Plaza deck, or waterproofed split-slab, joint sealing is serious business. Usually over occupied space, plaza decks are actually heavy duty roofs. Until the emergence of a watertight, purpose-designed system about 30 years ago, designers were left with the ineffective option of a buried looped membrane, "band-aid" approach to addressing these critical joints.
Buried-membrane options offered today are nothing more than a throwback to band-aid solutions for plaza and roof deck joint sealing. These out-dated solutions in no way respect an owner’s desire for durability nor do they honor the reputation of designers who research, engineer, detail and specify solutions in the long-term interest of building owners.
MIGUTAN is a watertight, plaza, roof deck, and roadway joint system specifically engineered to address the shortcomings of buried, sheet-membrane joint treatments that pre-date it by decades.
Specification of the MIGUTAN system results in attention to detail and quality assurance appropriate to the achieving watertightness in this critical application. It is precisely this lack of attention on many projects that causes joints to leak prematurely and result in exorbitant costs of inspection, investigation, repair and replacement of buried systems. These direct costs are compounded by the costs of disruption of operations of the affected facility.
The list of criteria on which band-aids
(buried-EPDM-membrane type products) do not match the
for plaza deck sealing is lengthy. Fundamentally, however, the buried
membrane approach does not meet split-slab design philosophy in the following ways:
1) DESIGN PHILOSOPHY AND PRINCIPLE OF OPERATION: Buried, Band-Aid Approach vs. Static Membrane Integration with Positively-Anchored, Purpose-Designed, Repair-Accessible, Movement Gland
Plaza and roof deck waterproofing involves a waterproofing membrane applied to a structural deck. These components are covered with some sort of topping. The topping is porous by design and allows water to reach the membrane on the structural slab where it is managed to drains. When expansion joints are necessary through plaza or roof decks they must be waterproofed using a method and material that accommodates movement while reducing or eliminating the stresses that will cause a buried membrane to fail.
Furthermore, while achieving the waterproofing at the structural level, by virtue of its retainer legs, project upward to the level of the top of the wearing course. This means that the topping slab or pavers are separated at the wearing surface and sit adjacent to the sealing gland that handles the structural movement. This prevents random cracking and buckling of the wear course materials.
Membrane Design Philosophy:
Furthermore, structural movement that occurs at the expansion joint in the structural slab is referred to the surface where the pavers or topping slab are usually inadequately isolate to accommodate movement. The result is buckled pavers that are a safety hazard or unsightly random cracking in concrete overlays.
These causes when combined with joinery required to handle changes in plane and direction exacerbate the tendency to failure. Remediation of failures of these buried systems involves nothing short of the removal of the entire surrounding topping system to expose the membrane. Because the location of roof and plaza decks is over occupied, often sensitive interior space, the disruption to tenant operations of this type of remediation is work usually renders the space below unusable for the duration of the repair or replacement. (Incidentally, EMSEAL conducts a considerable remediation business using the MIGUTAN system for precisely this type of failure in buried, “band-aid” plaza deck joint sealing attempts. In medical facilities, like for example the MRI unit at Vanderbilt University Hospital, the impact of failure of the buried “band-aid” system was not only huge in respect of equipment damaged, but facility use was severely disrupted during repair. The repair was made using the MIGUTAN system to impart watertightness to the structure).
The waterproofing components are all state-of-the-art thermo-plastic, rubber materials. These materials can be heat-welded in the factory to produce transitions for addressing changes in plane and direction. In addition these materials can be welded in the field using simple hot-iron tools for attaching transitions to straight runs and to address field conditions as they arise.
“Buried Band-Aid” Composition:
The use of wood blocking to build up the system where elevation is necessary is inappropriate in several respects. It is a validation of the need for a system that stands proud of the deck in certain application areas. In fact, the MIGUTAN mounting rail legs form an integral part of multi-layer deck composition ensuring that water is kept away from structural joint-gaps. Given this, wood blocking is a far cry from having non-corrosive metal supports specifically designed for this purpose. Wood blocking which eventually decays, even if treated, cannot be considered a lasting construction method for this purpose.
In contrast to thermoplastic rubber, thermoset rubber is an earlier generation of material that has been nearly totally replaced in most industrial sectors including automotive and construction, by better-performing thermoplastic alternatives. EPDM’s limitations in respect to flex-fatigue resistance, abrasion resistance, and chemical resistance have been understood for years. The use of EPDM lying flat on a roof as roofing material requires vastly different physical characteristics when offered for use in a dynamic structural expansion joint application.
The addition, by some manufacturers, of a fleece to the EPDM in is further recognition of the EPDM’s fundamental shortcoming in respect to long-term bondability to other materials. This degradation of bond is caused by the migration of plasticizer oils to the surface of EPDM. (It is for this reason that other deck waterproofing manufacturers, ex. WR Grace, specifically recommend uncured Neoprene and exclude EPDM for flashing details).
The need to have factory representatives execute all field splices using specialized equipment is a warning flag. It is the fundamental nature of thermoset rubber that it cannot be reliably joined except through vulcanization. Vulcanization a process normally confined to manufacturing facilities to achieve a finished state of certain rubber compounds using specialized equipment. The term, “thermoset” refers to the final application of heat to a rubber compound to achieve its final, finished, unalterable, solid state. It is precisely this characteristic that led to the evolution in rubber technology of thermoplastic materials. Unlike thermoset rubber, thermoplastic materials can be, through the application of heat, softened, joined, and added to, to achieve desired shapes and joins. The resulting joins are as strong as the original material particularly when reinforced as part of the welding process.
The assertion by some that buried membranes facilitates deck drainage across the joint should be considered in light of the following: Incorporating a structural expansion joint into a drainage plane, while sometimes unavoidable, is generally considered a waterproofing-design compromise. This condition can usually be addressed through attention to drain location.
While it is true that the MIGUTAN, by design, typically stands proud of the structural slab, only in extremely rare retrofit occasions might this pose an obstruction to drainage. This instance is where a joint has been located mid-span in a ramp where due to other constraints no option existed to locate it at the preferable location at the top of the ramp and details are available for addressing this condition.
3) TRACK RECORD
Band-aid joint treatments were historically the only choice available to designers and therefore were widely specified in years past. The existence of a place in the market for a purpose-designed plaza-deck joint system like MIGUTAN is the direct consequence of owners’ having to spend a fortune replacing failed “buried band-aid” and looped membrane materials.
To avoid specifying “buried band-aid” materials based on the very technology that MIGUTAN was engineered to replace seems common sense and should prevent deficiencies in philosophy, principle of operation, composition and track record from being “swept under the rug”.
John Ruskin, a nineteenth-century commentator on architecture among other things warned:
“It is unwise to pay too much, but it’s worse
to pay too little. When you pay too much you lose a little money—that is
all. When you pay too little you sometimes lose everything, because the
thing you bought was incapable of doing the things it was bought to do. The
common law of business balance prohibits paying a little and getting a lot.
It can’t be done. If you deal with the lowest bidder, it is well to add
something for the risk you run, and if you do that you will have enough to
pay for something better.”
Last Modified: May 21, 2013