How to Write a Mosaic Tile Specification: CSI Division 09

Category: Specification & Documentation
Published by: MosaicPeel Technical Team
Last Updated: 2026
Reviewed by: MosaicPeel Product Engineering & Quality Control Department

Quick answer for specifiers: A mosaic tile specification fails when it names a product but not a test method, a tolerance without a measurement protocol, or a sample without an acceptance rule. Write it in three parts, put every performance claim next to the method that proves it, and state what happens when a lot does not match the approved sample. Our sample approval workflow covers what happens after the section is written; this page covers how to write it.

Introduction: Why a Mosaic Tile Specification Decides the Outcome
Where Mosaic Tile Sits in MasterFormat and Division 09
The Three-Part Structure Every Mosaic Tile Spec Section Uses
Performance or Prescriptive: Which Mosaic Tile Spec Type Fits
What to Write in Part 2 About the Mosaic Tile Unit
Sheet Format, Backing and Dimensional Declarations
Setting Materials, Grout and Movement Joints
Tolerances, Substrate and Verifiable Workmanship
Submittals, Samples and Mock-Ups in a Mosaic Tile Spec
Common Defects in Mosaic Tile Specifications
A Mosaic Tile Specification Writing Framework
Conclusion: Write the Section You Would Want to Be Held To
Frequently Asked Questions

1. Introduction: Why a Mosaic Tile Specification Decides the Outcome

A mosaic tile specification is the only document that turns a design intent into something a factory can quote and an installer can be measured against. Drawings show where tile goes. The section says what the tile has to be.

Most mosaic problems trace back to a thin section. A sheet is rejected at goods receipt because nobody wrote an acceptance rule. Two lots read differently because shade control was never specified. A floor fails because the slip value was quoted without the method that produced it. Each of those is a writing failure, not a manufacturing one.

Mosaic needs more words than field tile. A sheet is an assembly of units, a backing, a joint pattern and a mounting adhesive, so one product line can satisfy a thickness clause and still fail a finished-plane clause.

What the section controls	What fails when it is missing
Product identity	Substitution with a lookalike
Performance with method	Unverifiable marketing numbers
Tolerance with protocol	Disputes that neither side can settle
Sample and lot rules	Shade drift between deliveries
Submittal list	Approvals that arrive too late to matter

2. Where Mosaic Tile Sits in MasterFormat and Division 09

Mosaic tile belongs in Division 09, the finishes division, alongside other tiling and flooring work. Within that division it sits with ceramic and stone tiling rather than with resilient or wood flooring, because the assembly shares setting materials, movement joints and substrate preparation.

Do not assume the numbering system on one project matches the next. Owners and large operators often run a master guide specification with their own numbering. Confirm the applicable system before drafting, then keep the section self-contained enough to survive being renumbered.

Division	What it covers	Mosaic relationship
09 Finishes	Tiling, flooring, ceilings	Primary home for mosaic tile
07 Thermal and moisture	Waterproofing, membranes	Referenced, not duplicated
22 Plumbing	Fixtures, drains	Interfaces at wet areas
03 Concrete	Slabs, toppings	Substrate and flatness source
06 Wood, plastics	Backer units, trim	Interface at transitions

Mosaic Tile in the Division 09 Numbering System

Within tiling, sections are typically split by tile type and by installation method. Mosaic usually appears as a distinct subsection because the mounting system and sheet format are product attributes rather than installation choices. Keep it distinct even when the project also uses field tile.

How Mosaic Tile Differs From Field Tile in a Spec Section

Field tile is specified per unit. Mosaic is specified per sheet and per lot. That single difference changes what the clauses have to say: unit size becomes sheet size, unit tolerance becomes sheet tolerance plus inter-sheet spread, and unit shade becomes lot shade plus sheet-to-sheet drift.

Attribute	Field tile clause	Mosaic tile clause
Unit of measure	Piece	Sheet
Tolerance	Piece deviation	Piece plus sheet plus lot
Color control	Shade range	Shade range plus lot identity
Setting	Individual placement	Sheet placement and alignment
Cutting	Per piece	Per sheet and per unit

3. The Three-Part Structure Every Mosaic Tile Spec Section Uses

Construction specifications follow a three-part structure: General, Products, Execution. It persists because it maps to how a project is actually administered, procured and inspected.

Part 1 General: Mosaic Tile Scope and Administrative Controls

Part 1 carries scope, related sections, references, submittals, quality assurance, delivery and storage, and warranty. It is where you say which standards apply and which documents the contractor must produce before work starts.

Part 2 Products: Mosaic Tile Materials and Performance

Part 2 describes the tile, the backing, and the setting and grouting materials. Every performance statement belongs next to the test method that produces it. This is the part that decides whether two suppliers are quoting the same thing.

Part 3 Execution: Mosaic Tile Installation Requirements

Part 3 covers substrate preparation, layout, setting, grouting, movement joints, cleaning and protection. It should reference the installation method rather than restate it, and it must name the acceptance criteria.

Part	Answers	Common omission
1 General	What is required, and what paperwork	Submittal deadlines
2 Products	What is being bought	Test method beside each value
3 Execution	How it is installed and judged	Measurement protocol for tolerances

Sections usually cross-reference rather than restate. The aim is one authoritative location for each requirement, because two conflicting clauses are worse than one thin one.

Requirement	Best placed in	Cross-reference from
Membrane type	07 or tiling section	Whichever does not own it
Substrate flatness	Tiling section	Concrete or framing section
Drain integration	Plumbing section	Tiling section
Movement joint layout	Tiling section	Structural and design drawings

4. Performance or Prescriptive: Which Mosaic Tile Spec Type Fits

There are four specification types: performance, prescriptive, proprietary and proprietary with equals. Mosaic projects usually mix them, and the choice determines who carries the risk when something fails.

When a Mosaic Tile Performance Specification Works Best

A performance spec states the outcome and leaves the means open. It works when the requirement is genuinely measurable and the buying organization has the capability to verify it. Absorption, abrasion class and breaking strength are all writable as performance requirements, provided the method is named.

When a Mosaic Tile Prescriptive Specification Is Safer

A prescriptive spec states the material, the composition and the construction. It is safer where appearance, color or a particular finish is contractual, and where the site cannot run verification testing. Marble and other natural stone are usually written prescriptively because variation is inherent.

Mosaic Tile Proprietary Specs and the Basis-of-Design Trap

Naming one product as basis-of-design is legitimate. Naming it and then forbidding equals is not, on most public work. Write the basis-of-design product, then write the performance criteria any equal must meet, or the substitution request becomes a negotiation with no yardstick.

Spec type	Risk bearer	Best used for
Performance	Supplier	Measurable physical properties
Prescriptive	Specifier	Appearance-critical or variable materials
Proprietary with equals	Shared	Design intent plus competition
Closed proprietary	Specifier	Matching existing work only

The same requirement reads very differently depending on type. Writing both columns during review is a fast way to catch a clause that sounds firm but cannot be enforced.

Requirement	Prescriptive wording	Performance wording
Body	Porcelain, unglazed	Absorption class plus method
Finish	Matte glazed	Abrasion class plus traffic zone
Strength	Stated value plus method	Minimum value plus method
Color	Approved reference sample	Shade range plus lot identity

5. What to Write in Part 2 About the Mosaic Tile Unit

Part 2 is where most mosaic sections are either too thin or too vague. Four declarations do the heavy lifting: material family, absorption, abrasion, and strength.

Mosaic Tile Material Family and Body Declaration

Name the body type and the finish, not just the trade name. Glass, porcelain, ceramic and natural stone each have their own method families, and a requirement written for one is meaningless when applied to another. Our ceramic vs porcelain body comparison explains why the body changes the clause.

Mosaic Tile Absorption Class and Test Method

Water absorption is measured under ASTM C373; the classes used to group tile in procurement follow from that result. Write the class and the method together, because a number quoted without a method cannot be checked. Confirm against the supplier’s current test report.

Declaration	What to require	Why method matters
Absorption	Class plus test method	Method changes the result
Body type	Family and finish	Families use different methods
Finish	Glazed or unglazed	Changes abrasion and cleaning
Origin	Plant and lot identity	Enables traceability

Finish deserves its own line. A glazed and an unglazed unit from the same body behave differently under abrasion, cleaning and chemical exposure, so a finish clause that says only “as selected” leaves the supplier guessing.

Finish	Spec implication	Watch for
Glossy glazed	Abrasion class governs	Shows wear and scratching
Matte glazed	Cleaning method matters	Haze retention
Unglazed	Absorption governs	Staining risk
Honed stone	Sealing required	Acid sensitivity

Mosaic Tile Abrasion Class and Surface Durability

Visible abrasion resistance for glazed tile is measured under ASTM C1027, and the classes used in specifications come from that method. Match the class to the traffic zone rather than specifying the same class everywhere. Confirm against the supplier’s current test report.

Mosaic Tile Breaking Strength and Structural Declarations

Breaking strength is measured under ASTM C648. It matters for mosaic mostly at floors, stair treads and any area receiving point loads. State the method and the sample basis, not just a value. Confirm against the supplier’s current test report.

6. Sheet Format, Backing and Dimensional Declarations

Mosaic is bought by the sheet, so the sheet is what the specification has to describe. Three sub-clauses cover it.

Mosaic Tile Sheet Size and Joint Width Declaration

State nominal sheet size, nominal unit size, joint width, and whether joints are grouted at the factory or on site. Sheet size drives layout and waste; joint width drives the finished look and the grout volume.

Declaration	Drives	Typical conflict
Sheet size	Layout and waste	Sheet does not fit setout
Unit size	Visual scale	Substituted lookalike
Joint width	Appearance and grout volume	Factory vs site grouting
Sheet squareness	Cutting and alignment	Drift across large areas

Mosaic Tile Backing System and Sheet Mounting

Name the backing: mesh, paper-faced or dot-mounted. Each behaves differently in cutting, setting and wet areas. The backing system comparison covers the trade-offs.

Backing	Strength	Limitation
Mesh-backed	Flexible, good on curves	Can telegraph through grout
Paper-faced	Flat, clean face	Requires soaking and removal
Dot-mounted	Precise spacing	Adhesive dots affect bedding

Mosaic Tile Thickness and Dimensional Tolerance

Write nominal thickness, permitted piece deviation, permitted spread within a sheet, and permitted spread between sheets. Our thickness and dimensional tolerance guide sets out why spread matters more than nominal.

7. Setting Materials, Grout and Movement Joints

Setting and grouting materials can live inside the tiling section or be cross-referenced. Either is defensible; the failure mode is writing them in two places with conflicting requirements.

Decision	Keep in tiling section	Cross-reference out
Adhesive class	When tile-specific	When shared with other trades
Grout type	Almost always	Rarely
Membrane	Only if tile-scoped	Usually to 07
Sealant color	Always	Never

Whichever route is chosen, name the standard the material must meet rather than a brand. Brand-level clauses prevent substitution but also prevent competition, which matters on volume work.

Mosaic Tile Adhesive and Mortar Requirements

Name the binder by performance class and by compatibility with the tile body and the substrate. Low-absorption bodies need a different bond strategy than absorbent ones. See the adhesive and mortar selection guide.

Mosaic Tile Grout Specification and Joint Treatment

Choose grout by exposure, not by habit. Cementitious grout suits most interiors; epoxy suits high-chemical or high-cleaning-frequency areas. The epoxy vs cement grout comparison covers selection, and the chemical resistance guide covers aggressive environments.

Mosaic Tile Movement Joint Requirements

Movement joints are a design responsibility, not an installer preference. Specify location, width, and sealant type. The movement joint guide explains the positioning rules.

Material clause	Must state	Often omitted
Adhesive	Class and substrate compatibility	Open time and coverage
Grout	Type and color source	Cure and cleaning window
Sealant	Type and movement capability	Backer rod and depth
Membrane	Type and compatibility	Integration at drains

8. Tolerances, Substrate and Verifiable Workmanship

A tolerance without a measurement protocol is unenforceable. Every tolerance clause needs an instrument, a sample size and a ruling on borderline readings.

Protocol element	What to state	Why it matters
Instrument	Named tool	Removes method argument
Sample size	Number of readings	Defines statistical weight
Location	Where readings are taken	Prevents cherry-picking
Remedy	Action on failure	Avoids stalled handover

Mosaic Tile Substrate Flatness and Acceptance Tolerances

Name the substrate, the flatness expectation, and who verifies it before setting begins. Mosaic is thin and follows the substrate closely, so substrate defects read through.

Mosaic Tile Lippage and Finished Surface Tolerances

State the permitted lippage and how it is measured. Because sheets carry many small units, a straightedge reading across several units is more representative than a point reading. See the lippage and flatness guide.

Mosaic Tile Shade and Lot Control Clauses

Require one lot per contiguous area, declare the acceptable shade range by reference to an approved sample, and require attic stock from the same lot. The shade variation guide details lot control.

Clause	Instrument	Acceptance rule
Flatness	Straightedge	Reading taken before setting
Lippage	Straightedge and gauge	Across multiple units
Shade	Approved reference panel	Under site lighting
Bond coverage	Pull-off or lift check	At defined intervals

9. Submittals, Samples and Mock-Ups in a Mosaic Tile Spec

Submittals are how a specification gets enforced. Write them as a dated list with a review period, not as a general obligation.

Mosaic Tile Submittal Package Contents

Require product data, test reports with method names, shop drawings showing layout and joint pattern, samples, and maintenance instructions. Ask for the test report to name the issuing laboratory and date.

Mosaic Tile Sample Approval and Reference Panels

Require a production sample from the actual lot, not a showroom chip. Keep a signed reference panel on site as the acceptance benchmark. The sample library guide covers presentation formats.

Mosaic Tile Mock-Up and Field Panel Requirements

A mock-up settles layout, joint treatment, transitions and workmanship before bulk installation. Require its approval before the first production sheet is set. See the mock-up guide.

Mock-up element	Purpose	Who approves
Layout and setout	Confirms pattern and cuts	Designer
Joint treatment	Fixes grout color and profile	Designer
Transitions and trim	Settles edge conditions	Designer and contractor
Lighting review	Confirms shade acceptance	Owner representative

Submittal	Timing	Purpose
Product data and reports	Before procurement	Verifies declared performance
Shop drawings	Before layout	Confirms pattern and cuts
Samples	Before ordering	Fixes appearance
Mock-up	Before bulk setting	Fixes workmanship standards
Closeout documents	At handover	Supports warranty

10. Common Defects in Mosaic Tile Specifications

Three defects account for most disputes. All three are cheap to fix at writing time and expensive to fix later.

Mosaic Tile Spec Defect 1: Performance Without a Test Method

A value with no method is an opinion. Pair every number with the standard that generates it, and require the report to say so.

Mosaic Tile Spec Defect 2: No Lot or Batch Control

Without a lot clause, a supplier can legitimately deliver a different production run. Require lot declaration per delivery and matching attic stock.

Mosaic Tile Spec Defect 3: Tolerances With No Measurement Protocol

State the instrument, the number of readings, the locations, and how a failed reading is handled. Otherwise acceptance becomes a negotiation at the worst possible moment.

Defect	Symptom	Fix in the section
No method	Quote cannot be compared	Name the standard
No lot control	Shade drift mid-project	Lot per area clause
No protocol	Endless argument at handover	Instrument and sample size
No sample rule	Subjective rejection	Signed reference panel

11. A Mosaic Tile Specification Writing Framework

Work through the section in a fixed order. Skipping step three is where most specifications go wrong.

Step	Action	Output
1	Confirm numbering system	Correct section number
2	Define scope and interfaces	Part 1 draft
3	List every performance claim	Method pairing table
4	Write product clauses	Part 2 draft
5	Write tolerances with protocols	Verifiable criteria
6	Define submittals and samples	Dated list
7	Set acceptance and remedies	Closeout clause

Mosaic Tile Specification Review Checklist

Before issuing, confirm that every performance value names a method, every tolerance names an instrument, every sample has an acceptance rule, and every lot has an identity. Our handover checklist shows how the section is used at the end of the job, and the warranty and claims guide explains what happens when it is not.

Review question	Pass condition
Is every value paired with a method?	Yes, in Part 2
Is every tolerance measurable on site?	Yes, instrument named
Is lot identity required per delivery?	Yes, in Part 1
Is there a signed reference sample?	Yes, before ordering
Is the remedy for nonconformance written?	Yes, in Part 3

12. Conclusion: Write the Section You Would Want to Be Held To

A good mosaic tile specification is boring on purpose. It names the product, pairs every claim with a method, states tolerances that can be measured on site, and says what happens when a delivery does not match.

Write it as if you will have to argue from it in six months, because on a large project you probably will. The importer buying guide and the quality certification checklist extend this into procurement. For project-specific help, contact the team through the specifier enquiry page.

13. Frequently Asked Questions

What CSI division is mosaic tile specified under?

Mosaic tile is specified under Division 09, the finishes division, alongside ceramic and stone tiling. Within the tiling group it usually appears as its own subsection because sheet format and mounting system are product attributes rather than installation choices. Confirm the numbering system with the project’s master guide specification before drafting, since large owners often run their own.

Should a mosaic tile specification be performance-based or prescriptive?

Use performance clauses for measurable physical properties such as absorption, abrasion class and breaking strength, and prescriptive clauses where appearance or inherent variation is contractual. Natural stone is usually written prescriptively. Most mosaic sections mix both, with the performance clauses carrying the verification burden.

What test methods should a mosaic tile specification reference?

At minimum, reference a method for water absorption, visible abrasion resistance and breaking strength, and name the method next to each declared value. A number without a method cannot be verified against a competing quote. Confirm against the supplier’s current test report.

How do you specify mosaic tile sheet size and joint width?

State nominal sheet size, nominal unit size, joint width and whether joints are grouted at the factory or on site. Sheet size drives layout and waste, while joint width drives the finished appearance and grout volume. Keep these as separate clauses so a change to one does not silently alter the other.

What tolerances belong in a mosaic tile specification?

Include substrate flatness, permitted lippage, thickness spread within and between sheets, and the acceptable shade range. Every tolerance needs an instrument, a sample size and a reading location. Without those three, acceptance turns into a negotiation at handover rather than a measurement.

Do I need a mock-up clause for mosaic tile?

Yes. A mock-up settles layout, joint treatment, transitions and workmanship before bulk installation starts, and it becomes the reference the finished work is judged against. Require written approval of the mock-up before the first production sheet is set, and keep it standing until closeout.

How should mosaic tile lot and shade control be written into the spec?

Require one production lot per contiguous area, a signed reference sample from that lot, shade acceptance judged against the reference under site lighting, and attic stock drawn from the same lot. Also require the lot identity to be declared on each delivery so drift can be caught early.

What submittals should a mosaic tile specification require?

Require product data, test reports that name the issuing laboratory and method, shop drawings showing layout and joint pattern, production samples from the actual lot, a mock-up, and closeout documents. Attach a review period and a deadline to each item so approvals arrive before they are needed.

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