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Lightweight, acoustic and "insulating", this type of coating improves the interior comfort of old houses whose thick stone walls remain cold on contact. It also offers different aspects, warm and decorative.

Make a plaster hemp lime yourself

Difficulty: 3/4
Cost: 20 € the bag of 30 kg of aerated lime formulated for projected plaster + 15 € the bag of 200 liters of chènevotte
Time: 1 week (excluding preparation support)
Equipment: cutter, trough, round trowel, large platter, glue brush, tarpaulin and protective adhesive, wheelbarrow, concrete mixer...

In this kitchen, the original walls are stone jointed and plastered to the ground. To maintain the traditional appearance of the place and to remedy the sensation of cold walls, the owners have opted for a repair of the walls using a coating of lime and hemp.

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Limit the feeling of cold walls

At first, it was necessary to decrepit all the stone surfaces. A cinderblock partition wall has not undergone any special treatment.
To ensure the adhesion of the coating, a dry sandblasting was then carried out by a company using a sander mounted on a compressor.
Then, the ceiling and beams in particular were covered with a thick polythene tarpaulin and held in place by adhesive site.
Finally, the old wooden window has been replaced by a tilt-and-turn PVC model. In addition to its hydro-regulating power, the main advantage of a plaster based on lime and hemp is to ensure the thermal correction (and not insulation) of thick stone walls, eliminating the sensation of cold walls, very uncomfortable in winter. The application of a layer 3 to 5 cm thick allows to benefit from the inertia of the walls continuously.

A breathable natural coating

Since hemp is naturally water-hungry, the use of a binder based on aerial lime prevents the coating from being hard on the surface and powdery on the inside, leading to a risk of "grilling" the mortar.
On this site, the owners favored a coating based on aerated lime formulated (Tradical PF 80 M, composed of 35% of mineral fillers based on limestone and 65% of air lime) associated with the chènevotte (fibrous cellulose extracted from the inside of the hemp stem) of the same manufacturer. This type of coating does not require sand supply, which avoids weighing down the material causing a lack of adhesion during application.
Note that due to the slightly corrosive and irritating nature of the lime, it is strongly recommended to wear gloves, goggles and to avoid the release of dust.

1 Preparation of lime / hemp mixture

1 Preparation of lime / hemp mixture

In a concrete mixer, pour 40 l of clear water using a graduated bucket, then add 60 kg of aerated lime formulated (here two bags).
Let it run for 5 to 6 minutes to obtain a whitewash.

Apply lime and hemp wall coating: hemp

Then add 100 liters of hemp, little by little to decompress.
Allow to mix so that the mixture is homogeneous.

Apply lime and hemp wall coating: hemp

Pour a small amount of the mortar obtained in a wheelbarrow to check the consistency of the mixture, which must be greasy and unctuous: a trowel must easily penetrate and the coating amalgamate around.

2 Application of hemp mortar

2 Application of hemp mortar

After making a general rubbish, moisten the wall with a sprayer, then spray the plaster with a wide plaster.

Apply lime and hemp wall coating: lime

Continue the application by positioning the plate against the wall.
Then trowel the plaster upward to obtain an even layer of about 3 cm.

Apply lime and hemp wall coating: wall

Apply some plaster with the back of the trowel to the periphery of the electrical boxes (protected by masking tape), then smooth it.

Apply lime and hemp wall coating: apply

Proceed in the same way to trim the corners.
Start from an angle towards the wall of the wall until you reach the areas where the plaster has already been applied.

Apply lime and hemp wall coating: wall

On the still-cool plaster, apply the trowel in circular motions until the desired smoothness is achieved.
So work square meter per square meter.

Apply a gobetis on masonry stones

Apply a gobetis on masonry stones

On stone walls, first apply a gobetis (35 kg of hydraulic lime, 110 to 130 kg of sand, 20 l of water) to ensure the adhesion of the coating.

Apply lime and hemp wall coating: hemp

As before, then apply the hemp mortar, smooth the coating having a little fired, then iron the trowel to complete the desired finish.

Apply lime and hemp wall coating: apply

After plastering the plaster on the surface of the wall, the re-entrant angles and the stone contours of the chimney are refined with a trowel.

Supplies

• Air lime formulated (Calcia Cements, Lime & Coatings from Saint-Astier, PRB, Tradical...)
• Hemp in bag (Tradical, Technichanvre, Vegetable concrete...)

Opt for a paste coating

The renovation of an old house is not satisfied with smooth walls with flat and plain paintings.
To reproduce the style of yesteryear, you can use ready-made kits. Almost all brands offer products that mimic old-fashioned coatings. In most cases, these decorative coatings can be mixed or tinted. Some of them must be implemented on an underlayment. Pasty, they apply to the trowel 1 to 2 mm thick and are covered with a layer of wax that protects them and makes the walls leachable. The tools are usually cleaned with water.

Apply lime and hemp wall coating: lime

Before using the product, it is imperative to pass the undercoat which will provide better grip and easier application of the coating.

Apply lime and hemp wall coating: lime

Add the dye in the water, then the powder, and knead using an electric mixer until you obtain a homogeneous paste.

Apply lime and hemp wall coating: coating

When the dough is unctuous and lump free, let it rest for 5 minutes.
Then put it on a trowel to start the application.

Apply lime and hemp wall coating: lime

Apply the paste on the wall: the trowel is open, that is to say that it is not held parallel to the wall, but slightly at an angle.

Apply lime and hemp wall coating: coating

Allow the marks of the trowel to appear in the thickness of the product.
If you prefer a more uniform flatness, smooth before drying the dough.

Apply lime and hemp wall coating: apply

Allow to dry for at least 24 hours (depending on the environment and the thickness of the layer).
As time goes by, the product clears up.

Apply lime and hemp wall coating: lime

Using a spatula, place the wax on a vegetable sponge.
If the product is too liquid, place the pot a few hours in the refrigerator.

Apply lime and hemp wall coating: apply

Apply the wax in successive circles without leaving any white marks.
The final color appears after 3 to 4 hours.
The wall is now washable.


Video Instruction: Insulating a Solid wall with Lime Hemp Plaster