Maintenance and Repairs

October 16, 2024 Published by Golden Horseshoe Chapter - By Jeremy Cha

PMMA Waterproofing in Parking Garages

From the Volume 21, Fall 2024 issue of the CCI GHC Condo News Magazine

I think we all understand that it is of utmost importance that the structural elements of your buildings are protected from damage. Failure to do so, in the worst case, can lead to significant harm and breakdown of the structure to perform as needed. In the case of underground parking garages, this protection is often provided by an elastomeric waterproofing system, which is in place to protect the underlying concrete from elements that can potentially cause damage, namely, moisture, road salts, and chlorides.

Most of us reading this are probably quite familiar with these elastomeric waterproofing systems, along with the issues that often arise with them. In general, if properly cared for and maintained, a typical elastomeric waterproofing system within an underground parking garage has a service life of approximately 15 to 20 years, depending on use, after which they typically need to be stripped and reapplied. This maintenance, of course, includes locally repairing areas that may have debonded, worn away, or deteriorated, in addition to localized repair of the underlying concrete. If left unrepaired, these areas of deteriorated concrete expand at an exponential rate, increasing related repair costs and service disruptions.

There are often areas in a garage that experience higher levels of traffic, such as ramps and main drive lanes, where all cars must drive through to get to and from their designated parking spots. There are also areas like the corners and turning radii that experience much higher forces and wear due to increased shear (lateral) forces (think about the cars whipping around corners at speeds much higher than the posted limit). It is at these areas that the elastomeric waterproofing system tends to deteriorate and wear away more quickly. It is also at these areas where there’s more headache associated with partial or full closures, traffic management, and other logistics. There are often times when it is not feasible or practical to close whole sections of the garage to complete repairs and phasing the work is awkward, time consuming, and more costly due to lost productivity and temporary vehicle relocation. It’s at these times that an alternative waterproofing can be used to decrease all the headaches and frustration that comes with repairs and maintenance.

Polymethyl methacrylate waterproofing systems, or PMMA for short, are a premium alternative to conventional elastomeric waterproofing systems at higher traffic areas, and locations where closures are difficult or not feasible. These waterproofing systems are growing in popularity due to the fast turnaround and increased durability that they offer in comparison to elastomeric waterproofing.

The first, and arguably most important, benefit of using PMMA waterproofing is that it only takes an experienced crew about 6 to 8 hours to install from start to finish at a given area, including installation and cure times. In comparison, elastomeric waterproofing takes approximately 2 to 3 days to complete (primarily due to required cure times), depending on the thickness of the wear coat, meaning that sections of the garage need to be closed for that portion of time. With this advantage, PMMA systems can be installed within a working day or overnight, when garage traffic is significantly lower, greatly reducing impacts to daily operations.

Granted, a full closure of the area will still be required; however, this is often much preferred to closing areas for 3 days or phasing the work in halves. In larger projects, the reduced timeline can reduce the overall schedule and impact on building residents. The benefits only increase when installing these systems at high traffic areas, such as ramps or main drive aisles, where phasing is a nightmare and closures just aren’t feasible.

The second strength of PMMA systems is that they are considerably more durable than conventional elastomeric systems and bond better to concrete substrates. Typically, when using elastomeric waterproofing systems, an additional coat of wear course (or two) will be installed at high traffic areas such as drive lanes and turning radii since the material is anticipated to wear away with time. While effective, this also means that there will be increased application times (and related closures) associated with installation as each layer of waterproofing cures.

Without boring you with the science of why, PMMA membranes are more robust and less susceptible to wear than conventional elastomeric systems, making them ideal candidates for these high traffic areas as previously mentioned. The surfaces of the PMMA are harder and more durable (due to an additive mixed into the pail), making them more resistant to the shear forces applied by tires, particularly at turning radii. This durability also means that periodic maintenance and repairs are less frequent, further reducing impacts to garage operations. It should be noted that this also makes them less pliable, meaning that they are more prone to cracking in extreme cold or significant thermal variation; however, this isn’t often a concern in underground parking garages.

An added benefit, and more assurance to the quality of PMMA waterproofing systems is that most manufacturers require proper training, approved applicators, and for the manufacturer to be on site during installation. This is partly because the installation process is slightly more complicated and time sensitive, but also because manufacturers often offer extended warranties. With conventional elastomeric waterproofing, warranties are often limited to 2 years, perhaps up to 5 if you pay a premium and ensure that an approved applicator is completing the installation. In comparison, most PMMA manufacturers will supply a 5 to 10 year warranty on the system, which allows for better assurance that the waterproofing will last and be effective at protecting the suspended garage structure.

Further, when installing a PMMA waterproofing system, one thing you won’t need to worry about is cost 2.5 to 3 times more to install. This is often a hefty fee to pay up front and, in reality, it’s not always feasible to install such a premium system throughout the entirety of the garage. Rather, PMMA can be used selectively in combination with elastomeric waterproofing to create a system which is durable and able to adequately resist constant wear and vehicular traffic where required. Realistically, it’s a little overkill to be installing such a robust system in parking stalls in most cases; but in high traffic areas, which just so happen to be the areas which are most difficult to near future, talk to your building Engineer about the potential use of this material!

Jeremy Chan, P.Eng. is a Project Engineer at Brown & Beattie Ltd., a building science engineering firm dedicated to providing clear and sensible building improvement, maintenance, and repair planning advice by listening to clients’ objectives. Mr. Chan specializes in investigations and condition assessments of low-rise and high-rise buildings, primarily focusing on structural components. He has developed a deep understanding of the role of various building components, including moisture protection systems, and their interactions, which allows him to critically assess buildings for areas of existing or potential failure.