square draw-down bar. The panels were
allowed to air dry for seven days prior to
stain testing. The staining agents were
compiled from the following sources:
•ASTM D1308 – Standard Test
Method for Effect of Household
Chemicals on Clear and Pigmented
Organic Finishes4
•ASTM D3450 – Standard Test
Method for Washability Properties
of Interior Architectural Coatings5
•ASTM D4828 – Standard Test
Method for Washability of Organic
Coatings6
• Ceramic Tile Institute of America,
Inc., CTIOA Field Report T- 72
(R-02) 7.
•Stain Repellency Testing of
Cementitious Grouts8
• Grout Market Survey15
The stains used were:
• Mustard
• Ketchup
• Red wine
• Red lipstick
• Coffee
• Vegetable (soybean) oil
• Soy sauce
• Cola
• ASTM stain media
Stains were applied in lines across the
surface of the paint samples so that all
the stains could be cleaned using a lin-
ear wash/abrasion machine. Various test
methods stipulate stain residence times
varying from 15 minutes to 24 hours. We
chose one hour so that none of the liquids
had sufficient time to completely dry, and
we would have a wide range of perfor-
mance from good to bad.
After the one hour stain residence time,
the panels were blotted dry with a paper
towel, and quickly rinsed off under run-
ning water. The panels were then clamped
into the stainless steel tray of the abrasion
testing machine. Standard ASTM sponges
were pre-wetted and 25 mL of pre-pre-
pared cleaning solution ( 3 g of water to 2 g
of ASTM non-abrasive scrub media) were
applied to the sponge according to ASTM
D3450 ( 100 back-and-forth scrub cycles).
The panels were rinsed again and allowed
to dry for 24 hours prior to determining
stain repellency.
Stain repellency data was collected
using a colorimeter with L* from the
L*a*b* color space as the evaluation pa-
rameter. The unstained control value was
measured on an unstained and clean area,
while values were also measured at each
of the stained and cleaned areas.
For example, the L* value for sample
1 was 96. 51, and the L* for the red wine
stained and cleaned area for the same sam-
ple was 94. 53. The difference of 1.98 was
used for the stain repellency data. The low-
er the number, the closer the actual L* val-
ue is to the original unstained area equating
to better stain repellency. Conversely, the
higher the L* value, i.e., further away from
the value for the original unstained area,
the worse is the stain repellency.
A Kruss DSA30 Drop Shape Analysis
System was used to measure the contact
angle of the liquids. Using the sessile
drop technique, water and dodecane were
used to measure contact angles, However,
dodecane spread too quickly and flat to
be read over 13 of the samples so diiodo-
methane was used for those 13 samples
as the second required contact angle mea-
surement used to calculate surface energy.
An average of three readings was used to
determine the contact angle for each liq-
uid over each sample. The two solvent
method of Wu was used to calculate sur-
face dispersive, polar, and total surface
free energies.
The data was entered into an Excel®
spreadsheet and analyzed using a correla-
tion coefficient data analysis tool pack in-
cluded in the software. We evaluated for
correlations between all contact angles,
all surface energy calculated values, and
all L* absolute values for each staining
agent to determine what, if any, correla-
tion existed.
Equipment
• 10 mil stainless steel, 4 inch wide,
drawdown square
• Black vinyl scrub charts
• Goniometer – Kruss DSA30 with
Advance Drop Shape Software
• Colorimeter – Byk Spectro Guide
Sphere
Results and Discussion
Given the magnitude of the data generated from this work with 171 samples, this
discussion is focused upon selected data
to highlight specific information and with
summarized data to highlight trends.
Table 3 shows the stain repellency
data for one set of commercial paints.
The stain repellency performance range
exhibited minimum values of L* around
0.2, which may not be discernible to the
human eye, while other stains resulted in
L* values > 5.0, which are clearly noticeable and do not appear to have been either repelled or easily removed. Table 3
exemplifies the range in stain repellency
performance for the commercial paints in
this study.
Table 3: Example of commercial paint stain repellency data
Sample 56 57 58 59 60
Ketchup 0.57 0.06 0.97 0.51 0.54
Redwine 1.18 0.93 2.19 1.35 0.86
Mustard 1.05 0.27 0.65 0.21 0.84
Soybeanoil 0.81 0.22 1.12 0.31 0.38
Soysauce 0.88 0.25 1.07 0.55 0.38
Coffee 0.97 0.61 1.22 0.19 0.22
Cola 0.12 0.33 1.17 0.13 0.15
Redlipstick 0.22 0.52 0.50 0.20 0.31
ASTMblackstainmedia 5. 43 5. 54 7. 28 3. 98 4. 98
Total 11. 23 8. 73 15. 90 7. 43 8. 66
