WPB (WATER PENETRATION BARRIER)
EIF RAINSCREEN SYSTEM


Description
"Preswitt WPB EIF Rainscreen System" is a cladding system composed of the following key components:

  • A specific substrate
  • A water penetration barrier coating
  • An adhesive coating
  • An insulation board
  • A synthetic coating system

These systems may be assembled in panels under factory-controlled conditions, or field-applied.

The following is a detailed description of "Preswitt WPB EIF Rainscreen System" and its different components.


Figure1. Example of "Preswitt WPB EIF Rainscreen System" Installation

Substrate
The substrate could be brick, masonry, monolithic concrete walls, cementitious panels and/or glass-mat-surfaced gypsum sheathing board. Gaps between sheathing boards shall not exceed 1.5mm. Joints in the sheathing shall be sealed with Preswitt Basecoat and Reinforcing Mesh.

Water Penetration Barrier (WPB) Coating
Note: The water penetration barrier is a coating installed continuously over the substrate and around penetrations and openings to provide, along with other built-in features, the second line of defence against water infiltration reaching the structure.

"Preswitt WPB EIF Rainscreen System" is a weather resistant, polymer based, non-cementitious coating. This membrane acts as a primary water-resistant air barrier over the substrate prior to installing the EIFS. The coating is flexible and vapour permeable.

Adhesives
Note: The adhesives are products for bonding the insulation to the substrate coated with the WPB. They are available as a wet paste requiring the addition of cement on-site.

"Preswitt Adhesive Compound" is a polymer-based, wet-mix, adhesive and basecoat, supplied in 26 kg pails and mixed on-site with Type 10 Portland cement (1:1 cement by weight).

When used as an adhesive, "Preswitt Adhesive Compound" is applied in vertical ribbons 102mm wide x 10mm thick at 305mm on center onto the back of the insulation boards. The adhesive is applied with a stainless steel trowel.

When used as a basecoat, "Preswitt Adhesive Compound" is applied with a stainless steel trowel to the entire surface of the insulation to a uniform dry thickness of not less than 2mm. The basecoat thickness needs to be thicker when more than one layer of reinforcing mesh is incorporated into the lamina.

Insulation
"Preswitt Insulation Board" is an EPS board conforming to CAN/ULC-S701 and having a minimum density of 16kg/m3 and a flame-spread rating of less than 25. The expanded polystyrene-foam insulation boards are aged in ambient air for a minimum of five weeks or kiln-dried.

"Preswitt Insulation Board" is manufactured and packaged by a Preswitt-approved manufacturer/ moulder and shall conform to the following:

  • CAN/ULC-S701-97
  • Minimum board thickness of 19mm
  • Maximum board thickness
    - as designed, when used in combustible construction
    - 76mm (3 in.), when used in noncombustible construction
  • Maximum board size is 600mm x 1219mm
  • Average density of 16kg/m3
  • Flame-spread rating: Less than or equal to 25, per CAN/ULC-S102.2

Synthetic Coating System (Lamina) Over the Insulation
The synthetic coating system (lamina) consists of the basecoat embedding the reinforcing mesh and a finish coat. A primer is recommended in some instances to improve the finish application.

Basecoat
"Preswitt Adhesive Compound": As described in the section on adhesive, above.

Reinforcing Mesh
"Preswitt Mesh": An alkali-resistant, glass-fibre reinforcing fabric, having a minimum 200g/m2 nominal weight, used with the adhesive/basecoat and "Preswitt WPB Rainscreen System". The mesh is white in colour and is available in rolls 965mm wide. Starter mesh for rendering surface articulations and terminations is available in rolls that are 240mm wide.

The reinforcing mesh is available in different grades, represented in descending order of strength: Intermediate, minimum 200g/m2; and Heavy duty, minimum 480g/m2. Higher-grade meshes are intended to be used in areas requiring high impact resistance.

Primer
"Preswitt Acrylic Superbond": A water-based pigmented acrylic primer may be applied over the basecoat to provide a uniformly absorbent surface for "Preswitt Quality Finish".

Finish Coat
"Preswitt Quality Finish": A ready-mix 100% acrylic-based finish coat, supplied in a 26kg pail. It is factory tinted to the desired colour.

The finish coats provide a texture that is governed by the aggregate size as well as the trowel motion used to render the wall surface. The following represents the different textures offered: "Coarse" (2.0mm), "Medium" (1.5mm), and "Fine" (1.00mm).

Usage and Limitations

  • "Preswitt WPB EIF Rainscreen System" is intended for use as an exterior insulation wall cladding system, applied directly to vertical walls of masonry/concrete, cementitious panels to glass-mat gypsum sheathing over wood or steel framing.
  • The system is acceptable for use on new and existing exterior, vertical walls. The systems are not acceptable for use on horizontal or sloped surfaces.
  • In retrofit construction, the addition of low permeance materials over existing exterior walls may lead to the detrimental effects of moisture accumulation, as highlighted in Appendix Note A-9.25.12. of the NBC. As a result, existing exterior walls that are intended to be retrofitted with EIFS must meet the requirements of the NBC for heat transfer, air leakage and condensation control.
  • The possibility of moisture accumulation within the wall construction is mainly a function of the physical properties of the material being installed and its impact on the thermal, air leakage and vapour diffusion characteristics of the existing wall. Consequently, the potential for moisture accumulation resulting from the addition of materials is very specific to the existing wall construction being retrofitted.
  • "Preswitt WPB EIF Rainscreen System" can provide additional thermal resistance to the wall assembly, with no detrimental effects, if installed properly with the knowledge of the existing wall configuration and performance.
  • When used in new construction, the thickness of the EPS insulation of "Preswitt WPB EIF Rainscreen System" shall be in conformance with the requirements of Article 9.25.12. of NBC 1995.

Note: The air leakage and condensation control measures that need to be considered in the design of walls using Preswitt WPB EIF Rainscreen System" shall take into consideration the combination of the substrate and the "Preswitt Water Penetration Barrier" coating as if having an air leakage characteristics of less than 0.1 L/(s.m2) at 75 Pa and water vapour permeance less than 60ng/(Pa-s-m2)

  • Where permitted by the NBC through conformance to Article 3.1.5.5., "Preswitt WPB EIF Rainscreen System" is acceptable for use in the exposed face of buildings required to be of noncombustible construction, provided the interior surface of the wall assembly are protected by a thermal barrier conforming to Sentence 3.1.5.11.(3) of NBC 1995.
  • When used in noncombustible construction the polystyrene insulation shall be protected from the inside of the building in accordance with NBC 1995, Clause 3.1.5.11.(2)(e).
  • When used in noncombustible construction, the polystyrene insulation shall be protected from the inside of the building in accordance with NBC 1995, Articles 3.1.4.2. and 9.10.16.10.
  • "Preswitt WPB EIF Rainscreen System" is not intended for use as a below-grade insulation and should terminate at least 200mm above grade level.
  • The system should be kept at least 50mm, or as required in building regulations and safety codes, from heat-emitting devices, such as recessed light fixtures and chimneys.
  • The requirements of NBC 1995 regarding fire stops shall be maintained.
  • "Preswitt WPB EIF Rainscreen System" shall be designed to resist the wind load (Q10) for the specific geographical location in accordance with Part 4 of the NBC, by a professional engineer skilled in structural design and licensed to practice under the appropriate provincial or territorial legislation.
  • The polystyrene thermal insulation shall have a flame-spread rating of not more than 25 when tested in accordance with the requirements of CAN/ULC-S102.2-M88 and Sentence 3.1.12.1.(2) and Article 9.10.3.2. of the NBC.
  • The polystyrene thermal insulation shall be aged for a minimum of five weeks or kiln-dried before installation.
  • The polystyrene thermal insulation shall not be thicker than 75mm when used in buildings required to be on noncombustible construction.
  • The system alone may not provide the full amount of the required wall insulation. The thermal resistance of the wall system shall conform to the energy requirements of the applicable building code. The wall system may have to conform to the Model Energy Code of Canada for Buildings 1997 as a minimum to meet Canada Mortgage and Housing Corporation technical requirements.
  • Expansion joints must be carried through the exterior insulation. Movement joints are required to accommodate expansion and contraction of building materials due to thermal changes, moisture, wind, gravity, vibration and seismic activity. Expansion joint locations in the EIFS cladding shall be determined by a professional engineer/architect. The following situations, in particular, should be considered:

    - at expansion joints that occur in the substrate
    - at any abutment of the system with other materials
    - where there is a change in substrate
    - where structural movement is anticipated
    - where deflections that might be in excess of L/240 are expected
    - at floor levels in wood frame construction (may not be required when using engineered wood beams)

  • Closed cell backer rods should be used at expansion joints so that the low-modulus sealant may be installed as per sealant manufacturer's instructions.
  • "Preswitt WPB EIF Rainscreen System" must be installed according to Preswitt Manufactring Ltd. specifications and typical details, by applicators recognized by Preswitt Manufactring Ltd.
  • The top edges of the standard EPS panels in "Preswitt WPB EIF Rainscreen System" shall have a 13mm bevel cut to facilitate the direction of water flow to a proper drainage trough.
  • Starter strip insulation boards shall be used at the bottom of every EIFS section wall. Slots at the back of the insulation strips are sized on-site to allow for drainage.

Note: Installation of the starter strips is of primary importance to the performance of the system.

  • When "Preswitt EIF Rainscreen Barrier System" is part of a prefabricated panel system that incorporates structural components, the prefabricated panel system shall be designed by a professional engineer or architect in accordance with the manufacturer's criteria and the requirements of the NBC 1995.
  • "Preswitt WPB EIF Rainscreen System" is not suitable for use as a structural sheathing for bracing purposes.
  • Wet materials must be applied at temperatures above 40C for a period of not less than 24 hours. Cool and humid climatic conditions may extend the drying time beyond 24 hours. The substrate must be maintained at a temperature above 40C for a minimum of 24 hours. Materials must be stored at a temperature between 40C and 320C. Previously frozen materials must not be used.
  • Wet, finished surfaces must be protected from rain and wind-driven moisture until the materials have set and hardened. Wet plaster must be protected from uneven and excessive evaporation during dry weather and from strong blasts of air.
  • Cap flashing and sealant must be installed immediately after completion of the finish coat, or temporary protection must be provided.
  • Glass-mat gypsum sheathing must be in conformance with the requirements of ASTM C 1177 or have been evaluated by CCMC.
  • Specification and description of surface sealers must be furnished by the manufacturer.
  • A high level of quality control at all stages of application is imperative for obtaining an acceptable level of performance. Regular maintenance checks should be made at joints in the system. Accidental damage to the surface finish should be repaired immediately to prevent water ingress.
  • Each container and package of material used as part of "Preswitt WPB EIF Rainscreen System" shall be marked as follows:

    Water Penetration Barrier (WPB) Coating
    - manufacturer's name or trademark
    - product name
    - storage precautions, temperature range
    - application instructions and intended use
    - quantity of material

    Adhesive/Basecoat
    - manufacturer's name or trademark
    - product name
    - storage precautions, temperature range
    - application instructions and intended use
    - quantity of material
    - CCMC #12973-R

    Portland Cement
    - manufacturer's name or trademark
    - CSA standard A5, Portland Cement

    Insulation Board
    - manufacturer's name or trademark
    - type
    - CAN/ULC-S701-97
    - surface-burning characteristics

    Reinforcing Mesh
    - manufacturer's name or trademark
    - length and width
    - type

    Finish Coat
    - manufacturer's name or trademark
    - product name
    - storage precautions
    - application instructions
    - quantity of material
    - CCMC #12973-R

Testing of Preswitt WPB EIF Rainscreen System materials were conducted by laboratories recognized by CCMC.