Polyurea Expansion Joints by PennCoat, Inc.

How Important is Polyurea Joint Filler?

One of our “go to” products at PennCoat is Spal-Pro RS 88 semi-rigid polyurea joint filler. We find it performs well as a expansion joint filler for indoor concrete floors, especially in retail and industrial applications, where it supports traffic and protects joint edges. The material can also be used to fill the occasional crack in industrial floors. This product isn’t recommended for non-breathing flooring systems or in outdoor situations where temperatures can vary greatly year round.


The polyurea joint filler is a two-part elastomeric product with 100-percent solids content, consisting of:

When brought together, the two parts polymerize into a rapid-setting liquid that cures into a gray, rubberlike solid. The material has excellent adhesion to concrete, in the range of 350 to 400 psi, and a tensile strength of 970 psi. The mixture ratio of 1:1 is stable when cured, with negligible shrinkage and unusual hardness for a polyurea product. The product contains no volatile organic compounds and is fully compliant with LEED standards. The USDA and FDA approve the product for the food-related facilities they regulate.


The formulated hardness of RS 88 makes it especially useful as an edge protector and for withstanding heavy foot or mechanized traffic. It is colorfast, resisting fading and discoloration. Unlike other semi-rigid fillers, the product won’t stain concrete and can be use on polished concrete floors. During grinding and polishing operations, the product doesn’t smear or smudge. Care should be taken not to apply in conditions in which the ambient air or the concrete are excessively moist, as this may compromise adhesion and cause bubbling. It is suitable to applications that remain in a temperature range of 32˚F (0˚C) to +120˚F (49˚C). The material cures quickly, becoming tack free in only five minutes and ready for traffic in one hour, assuming ambient temperature of 70˚F. RS-88 meets or exceeds the floor joint filler guidelines issued by the American Concrete Institute and the Portland Cement Association.


Good installation practice is to wait at least 30 days after pouring a concrete slab before applying the filler, with the objective of maximize adhesion. A waiting of period of 60 or 90 days is even better, since it gives the concrete time to dry and shrink. Special two-feed power dispensing equipment or pre-filled, dual-dispense cartridge kits must be used to apply the filler to joints. You can’t apply it manually, because it takes only two minutes for the mixture of Part A and Part B to gel. The two parts are mixed in a 1:1 ratio. To ensure proper material dispensing and mixing, the manufacturer recommends using a static mixer with a 0.5-inch inner diameter and 30 to 32 elements.

First, thoroughly clean the joint, using either a dustless concrete saw or a sandblaster. No primer is needed. As is usual for all professional installations, the pump tanks, lines and dispenser must be clean and free of residual substances.

Depending on joint depth, applications normally require one or two passes. A good installer will slightly overfill, to create a crowned surface for curing. After about 15 minutes, we shave off the crown. We wait at least an hour before grinding or polishing the filled joint.