Plaza Deck Restoration: Principles of drainage and waterproofing

January 1, 2012

All photos courtesy CETCO[1]
All photos courtesy CETCO

By Stacy Byrd, LEED AP
Plaza deck waterproofing typically requires replacement at some point during the building’s life. Restoration of the waterproofing system over occupied space poses many challenges, both in design and construction. Typically, plaza decks now being subject to restoration were constructed many years ago and do not include subsurface drainage or adequate deck slope at the waterproofing membrane level. Correcting these deficiencies can result in increased plaza deck thickness and dead loads.

The designer is often faced with the building not being constructed exactly per plans and specifications because of changes implemented during the construction process. These ‘as-built’ changes may or may not have been documented, or the documentation may no longer exist. This makes it especially challenging for consultants to determine causes of the water ingress and develop plans to remediate problems at the plaza area without doing extensive and expensive intrusive investigations.

Inspection and design challenges
If there is a leak in the plaza deck, the waterproofing membrane is buried under reinforced concrete, heavy pavers, pavement, or soil with plantings. Their removal and replacement represents a significant cost to the building owner. With waterproofing membrane restoration, the designer must address related issues with the existing building components and provide installation details that take into account the limitations posed by the existing conditions and building occupancy. These issues typically include:

Exploratory openings are almost always required to determine the configuration and condition of the plaza assembly materials, including the concrete deck’s condition. These openings can also provide data on existing drainage patterns. One should select locations for the openings based on:

The photo above shows the beginning of a concrete topping slab removal in order to replace a failed peel-and-stick waterproofing membrane. Deck construction did not incorporate a drainage layer at the membrane level, which led to premature failure.[2]
The photo above shows the beginning of a concrete topping slab removal in order to replace a failed peel-and-stick waterproofing membrane. Deck construction did not incorporate a drainage layer at the membrane level, which led to premature failure.

However, it should be noted these openings represent only a small area of the deck, and the conditions discovered by exploratory openings should only be relied on to conclude a ‘general’ estimate of repair requirements. Typically, the plaza deck assembly’s actual condition and the extent of deterioration, if any, will not be known with certainty until the remedial construction operations. Therefore, the construction documents should incorporate various repair work that may be required to restore the structural deck condition. To protect the owner, prices for such repairs should be incorporated into the contract bid documents. (This is a project by project ‘cost’ issue based on the existing construction of the building and the anticipated repairs as related to the condition and construction of the structure. For example, the owner and contractor, even with up-front investigation work, may not know the extent to which the concrete deck has deteriorated and needs to be repaired before a new waterproofing membrane can be installed. In this case, the contractor would be directed to provide a unit price for deck repair at the time of bid. The contractor can also place some conditions on the unit price to protect his interest as well. However, at the least the owner gets a bid that tries to cover all of the assumed repairs based on the building’s existing construction).

Many investigations have revealed the deterioration and subsequent water ingress was a result of water trapped within the plaza deck assembly directly atop the waterproofing membrane and the project did not incorporate a subsurface drainage layer. Therefore, this article focuses on subsurface drainage and selecting and installing a proper waterproofing system for plaza deck restoration.

A hospital deck rehab used a welded polyvinyl chloride (PVC) system to reduce the existing deck preparation time and complete the construction faster to get the emergency room entrance back into its regular working service.[3]
A hospital deck rehab used a welded polyvinyl chloride (PVC) system to reduce the existing deck preparation time and complete the construction faster to get the emergency room entrance back into its regular working service.

Positive drainage
A good plaza deck waterproofing design incorporates drainage at both the deck wearing surface and subsurface at the waterproofing membrane level. Many plaza deck waterproofing failures are a result of the deck surface not sloped to properly drain. It is essential to provide drainage at the waterproofing membrane level as a component of the design. This ensures water that infiltrates the deck assembly will flow to the drains and minimize freeze-thaw-heaving and deterioration of the wearing surface. Additionally, if the deck-wearing surface is continuous, it should be sloped to internal drains or off the slab’s edge.

Drainage at both levels can be achieved with ‘two-tiered’ drains or by separate surface and subsurface drains. Good drainage slope at the membrane level will minimize water ponding, reduce deterioration of the membrane, minimize hydrostatic pressure on the membrane, and decrease the potential for deterioration of other plaza deck components from prolonged exposure to moisture.

Wearing course drainage
Plaza designs can incorporate one or several materials in different locations as the wearing course. These include continuous materials such as reinforced concrete, or unit materials such as precast concrete pavers, brick, or stone. Additionally, the precast concrete pavers can be installed either in an open- or closed-joint configuration. The former indicates the pavers are suspended on support pedestals which provide a gap between each adjacent paver and an air space beneath the paver––separating it from the assembly materials underneath. The latter indicates the pavers are installed on a cementitious grout bed with the joints between adjacent pavers filled with grout.

This is a poor deck drain location, as it is next to a wall within a perimeter flashing detail.[4]
This is a poor deck drain location, as it is next to a wall within a perimeter flashing detail.

Pavers on pedestals generally provide the best means to promote drainage at both the wearing course level and under the wearing course. Pedestals suspend the pavers up and out of the water on the membrane, and provide an air space underneath the plaza surface so water can flow freely to a drain. Paver-on-pedestal systems also allow easy removal and reinstallation of the wearing course for inspection and maintenance of the drains and waterproofing membrane. However, pedestals are not suitable for bricks and irregular natural stone.

An advantage offered by open-joint paver systems is the wearing surface can be constructed level for improved plaza use and esthetics. Typically, there is no need to use surface drains; therefore, deck drains can be concealed below the pavers. However, pavers on pedestals have their disadvantages. Without proper installation, the pavers can move or shift when loaded, consequently becoming a hazard. Additionally, paver-on-pedestal systems have limited load-bearing capacity and are generally intended for pedestrian traffic.

 A poorly bonded hot-applied rubberized asphalt waterproofing membrane is being removed from a concrete plaza deck.[5]
A poorly bonded hot-applied rubberized asphalt waterproofing membrane is being removed from a concrete plaza deck.

Subsurface drainage
The plaza assembly design should enable water infiltrating the wearing surface and system components to be drained at the waterproofing membrane level. Providing membrane-level drainage can prevent premature deterioration of the wearing course and greatly reduce the likelihood of waterproofing and structural deck deterioration.

Many older concrete plaza decks were constructed with a level, or near level, deck. Considering normal construction tolerances, deflections in concrete slabs, and normal building settlement, it is not unusual to find certain areas of a structural plaza deck intended to drain do not perform this function. These areas vary in elevation from dead level to very low-slope to positive slope in the wrong direction.

An important factor in the evaluation of the existing conditions is to determine the drainage slope at the surface where the new waterproofing membrane will be installed. A best practice is to provide positive slope-to-drain at the waterproofing membrane level. Generally, the deck slope should be a minimum of 6.4 mm (0.25 in.) over 0.3 m (1 ft) in deck length (an approximate two per cent slope). Since all decks have some unevenness due to construction tolerances and materials, low deck slope will increase the likelihood water will be retained on the membrane. Additionally, the slope should take into account the deck will experience deflection when loaded. The structural engineer can estimate the deflection of the plaza deck to be incorporated in the slope design.

An inverted pyramid pattern providing a four-way slope to an interior deck drain is an efficient subsurface slope layout. Even with proper slope-to-drain, it is advisable to provide a further recessed area (i.e. a drain pan) directly around the deck drain. This is to accommodate the buildup of waterproofing materials at the drain ring so it does not restrict the water flow into the drain.

This cold fluid-applied polyurethane waterproofing membrane in a plaza deck planter did not bond well to the substrate. It suffered subsequent physical damage.[6]
This cold fluid-applied polyurethane waterproofing membrane in a plaza deck planter did not bond well to the substrate. It suffered subsequent physical damage.

One should co-ordinate the slope and drain positions with planters, curb walls, and other building elements that could interfere with drainage. Locating internal plaza drains near the mid-span between support columns can help account for load deflection. If a drain cannot be located at the centre of each span, one should consider providing greater slope-to-drain. One critical design element is to slope the deck in a manner that does not cause it to drain across an expansion joint. A best practice is to actually construct the expansion joints in an elevated curb to limit the opportunity for water to flow across the joint.

Restoration of an existing plaza with little or no slope may require adding a tapered layer of concrete over the existing concrete deck––before the waterproofing––to improve drainage. The structural deck-loading capacity and the height of perimeter conditions (i.e. doors and flashings) may limit improvements to the existing slope. When adding a tapered topping slab, a structural engineer must confirm the existing structure can safely support the tapered concrete’s additional weight. It is also good practice to co-ordinate slope on the wearing surface with the slope on the membrane level, and with drains spaced to accommodate desired drainage. To assist with this process, elevation measurements using conventional surveying tools can yield relatively accurate contour results of the structural slab and surrounding elements.

Topping slab removal at a helicopter port to replace an old built-up roof (BUR) waterproofing system.[7]
Topping slab removal at a helicopter port to replace an old built-up roof (BUR) waterproofing system.

Once the existing elevations and drainage slopes are determined, the designer can assess the need for improving the drainage slope and specify methods to improve it. However, providing a 6.4-mm per 0.3-m drainage slope to an old plaza deck is not generally practical since the existing building elements such as doors and curbs were built in relation to the surface of the existing plaza finishes. Thus, providing a 6.4-mm per 0.3-m drainage slope may require the existing building elements be altered.

In lieu of concrete, tapered rigid insulation has been used on projects when additional load capacity is restricted. This option limits the choice of waterproofing membranes because the insulation is installed first and may change the condensation potential in the plaza deck assembly. Another option is to provide additional drains in the plaza. While this may appear to be a simple solution, adding drains to occupied structures is not always practical.

Prefabricated drainage composites
On decks with a continuous concrete or paving surface for traffic-bearing properties, a prefabricated drainage composite placed over the waterproofing membrane can provide both drainage and uniform support for the assembly.

Subsurface drains should have large openings to promote water flow and be less likely to clog. Pedestals allow for easier access.[8]
Subsurface drains should have large openings to promote water flow and be less likely to clog. Pedestals allow for easier access.

Drainage composites consist of plastic formed into a 3-D dimpled sheet or geonet cross-grid. The composites maintain a path for drainage between the dimples or cross-grid while supporting overlying materials. Drainage cores are more easily clogged than a paver-on-pedestal system because the drainage area is generally thinner. Soil, concrete, or mortar placed over them can run or be washed into the drain core where the filter fabric is not properly installed. Designs using a drainage composite course should consider the following:

One should co-ordinate the use of drainage composite with support requirements for the paving system––both during installation and in-service. Drainage composites are available with overall compressive strengths high enough for most applications. The design should also include not installing the paver pedestal directly to the drainage composite. General composite plastic drainage cores have high compression strength when dead loads are distributed through a thick, uniform material layer. However, they are not as good when the load is applied directly at a point to the drainage core.

A drain composite with capacity exceeding the expected flow rate should be selected. For continuous paving systems where most of the water drains off the exposed surface, the expected flow rate at the membrane level is low. However, since access is limited or not an option, thicker drainage cores with higher drainage capacity are still preferred because the larger drainage space is less susceptible to clogging. Continuity of the drainage pathway is imperative––the drainage core should extend all the way to the drain.

Most drainage composite is approximately 6.4 to 11.4 mm (0.25 to 0.45 in.) thick with published flow rates of 10 to 25 Lpm per metre width (9 to 22 gpm per foot width). This test is typically reported for a hydraulic gradient of 1.0 under a pressure load of 172 kPa (3600 psf). For specific product properties, one should refer to current manufacturers’ published literature. Geonet versions have a very low profile and, as such, have a thinner area to transport water and generally have a lower flow capacity than dimple-formed prefabricated drainage cores.

The deck of a heliport waterproofing rehab project was four storeys up. A welded PVC system with an active polymer core layer was installed to replace the old BUR waterproofing system.[9]
The deck of a heliport waterproofing rehab project was four storeys up. A welded PVC system with an active polymer core layer was installed to replace the old BUR waterproofing system.

Another item one should consider when selecting a prefabricated drainage composite is the type and properties of the filter fabric bonded to the core. The filter fabric for plaza decks with concrete slabs is generally a woven polypropylene geotextile with high tensile strength properties. In planters, the filter fabric is generally a thick nonwoven geotextile for better filter properties of soil particles. However, no matter which filter fabric is specified, careful installation is needed to prevent debris from washing through the fabric at joints, core edges, or terminations and potentially clogging the drainage composite. For example, a paver bed should not consist of extremely fine granite dust or sand able to migrate through the filter fabric.

Compressive strength is another important design consideration with prefabricated drainage composites. As with flow capacity, one should choose the composite with a compressive strength that exceeds the loads expected. Additionally, the thickness and type of wearing course material is also a consideration with regard to load capacity because the load is disbursed over a greater area with a thicker wearing course than a thin-wearing course. Assembly thickness is extremely important to consider when designing a plaza with pavers laid into a sand or gravel bed. Thin-wearing course coverage can point-load the composite and may cause it to collapse, making the pavers shift and further displacing the sand bed.

Gravel or sand can be used as a drainage layer in plaza paving systems, but this is generally less desirable than either pedestal systems or prefabricated drainage composites because gravel or sand can have lower drainage capacity and adds more weight to the structure. With sand, one should confirm the filter fabric of the drainage composite is suitable with the sand’s particle size.

Drain outlets
Drains at low points of the waterproofing membrane are needed to receive and carry away water that collects in the drainage layer; these are in addition to the drains at the paving’s surface. Drainage at both levels can be achieved via two-tier drains or by separate systems of surface and subsurface drains. In some cases, water on the membrane level drainage can be drained off the deck’s edge, but this may expose the wall to additional water and potential leakage.

Many two-tiered plaza drains have only a small number of weep openings to collect water on the membrane level. These are prone to clogging with debris or minerals that seep out of the paving and cannot be relied on to provide membrane-level drainage over the long term without maintenance. One should use drains containing large weep openings, providing easy access for clean out wherever possible in the design.

During construction, it is important to maintain a clean work area and remove debris.[10]
During construction, it is important to maintain a clean work area and remove debris.

Waterproofing selection
With plaza deck restoration, selecting a waterproofing membrane deserves a thorough evaluation and review process. The designer has a responsibility to specify materials appropriate for the intended application and construction site conditions. The waterproofing system design should be adequately depicted through the details and installation described through the specification. Before selecting the proper waterproofing system, it is also a good practice for one to discuss and fully define all of the performance expectations with the owner.

An important factor in selecting a membrane is the installation’s ‘practicality,’ both as a product and with regard to the site conditions. For example, cold-applied fluid membranes typically require longer curing times and are more susceptible to problems associated with moisture release from the concrete substrate. If the construction schedule does not allow enough time for the substrate concrete to ‘dry,’ an alternative waterproofing membrane such as a single-ply polyvinyl chloride (PVC) sheet system should be considered. Another example can be found in hot-rubberized asphalt membranes, which may pose challenges when the installation is at a hospital or other occupied building with little or no tolerance to odours and fumes. Additionally, local building codes can have restrictions on the use and placement of hot melter equipment––including restrictions on the transport and storage of propane tanks.

Rehabilitating a plaza deck over occupied spaces will almost always involve the full or partial removal of the existing membrane to repair the concrete substrate. In many instances, the existing waterproofing membrane is already deteriorated and leaks in several locations, but its complete removal can only increase the potential for water ingress during construction. If the entire existing membrane is not to be removed, it is extremely important for one to select a new one compatible with what is in place to prevent chemical attack to the new membrane. For example, bonded residue from a failed coal-tar membrane on the deck surface can chemically degrade many membrane types, including self-adhering bitumen sheets and hot-applied asphalt membranes.

Hot-applied rubberized asphalt membrane being installed.[11]
Hot-applied rubberized asphalt membrane being installed.

Fluid-applied membranes
Hot-applied rubberized asphalt systems are typically installed at a 5.5-mm (215-mil) thickness, often reinforced with polyester scrim. This installation requires two fluid applications of the membrane, which minimizes pinholing and thin spots in the membrane. Cold-applied liquid membranes are typically installed at a minimum 1.5-mm (60-mil) thickness over a concrete substrate by spray, squeegee, roller, or brush per guidelines by the membrane manufacturer.

ASTM C 836, Standard Specification for High Solids Content, Cold Liquid-applied Elastomeric Waterproofing Membrane for Use with Separate Wearing Course, is a performance specification describing the required properties and test methods for cold-applied, elastomeric-type waterproofing membranes for both one- and two-component systems. Common types of cold fluid membranes include polymer-modified asphalt, asphalt-modified polyether, and single- and two-component polyurethanes.

The advantage of adhered membrane systems is the decreased potential for leaks to migrate under the membrane. The disadvantage is the need for meticulous surface preparation of the substrate, which must be dry, with a lightly broomed texture, and contamination free––including free of the initial waterproofing membrane. Liquid-applied membranes should never be used to fill or level substrate surface irregularities. Moisture is the adversary of these systems. Moisture in the substrate can cause pinholing, blistering, and entrained air bubbles in the membrane. Unsuitable curing agents, form release agents, and other contamination (e.g. dust) can inhibit adhesion. Some manufacturers claim these products are sufficiently elastic to bridge cracks, but typically this requires additional strips of reinforcing material.

The objective with a fluid-applied membrane is to achieve a good bond to the substrate without blistering or pinholes. To that end, a simple patch test (i.e. applying the waterproofing membrane to a small area) may provide the best site-specific results. In the case of hot fluid-applied membranes, this may be the most practical method. However, for chemical and moisture-curing membranes that take longer to set, this may not provide a practical solution for evaluating substrate moisture conditions.

Modified bitumen and bentonite sheets
Another material used for plaza decks is modified bitumen (mod-bit) sheets, often called ‘peel-and-stick’ or ‘rubberized asphalt.’ These are made of asphalt modified with polymers and a high-density polyethylene (HDPE) film backing. The sheets can be applied as a single-ply or multi-ply waterproofing system. When installed as a multi-ply, the overlying membrane course is typically oriented perpendicular to the prior course to maintain seam separation; but no matter the installation, the sheet lap orientation should consider the drainage slope so the membrane laps shed water.

Rainwater remaining on the waterproofing membrane indicates inadequate slope to the current deck drain position. An additional drain located in the low area should be installed to provide complete drainage.[12]
Rainwater remaining on the waterproofing membrane indicates inadequate slope to the current deck drain position. An additional drain located in the low area should be installed to provide complete drainage.

Modified bitumen sheets require a substrate primer and are fully adhered to the concrete substrate. They are sensitive to site conditions, moisture, and deck surface quality, and must be protected from ultraviolet (UV) exposure within a few weeks of installation. These sheets are generally not as preferred for a plaza deck application as fluid-applied or welded-single-ply due to the potential for leaking at membrane overlaps.

There are several sheet membrane composites made of sodium bentonite and a polyethylene liner. The sheet is installed with the bentonite side down directly against the concrete deck with the polyethylene liner facing up and sealed with seam tape. These sheets address the potential for leaking at the membrane overlaps by the bentonite activating and stopping the water ingress. Bentonite composite sheets require full confinement from the wearing course assembly and, therefore, should not be used with paver-on-pedestal systems.

Single-ply thermoplastic systems
Single-ply thermoplastic systems are another good choice for plaza deck waterproofing. General types include polyvinyl chloride (PVC), ethylene propylene diene monomer (EPDM), and butyl rubber membranes. Butyl rubber sheets have an advantage over EPDM sheets because of their lower moisture absorption––a property more important for a waterproofing membrane than EPDM’s greater resistance to UV exposure. PVC sheets are typically reinforced and offer high puncture resistance combined with fused, heat-welded seams. PVC sheets are either loose-laid or fully adhered to the substrate. When loose-laid, they can be compartmentalized by first adhering a grid strip to the concrete substrate and then welding the sheet to the grid. Typical grid size is 3 m (10 ft) square. The advantage of the grid system is it acts like a waterstop that limits water migration under the loose sheet if a leak occurs. The disadvantage is it is expensive and requires additional substrate preparation.

In lieu of a grid, there are PVC membrane composites with a separate polymer layer that also prohibits water migration if the vinyl sheet is damaged. These membranes are installed with the polymer layer directly against the substrate to react and stop water ingress if water circumvents the welded thermoplastic sheet. In this orientation, the polymer layer also functions as a separator sheet with regard to substrate surface contamination (which allows less substrate preparation) and functions as a protective cushion for the thermoplastic sheet against any puncture from an irregular substrate texture.

Three-dimensional prefabricated drainage composites can provide high compression strength and engineered drainage flow.[13]
Three-dimensional prefabricated drainage composites can provide high compression strength and engineered drainage flow.

Like a fluid-applied membrane, the installation of a fully adhered thermoplastic membrane requires substantial substrate preparation. Typically, loose-laid single-ply systems are a good choice for areas where there are sensitivities to odours, volatile organic compounds (VOCs), and fumes generated during installation of chemically cured or hot-applied systems. A big advantage of PVC and EPDM single-ply systems is either the membrane or an accessory sheet can be used as an exposed flashing if required in the restoration design.

Multi-membrane system
The ultimate restoration of plaza waterproofing may include more than one membrane system to provide redundancy barrier performance. For example, restoration of the waterproofing may include a loose-laid and seam-welded PVC thermoplastic membrane installed overlaying a fully adhered fluid-applied membrane. Additionally, there are PVC membranes with a hydrophilic polymer layer that provides self-sealing properties for even yet a third functional layer of stopping water ingress. This polymer layer also provides a separation between the PVC and any asphalt materials for material compatibility.

Multi-membrane installations provide performance features and advantages not available in a single system. The designer must verify the materials are compatible with each other and surrounding building components. Finally, if a multi-membrane system is chosen, it is best to have both membranes provided by the same manufacturer for a single-source warranty.

Protection course
A protection course over the plaza deck waterproofing membrane should be installed immediately after the membrane and quality assurance testing (i.e. flood-testing or low-voltage mapping) is completed. If the protection course installation is delayed, damage to the waterproofing membrane can occur during subsequent construction operations.

A membrane is worthless after it is damaged. That is why it is important to inspect the membrane to ensure the protection board is installed immediately after the testing is completed. If the membrane fails the testing, the protection course should not be installed until the membrane is repaired and retested.

Multi-layer membrane installation can be designed to provide redundancy performance. This membrane combination consists of a loose-laid welded thermoplastic membrane system installed directly over a reinforced hot-applied rubberized asphalt membrane fully adhered to the deck.[14]
Multi-layer membrane installation can be designed to provide redundancy performance. This membrane combination consists of a loose-laid welded thermoplastic membrane system installed directly over a reinforced hot-applied rubberized asphalt membrane fully adhered to the deck.

Installation challenges
One of the most common challenges in restoring the waterproofing on a plaza deck is the height limitation of existing flashings and penetrations. Typically, drainage for adjacent curtain walls, masonry wall weep holes, doors, and other penetrations are located at or within a few inches of the existing structural deck surface. This will make it difficult to modify the plaza assembly to provide subsurface drainage or tapered topping slabs. Facing such a dilemma, the designer may have to ‘compromise’ and reduce the slope of a tapered topping slab to maintain existing flashing heights or door levels.

On many retrofit projects, the challenge is not simply the flashing heights, but actually access to the existing conditions. Many plaza decks connect to adjacent curtain wall or cladding systems with precast panels or stone. Typically, these building components were put in place after the original waterproofing system’s installation. Therefore, in many instances, these existing building components will have to be removed to accommodate the installation and proper detailing of the new waterproofing system. One should not interrupt the waterproofing system to accommodate architectural elements. Instead, one should specify and install the waterproofing to be a continuous course under and behind these elements to provide proper restoration of the flashings and terminations.

In many cases, the existing concrete structural slab will require repairs. Depending on the conditions, these can take from a few days to several weeks to implement surface preparation using shot-blasting or similar methods.

When mechanical means are used to perform surface preparation, care should be exercised to avoid over-roughening the substrate, as irregular texture in the substrate can result in undesirable membrane thickness variations. After surface preparation, it may take many more days for the deck to properly cure before the new membrane can be installed. If the new waterproofing membrane is fully adhered, then moisture release issues from the newly repaired areas should also be considered. In some instances, the entire surface will have to be ground or scarified to remove the existing system. This is typically a time-consuming and expensive process that does not allow removal and installation of new membrane in the same day.

Moisture in concrete decks can result in pinholes through a fluid-applied membrane. Therefore, before membrane application, one should verify the deck is dry.[15]
Moisture in concrete decks can result in pinholes through a fluid-applied membrane. Therefore, before membrane application, one should verify the deck is dry.

Waterproofing the planters on the plaza should be a separate specification and work item. One should specify an engineered expansion joint material to provide a watertight seal at all expansion joints. Reliance on waterproofing membranes to provide a seal at the joints is risky and should be avoided. Waterproofing membrane can be installed to the expansion joint sealant’s exterior side to provide membrane continuity and possibly enhance the seal. It is good practice to elevate the expansion joint cross-section above the primary deck plane by means of concrete curbing and to design deck slope that drains the water without it passing over the expansion joint.

In addition to these issues, contractors and designers must consider logistical problems associated with rehabilitating plaza decks at occupied buildings. Every project has its own set of logistical and access issues ranging from surface preparation to temporary weather protection to environmental issues.

Quality assurance
A pre-installation meeting for the waterproofing work should be scheduled before the work proceeds. The architect, owner (or representative), inspector, manufacturer’s representatives, and general contractor should attend this meeting, along with subcontractors for waterproofing, concrete, backfill, formwork, and excavating.

The owner should also be required to retain an independent inspector for full-time monitoring with daily submission of reports on work completed with the location noted on drawings, photographs, and weather information.

Further, one should insist the waterproofing subcontractor be an approved applicator of the waterproofing system manufacturer to comply with warranty guidelines. One should have the contractor submit applicator certification at the time of bid. This timely certification requirement is to deter the general contractor from accepting a low bid from a non-approved installer that may not have any experience installing the specified system.

A best practice is to have all mechanical penetrations and drains installed in final set placement before the waterproofing application. However, if this sequencing cannot be achieved, the mechanical and electrical subcontractors are required to notify the waterproofing contractor, in writing, where the waterproofing has been breached or damaged during their work so the system can be repaired before backfilling or topping material placement.

Overlap seams of this PVC membrane are fused together with conventional hot-air welding to form a seamless water barrier. Insulation and the concrete wearing course were then installed over top.[16]
Overlap seams of this PVC membrane are fused together with conventional hot-air welding to form a seamless water barrier. Insulation and the concrete wearing course were then installed over top.

On completing the plaza deck waterproofing, the membrane system should be tested for leaks before the topping wearing course being installed. This can be achieved by means of electronic low-voltage mapping (ELVM). The former uses water as an electrically conductive medium that can quickly and accurately detect the point of water ingress. Unlike conventional water flood testing, ELVM can indicate breeches in the waterproofing system that are not actual active leaks, but instead breaches that could develop into active leaks during the structure’s life. A limitation of ELVM is that not all waterproofing materials are compatible with the test method due to electrical resistance properties, so one must consider the suitability of ELVM with the specified waterproofing materials.

Specifications should clearly communicate requirements under which all individual materials or systems are properly transitioned into adjacent construction or building envelope systems. Further, quality specifications should include termination requirements for each individual system or component, especially at building envelope material transitions. Project specifications must detail these requirements rather than leave the design to the discretion of contractor shop drawing submittals that may address terminations at material transitions by noting ‘work by others.’ However, proper waterproofing selection and a comprehensive specification with details provided by the specifier is an important part of ensuring waterproofing success.

Conclusion
The designer is faced with many challenges when rehabilitating an existing plaza deck. Premature deterioration and subsequent restoration of many plaza decks can be avoided with proper drainage and a waterproofing system. One should design the plaza with a proper drainage slope at both the wearing course and subsurface at the waterproofing membrane level, and provide enough drains with hardware not prone to clogging.

The design team should be wary of value engineering (VE) the waterproofing system––simply put, the amount saved by using an inferior waterproofing system can quickly evaporate and turn into enormous expenses when repairs are required. Yet, it is prudent the design team research, select, and specify a waterproofing system that meets the owner’s performance and cost expectations suitable with the site conditions and project construction.

Stacy Byrd, LEED AP, is the national products manager at CETCO and has 20 years of experience in waterproofing application design and fieldwork. He is a member of ASTM International Committee D 08 on Roofing and Waterproofing. Byrd can be reached via e-mail at stacy.byrd@cetco.com.

Endnotes:
  1. [Image]: http://www.constructioncanada.net/wp-content/uploads/2016/01/P5110078c.jpg
  2. [Image]: http://www.constructioncanada.net/wp-content/uploads/2016/01/031010-007.jpg
  3. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/042210-010.jpg
  4. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/Poor-Deck-Drain-Placement-next-to-Wall-Flashing.jpg
  5. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/IMG_1355.jpg
  6. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/Ardmore-Deck-003.jpg
  7. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/IMG_1343.jpg
  8. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/PA070603.jpg
  9. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/20090625-WO4T0073.jpg
  10. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/PA060522.jpg
  11. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/09.jpg
  12. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/PA080667.jpg
  13. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/DSCN2027.jpg
  14. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/DSCN2039.jpg
  15. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/Cold-Applied-Vapor-Bubbles.jpg
  16. [Image]: http://www.constructioncanada.net/wp-content/uploads/2012/01/P5110086.jpg

Source URL: https://www.constructioncanada.net/plaza-deck-restoration-principles-of-drainage-and-waterproofing/