Clay building material substrates in detail
Various substrates
Old plaster surfaces made of lime or lime-cement plasters must be checked for their load-bearing capacity. Often, defects and cracks must be repaired. This is best done with a mortar that matches the old plaster or a clay undercoat. In both cases, it is important that the repairs dry thoroughly. Highly sandy lime plasters must be treated with a deep primer before plastering. In order to standardise the absorbency of the substrate, as well as in the case of plastic-containing plasters, the surface is pre-treated with conluto wall and ceiling primer.
As with new plaster, the thickness of the plaster depends on the grip of the substrate and can be applied in thin layers up to a two-layer plaster.
Surfaces with new lime or lime-cement plasters can be easily covered with a clay plaster. It is important that the substrate is completely and sufficiently dry (at least 30 days), as otherwise discolouration may occur. The thickness of the plaster depends on the grip of the substrate and can range from a thin layer of plaster to a two-layer plaster.
On gypsum plasters, conluto wall and ceiling primer should generally be applied before the surfaces can be covered with a thin layer of clay plaster.
Old masonry must be carefully checked for contamination, efflorescence and stability. Particular attention should be paid to rising damp and salt efflorescence. These areas must not be plastered with clay.
Old masonry is usually plastered in two layers. The existing surface must first be thoroughly cleaned. Highly absorbent masonry should be pre-wetted. Calcium silicate bricks and low-absorbent masonry, such as some natural stones, should not be pre-wetted under any circumstances. In most cases, a level surface must first be created or the substrate levelled. This is done with clay undercoat, whereby the thickness of the plaster depends on the unevenness of the substrate.
For layer thicknesses of more than 2-3 cm (e.g. natural stone masonry), it is advisable to apply the clay undercoat in several layers. It is important to allow each individual layer to dry completely before applying the next layer of plaster. The total plaster thickness can be up to 10 cm.
Masonry made of small-format bricks with joints is usually plastered in two layers to prevent the joints from showing through. Either conluto clay base coat or conluto clay finish coat can be used as the first layer of plaster. All conluto finishing plasters (clay finishing plaster, clay fine plaster, clay premium plaster) are suitable for the second coat of plaster.
Masonry made of flat bricks is usually heavily contaminated with powdery dust. This must be removed in all cases. Both aerated concrete and flat bricks are highly absorbent substrates and must be pre-wetted. Calcium silicate bricks are also highly absorbent, but must not be pre-wetted. In this case, a thin layer of spray plaster or a suitably wet plaster should be used as the first coat of plaster.
As the proportion of joints in masonry made of large-format bricks is very low due to the bonding of the bricks, the first coat of plaster can be replaced by a pre-spray or roughcast plaster made from conluto clay finishing plaster. It is important here that any defects in the masonry and all slots are filled in advance and allowed to dry. However, the second coat of plaster after the pre-spray or roughcast must then consist of a clay finishing plaster in order to achieve sufficient plaster thickness.
conluto clay bricks in accordance with DIN 18945 application classes 3 Ia and Ib as well as II are plastered in two layers. Pre-wetting the bricks increases the processing time of the plaster. Reinforcement mesh is only necessary for masonry if there is a change of material in the surface, e.g. in the lintel area.
Alte Lehmflächen sind hervorragende Untergründe für die conluto Lehmputze. Eine Haftbrücke ist nicht nötig, da der Verbund zwischen altem und neuem Lehmputz gut funktioniert. Oftmals sind jedoch alte Lehmputze stark ausgetrocknet und sehr staubig. Ein Anfeuchten der Fläche durch Besprühen ist in diesem Fall nicht ausreichend, der Untergrund muss gut angenässt werden. Dieses erfolgt am einfachsten durch das Einreiben des Wassers mittels eines Quastes oder eines Schwammreibebrettes.
Fehlstellen, die durch das Entfernen loser Stellen oder ungeeigneter Materialien entstanden sind, werden vorher ausgebessert und müssen anschließend erst durchtrocknen. Befinden sich Balkenanteile in der Putzfläche, müssen diese vorab mit einem Putzträgergewebe versehen werden. Hierfür eignet sich am besten ein Schilfrohrgewebe, das in Balkenbreite geschnitten auf dem Holz festgetackert wird. Im oberen Drittel des Lehmputzes wird dann zusätzlich ein ausreichend überlappendes oder flächiges Armierungsgewebe eingebettet.
Auf alte Lehmuntergründe wird in der Regel zweilagig geputzt, es ist bei sehr intakten, einheitlichen Flächen auch möglich, einlagig zu arbeiten, dann jedoch nicht mit Dünnlagenputzen.
Concrete surfaces must be carefully checked for contamination. Formwork oil residues or other release agents are often present, which prevent the clay plaster from adhering (see point: Requirements for the substrate "Formwork oil residues"). Smooth concrete surfaces must be prepared with a coarse adhesive primer or sprayed render, e.g. a sand-cement slurry, as otherwise bubbles may form during repeated smoothing. To check adhesion, it is advisable to carry out a test application.
Steel components must be protected against corrosion by applying appropriate coatings or galvanising before applying clay plaster. Mineral plaster mortar (e.g. lime-cement plaster) in combination with ribbed expanded metal or similar serves as a plaster base, with which the steel components are coated with sufficient coverage in accordance with recognised technical rules.
Once the substrate has dried sufficiently (approx. 30 days until the mortar has completely set), the clay plastering can begin. The different absorption properties of the substrate must be taken into account. Furthermore, if there are changes in the substrate in the upper third of the clay plaster layer, additional reinforcement fabric must be inserted.
Substrate requirements
| 2.1 Maßgerecht | Grobe Unebenheiten und Schlitze schließen. |
| 2.2 Ausreichend rau | Aufrauen mit entsprechenden Werkzeugen, Sinterschichten entfernen (z. B. Stahlbesen), Haftbrücken wie z. B. conluto Grundierung aufbringen, Spritzbewurf aufbringen. |
| 2.3 Tragfähig | Abschlagen von losen Altputzen, Verfestigen des Untergrundes, Anbringen von conluto Schilfrohr-Putzträgergewebe auf Holzbauteilen, Entfernen von Tapeten, Fliesen und Altbeschichtungen. |
| 2.4 Sauber u. frei von durchschlagenden Stoffen |
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| 2.5 Trocken | Neubauten: ausreichend trocknen lassen, ggf. Bautrocknung einsetzen. Altbau: aufsteigende Feuchtigkeit muss verhindert werden, Mauerwerk trockenlegen. Trocknungsprotokoll anlegen! |
| 2.6 Gleichmäßige, gute Saugfähigkeit | Vermindern: Vornässen. Erhöhen: Aufbringen eines Spritzbewurfes oder einer Haftbrücke. |
| 2.7 Einheitlich | Spritzbewurf, conluto Wand- und Deckengrundierung, conluto Schilfrohr-Putzträgergewebe. |
Plaster base:
When are they required?Plaster bases are used when there is no sufficiently solid and load-bearing substrate or when surfaces that are not suitable for plastering, such as wooden beams, need to be plastered. Conluto 70-strand reed fabric is used as a plaster base. It is fastened using galvanised staples. The reed fabric has a tightly stretched wire on one side, the tension wire or running wire, and on the other side the winding wire, which winds around the individual stalks. The fabric is fastened to the substrate in such a way that the tension wire faces the installer and the winding wire lies on the substrate.
- Three layers of plaster are applied to the wall heating pipes (e.g. Ø 16 mm). To achieve the best possible plaster finish, the first coat of plaster is applied in two steps using conluto clay undercoat plaster: Step 1: The clay undercoat plaster is applied in a single layer approx. 25 mm thick up to the upper edge of the heating pipes and then levelled off. The first layer can be dried out, or the wall heating can be plastered while in operation. Any shrinkage cracks that occur are closed again with the second layer of plaster.
- Step: Once completely dry, a second layer of clay undercoat plaster approx. 3-5 mm thick is applied to cover the heating pipes (pre-wet if necessary). A reinforcement fabric is pulled into this layer to prevent cracking due to the expected thermal stresses. The mesh must overlap sufficiently at the butt joints (min. 10 cm).
- Step: Once the clay base coat is completely dry, apply the final coat of plaster to a thickness of 3-5 mm, depending on the type of plaster. You can use clay top coat, clay fine plaster or clay plaster terra. To ensure a fast response time of the wall heating, the plaster thickness above the pipe should be max. 7 - 10 mm. The surface of the final plaster layer can be finished with a clay paint or a clay fine plaster.
Reinforcement or plaster reinforcement has the task of absorbing tensile stresses that can occur in the plaster. This is intended to prevent or reduce the risk of cracking. In the case of uneven plaster substrates made of different materials, the processing of insulation boards and the reworking of slots, cracking is to be expected and reinforcement fabric must be used. The conluto glass fibre mesh or the conluto jute mesh are used here. The meshes are inserted into the outer third of the plaster structure and must overlap by at least 10 cm at the mesh joints.