THE DEVELOPMENT AND WIDE-SPREAD ACCEPTANCE of modern, quick-setting Portland-cement-based plasters and stuccos has not been without significant penalty. The love for a fast-set has a bitter price: the loss of flexibility, breathability, durability, and a unique aesthetic.
A POZZOLANIC LIME PLASTER
odern Portland-type cements have only been widely used since the 1850s. Before then—before we had the means and know-how to produce and sustain the intense temperatures necessary to heat limestone to a calcining temperature of above 1112°F (600°C), and then to the fusion temperature of about 2640°F (1450°C) necessary to produce the Portland cement clinker—before then, incredibly effective cements were made with less energy-intensive methods. These “Old-World” cements and the cementitious products made from them are amazingly durable, economical to produce, and user-friendly to mix and apply. In particular, the concrete the Romans used was a simple formulation of hydrated lime, pumice pozzolan, aggregate and water—a formulation they used to build an empire of roads, aqueducts, piers, and structures. The genius of that now time-proven concrete formulation is in evidence today, as many of their constructs are still standing some 2000 years later.
The switch to modern, quick-setting Portland-cement based products has not been without penalty, both in aesthetics and in durability. The frustrating and costly durability issues of modern concrete is a subject unto itself, but Portland-cement based products, including plasters and mortars, also inherit that performance penalty. Even putting aside the energy hit and process costs of producing Portland cement, what is gained in quick set and early strength in the front end is offset by performance losses going forward—losses in terms of flexibility, breathability, durability (functional life-span), aesthetic beauty, and ease of application. Such performance shortcomings need not be “lived with.” Not when there's a better product, one based on two millennia of tired-and-true: LimeStrong™.
CHOOSE LIMESTRONG™ FOR PERFORMANCE
Pozzolan-lime plaster owes its long history of use and functional longevity to several factors:
Breathability—by taking moisture in, then releasing it back into the atmosphere, a LimeStrong finish doesn’t trap water behind it—a vapor barrier and/or weeping spaces are not necessary when using LimeStrong plaster products. Internally-generated moisture from bathing or cooking is able to pass through the plaster and escape, effectively averting mold, rot, and decay.
Flexibility—A LimeStrong finish moves with the inevitable shrinking and expansion of wood and steel building materials instead of cracking like brittle, inelastic stuccoes can.
Autogenous Healing—the long-lived reaction of lime and pumice and water to each other and the surrounding atmosphere means LimeStrong can repair itself on a microscopic level, sealing cracks and filling voids, maintaining strength and integrity. Synthetic stuccoes and Portland-cement based plasters and mortars can’t do that—they quickly set hard and brittle, unable to adjust to changes.
Strength—pozzolan-lime plaster gains its strength and durability from two curing reactions. The first is a pozzolanic reaction between the pumice in the LimeStrong formulation and the hydrated lime, creating a flexible cementitious binder that provides both bonding strength and compressive strength. This amplifies the inherent strength derived from the second curing reaction—the atmospheric carbon dioxide transforming the hydrated lime back into limestone.
Unique Beauty—The beauty of a LimeStrong-finished wall is limited only by the creativity and skill of the hand that applies it. And over time, the permanent lime-wash finish develops a soft patina that enriches the visual appeal.
Durability—Properly protected from direct assault by water, a LimeStrong Build finish will last for the life of the building.
Depending on the surface finish type, LimeStrong holds up well to impacts, flexing and shedding crushed material rather than shattering like brittle stuccos and cementitious plasters. As a rule of thumb, the rougher the exterior finish, the more durability is inherent in the finish. Rough textures are not only quicker and easier to apply, they soften the look of the structure, as reflected light dissipates and defuses. Rough finishes, such as a harling or thrown finish, are durable, easy to repair, show less imperfections, and are quick to apply. Unlike smooth finishes, rough finishes are quite suitable for sever climates, as evidenced by the traditional use of rough lime plaster finishes throughout Scotland.
Like any exterior finish, LimeStrong must be protected from direct and relentless contact with water. A roof with deep gable ends and generous eaves is ideal. Exterior plaster must not come in contact with the ground.
Repairs are simple. Cracks from settling foundations or improper framing, impact craters, gouges and scratches—all are easily repaired and restored.
CHOOSE FOR EASE OF APPLICATION
LimeStrong works the same way every time. Without the ticking-clock of a hot chemical reaction (as with Portland cement products), mixing LimeStrong is stress-free, allowing for the ideal mud stiffness to be achieved.
And, as the chemistry of the curing reactions is well known and the ingredients in LimeStrong products carefully balanced, the performance characteristics are predictable and sustainable across the entire scope of the job.
LimeStrong cures as it dries, from the outside in. The reaction with the carbon dioxide in the atmosphere transforms the hydrated lime back into limestone, while the pumice pozzolan ignites a cementitious reaction that forms a concrete binder that amplifies the durability, density, and strength of the cured plaster (or mortar). Unlike synthetic stuccos and Portland cement-based plasters and mortars, the curing process is not a hot, hard-charging chemical reaction that leaves little time for working or fixing mistakes.
Once mixed, LimeStrong Build can be kept indefinitely if protected from air—a lid on a bucket; a plastic cover sheet over a wheelbarrow. That fact provides the applicator with a generous window to not only apply and blend section with section and control larger areas of work, but also to build up layers and then trowel the type of finish desired.
LimeStrong can be applied with a hawk and trowel, thrown on, or sprayed on using a conventional air-driven applicator gun. Once it's on the wall, it is troweled to the desired finish.
LimeStrong can be applied and worked in a wide range of temperatures and climates. It should be protected from freezing as it cures, but if frozen, can again be worked when it thaws. Drying or curing time is greatly influenced by the humidity and temperature of the surrounding air. Extra care must be taken in hot, low-humidity conditions, especially when wind is present. A plastered wall can be draped with wet burlap to create a moist environment. Use multiple light mistings of water to keep the plaster moist and prevent to surface from drying too quickly, taking care not to saturate the plaster with water (see application tips).
It can be months before a LimeStrong finish fully cures, (hence its ability to flex, breathe and autogenously heal) although a functional cure is typical within 48 to 72 hours.
LimeStrong can be applied directly to adobe bricks, straw bales, and wood lath. With a prep coat, it can be applied to wall board, styrofoam, masonry blocks, or poured concrete.
Refer to the Prep and Applications Tips page for more information on correcting applying and curing LimeStrong Build.
CHOOSE FOR COST EFFECTIVENESS
The lime used in LimeStrong is a hydrated or slaked lime, produced from a low-temperature firing that drives off the carbon dioxide. The pozzolan is made from a pure white pumice mined and refined in southeast Idaho. Pumice is naturally calcined by virtue of its volcanic origin, and so is simply mined and crushed. The rest of the trace ingredients that round out the mix design are equally economical to source. Without an intense energy requirement and expensive chemical admixtures, LimeStrong Build™ is a financial fit for any job...both inside and out.
The easy-going nature of the LimeStrong curing process means you don't need a big crew to stay ahead of a fast-setting point-of-no return. A small crew can work at an efficient and effective pace. Mistakes are simply troweled off, mixed back in and applied again.
The ability to protect LimeStrong mud from air (and thus abate the curing process) means less wasted product: what's not applied before lunch can be used after; what remains at the end of the day can be covered and used at the beginning of the next.
CHOOSE FOR BEAUTY
There is nothing plastic and industrial-looking about a LimeStrong finish. In the hands of a skilled applicator, the finish can be glass smooth (interior) or old-world rough or one of any number of troweled-in textures. But it's the use of lime washes that truly create the character and deep vibrance that combine for a one-of-a-kind finish. Naturally light, off-white LimeStrong can be colored using a wash of natural pigment dyes (or liquid paint pigments) that become integral to the finish itself. Such imbued color richness, even for the lightest of colors, is possible because both the white lime and the pumice in the LimeStrong formulation readily accept and hold the natural pigments.
If desired, the plaster finish can be re-color-washed in 8 to 10 years to recharge the color's vividness (depending on climate). But avoid paint—it destroys the breathability of the lime plaster, filming over the pores.
A skilled applicator will work in both color and texture, applying thin finish coats (washes) to build deep, rich, fascinating color and texture interplays that are not possible with conventional paster finishes and certainly not typical painted surfaces. The process is a true fresco technique that penetrates the plaster and becomes part of it, preserving the plaster’s ability to breath. The color will mellow and soften with time, resulting in a beautiful patina that creates character and amplifies interest.
Even compared to painted surfaces specifically rubbed and/or sponged to look interesting, a LimeStrong finish has an enduring depth and visual resonance that a painted-on faux finish will never have.
THINK INSIDE THE BOX
Synthetic and plastic stuccos are rarely used inside a living space because of volatility and off-gassing. That, and the bland nature of synthetic stucco, has relegated plaster applications to exterior finishes. Those longing for the timeless beauty found inside historic homes with those grand plaster-finished interiors have been struck with trying to fake it with gypsum-mud texture wipes and faux painting techniques.
No longer. LimeStrong, when applied and finished by a skilled craftsman, wraps a room with a gentle, intricate beauty and does away with the need to paint and repaint. Those living or working in the building also avoid the VOC concerns that plague paints. And the acoustics are better too...lime-pumice plaster absorbs more sound waves.
For builders and architects trying to recreate interior themes that mimic outside finishes and natural rock textures—casinos, lodges, restaurants and bars, movie-sets—LimeStrong fits the need.
LimeStrong Build™ is not a pure natural lime plaster (NHL) product, nor is it a cement lime product (see below). Rather, LimeStrong is a lime-pozzolan product. LimeStrong uses the natural adhesive property of hydrated, or slaked, lime and the cementitious chemical bonding reaction introduced by the pumice pozzolan ingredient to create a hard yet flexible matrix that can be applied as a plaster or used as a mortar.
For as long as ordinary lime plaster and mortars have been around, people have been amping performance and strength with reactive additives, or pozzolans (an effect known as gauging). A pozzolan is defined as a material that is capable of reacting directly with lime in the presence of water at ordinary temperatures to produce cementitious compounds. One of the most effective of these (as the Romans discovered and modern research done by the University of Utah and others confirms) is a pozzolan made from volcanic pumice. LimeStrong, then, by deliberately pairing lime with a reactive pumice pozzolan, is a Artificial Hydraulic Lime (AHL) product.
The reactive quality of the ingredients, the wisdom behind the mix design, and the consistency in production make LimeStrong a dependable and predictable lime-pozzolan product.
The lime-plaster marketplace also features Natural Hydraulic Lime (NHL) products that are mined from very specific lime deposits (typically European) that inherently/naturally contain the necessary hydraulic properties needed, although the high costs of NHL products put them out of reach for most.
NOTE: HYDRATED lime is not the same as HYDRAULIC lime. Hydrated lime cures only via recarbonation.
LIMESTRONG™ IS NOT A CEMENT-LIME PRODUCT. The workability and durability characteristics inherent in hydrated (slaked) lime plaster and mortar are so desirable that lime is commonly added to standard cement-and-sand plaster and mortar product formulations to amplify ease-of-use and increase performance. Unlike these tweaked-up cement-lime products, LimeStrong products eschew the use of brittle-setting Portland cement altogether. LimeStrong is formulated with lightweight pumice aggregate and fine pumice pozzolan (the Rusticus grade uses sand as well) realizing every performance and usability gain while completely avoiding the Portland-cement problems.
Chemically, slaked (hydrated) lime and fine-grained pumice perform together beautifully. The impressive durability of cured LimeStrong plaster happens on two levels.
THE FIRST: Hydrated lime, when mixed with water, will return to its limestone (CaCO3) origin as it dries, acquiring carbon dioxide from the atmosphere that “carbonates” and hardens, or sets, the hydrated lime.
THE SECOND: Lime has no hydraulic cementitious properties on its own, but in the presence of water and pozzolan (pumice), a pozzolanic reaction occurs and Calcium Silicate Hydrate (CSH) is formed. CSH is the chemical binder that makes concrete what it is. This binding glue further strengthens the limestone being formed as the hydrated-lime-to-limestone curing process takes place, resulting in a plaster that melds the compressive and bond strength of hydraulic cement and the breathing, self-healing, enduring flexibility inherent in lime plasters and mortars.
The lime+pumice+water formulation works beautifully! It has worked for millennia, as the evidence readily attests. Why? Because 100% of the lime is converted to the cementitious binder CSH. This simple lime + pozzolan + water combination triggers none of the deleterious by-products that make modern plaster, mortar and concrete—made using Portland cement—so problematic and short-lived. Thus, Roman methods produce densified, flexible, self-healing mortars and plasters that are not nearly as susceptible to brittleness, chemical attacks, and other problems that plague modern cement products.
SUSTAINABLE AND GREEN
Simple water + lime + pumice pozzolan cementitious finishes not only out-perform modern equivalents, they stand as environmentally sound alternatives to synthetic stucco and other Portland cement-based products. Unlike the energy-intensive process to produce Portland cement, hydrated lime is obtained by low-temperature firing. As for the pozzolan component, our pozzolan is made by mining and crushing a clean, pure pumice—an amorphous white silica, created by volcanic events millennia ago. Pumice pozzolan is not a by-product of pollution control processes and contains no hazardous materials. Recent studies corroborated previous test data indicating that natural pumice pozzolans are free of Crystalline Silica and other hazardous materials.
MADE IN THE USA
LimeStrong is a product of Hess Pumice, located in Southeast Idaho, USA. With the guidance of Stan Petersen, the renowned expert in old-world masonry and lime plastering, Hess formulated the LimeStrong plaster products to bring the strength, durability, and beauty of a lime-and-pumice finish out of obscurity and make it widely available to modern architects, builders, and homeowners.
Hess Pumice mines and refines the world’s purest commercial deposit of white pumice and ships it all over the planet.
LimeStrong Build is available in super sacks or 50 lb bags. Sample-size quantities are also available.