There are literally thousands of different polyurethane compounds (PUR) available on the market today and many have an extensive history of use as CASE materials, (coatings, adhesives, sealants and elastomers) and in particular for waterproofing membranes. However, selecting the wrong product could have disastrous results.

With the development of polyurethane elastomers, the performance of waterproofing membranes has significantly improved and they have become widely utilized for most exterior applications. Polyurethane membranes can be made from the array of commercially available isocyanate and polyols, each of which will result in differing physical properties and affect the durability of PUR coating.

An example is the type of polyol used in the PUR coatings. There are basically two types of polyols used, polyethers and polyesters, each of which bestows different properties or levels of resistance on a polyurethane compound.

Polyester polyols are the most widely used due to their good tear and abrasion resistance, as well as their resistance to oil and long-term heat. However, Polyester PUR are hydrolytically labile and as such are highly susceptible to slow chemical degradation by hydrolysis as a result of contact with the combination of heat and water (humidity). Polyester PUR therefore have a limited use in application were they are exposed to water wet applications and are not recommended for wet or high-moisture conditions. Polyester PUR not only absorbs water physically but also consumes water chemically through hydrolysis until the polyurethane is destroyed.

Polyether-based PUR offer increased water resistance and superior low temperature properties in comparison with polyester based PUR.  The ethers have a higher resilience which gives them the capability of not taking on heat in dynamic applications as well as having a higher compatibility with water than polyesters in moist environments.

Hydrolysis is a common problem (see image below) with many urethanes especially the less expensive general-purpose grades. Hydrolysis is the reaction by which a molecule of water breaks a bond in the polymer. At higher temperatures, the impairment of the mechanical material properties arises increasingly in the case of polyester PUR.

Water damage is second only to fire as a cause of building decay and deterioration. Furthermore, the majority of building materials have a considerable shorter life span when subjected to moisture or immersion over a prolonged period of time.

Currently there is only one Australian Standard that applies to waterproofing, however the standard relates only to waterproofing in internal wet areas. While a certain polyester PUR may be satisfactory for waterproofing of internal wet areas, the same PUR could be a disaster in an external waterproofing application where it is could be exposed to a combination of water and high temperatures.

Cetec is often called upon to investigate why a product has failed and provide a suitable solution.  At this stage, it is usually too late to avoid some level of financial loss.  An independent appraisal of any new material being proposed for usage prior, to construction, can save millions. Cetec has extensive experience in evaluating new products for a vast range of different applications.  This expertise has proved valuable to construction and industrial projects at the design and/or construction stages.