Control joints are essentially deliberate cracks cut into concrete floors that allow for movement caused by temperature and moisture changes. Put another way, when the concrete does inevitably shrink and crack, it does so on a line (at the bottom of the control joint) instead of randomly across the slab. If left unfilled, control joints can become areas for dirt, debris, and moisture to collect and cause problems. Filling joints with a non-compressible, hard material supports the edges of the joint from stresses imposed by heavy, hard-wheeled traffic. Joint filling should be put off as long as possible to allow the joint to widen, although in practice joints are usually sealed or filled sooner than ideal.

Selecting a joint filler can be challenging; not only are there several brands to choose from, but the joint fillers themselves are available with different chemical compositions and physical properties. The two most common joint filler types are epoxy and polyurea. Polyureas have grown in popularity over the last twenty years or so, but epoxy fillers have been in use for much longer and are still popular today. So which is better?

To answer that, the intended use of the concrete floor, the facility, and the application environment must be considered. Requirements for appearance and turn-around time are also important considerations. The following comparison of epoxy and polyurea joint filler characteristics will provide guidance to select the right filler for your next project. 

Shore (Durometer) Hardness

The Shore durometer gauge measures the relative hardness of a material by pressing a tiny needle into its surface and recording a value between 1 and 100. Higher Shore hardness numbers indicate a greater resistance to indentation, and thus indicate harder materials. The Shore A scale is used for more rubbery materials; the Shore D scale is used for harder plastics. Both Shore A and Shore D values are sometimes published for joint fillers because engineers and specifiers often require one or both scales.

Concrete industry standards, most notably ACI 302 (Guide for Concrete Floor and Slab Construction), require that a concrete floor joint filler have a minimum Shore A hardness of 80. Epoxy joint fillers and polyurea joint fillers both meet this requirement. ADVANTAGE: EQUAL

Elongation

Don’t be misled by tensile elongation results. A polyurea joint filler with a Shore A of 80 may have a tensile elongation of 400%, but is able to expand only about 5-15% laterally (side-to-side) before splitting or losing adhesion along the concrete bond line. A Shore 80 epoxy joint filler epoxy with 25% elongation will usually tolerate 5-8% lateral expansion. Thus, the high elongation polyurea joint filler offers very little in expansion advantage over an epoxy. ADVANTAGE: EQUAL

Adhesion to Concrete

Both epoxies and polyureas have adequate adhesion to concrete. ADVANTAGE: EQUAL

Application Temperature

Freezing temperatures will prevent epoxies from curing completely. Thus, epoxies should be used only when the installation temperature is above 32°F. Polyureas are the best choice for use over a wide range of temperatures, even below freezing, as most can be installed as low as -20°F. ADVANTAGE: POLYUREA

Installation & Cure

Both epoxies and polyureas can be dispensed with meter-mix pump equipment. Epoxies can also be dispensed with manual bulk guns. Polyureas generally cannot be dispensed with manual bulk guns because their pot life (a few seconds) is too short. However, the short polyurea pot life coupled with the efficiency of a meter-mix pump application leads to faster turn-around time, reduced labor and cost savings. ADVANTAGE: POLYUREA

Appearance

Epoxy joint fillers, and most polyureas, have poor UV stability. This means that when exposed to UV radiation from sunlight or even some types of interior lighting, the filler will discolor – most often taking on yellow or greenish hues.  Euclid Chemical’s QWIKjoint UVR is formulated to absorb UV radiation without discoloring. This, along with its availability in over 30 standard light-stable colors, makes QWIKjoint UVR the only choice for decorative, integrally colored, or polished concrete floors. ADVANTAGE: POLYUREA (QWIKjoint UVR)

Separation

All joint fillers separate, either adhesively or cohesively, as joints open due to slab shrinkage. Separation is exaggerated when the filler is installed soon after placement, before the majority of slab shrinkage has taken place. The best way to reduce joint filler separation is to delay filling as long as possible. ADVANTAGE: EQUAL

Removal

If a joint filler is improperly installed (filled less than full depth, has concave profile, etc.), or if it must be removed for other reasons, epoxies are easily removed by saw-cutting. Most polyureas are not easily removed and typically shred upon contact with a sawblade. ADVANTAGE: EPOXY