Frequently Asked Questions

What is the correct depth-to-width ratio for an expansion joint sealed with Expoband One and why does it matter?

The depth-to-width ratio of a sealant in a joint is a critical parameter for long-term sealant performance. When a joint opens (expands), the sealant is pulled in tension across its width — the strain in the sealant is equal to the change in width divided by the effective gauge length (which is the depth of sealant bonded to the joint faces). A sealant that is deeper than it is wide has a high depth-to-width ratio and the same movement causes a higher strain in the sealant than if the joint was shallower. Most modern elastic sealants including Expoband One perform best at a depth-to-width ratio of approximately 0.5 to 1.0 — meaning the sealant depth should be approximately 50 to 100 per cent of the joint width. A foam backing rod is used to control the sealant depth — the rod fills the joint to the correct depth below the surface, and the sealant is applied on top of the rod to the specified depth. The backing rod also prevents the sealant from bonding to the back of the joint (a three-sided bond which prevents the sealant from deforming correctly and causes premature adhesive or cohesive failure).

What primer is required before applying Expoband One to a concrete joint and what preparation steps are needed?

Concrete joint faces must be primed with a compatible polyurethane primer before Expoband One is applied to achieve the required bond strength. Concrete is porous and can have variable surface chemistry and moisture content that reduce direct adhesion of the polyurethane sealant — the primer penetrates the concrete surface, consolidates surface laitance, and provides a chemically active adhesion surface for the sealant. The specific primer must be confirmed from the Expoband One technical data sheet. The substrate preparation sequence is: remove all loose concrete, dust, old sealant, and contamination from the joint faces; blow out the joint with clean compressed air and vacuum; allow joint faces to dry to surface-dry condition; install the backing rod at the specified depth; apply primer to the joint faces with a brush and allow to cure to the specified tack (typically 30 to 60 minutes); apply Expoband One by caulking gun into the joint; and tool the sealant surface to a concave profile and remove masking tape immediately after tooling before the sealant begins to skin.

How long does Expoband One take to cure and when can building movement joints be painted over after sealing?

Expoband One cures by reaction with atmospheric moisture. Under normal Indian conditions (25 degrees Celsius, 50 to 70 per cent relative humidity), the sealant forms a surface skin within 30 to 60 minutes of application and achieves full cure through the depth of the joint in approximately 7 to 14 days depending on the joint depth. Painting over the cured sealant with water-based paints (emulsion, acrylic texture coat, or mineral silicate paint) should wait until the sealant has fully cured through its full depth — typically 14 days for joints up to 15 mm deep. Applying paint over partially cured sealant (which is still undergoing volume change as it cures) can cause the paint film over the joint to crack. At high humidity (above 80 per cent) the curing rate increases. At low humidity or in air-conditioned areas (internal joints in air-conditioned spaces), the curing rate is slower and the full cure time may be extended to 21 days or more for deeper joints.