Polyureas vs. Epoxies
Polyureas are now a popular choice for filling and repairing control joints on commercial, industrial and warehouse floors, as well as some public areas where high heels or skate wheels cross joints. In the good old days, semi-rigid epoxies were more widely used. Which product is better?
Control joints are typically filled for several reasons: a) protect the integrity of the joint (reduce joint nose spalling), b) safety, c) reduce maintenance costs and d) prevent accumulation of foreign debris. The choice of the polymer may relate to the the type of traffic that uses the floor.
Polyurea Control Joints
Cure speed is the most desirable feature as often the filled joint can often be opened to traffic within 1-2 hours or sooner. Since time is money and finishing the floor is one of the last steps prior to opening, the faster cure speed of the polyurea is often the most valuable benefit.
Because of very fast gel times, it is may be impractical to hand-mix the faster curing polyureas, so using a special pump such as our Model C may be useful on very large jobs for high production rates.
Unlike epoxies, polyureas can cure in very cold conditions, in some cases as low as -25°F. In fact, polyureas are used frequently to fill joints in large freezer floors while the freezer is in service. At this low temperature, an epoxy is dormant and will likely freeze. Usually, an epoxy will cure when the ambient air increases to 40°F or more.
Polyureas are often touted for their greater elongation capability (up to 200%+ vs. ~90%). Yet neither material is intended for use in joints designed to move (such as expansion joints). However, the tall proportional cross-section of most control joints causes either material to separate from the side wall if there is significant joint movement because neither can stretch across its thick middle.
Though polyureas are generally softer, they are very tough under abrasive conditions. Tested in a standard Taber test rig, they may exhibit 40% less weight loss after 1000 cycles than control joint epoxies.
A cautionary note—use an epoxy primer with a polyurea when in doubt about dampness or moisture. The isocyanate portion of a polyurea reacts very quickly with moisture and this interaction may decrease the performance of the cured polymer or cause gassing or foaming.
Epoxy Control Joints
Although generally slower curing, this may be an advantage if the crack filling is done by hand pouring or a bulk caulk gun because of longer working time.
When the substrate is damp, wet, or contaminated, an unprimed epoxy has a better chance of bonding to the sides of the joint than a high speed polyurea.
In exterior applications, UV exposure causes fading and sometimes chalking of an epoxy. With aromatic-type polyureas often used in control joints, there can be significant color changes caused by sunlight which may be cosmetically unappealing.
When it comes to mixing and tolerance for “eye-balling” the A & B components, epoxies are more forgiving. Polyureas may lose some of their properties as soon as the mix ratio is off by 3-6% or more, whereas epoxies will often cure when the proportions are even further apart.
Most semi-rigid epoxies are harder (higher durometer) than comparable polyureas. This may be a critical factor in uses when there is high point loading across floor joints such as the steel wheels on some pallet jacks.
Both product types are relatively chemical resistant, but the epoxy usually has a slight edge with organic solvents, many acids and some oxidizers and sanitizers used on floors such as bleaches.
Both products can be blended (extended) with carefully selected aggregates or natural sands for deep repairs. Please ask for our help if this option is of interest. It's most important to use only dried sands containing less than 0.2% moisture by weight for either binder.
If you can‘t decide , call us (800-757-6773) for friendly technical assistance and the best selection anywhere. We're usually in the office by 6:30 and out by 5:00 California time.