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An alternative to gypsum board or wood cladding, an earthen and straw coating, ready-to-use or homemade, combines a warm finish with simplicity of application.

Application of a plaster made of earth and homemade straw

Why choose a coating

Ignored for a long time, the earth-based coatings have more than remarkable advantages: they are ecological, economical and easy to use.

Excellent hygrometric regulators, they allow the supports to "breathe", and also offer a natural aesthetic with various decorations that depend on the color of the earth.
On this site (// story of a house construction project made of wood and straw)the choice was made of a ready-to-use interior plaster (AKterre) applied on straw walls (wood frame and straw bales) covered with lime mortar / sawdust.
Predicted in 25 kg bags or 1 m big bag3, this product contains all the necessary ingredients: sand, clay soil (we can choose from several colors) and strands of straw, to give body and a more authentic appearance to the coating. It only remains to add water.

Fastening primer and wood slats

However, it is possible to make this coating yourself by purchasing sand, earth (containing 30% clay) and straw.

This mixture is a little more complicated to prepare but it is much more economical than a product bought on the market.
Side implementation, the earth adhering poorly on the wood that absorbs water mortar and causes shrinkage, must be applied to the wood frame a primer (from the same manufacturer).
Since lime is very greedy for water, it is best to moisten the walls the day before and one hour before the start of the work using, for example, a garden sprayer.
To obtain a regular and flat plaster, it is better to use (as here) guide slats that allow to "pull" the plaster straight.
It is however possible to do without it if one wants to keep a very rustic effect. The coating is prepared for the concrete mixer or in a large container (for example a 100 l bin) using a mixer.
In two layers, the application is very simple: the coating can be applied manually to the trowel or sprayed with a sablon connected to a compressor.

A refined finish

The most suitable finish for this type of plaster is the sponge float.
Not only does it blur application defects such as trowel marks, but it also highlights mineral fillers and emerge fibers. Which gives it a velvety appearance.
After drying, the passage of a brush discharges the sand on the surface.

The application steps of a soil and straw coating

exposed lime and exposed structure before plastering

The slaked lime and the frame are apparent. Before applying the plaster, wet the walls and brush the wood with a primer.

make a guide slat to coat

Obtain 10 x 30 mm battens or plywood boards (10 mm thick) to serve as guiding slats to "pull" the plaster body.
Screw them on the frames.

prepare a coating to the ground

Prepare the coating in small quantities: pour 2 buckets of water and add the ready-to-use coating.
Mix until creamy without lumps.

Apply the two layers of earth rendering

Project the plaster up and down on the wet wall, slightly protruding from the bare guide slats.
A first layer first, a second a few hours later.

Smooth a natural coating

Apply a mason's rule against the guide slats.
Slide it up to remove excess coating. In case of hollow, fill with plaster and re-grease.

remove the support slats from a plaster

Leave for 2 to 3 hours then remove the slats.
Bridging the gaps.
Using a stainless steel plate, crush the coating sufficiently to pick up the fibers that protrude above the surface.

Smoothing trowel strokes on a plaster

Apply the finishing plaster to the stainless steel trowel to a thickness of about 5 mm, 24 to 48 hours later.
After 1 to 2 hours of break, smooth trowel strokes too obvious.

smooth a natural coating of earth and straw

The next day, use a moistened sponge trowel (circular movements) to fade all the trowel strokes and unify the plaster.
Rinse and wring the trowel very often.

• Particularly interesting, the coating of earth can be prepared in advance and preserve itself for several months, in a well sealed container. If it is dry, as it is reversible, it is enough to rewet it to be able to use it.
• Although the soil is easy to clean, it can permanently stain porous materials. Protect the immediate surroundings (floor, ceilings and door frames) with a plastic tarpaulin or tape.

Video Instruction: Install an Earth Ground For Better Powder Coating