Author: T. Rondou
Gable skirting in natural stone coming loose is a common problem. Loosening of natural stone baseboards often occurs due to improper bonding or an unfavorable connection to the pavement. In this fact sheet, we discuss the causes and provide recommendations for repair and prevention.
Context and problem statement
The facades of the building were finished with natural stone plinths glued to the masonry with mortar dots. Afterwards, they applied permeable paving with joints filled with crushed natural stone granules (gravel). The level of the paving is higher than the underside of the skirting boards.
Several months later, several baseboards come loose.
Findings
Loose baseboards tilt outward from the underside. The connection between skirting and pavement consists of a narrow joint filled with gravel. This allows the joint to absorb hardly any deformations in practice.
Causes of gable skirting loosening in natural stone
Loosening occurs when the stresses become greater than the bond strength of the adhesive. Shear stresses arise in the adhesive bond due to the self-weight of the baseboards and hygrothermal deformations. In addition, forces act perpendicular to the bonding surface due to the pressure of the pavement against the baseboard.
When temperatures rise, the pavement expands. Because the joint is filled with gravel, this movement can hardly be absorbed. As a result, the pavement begins to press against the baseboards.
Bonding with mortar dots creates hollow spaces behind the baseboard. Adhesive is often missing on the underside. When the pavement pushes against the baseboard, a leverage effect is created, causing the baseboard to loosen and tilt outward. The more limited the adhesive contact, the greater the risk of detachment.
Important nuance
This claim is not a result of one obvious execution error. The problem arises from a combination of factors. Both the bonding with mortar dots and the rigid connection with the pavement are common implementation methods in themselves, but in this case they reinforce each other in an unfavorable way.
Prevention
The most effective solution is to place the underside of the baseboard above the level of the pavement. One can mechanically fasten the skirting board, which is preferred, or glue it. When gluing, full-surface gluing is preferred. This reduces the risk of loosening and also reduces the risk of staining.
If a visible connection is desired and the skirting is flush with the pavement, it is best to provide a joint of 1.5 to 2 cm. Fill this in depth with a compressible material and finish at the top with an elastic, non-staining sealant.
In situations where there is no control over the pavement, for example on public property, it is best to take into account possible pressure on the baseboard. In this case, a coping stone can be placed between skirting and pavement, separated by an elastic joint. For glued skirting boards, full-surface gluing usually remains the safest choice.
In addition, it is important to avoid water behind the baseboard. This prevents damage from freezing. With a cavity wall, the cavity drainage should be above the baseboard.
Repair
One can reattach loose skirting boards, preferably with full-surface bonding or via mechanical fastening. In doing so, one must take into account the correct connection details to avoid repetition.
Conclusion
Loosening of facade skirting in natural stone usually occurs due to a combination of circumstances. Paying attention to the bonding and connection to the pavement can prevent this problem in most cases.
