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Clay undercoat plaster for natural wall constructions
Clay undercoat provides a strong base for eco-friendly interior walls: it evens out uneven surfaces, anchors the reinforcement mesh and optimally prepares masonry, reed, underfloor heating or internal insulation for the top coat, finishing plaster and clay paint.
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What is clay undercoat plaster suitable for?
Clay undercoat is the first levelling and base coat in a natural wall structure. It is used when walls are uneven, when plaster bases need to be reworked, when underfloor heating is to be embedded, or when surfaces need to be prepared for topcoat and finish coat.
Typical areas of application:
- Levelling of masonry and walls in old buildings
- Substrate for clay topcoat and clay fine finish
- Embedding reinforcement mesh
- Construction using reed, clay building boards and plaster bases
- Plastering over wall-mounted heating panels
- Preparation of internal insulation systems
Which clay undercoat plaster is right for my project?
The most important decision: with or without straw.
Clay undercoat plaster like conluto clay undercoat plaster is ideal for robust base layers and thicker coats of up to approx. 30 mm. The chopped straw acts as a natural fibre reinforcement: it stabilises the render layer, improves adhesion and helps to create an even surface.
Clay plaster without straw, such as the conluto Terra clay plaster coarse is the mineral-based alternative for people with sensitive skin, grass allergies or for long-term storage. It is suitable for use as a base coat, finish coat and levelling coat in application thicknesses of 5–15 mm.
Advantages of clay plaster
Clay-based undercoat plaster is the right choice if you want the wall structure to remain natural, breathable and functionally sound in the long term. It is made from mineral raw materials, is vapour-permeable and has capillary action. This allows the wall to absorb, distribute and release moisture.
This brings benefits for the interior and the building structure:
- promotes a balanced indoor climate
- protects the building structure from moisture damage
- retains heat and enhances comfort
- Can be re-moistened and is easy to finish
Processing and drying
Clay base coat can be applied by hand or using a plastering machine. The substrate must be solid, clean and provide a good grip. Depending on the wall and the desired finish, the coat is applied in one or more layers.
Important for clay plaster: The drying process must be carefully planned. Particularly in the case of thick layers, underfloor heating or high levels of moisture on site, adequate ventilation, air circulation or mechanical drying is required. This ensures that the plaster dries evenly and remains a secure base for the next layer.
The further structure
Once dry, the clay base coat is built up further depending on the desired finish. Traditionally, this is followed by a Clay finish coat plaster as a natural top coat, which can be sanded or smoothed and prepares the wall for further finishing.
For finer surfaces, you can then use a If you want to create a colourful and decorative design straight away, choose a Deco clay facing plaster or colourful Clay finishing compound. For painted surfaces, vapour-permeable Clay paint or Brush applied clay plaster are the best choice.
Frequently asked questions about clay undercoat plaster
How long does clay undercoat plaster take to dry?
Drying time depends on the thickness of the coat, the substrate, temperature, humidity and ventilation. As a rule of thumb, the thicker the coat, the longer it takes to dry. Clay-based skim coat should not be worked on further until it is completely dry. Good ventilation and frost-free conditions are particularly important.
How much clay undercoat plaster is required?
Consumption depends on the grain size, product, substrate and application thickness. As a rough guide, the amount of material required increases significantly with every centimetre of plaster thickness. Uneven substrates, joints or levelling work will further increase consumption. For an accurate calculation, always refer to the manufacturer’s specifications.
Is clay undercoat plaster available in earth-moist or dry form?
Depending on the manufacturer and product, clay-based skim coat is available in both earth-moist and dry forms. Earth-moist products can usually be mixed directly with water and are well suited to larger building sites. Dry products have a longer shelf life, are easier to transport and are mixed with water on site.
What is clay-based undercoat plaster?
Clay base coat is the base layer in a clay plaster system. It serves to level out unevenness, build up a load-bearing layer of plaster and prepare the substrate for further coatings. Depending on the desired finish, this is followed by a clay top coat, a fine clay plaster, clay paint or a premium clay plaster.
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