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Stretch Marks, Raised Joint Lines & Cracks – OH MY!

December 7, 2018

We’ve all seen it, stretch marks, raised joint lines and cracks in the concrete substrate that affect the bonding of the resinous flooring that had been so carefully installed. Many times these are caused due to large or rapid changes in the substrate temperature.

Changes in the substrate temperature produce movements as the length and volume of the materials increase and decrease proportionally to the changes in external temperature.

The composition of the concrete impacts how much expansion or contraction occurs relative to a change in temperature.

So what does this mean exactly?  Typical concrete exhibits an average linear coefficient of thermal expansion that is approximately equal to 5.5×10-6/°F, meaning that for a concrete slab measuring 100 feet long will expand or contract roughly 1/16 of an inch for every 10°F increase or decrease in temperature.

Keep in mind, certain heating and cooling systems such as radiant heat and industrial chillers rapidly change the substrate temperature over a short period of time and must be carefully adjusted to avoid damage to the installed floor. We recommend adjusting the set temperature by no more than 1°F per hour, and no more than 10°F in a 24 hour period during the installation process. This gradual change reduces the impacts of expansion and contraction movements by allowing time for the materials to adjust more evenly.

The best practice is to address joints per our Joint Guidelines. Honoring joints allows for maximum movement without damage to the substrate or the coating, and minimizes the risk of stretchmarks, scarring, raised joint lines, and cracks. This practice eliminates the need for tight temperature control, leaving plenty of room for the substrate to expand.

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