Lap sealant is a specialized compound engineered to create a durable, waterproof seal where two materials overlap, a joint known as a lap joint. Its primary function is to prevent water intrusion in exterior applications that are subject to movement and harsh weather conditions. This type of sealant is formulated to maintain flexibility over a long period, accommodating the expansion and contraction of building materials caused by temperature fluctuations. It provides a secure seal along seams and around penetrations, which is particularly important for maintaining the integrity of exterior surfaces.
What Makes Lap Sealant Unique
Lap sealant is chemically distinct from standard caulks or adhesives, often utilizing polymer-based compounds like EPDM, butyl, or polyurethane to achieve its specific performance characteristics. A defining property is its superior resistance to ultraviolet (UV) radiation, which prevents the material from breaking down, cracking, or discoloring when exposed to direct sunlight. This chemical makeup allows the sealant to remain pliable, a necessary feature for dynamic joints that experience constant thermal movement. Unlike rigid caulks, lap sealant is designed with a high movement capability, ensuring the bond remains intact as materials expand and contract. It is formulated to adhere strongly to a variety of substrates, including metal, rubber, fiberglass, and wood, making it a versatile solution for complex exterior assemblies.
Primary Uses in Home and RV Repair
The most frequent application for lap sealant is in the maintenance of recreational vehicles (RVs) and campers. RV roofs, often constructed from materials like EPDM or TPO rubber sheeting, require a flexible, long-lasting seal around all openings and edges. Lap sealant is used extensively to seal the perimeter of the roof, around air conditioning units, vent pipes, skylights, and screw heads, creating a secure barrier against moisture intrusion. This is a frequent maintenance task because the constant vibration and temperature changes experienced by an RV place significant stress on exterior seams.
Lap sealant is also a preferred material for sealing seams and fasteners on metal roofing systems, including corrugated panels. The overlapping nature of metal roof panels and the numerous points where fasteners penetrate the material create potential leak points that require a highly adhesive and weather-resistant compound. Applying the sealant to the edges of flashing and around exposed screws ensures a watertight system that can withstand years of exposure.
Another common use is in the installation and repair of exterior gutter systems, particularly at the joints where two sections overlap or where end caps are attached. These joints are subject to constant water flow and temperature changes, demanding a sealant that will not wash out or crack. In general exterior repair, lap sealant is the appropriate choice for any joint where two different materials meet and overlap, requiring a flexible, waterproof seal that can handle dynamic movement.
Proper Application Techniques and Curing
Successful application of lap sealant begins with meticulous surface preparation for achieving a lasting bond. The area must be completely clean, dry, and free of any dirt, oil, grease, or old sealant residue. Any foreign material on the substrate will compromise the sealant’s adhesion, leading to premature failure.
When applying the product, users must select between two primary formulations: self-leveling and non-sag. Self-leveling lap sealant is a fluid compound designed exclusively for horizontal surfaces, such as flat RV roofs, where gravity allows it to flow and spread evenly to fill voids without tooling. Conversely, non-sag sealant is a thicker formula intended for vertical or sloped surfaces, such as RV sidewalls or trim, where it must hold its shape and resist dripping or slumping after application.
The sealant is typically dispensed using a standard caulk gun, and a steady bead should be applied directly over the seam or penetration. While self-leveling formulas require no tooling, non-sag sealants may be lightly smoothed with a tool or gloved finger to ensure full contact with both surfaces. Curing times vary based on chemical composition and environmental conditions, but most lap sealants will skin over within five to thirty minutes. They generally achieve a waterproof state within four to 24 hours, though a full cure can take anywhere from 48 hours to 30 days.