Straw Bale Construction Using a Clay Plaster Finish

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Plainsman Clays is the premier clay mining and processing company in Canada. You cannot see the straw in a straw bale home, but everyone sees the surface finish. Clay is a better choice than stucco for a variety of reasons. However there are an infinite variety of clays, obviously some are better than others. In addition, each clay type can vary widely in working properties. These are major headaches for workers who find that by the time they have adapted the house is finished! Now that has changed, Plainsman Clays brings reliable, consistent and adapted clays to straw bale construction (click here to see them).

Why are Straw and Clay Plaster Houses Popular?

Earthen Floors

An earthen floor is a natural, environmental option that is cheaper and softer than concrete. You can also make it a radiant floor.

From "Alternative Construction Contemporary Building Methods"
ISBN 0-471-24951-3

Made of clay, chopped straw, sand and sealed with linseed oil. It can be waxed. Like a concrete slab, it can function as a radiant heat floor and take advantage of the mass of the materials.

From "Small Strawbale" ISBN 1-58685-515-8

Moulded and Natural Finishes

Clay Shelves

A practical and aesthetic example of shelves integrated into a wall.

From "Small Strawbale" ISBN 1-58685-515-8

Arch Doorways and Windows

Arch opening with window opening, the finish coat could be lime plaster, gypsum or a clay.

Large Overhang

Natural clay finish needs good protection if used without an additive.

From "The Beauty of Straw Bale Homes" ISBN 189013277-2

Interior Finishes Using Clay Plaster

The aesthetic appeal of clay is quickly evident after when you see examples like this. Hardeners can be mixed with the clay to impart any degree of durability needed.



Arches, moulded corners, earthen natural tones and tactile finishes. Clay finishes are a perfect match for other eco-friendly and highly aesthetic building technologies.

Earth Baking Ovens

Another use of clay is to bake bread and other foods. These are used in many countries e.g. Mexico, Quebec.

From "Small Strawbale" ISBN 1-58685-515-8



Meet Mario Houle and his crew.

Phone: 780-236-2369, Email:
PO Box 6117, Hinton, Alberta T7V 1X5

Let's watch them build a straw bale and clay house in Elie Labberte, Quebec


The mix:
1 part Plainsman SBC Clay
3 parts masonry sand
1.5 buckets of chopped straw

Mixing the Clay

Water first (a little less than a 5 gallon pail), then the clay, then the straw (one-half to one inch long) and finally the masonry sand. The finished result should be like a porridge or cow pie texture.


Mario mixing the clay, sand and chopped straw.

For the second coat reduce the chopped straw to 3/4 of a bucket (3 gallon pail).

Gluten, the Secret of Making a Hard Surface

The gluten mix is made from ordinary flour.

Boil water and add the flour slowly as you stir
and mix until it becomes translucent.
It will be very sticky and will dry amazingly hard.

Chopping straw.

A wood chipper is a good way to make chopped straw. You can also use a lawnmower.


This is the consistency needed for straw.

Making Tests

Build a frame, fill with straw, burlap it in place and then apply the first and second coats of clay, straw, sand mix.

Create square test panels and try different mixtures of colors, clay, white sand and hardeners in each. Here we are testing 1:1, 1:2, 1:3 clay:white sand.

When mixing each color coat pay attention to the amount of water used and remember the amount for the best consistency. Practice and perfect a method of application.

Apply the mixtures in each panel and allow them to dry. Now you have a range of colors (and hardnesses) to pick from for each part of the house.



A scale will give you consistent results.

Preparing the Structure

Using the stick frame structure (as opposed to just using bales to form the structure) enables fairly straight walls. The straw bales have simply been placed vertically between the studs and secured in preparation for the clay plaster coating inside and out.


Where appropriate other finishes (like siding) can be employed where there is no protection from rain. However it is advisable to cover the bale first with a coat of clay to in increase fire resistance.


Because this house is covered by deck and veranda, the clay exterior will not get damaged by rain.

Application of the First Coats

Here the crew is applying the first coat of clay, sand and chopped straw.


The first coat sticks very well on the bales because we shave the folded side of the bale with a chain saw or a lancelot disk on a grinder.

The cracks that may develop where the wood is are filled with a second coat.


Applying Over Wood Surfaces

An adhesive coat made of gluten, horse manure and coarse sand is used where you have more than 3 inches of wood surface to cover before the first coat.


Where you have lots of wood you should use the gluten consistently on the first and second coat to prevent the clay from bringing the gluten to the surface. The addition of gluten makes a harder finish.

Second Coat Front Entrance

Second coat with two outdoor integrated lamp shades.

Preparing an Interior Wall to Make an Endcase Bookshelf.

The straw is covered with burlap first and shelves are integrated. The burlap is a perfect base to receive the clay plaster. This technique makes it possible to create very fluid contours and rounded corners.




Plainsman Materials

Clays and Pigments