How To Fix Cracks in an Earthen Building Structure

Learn how to identify and fix cracks within your earthen structure that are more harmful than beneficial.

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by Flickr/Neighbourhood Construction
Some cracks in earthen clay are tiny little breathing spaces which help to cool or heat the space, but sometimes the cracks are too large and can cause structural damage.

Mudgirls Manifesto Handbuilt Homes Handcrafted Lives (New Society Publishers, 2018) by The Mudgirls Natural Building Collective is a guide to building eco friendly homes from natural and recycled materials to cut down on the mass pollution and waste that comes from conventional construction methods.  The Mudgirls collective is about more than alternative building practices, each woman that spends time as a member of this group is taught building techniques, leadership qualities, and a new way of life where one can live in harmony with the earth and in equality with all of its people. While this book does include many helpful tips on building and techniques for effective and eco-friendly projects the main goal is to focus on the groundbreaking process and practice this group of women embody.

You can purchase this book from the Grit Store: Mudgirls Manifesto.

How to Fix Cracks

There is a crack in everything. That’s how the mice get in.

– Leonard Cohen via Mudgirls

Clay is motion. With water it swells, with heat it shrinks. All this moving is wonderful as it regulates moisture, creating comfortable climates – cooling the heat of the summer and holding the warmth of the stove in the winter. Natural plasters in a bathroom or kitchen help regulate precipitation and keep mirrors from fogging up. Clay really is amazing stuff.

Earthen finishes can crack. We can think of the cracks as the beautiful details of the handmade and natural . . . tiny little breathing spaces.

Sometimes, however, the beautiful little fissures are too big to be doing their job; earthen finishes are meant to create a skin that will keep droplets of moisture out, while letting water vapor pass right through.

When your cracks are too big, it is best to understand what caused them. This will depend on what you are working on.


Floors consist of a large area of moist material that will crack when not dried uniformly, or crack where there’s an intentional break in the floor (thresholds between rooms). Floors require a slightly different mix than walls or plasters – making the mix a bit sandier will help prevent cracking, as will applying the layer in a uniform thickness, making use of dehumidifiers and fans to dry floors evenly, and being extra careful when filling in breaks. Compressing and hard troweling the floor when it is almost or just dry is also beneficial.

Even then, some cracks are likely to appear. When fixing cracks in floors:

  1. Rough up the edges of the cracks
  2. Dig out a v-shaped groove
  3. Dampen the groove
  4. Fill it in with a bit more floor mix
  5. Trowel the floor smooth

When cracks are repaired and dried, a thin color wash on the floor will cover any marks made during the repair. Apply the wash before oiling and waxing the floor. When the floor cracks are super small, they can be filled with extra wax and oil. A good melted crayon can do wonders.

Clay Plaster

Clay plasters crack when the mix is a bit off, or because new buildings can settle and shift – or where there’s a transition between two different surfaces. If plaster hasn’t enough fiber or has too much clay, it can crack. Mixing in more sand, powdered milk, or extra sticky binders like wheat paste and cactus juice can prevent this, as will using a mesh fabric, like burlap, over transitions. Clay plasters can be wetted again using a light misting bottle or a sponge, and the plaster can generally be worked and compressed again, fixing cracks. Blend the fix by rehydrating the surrounding area and working it all together gently with a soft plastic trowel. A recycled yogurt container lid with the edges cut off is the best soft plastic trowel in our tool boxes. Be wary of over­working/compressing the area as it can leave darkened, smudgy “burn marks” on your surface that remain obvious.

Lime Plaster

Lime plasters are a slightly more serious business, as lime plaster can crack easily. If the plaster is still fresh, mist and scratch the cracks a bit, like how we open floor cracks with a slight v-shaped groove; a knife or trowel can help here. Using the same lime plaster mix, add a bit of water, and strain the plaster through cheesecloth to remove the bigger sand pieces, put the blob of new wet plaster on something that will absorb the excess water, like cardboard. This creates a lime plaster putty that can then be added to the slightly v’d-out grooves. Now, use your little plastic yogurt lid trowel to compress the area. Once dry, you can then use superfine sandpaper to smooth your fix.

If your lime plaster is already compressed and cured, the cracks can be sanded first, fixed as above, then sanded again.

More from The Mudgirls Manifesto:

Excerpted from Mudgirls Manifesto Handbuilt Homes Handcrafted Lives by the Mudgirls Natural Building Collective and published by New Society Publishers, 2018.

brown book cover with people working with clay on it

Hand-built Homes

On North America’s West Coast, there’s a group of rebel women who 10 years ago chose to break free from a rigged economic and social system. They didn’t take to the streets to lobby banks and governments to change their ways – they didn’t have time for that. They had babies to feed and house. They reckoned that if nobody else was going to change the rules to support basic human needs and respect the biosphere, then we were all free to make our own rules. They chose action. They decided to teach themselves how to build houses using the most abundant material on earth – mud. They’d learn by building, gathering skills and allies. They’d have fun, sharing whatever they learned with whoever wanted to come along for the ride. The Mudgirls revolution was born. Part story of rebel women, grassroots self-governance, and community-building, part incendiary political and economic tract, and part practical guide to building natural homes for real people, Mudgirls Manifesto is about respecting the earth, each other, and crafting meaningful lives.The Mudgirls is an all-women’s natural building collective from coastal British Columbia. They build houses and offer workshops that empower people to take back the right to provide themselves with shelter. They champion respect for the earth and each other. Order from the Grit Store or by calling 866-803-7096. 

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