Correct rendering of XPS-R-insulation boards

In the case of heat-insulating masonry, thermal bridges (e.g. ceiling edges, lintels, columns, projections and skirting areas) are often formed with XPS-R insulation boards.

Simple & safe to the goal


    1. If the XPS-R insulation boards are already installed, their bonding strength must be tested; eventually a post-dowelling must occur. The board surface must be roughened.

  2. Case 1: Partial surfaces

    2. Parts of surfaces, e.g. as ceiling insulation or for roller shutter boxes, are rendered.

  3. Preliminary works

    3. Apply the bonding and reinforcing mortar weber.therm 300 in a thickness of 5 mm and comb horizontally with a notched trowel. For better stability, lay the coarse woven mesh weber.therm 310 (mesh size 8 x 8 mm).

  4. Application

    4. After a waiting time of at least 5 days apply a lightweight underlay render, for ex. weber.dur 132.


    5. Eventually, apply a full-surface reinforcement layer with weber.therm 300 (bonding and reinforcing mortar) and weber.therm 310 (woven mesh). The meshcloth must lay in the upper third of the reinforcing mortar layer and overlap the adjacent building part by a minimum of 30 cm.


    6. Depending on the type of underlay render / reinforcing mortar leave the render surface as required for the post-applied topcoat; for scratch renders, for ex. with a hard broom or a notched trowel after first stiffening.

  7. Case 2: Large-size surfaces

    7. Under certain circumstances, entire facade areas, such as larger skirtings, are insulated with XPS-R boards. In principle, an ETICS is better suited for this purpose. If no XPS-R boards were used, dowelling must be carried out above ground level.


    8. Apply the bonding and reinforcing mortar weber.therm 300 in approx.7 mm thickness and insert a woven mesh, e.g. as weber.therm 310 full-surface. Eventually, roughen the mortar layer.


    9. Alternative: apply the first weber.therm 300 and comb horizontally. After a waiting time of 5 days apply the lightweight underlay reinforcing mortar (base coat) weber.therm 376 in a thickness of 15 mm and insert the woven mesh weber.therm 310.


    10. Depending on the type of overlay render and weather conditions, the reinforcement layer must be eventually pre-wetted or pre-treated with the universal primer weber.prim 403.


    11. The overlay render is hand or machine applied.


    12. Depending on type of topcoat render roughen the surface with an appropriate tool.