Dictionary of Moisture Protection & Restoration

Polyurethanes: Various polymers produced by chemical reactions formed by mixing di-icocymate with hydroxyl, used to make flexible and rigid foams, elastomers and resins. Many urethanes are moisture-cured materials. Other two-component urethanes are chemically curing mixtures. Their compatibility with most substrates and waterproofing capability has made them a commonly specified sealant for most waterproofing projects. Their formulations range from one-component and two-component self- leveling grade for horizontal joints, to one- component and two-component non-sagging grade for vertical expansion joints. Some urethanes are manufactured to meet the USDA requirements for food processing plants. Urethanes have excellent recovery capabilities, 90% or more, and have very good weathering characteristics. As urethanes are extremely moisture-sensitive during curing, closed-cell backer rod should be used, except for the one-component materials where open-cell is acceptable. In most applications, priming is not required, however, manufacturers differ in their specifications especially for very smooth substrate surfaces. So it is important to follow the manufacturer’s specification. Do not use urethanes in joints containing polysulfide or asphalt base sealants or residue unless they can be completely removed. They should not be used in glazing applications or high performance glass, plastics or acrylics. Most sealants, except latex, exceed the movement capabilities of paint, so they should

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