The specification document occupies a peculiar position in the design process. It is written after the creative decisions have been made but before any material has been mixed or applied. It must describe, with precision and without ambiguity, a surface that exists only in the designer's imagination. And it must do so in language that can be interpreted consistently by contractors, applicators, and project managers who may not share the designer's aesthetic vocabulary.
What a Specification Must Address
A complete coating specification for cementitious architectural finishes should address seven essential domains: substrate requirements, material selection, application methodology, environmental constraints, quality standards, protection protocols, and warranty terms.
Each domain requires specific, measurable criteria rather than subjective language. "The surface shall be smooth" is not a specification — it is a wish. "The surface shall achieve a Profile Class 2 per ICRI CSP guidelines, with maximum peak-to-valley variation of 0.5mm over any 300mm span" is a specification that can be measured, verified, and enforced.
Substrate Requirements
The specification must define acceptable substrate conditions at the time of coating application. These conditions are measurable and non-negotiable:
- Concrete cure age: Minimum twenty-eight days from date of pour
- Moisture content: Less than ten percent by mass (calcium chloride method) or less than seventy-five percent internal relative humidity (in-situ probe method)
- Surface pH: Between 7 and 10, measured by pH indicator solution
- Surface tensile strength: Minimum 1.5 N/mm² (pull-off adhesion test)
- Contaminants: Surface must be free of laitance, curing compounds, form oils, paint, and efflorescence
- Profile: ICRI CSP 2 to CSP 4, achieved by diamond grinding or mechanical preparation
These criteria should be specified as hold-point inspections — stages at which work must stop and the substrate must be formally accepted before coating application proceeds.
Material Specification
The coating material should be specified by performance criteria rather than brand name alone. This approach — known as performance-based specification — allows competitive sourcing while ensuring that the selected product meets the design requirements.
Key performance criteria include compressive strength, flexural strength, adhesion to substrate, abrasion resistance (Taber test), water absorption, fire classification, and VOC content. These values should be drawn from the manufacturer's published technical data sheet and, where possible, verified by independent third-party test certificates.
A specification that names only a brand without defining performance requirements is not a specification — it is a procurement instruction. True specifications define what the material must do, not merely what it is called.
Application Methodology
The specification should define the complete application sequence — from surface preparation through to final topcoat — with coverage rates, minimum and maximum film thicknesses, inter-coat intervals, and acceptable ambient conditions for each layer. It should specify the tools and techniques permitted (steel trowel, roller, spray), the mixing equipment and ratios, and the maximum batch size.
Particular attention should be given to textured finishes, where the specification must communicate the desired aesthetic through sample panels. The specification should require the applicator to prepare reference panels — typically one square metre minimum — for designer approval before proceeding to full-scale application. These panels become the project benchmark against which all subsequent work is assessed.
Environmental Constraints
The specification must define acceptable environmental conditions during application: minimum and maximum ambient temperature, maximum relative humidity, minimum substrate temperature above dew point, and maximum wind speed for exterior application. These constraints should be monitored and documented throughout the application process, with clear protocols for suspending work when conditions fall outside acceptable limits.
Quality Assurance and Acceptance
The specification should define the criteria by which the completed work will be assessed and accepted. For cementitious coatings, these typically include:
- Adhesion: Minimum 1.0 N/mm² (pull-off test per ISO 4624)
- Visual uniformity: Consistent colour and texture when viewed from a distance of two metres under diffused natural light
- Surface defects: No blistering, delamination, cracking, or efflorescence visible under normal viewing conditions
- Film thickness: Within the specified range, verified by non-destructive measurement
The viewing conditions for visual inspection should be defined — viewing distance, light source, and angle — to prevent disputes arising from unreasonable inspection standards. A surface that appears flawless at two metres but shows trowel marks under raking light at thirty centimetres has not failed; the inspection criteria have been misapplied.
The Specification as Protection
A thorough specification protects every party in the construction process. It protects the designer by ensuring that the finished surface matches the design intent. It protects the client by establishing measurable quality standards that can be verified. It protects the applicator by defining achievable standards and documenting the conditions under which the work was performed. And it protects the material manufacturer by ensuring that their product is applied in accordance with their published guidelines.
The time invested in writing a complete, precise, and enforceable specification is repaid many times over in the clarity, quality, and accountability it brings to the project.