Sephaku Cement explains the ddifferences between drying and curing and the various phases that concrete sealers go through as they set.

Understanding the differences between drying and curing and the various drying phases that concrete sealers go through as they set can be intricate. While sealers and coatings typically follow the same setting process, some dry while others cure. To follow, we note the differences between concrete sealants that dry and concrete floor sealers that cure and what this means for the application of polyurethane sealants to stained concrete flooring.

To begin, let’s make sure we understand what it means when a sealant cures and how this is different to an application that dries. In the concrete industry we understand that curing is the process by which materials undergo hardening by way of a chemical reaction when various compounds are mixed. Much the same as the chemical reaction that cement undergoes when hydrating, two part sealants will also undergo a hardening phase when different parts of the 2 part sealants mix, this can also be referred to as a catalysed system.

So now that we understand the fundamentals of curing, let’s explore the differences between sealants that dry versus those that cure.

All sealants and concrete coatings contain liquid solvents which are known as carriers. Depending on the type and the volume of solvents present in the concrete coating will determine how the sealant will dry (or cure).

One-part Concrete Sealers One part sealants dry without curing whereby the solvent or liquid carrier evaporates as it becomes exposed to air, which in turn causes the resin or solid compounds of the sealant to dry creating a resin-like membrane on top of the concrete floor.

Two-part Concrete Floor Sealants Two-part sealants or catalyzed systems cure as they dry. When the two parts of the sealant mix, crosslinking occurs which forms a type of bonding that takes place during this chemical process. The bonding results in greater durability which in turn results in the coating being classed as a more high performance application, typically used on high traffic zones and hardworking floors.

While each concrete sealant offers various pros and cons each suited to different uses and needs, each coating follows very similar set of phases when drying, these include:

  • Shelf Life – This is pre-application where the concrete sealant is stored in an airtight container usually for no longer than a period of 1 year before sealant compounds become compromised. It’s important to note that two-part sealants tend to be more sensitive to a lengthy shelf-life and the appropriate storage needs to be adhered to. Every manufacturer can determine a different shelf life for their products, these guidelines must however be followed by the consumer/client.
  • Working Life – also referred to as “pot life” is when the sealant is in the application process. Affected by the environment and conditions under which the coating is applied (hot, cold, moist, dry, windy conditions), warmer conditions speed up drying and curing as well as shorten the shelf life of the product once it has been exposed to air and heat.
  • Open Time – Exposed to air after the initial application this drying phase is hugely affected by exposure to various conditions, depending on the chemistry of the sealant, open time can vary between 15 minutes and a number of hours.
  • Tacky – as the name suggests the tacky phase during the drying and curing of decorative cement sealants is when the coating film is tacky to the touch. While this may be so, it is important not to touch the surface of the sealant as finger marks and blemishes will remain as the coating continues to dry. It is critical that two-part sealants dry beyond this phase before re-applying a second coat to avoid the risk of trapping solvent that is still evaporating.
  • Tack Free – considered the final phase in the drying and curing process, the tack free phase has taken place when the cement sealant is no longer tacky to the touch, it is not that two-part coatings will be re-applied during the recoat window. Allow a period after this final phase before use, to ensure longevity of your chosen floor coating.