Material
Clay
Clay is one of the oldest materials known to mankind. Not only is it the material used to make pottery since the dawn of civilization, it is also one of the oldest known building materials next to wood and stone. We use a refined clay for our clay finish coats and we use a coarse local clay for our thick brown coats, cob, and earthen floors.
Sand
In most cases sand accounts for half of our plaster recipes. For our heavier brown coats, cob and earthen floors it accounts for even more. We utilize a wide variety of sands to get the specific size, angularity and sometimes color that we need for a specific plaster or floor
Limestone
Lime is kiln fired and water slaked limestone. Once the lime is applied and allowed to cure properly it returns to its original limestone state. Lime is a great plaster for exterior walls as it holds up against erosion. We also use it as an interior finish and as part of our Tadalkt system for wet areas like showers.
Straw
Another age old material, but accessible in much greater quantity in our times due to being a byproduct of growing wheat. Straw is an excellent fiber that greatly increases the tensile strength of plasters and earthenfloors .
Gypsum
Gypsum is a very conventional plaster material. We utilize gypsum for its fast setting times and strength, primarily when restoring/prepping existing walls for a clay or lime finish coat. Gypsum does not have the same wonderful to touch finish that clay and lime has, so it is not a material we use for a pigmented finish coat.
Pigment
Although many people love the color of the plaster itself without additional pigment, we often add pigment to the finish coat.The most common pigments we use are iron oxide based. Combining yellow, red and black oxides can create many of the colors that people are after.
Oil and wax
Drying oils are oils that oxidize to create long polymer chains that harden and create the water repellent quality necessary for floors. We use drying oils without chemical dryers, hardeners or other synesthetes. The raw natural occurring oils are heat treated to speed up the curing time. Beeswax is also used to repel water from our earthen floors. Although all of our floors receive oil and wax treatments, it is generally only our Tadalkt showers and an occasional kitchen or bathroom wall that receives any oils or waxes.
Suitable plaster substrates
Wood lath
Many turn of the century homes are lath and plaster. If plaster sections need to be removed, we can fix the original lath and apply a clay or gypsum brown coat directly to the lath, We can also apply new lath.
Masonry/Faswall
Plaster can be applied directly to any type of masonry surface. We have applied plaster over many Faswall projects as well.
Existing plaster/ painted walls
We can apply a veneer coat over existing walls. If they are painted they require a bond coat before plastering. For old plaster homes there is often crack fixing, hole filling and leveling done before the veneer is applied.
Sheetrock/Blueboard
A veneer finish coat of clay or lime plaster can go directly onto sheet rock or blueboard. Depending on the type of finish plaster we generally do a bond coat or a sanded primer. The joints must be made flush before the final coat. This can be done with mud and fiberglass tape or with gypsum. Sanding is not required before plastering.
Strawbale/ Lightclay-straw
Natural buildings whether they are strawbale, light clay straw or cob, require a breathable and protective coat of plaster in order to function well. Lime exterior plaster and clay or lime interior plaster is a perfect fit.
Metal lath/Permalath
Exterior projects that do not have a permeable and rough surface to apply plaster to will require some sort of lath. We have found a product called permalath to work the best. It is made from fiberglass and will not rust.
Suitable Earthen Floor Substrates
Slab on grade
Since humans have been living inside homes, and all over the world earthen floors have been installed as a slab on grade. Contemporary earthen floors on grade are prepared like concrete slabs, in that the top soils are removed, sub soil is tamped, drain rock is laid, and in many cases vapor barriers and insulation are installed. Then engineered rock or a rough coat of earthen floor mix is laid down as the base for the finish layer.
New or old concrete
Yes, the old basement can have a beautiful earthen floor without much lost height. Some cracks can be mitigated and slopes can be leveled out.
Sub-flooring
Most people think of earthen floors as the slab on grade style, yet most of the floors we have been a part of are a finish layer on a stiff plywood, either remodel or new construction. At 3/4" thick, earthen floors easily meet up with tile and wood floors, or easily slope if necessary.
Products we love working with
American Clay
A wide variety of clay finishes and a streamlined pigment color chart and color pack solution.
Brush & Trowel
Many of our refined Italian style plasters, including plaster for our Tadalkt system, come from Brush & Trowel. They have an excellent plaster pigmenting system and can match almost any color desired.
Claylin
Claylin oils are hands down the best drying oils for finishing earthen floors. We pair these oil finishes with Claylin earthen floor application methods to consistently create wonderful floors.
Graymont Lime
For thinly applied interior lime plaster veneers we are able to use a much more commonly available air setting lime. We use a product from Graymont for these finishes.
Saint Astier Lime
Hydraulic lime from limestone deposits containing pozolanic trace minerals. This Lime will cure all the way through no matter how thick it is applied.
Shelterworks
Locally produced Faswall is a masonry block made from demineralized wood chips held together with a cement based slip with an internal rock wool insulation layer. This product has a perfect rough and permeable surface that can be plastered onto directly.