What type of joints commonly utilize sealant backers?

Sealant backers are specifically used in both vertical and horizontal joints to effectively control the depth of the sealant and to provide support for the sealant during application and curing. By utilizing backers, contractors can ensure that the sealant bond is optimal, as the backer rod creates a proper joint shape that enhances adhesion to the sides of the joint while preventing the sealant from adhering to the bottom. This allows for greater flexibility and movement of the joint as it expands and contracts due to temperature changes or building settling.

Using backer rods in both types of joints helps maintain the integrity of the seal, ensuring that it serves its purpose of preventing water ingress and air leakage. This makes them essential for a variety of glazing and construction applications where both vertical and horizontal joints are present. The other choices suggest a limitation on where backers can be used, which does not reflect the adaptable nature of these materials in different joint conditions.