ISO 23169:2020

Paints and varnishes - On-site test methods on quality assessment for interior wall coatings

This document specifies two on-site test methods (on-site cleanability [stain removal] and on-site wet-scrub resistance) for the evaluation of the quality assessment for interior wall coatings. These test methods are applicable to white coatings and light-coloured coatings of tristimulus value Y10 greater than 25 measured on a test specimen consisting of a coating applied to a black substrate. The cleanability test can differentiate the coating quality between 18 % of the pigment volume concentration (PVC) and the critical pigment volume concentration (CPVC). The on-site wet-scrub resistance test method can differentiate the coating quality when the PVC is nearly equal to the CPVC or above.

Titre manque

General Information

• Status: Published
• Publication Date: 06-Jan-2020
• ICS: 87.040 - Paints and varnishes
• Technical Committee: ISO/TC 35/SC 9 - General test methods for paints and varnishes
• Drafting Committee: ISO/TC 35/SC 9/WG 31 - Properties after application
• Current Stage: 9093 - International Standard confirmed
• Start Date: 15-Jun-2025
• Completion Date: 13-Dec-2025

Relations

• Consolidated By: ISO 12872:2022 - Olive oils and olive-pomace oils - Determination of the 2-glyceryl monopalmitate content
• Effective Date: 06-Jun-2022

Overview

ISO 23169:2020 - Paints and varnishes - On-site test methods on quality assessment for interior wall coatings - specifies two standardized, portable test methods to assess the performance of interior wall coatings in situ: on-site cleanability (stain removal) and on-site wet-scrub resistance. The methods are intended for white and light-coloured coatings (tristimulus Y10 > 25 measured on a coating applied to a black substrate) and are designed to evaluate the quality of the entire wall coating system (filler, primer and top coats) under real application conditions.

Key topics and technical requirements

• Two on-site methods:
  • Cleanability (stain removal) - applies standardized soiling agents, allows measurement of stain uptake and removal, and quantifies cleanability using tristimulus Y10 measurements before and after cleaning.
  • On-site wet-scrub resistance - measures film resistance to wet scrubbing cycles to detect film thickness loss and surface damage.
• Scope limits: Applicable to white/light-coloured coatings with Y10 > 25 on black substrate.
• Performance differentiation:
  • Cleanability distinguishes coating quality between 18% pigment volume concentration (PVC) and the critical pigment volume concentration (CPVC).
  • Wet-scrub resistance differentiates performance when PVC ≈ CPVC or above.
• Test apparatus & consumables:
  • Wet-scrub tester (manual, ~20 ±1 scrub cycles/min, stroke length 180 ±10 mm) with a specified sponge (100 × 35 mm, 15 ±1 mm thick, hardness 55 ±5 kPa) and optional black cloth for wet-scrub tests.
  • Spectrophotometer for tristimulus Y10 measurement (per ISO 6504-3).
  • Standard soiling agents (water-soluble Nigrosin, alcohol-soluble black solution) and optional agents (vinegar, black tea, blue-black ink).
  • Cleaning medium: sodium n‑dodecylbenzenesulfonate solution (2.5 g/l).
• Procedure highlights: apply standardized stains, dry (10 min), perform controlled scrubbing, measure Y10 before/after, calculate cleanability and resistance classes.

Practical applications and users

ISO 23169:2020 is practical for:

• Paint manufacturers (product development and QC)
• On-site quality inspectors and contractors (acceptance testing)
• Specifiers and architects (performance verification)
• Independent test laboratories and building owners (comparative evaluation) Benefits include objective, repeatable on-site assessment of stain removal and scrubbability, improved specification clarity, and better differentiation of coating systems under real use conditions.

Related standards

• ISO 6504-3 - hiding power and Y10 measurement
• ISO 3696 - water quality for analytical use
• ISO 4618 - paints and varnishes terminology
• ISO 13076 - lighting and visual assessment procedures
• ISO 11998 - laboratory wet-scrub terminology and background

Using ISO 23169:2020 helps stakeholders move from subjective visual checks to standardized, measurable on-site evaluation of interior wall coatings.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 23169
First edition
2020-01
Paints and varnishes — On-site test
methods on quality assessment for
interior wall coatings
Reference number
©
ISO 2020
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: [phone]
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Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 On-site cleanability (stain removal) test . 3
5.1 Principle . 3
5.2 Apparatus . 3
5.3 Reagents. 4
5.4 Procedure . 5
5.4.1 Division of test area . 5
5.4.2 Determination of the initial tristimulus value of the untreated coating . 6
5.4.3 Application of soiling agent . 7
5.4.4 Cleaning of soilings . 8
5.4.5 Determination of the tristimulus value after soil removal . 8
5.4.6 Calculation of the cleanability . 9
5.4.7 Evaluation with different soiling agents . 9
5.4.8 Comprehensive evaluation of stain removal of wall coating films .10
6 On-site wet-scrub resistance test .10
6.1 Principle .10
6.2 Apparatus .10
6.3 Procedure .11
6.3.1 Division of test area .11
6.3.2 Wetting of the wall .11
6.3.3 Scrubbing .12
6.3.4 Determination of wet-scrub resistance properties .13
7 Precision .14
8 Test report .15
Annex A (informative) Other types of stains used for evaluating stain removal performance
of coatings .16
Annex B (informative) Effects of different sponges on cleanability test results .18
Annex C (informative) Repeatability of cleanability (stain removal) test .19
Bibliography .20
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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committee has been established has the right to be represented on that committee. International
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee
SC 9, General test methods for paints and varnishes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

Introduction
Typical interior wall coating systems (see Figure 1) are comprised of a thick filler, one coat primer and
two top coats. Thus, the quality of the final interior wall is dependent on the whole coating system from
filler to primer to top coat. Besides, the quality of the application conditions, such as film thickness and
paint-water dilution ratio, contribute to the final wall coating system significantly.
Key
1 substrate (wall)
2 filler
3 primer (1 coat)
4 top coat (2 coats)
Figure 1 — Typical interior wall coating system
There is no standardized on-site test method on the market to check the performance of the whole
system worldwide. Currently, so-called “on-site test methods” are relying on visual tests, on fingernail
scrubbing and on touching. These methods are very subjective since results can vary from person to
person, even for the same wall coating system and these results are not repeatable. As a result, this
document provides standardized test methods for on-site wall coatings assessment. Using these
standardized test methods could help distinguish between high-quality and low-quality interior wall
coatings.
INTERNATIONAL STANDARD ISO 23169:2020(E)
Paints and varnishes — On-site test methods on quality
assessment for interior wall coatings
1 Scope
This document specifies two on-site test methods (on-site cleanability [stain removal] and on-site wet-
scrub resistance) for the evaluation of the quality assessment for interior wall coatings.
These test methods are applicable to white coatings and light-coloured coatings of tristimulus value Y
greater than 25 measured on a test specimen consisting of a coating applied to a black substrate.
The cleanability test can differentiate the coating quality between 18 % of the pigment volume
concentration (PVC) and the critical pigment volume concentration (CPVC). The on-site wet-scrub
resistance test method can differentiate the coating quality when the PVC is nearly equal to the CPVC
or above.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4618, Paints and varnishes — Terms and definitions
ISO 6504-3:2019, Paints and varnishes — Determination of hiding power — Part 3: Determination of hiding
power of paints for masonry, concrete and interior use
ISO 13076, Paints and varnishes — Lighting and procedure for visual assessments of coatings
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 4618 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
paint-water dilution ratio
ratio of water to the paint, given as percentage by mass
3.2
light-coloured coating
coating with tristimulus values Y greater than 25, measured with a spectrophotometer on a test
specimen consisting of a coating applied to a black substrate
Note 1 to entry: The test shall be in accordance with ISO 6504-3.
3.3
cleanability
ability of a dry coating film to withstand penetration by soiling agents and to be freed from them
through the cleaning process without removing more than a defined film thickness
[SOURCE: ISO 11998:2006, 3.1]
3.4
on-site wet-scrub resistance
ability of a dry coating film to sustain less than a specified loss in film thickness, averaged over a defined
area, when exposed to specified wet-scrub cycles (3.5)
Note 1 to entry: In ISO 11998, wet-scrub resistance is based on a lab test with 200 wet-scrub cycles.
3.5
scrub cycle
one reciprocal movement of the scrub pad over the scrub length (3.6) in both directions
[SOURCE: ISO 11998:2006, 3.2]
3.6
scrub length
stroke length (3.7) plus the length of the pad
[SOURCE: ISO 11998:2006, 3.3]
3.7
stroke length
distance traversed by one stroke of the apparatus
[SOURCE: ISO 11998:2006, 3.4]
4 Symbols
Y tristimulus value in accordance with CIE 1964 colour space
Y tristimulus value of the untreated (index “u”) test stripe
10,u
mean tristimulus value of the untreated (index “u”) test stripe x (x = 1, 2 and 3 for respec-
Y
10u,x
tively test stripes 1, 2 and 3)
tristimulus value measured in untreated (index “u”) test stripe x (for example x = 1, 2
Y and 3 for respectively test stripes 1, 2 and 3 on test stripe 1) on point y (y = 1, 2 and 3 for
10,u,x,y
respectively measuring points 1, 2 and 3)
Y tristimulus value of the treated (index “t”) test stripe
10,t
mean tristimulus value of the treated (index “t”) test stripe x (x = 1, 2 and 3 for respec-
Y
10,t,x
tively test stripes 1, 2 and 3)
tristimulus value measured in treated (index “t”) test stripe x (for example x = 1, 2 and
Y 3 for respectively test stripes 1, 2 and 3 on test stripe 1) on point y (y = 1, 2 and 3 for
10,t,x,y
respectively measuring points 1, 2 and 3)
C cleanability
mean value for the cleanability
C
C mean cleanability for test stripe x (x = 1, 2 and 3 for respectively test stripe 1, 2 and 3)
10,x
2 © ISO 2020 – All rights reserved

C mean cleanability of the water-soluble black solution (index “w”)
10,w
C mean cleanability of the alcohol soluble black solution (index “a”)
10,a
mean cleanability of the table vinegar (index “v”)
C
10,v
mean cleanability of the black tea (index “b”)
C
10,b
C mean cleanability of the blue-black ink (index “k”)
10,k
R resistance class for an alcohol soluble black solution
a
R resistance class for each tested soiling agent i
i
R mean value of resistance against all tested soiling agents
s
R resistance class for a water soluble black solution
w
n number of soiling agents tested
5 On-site cleanability (stain removal) test
5.1 Principle
The standardized stains are applied on interior wall coatings and dried for 10 min. Then the cleanability
test is run with the specified test apparatus (wet-scrub tester). The tristimulus value of the coating is
measured before and after exposure.
5.2 Apparatus
5.2.1 Wet-scrub tester.
The scrub testing machine is operated manually upwards and downwards with a stroke length of
(180 ± 10) mm and operating at approximately (20 ± 1) scrub cycles per minute. The number of scrub
cycles is recorded manually. Do not mix up the stroke length with the scrub length.
The apparatus for determination of cleanability and wet-scrub resistance of interior wall coatings is
shown in Figure 2. The apparatus can give consistent pressure and contact area when running the
test through the below designs. Three wheels are used to control the track when running the test. The
height of the wheel is designed to be lower than the height of sponge plus the black cloth, to ensure
certain deformation and to provide a certain friction.
NOTE The force provided by the deformation of sponge has been determined by dynamic mechanical
analysis (DMA) to be (2,6 ± 0,2) N.
A sponge height of 15 mm is recommended to deliver the reasonable result. The contact area which is
set by the location of the wheels is about 60 mm × 35 mm. The sponge (cleanability test) or the sponge
covered by the black cloth (wet-scrub resistance test) is fixed by one balance bolt with two screws
on each side. When the sponge is used under the black cloth, the purpose is to provide some damping
when rubbing, not to bring extra damage to the coating due to the hardness of the main material. When
determining “cleanability”, the black cloth does not need to be used; when determining “wet-scrub
resistance”, the black cloth needs to be used.
Key
1 main body
2 sponge
3 wheel
4 black cloth
Figure 2 — Example of a wet-scrub tester
5.2.2 Spectrophotometer, as specified in ISO 6504-3:2019, 6.5.
5.2.3 Gauze, of absorbent cotton.
5.2.4 Adhesive tape, with a width of 20 mm.
5.2.5 Sponge, with a size of 100 mm × 35 mm, a thickness of (15 ± 1) mm, a hardness of (55 ± 5) kPa
and a density of (41 ± 2) kg/m . For the effects of different sponges on cleanability test results, see
Annex B.
5.2.6 Stirrer, for preparing homogeneous solutions.
5.2.7 Timer.
5.2.8 Lint-free tissues.
5.2.9 Blow drier.
5.3 Reagents
5.3.1 Cleaning medium for test
Use a 2,5 g/l solution of sodium n-dodecylbenzenesulfonate (CAS-No 25155-30-0) in water in
accordance with grade 3 of ISO 3696. Allow the solution to stand before use until all air-bubbles and
foam have dissipated.
5.3.2 Soiling agents
5.3.2.1 Water soluble black solution
Put water in accordance with grade 3 of ISO 3696, into a vessel, then add Nigrosin black (CAS-No 8005-
03-6), at a mass ratio of water : Nigrosin black of 97:3. Mix thoroughly till all the Nigrosin black is
dissolved totally. Prepare this solution 24 h in advance before test. Its shelf life is seven days.
4 © ISO 2020 – All rights reserved

ISO 23169:2
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