Sgraffito: how to make them

Sgraffito is an traditional scratching technique in which an image is created by scratching away different layers. This tutorial explains the process as taught in Scuol, Switzerland, that is full of sgraffitos. The course was organized by kalkwerk.ch

more information about sgraffito: Wikipedia

you can watch the procedure also on video: https://youtu.be/2B6o4i2a8G8?si=c7AaxIHEedS8z1nG^[1] (if the video isnt available, check this backup)

Planning[edit | edit source]

A sgraffito consists of a multi-layered structure of marsh lime. The drying time can vary greatly depending on humidity, temperature and, for example, exact composition. Its recommended to apply the last two plaster coats and the milk of lime "wet on wet". This means that you should work on the surfaces before they are completely dry. Keep in mind that the long drying times can lead to very long work days, because after a layer reaches a certain stage of dryness, its time to apply the next one. It can be e.g. 16:00 but this can also happen at 23:00 in the night.

Required tools[edit | edit source]

• Electric-Mixer or trowel
• Good stable Buckets
• Trowels
• Scraping tools and/or modeling irons
• Painting Brush
• Knifes/Cutters

Additional, optional tools[edit | edit source]

• Brush with long handle
• Broom
• String
• Metal brush
• Compass (to make circles)
• Ruler
• measuring tape
• spirit level
• Grinding machine with a round, strong attachment (e.g. to remove paint)
• Covering material such as tape and floor cover.

Cleaning: All equipment should be cleaned with water after work. Due to high alkalinity, trowels tend to rust. Do not leave trowels in water.

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Preparation of the working surface[edit | edit source]

All surface should be dust free and dry. Make sure the lime mix will stick to the wall: reversible plasters and paints should be removed - as on this surface doesnt stick lime enough. Major damage should be repaired. If there are for example bubbles with salt, its recommended to figure out, what is the source and if possible stop it. salt is the biggest enemy of lime and should be removed totally.

If the surface is in direct sunlight and there is a shadow casting object such as scaffolding in front of it, a burn-in effect may occur. This means that after removing the scaffolding, the shadow-like structures may remain visible in the surface. It is recommended to hang the facades with a linen fabric or similar. The linen sheets are often sprayed with water when it is very hot. This helps to reduce the temperature at the workplace so that the material can be worked well for longer, i.e. the humidity is kept high for longer (improved CO2 absorption for setting of the plaster)

When lime gets on glass surfaces, metal, etc., the high alkalinity can cause discoloration and surface damage. to prevent that, the surface can be protected with masking materials (covers, tape, etc.).

if the surface is very dry, water them with a brush or a hose. do not 'soak' them.

Sgrafitto on a conrete wall[edit | edit source]

On a smooth concrete wall, the surface must be roughened. So that the plaster can "claw" into the surface. look at the wall from multiple angles, to find a shining on the wall that has to be removes by sanding. There can be a milk-like layer from the concrete-wall-making and on this will nothing stick. Plaster will not hold on it and has to be removed by sanding.

Primer coat[edit | edit source]

A lime-cement plaster is used for the first coat. A plaster based on white cement rather than Portland cement is recommended. Portland cement has undesirable salt content, which is harmful.

Mixture:

• 6 parts of lime putty
• 2 parts of cement
• 4 parts sand a 4 mm
• Add water as required until a mixture that can be well filled is obtained.

Layer thickness: 0.5 to 1.2 cm (see *lime-layer-rule)

Drying-Time: 24 hours. It can vary. 24 hours is minimum.

when its dry: the surface must be dry to the touch but still soft. this means some markings can be made when you go over the surface by hand.

General information on subsequent finishing coats[edit | edit source]

The surfaces are now mixed with a mixture of lime, sand and powder pigments (suitable for lime plasters!). Important: the amount of pigment added must be measured out exactly. This is best done using kitchen scales or, if necessary, measuring cups. It is advisable to dissolve the pigment powder in a beaker of water, stir well and only then add it to the mixture.

Create a Paper or a Note on your Smartphone, with a recipe. If it turns out during processing that there is still a need for material, the same mixture can be produced again according to this recipe. so the wall and color looks continuisly the same.

Care must be taken that, if possible, all apply the same layer thickness. if you are not sure, if you have the same thickness, check it. together you have to agree to a certain amount of thickness, which is important for drying times. workers can use a ruler or even a nail with mark, to check if they are unsure.

The surface must not be smoothed too much with the trowel. A rough surface is desired - the next layer has to 'claw' on it. if necessary, add markings and scratches to the surface , so the following plaster can stick to it.

When adding pigment, its important to know that it can need a lot. when lime dries, it happens often that the color will heavily dissapear, so its much lighter in color than when wet. if you are not sure, do a test and let it dry fully.

Lime drys only if its in contact with air. if you cover the bucket with e.g. plastic, it will not dry. actually, the longer its 'soaked' the better it gets. the romans left the lime in barrels for minimum 10 years.

First Finish-Coat[edit | edit source]

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  mixing with electric stirrer

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  mixing in pigmente

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  plastering first coat

Mixture

• 10 parts of lime putty
• 1 part river gravel a 0.2 mm
• 3dl pigment ( it can vary heavily )

Add water as needed. it has to be more thick than soft-icecream.

Layer thickness: 0.2 to max. 0.6 mm (see *see *lime-layer-rule). Not too much smoothing should be done. Apply once, go over it once and thats it. the more you go over it, the 'closer' the plaster gets (which is bad in this case).

The edges should be given special attention. bring them in a basic shape, will retain later. With the following layer, only the finishing touches are made.

Second Finish-Coat[edit | edit source]

Mixture

• 3 parts of lime putty
• 1 part river gravel a 0.1 mm grain (so finer than the previous)
• 3dl pigment

Add water as needed until its nice to work with. it has to be more thick than soft-icecream. The amount of water is higher compared to the first layer. We are now working with a finer layer.

Layer thickness: 1-2 mm

It should not be smoothed over and over a hundred times. Compared to the previous layer, but here should be smoothed more, because it is the last visible layer of plaster. The surface does not have to be perfect. Edges shouldnt be sharp. make them slightly rounded. on sharp edges the material doesnt stick well (see also https://de.wikipedia.org/wiki/Kantenflucht).

Painting with lime-water mix ("milk of lime")[edit | edit source]

We now coat the entire surface with the brush or a large brush.

• In case of a semi-transparent coating (approx. three coats): paint in one direction, e.g. vertically. Otherwise, it can look very 'wild' and 'stressy' for the eye.
• In case of a covering coat (more than 3 coats): Paint in a cross, i.e. in a horizontal eight. Like ∞ (a layed down 8)

Apply, wipe once more and you are done. This is especially important after the first coat, because otherwise the previous layer will be dissolved and removed again. A coat should not be applied too thickly - more paint doesnt necessarly cover much better. The paint appears very transparent when painted and the color does not really appear until it dries. This can appear as if you are painting water, especially with subsequent coats.

Mixture:

• 1 part lime putty
• 3 parts water
• the mixture must be very thin, i.e. similar to water.

After each painting it is necessary to wait until the paint does not appear wet anymore. The coats must be repeated until the desired opacity is achieved.

Scratching[edit | edit source]

Using e.g. a nail, the images are scratched into the surface. It is important to first scratch the basic image-structure (the outlines) completely. Once this is done, the details can be worked out.

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Protective equipment[edit | edit source]

Lime or calcium hydroxide has a pH value of approx. 12 and is therefore highly alkaline. it works against mold by nature.

On the skin, lime has an irritating effect and can dry out the skin - for this reason, gloves are recommended. Contact with the eyes must be avoided as a matter of urgency. If lime gets into the eyes, rinse the eyes and consult a doctor.

IMPORTANT: IF LIME GET IN YOUR EYES, IN WORST CASES IT CAN DESTROY YOUR EYES

• Safety glasses, urgently required
• Work gloves
• Ear protection, if using machinery
• Dust masks

Do not allow undiluted or large quantities to reach ground water, water bodies or sewage system. Flushing away of larger quantities into sewers or water bodies may lead to increase of pH-value. A high pH-value damages water organisms. In the dilution of the application concentration, the pH value is considerably reduced, so that after the use of the product, the waste water entering the sewage system is only slightly hazardous to water.

Additional Information[edit | edit source]

Lime-Layer-Rule: the thickness should be maximum 3 times higher than the diameter of the gravel. Example: when using a gravel-diameter of around 2mm, the layer applied should be maximum 6mm thick.