How-to
How-to guides
With natural materials, much is decided by testing rather than by tables. Local clay behaves in its own way, every wall dries at its own pace, and an old finish does not always react predictably to a new coat. That is why we describe a sequence of observing and checking rather than recipes. Below are three jobs you can handle yourself, as long as you wear gloves and, when there is dust, a mask and safety goggles.
A test tile on the windowsill tells you more about your clay than any story about someone else's.
How this section works: we describe simple jobs in general terms, without ratios or schedules. Load-bearing walls, foundations, stoves, chimneys and electrics are not covered here; those are for professionals.
How to make a test clay mix
Take a soil sample
Remove the top layer with grass and roots and take a little soil from deeper down. If you take several samples, label where each one came from.
Roll a snake
Moisten a handful of soil and roll a thin coil between your palms. Rich clay bends without breaking, while lean soil crumbles or tears almost at once.
Make a patty
Flatten a moist ball into a patty and look at the edges. Heavy cracking along the rim suggests the clay may need more filler, while crumbliness points to too much sand.
Form test tiles
Make several small samples with different amounts of sand and straw and be sure to label each one. That way you compare the options on the same clay.
Dry them slowly
Leave the tiles to dry in the shade, out of direct sun and drafts. Fast drying causes cracks by itself and can mislead your comparison.
Draw conclusions
Compare the dried samples: which ones cracked, which crumble, which stayed strong. The best sample is a starting point, not a finished wall mix; decisions about the structure are made together with a professional.
How to check a wall for moisture
Inspect the base of the wall
Walk along the plinth outside and inside. Dark patches, peeling plaster, moss and salts at the base of the wall are the first signs of damp.
Watch the water from the roof
During rain, watch where the water goes: whether the gutter overflows, whether splash hits the wall, whether a puddle forms by the drip apron.
Compare with a moisture meter
A moisture meter for building materials does not give an exact diagnosis, but it is handy for comparison. Measure the same spot in dry weather and after rain, and a suspicious area next to one you know is dry.
Check the finish
If there is dense paint or a film over the clay or lime, moisture can build up underneath. Blistering and peeling are a reason to discuss replacing the coating with a vapor-open one.
Call a professional for serious signs
If the wall has softened, crumbles deeply or the moisture returns after every rain, you need a professional inspection. The cause may lie in the foundation, the roof or joints that you cannot fix yourself.
How to refresh clay plaster
Find the cause of the damage
Before patching, work out where the crack or gouge came from: an impact, shrinkage or moisture. If water is the cause, deal with it first.
Clean the area
Remove loose pieces and dust with a soft brush. Wear a mask: dry clay dust irritates the airways.
Dampen the base
Lightly mist the edges of the damaged area with a spray bottle so the new coat does not dry out too soon and bonds better with the old one.
Apply a suitable mix
Use a clay mix close in composition to the old plaster and press it in with a trowel. Compatibility matters: a mismatched material often comes away at the edges.
Float it and let it dry
Level the surface with a damp float and let it dry away from drafts and heaters. Once dry, judge the color and texture and repeat if needed.
Read next
- Tools
What comes in handy for tests and finishing: buckets, a sieve, mixing tubs, a trowel, a float, a level, a plumb line, a moisture meter and protective gear.
- Materials
Clay, cob, straw bales, timber, lime plasters and natural insulation: their properties and weak spots. The article catalog lives here too.
- Care
Caring for a natural-material house: water and walls, cracks, refreshing finishes, ventilation and the after-winter walk-around.
What we rely on
- General knowledge about building with natural materials
- Make Stroy editorial materials
Make Stroy retells widely accepted knowledge about building with clay, straw, timber and lime in its own words, without mix ratios, dimensions or calculations. Load-bearing structures, the foundation and the roof are designed and calculated by a professional; stoves, chimneys, wiring and gas are handled only by professionals. Look up your local building and fire rules before the first shovel goes into the ground, because the rules differ by country.