maintain a comfortable indoor temperature without the need for mechanical heating, cooling, or ventilation. It provides significant extra savings since you can use it as a wall with no need to leave a gap for insulation.

Allows Natural Ventilation Into the Building

Hempcrete is breathable and offers improved health of the building’s occupants. It allows for natural ventilation in the building, while modern highly insulated buildings rely on airtightness to trap air within the lightweight insulation layer.

Hempcrete works by storing heat from the sun or the heating system in its wall’s thermal mass, which is released slowly as the building cools down. The slow speed at which a hempcrete wall stores and releases heat has the effect of keeping your home cool in summer and warm in the winter.

Unlike modern insulated buildings, with a hempcrete building, you can open windows if it gets stuffy without worrying that all the heat will go out and get lost.


As seen in this article, hempcrete is waterproof and is a versatile and durable construction material that can withstand water and moisture

  • It helps in carbon reduction
  • It reduces energy cost
  • It is lightweight
  • It is breathable, and,
  • It is incredibly strong to last you a long time


By Giovanni Valle

Giovanni Valle is a licensed architect and LEED-accredited professional and is certified by the National Council of Architectural Registration Boards (NCARB). He is the author and managing editor of various digital publications, including BuilderSpace, Your Own Architect, and Interiors Place.


  1. Hi just finished reading your article on hempcrete and was wondering if hempcrete would be a good product for a root cellar. Can I have the outside earth up against the outer wall? Can hempcrete be used for the footings as well.
    Kind regards andrew.

    1. Hemprcrete by itself is not structural, so you would need a separate structural element to make it work below grade. Moisture and hydrostatic pressure would also be an issue if you have earth up against the outer wall. Best to stick to above grade applications.

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