July 7, 2009 - by Donna Buchan
The durability and permanence of an outdoor mural is dependant on many factors.
These factors are: Substrate, preparation of the substrate, type of paint, method of
applying paint, conditions during the paint's drying & curing time, final protective
coating or varnish, and weather extremes during painting as well as after completion.
2007 Mural Project
Substrate - Crezon (Trademark) Panel [from their product specifications sheet: “...
constructed of an MDO overlay on plywood... “The working face consists of resin
impregnated MDO cellulose overlay.”]
Preparation - single coat of Zinsser BIN primer [An alcohol/shellac-based
primer/sealer]
Paint - Tri-Art True Colour artists' acrylic paint
Method - It is not known if water was used extensively to reduce paint viscosity
and/or opacity in most of the murals.
Conditions - Seven murals were painted indoors, three outdoors (2 on the Algonquin
Theatre, facing South, plus the Community mural facing North), in mostly fair weather
except for 2 or 3 days of rain, without overall excessive humidity. They were left to cure
before varnishing.
Final Varnish – Speed Dry UV Acrylic 4005 Gloss by 1-Shot
Weather - as with all our murals, they are exposed to extremes of sun, heat, humidity,
rain & snow, cold & freezing throughout the year.
Observations - none of the 2007 murals appear to have suffered any deterioration
at this time. A closer examination and photos will follow.
2008 Community Mural
Substrate - Plum Creek MDO Sign Grade Plywood [from their website: “A quality
Medium Density Overlay plywood product, "B" grade veneer under paper”]
Preparation - single coat of Zinsser BIN primer [An alcohol/shellac-based
primer/sealer]
Paint - Tri-Art True Colour artists' acrylic paint
Method - water was used to reduce paint viscosity and opacity, mainly in the
preliminary layers.
Conditions - This mural was painted entirely outdoors. It underwent painting during
intermittently rainy and humid weather. The surface and back of the substrate were
sometimes exposed to heavy rain. Some blistering of the paint surface was apparent
after exposure to the rain.
Final Varnish - Speed Dry UV Acrylic 4005 Gloss by 1-Shot
Weather - as with all our murals, extremes of sun, heat, humidity, rain & snow, cold &
freezing
Observations - the 2008 community mural suffered complete failure. The blistered
areas peeled away first from the substrate, and other areas later flaked and/or peeled
off. In some areas, the paint separated from the primer, yet in other areas the primer
was visible adhered to the removed paint, leaving the substrate surface bare. The
peeling was first observed next to a central seam in the panel.
2009 Mural Project
Substrate - Crezon (Trademark) Panel
Preparation - single coat of Behr Acrylic/Latex Primer [the manufacturer's
recommendation for this product is for interior use]
Paint - Tri-Art True Colour artists' acrylic paint
Method - water was used in most of the murals to reduce paint viscosity and opacity
in preliminary layers. Subsequent layers of most of those murals included polymer
acrylic medium and not water.
Conditions -
1. The Community mural was painted outdoors (facing North). For the first 2 days,
painting took place in fair weather. For the subsequent 6 days, the mural was exposed
to direct rain and humid weather. Much of the time the painted surface was covered
closely with a tarp, though some rain leaked onto the surface, causing previously dry
paint to re-hydrate and run. Some blistering of the paint surface was apparent after
exposure to the rain.
2. Varley mural - this mural was attached to a South-facing wall. A lesser amount of
running and blistering occurred compared to No.1. Once dry, blistered areas were
sanded and painted over. At this point, Polymer medium was used with the paint, and
the surface was generally, though not always, protected from the rain with a tarp.
3. Carmichael mural - as with the Varley, attached to a South-facing wall. This mural
was moved indoors after 3 days of rain exposure. Slight blistering was sanded when
dry and painted over. No apparent failure noted at this time.
4. Jackson mural - attached to a West-facing wall. Severe blistering & running
occurred and it was moved indoors after 3 days of rain. Blistering was sanded when
dry and painted over. No apparent failure noted at this time.
5. MacDonald mural - attached to East-facing wall. Blistering & running occurred and
it was moved indoors after 3 days of rain. Blistering was sanded when dry and painted
over. No apparent failure noted at this time.
6. Harris mural - attached to East-facing wall, with a considerable overhang protecting
it from direct rain exposure. It was protected under a tarp with air circulation for most
of the time. No apparent failure noted at this time.
7. Johnston mural - attached to a West-facing wall. This mural was continually
protected under a tent-like tarp with air circulation. One corner was exposed to direct
rain, and blistering occurred in some areas of dry paint. It was sanded when dry and
painted over. No apparent failure noted at this time.
Other Murals
Two additional murals were completed in 2008, using the same substrate and paint as
the 2008 community mural, under similar rainy weather conditions. One of those
murals had suffered some repeated severe blistering, notably one particular area.
A number of previous murals have been painted here over the years, under varying
weather conditions. Those murals, mostly painted with Tri-Art Rheotech (Museum
label) paint have weathered very well, including those painted in rainy weather.
In October 2008, three murals were painted on Bell switching boxes. The painted
surface was first sanded then given 2 coats of Zinsser exterior-grade primer. All 3
murals used a combination of Tri-Art HV, True Color, Golden and M. Graham acrylics.
1. The mural on High Street was painted using True Colour plus polymer medium, in
fair weather, then covered loosely with a tented tarp as the weather changed to cool &
rainy. It cured for 10 days under a tented tarp before being varnished. No apparent
failure noted.
2. The West St. mural was painted during rainy cool weather, but the entire project
was protected by a waterproof tent, with an added heat source. It cured for at least 10
days under the ventilated tent before being varnished. No apparent failure noted.
3. The mural at Huntsville Place Mall was also painted using assorted acrylics with
polymer medium, during rainy cool weather, but the entire project was protected by a
waterproof tent. A small area of blistering occurred after exposure to rain, snow, and
freezing temperatures when the tent blew off. The blistering settled back as the area
became dry from circulating air. It cured for at least 5 days under a ventilated tent
before being varnished. No further failure noted.
Additional information
The method of applying paint would address the thickness of paint films, or the use of
water, a painting medium, or some other material or additive mixed with the paint. For
example, any ratio of an appropriate acrylic medium will have no ill effect, but excessive
use of retarder or water can alter the paint's binding properties. Any other additive not
recommended by the manufacturer can reduce the paint's film integrity as well.
Preparation can be as important as the method of painting. The manufacturers of sign
boards all recommend the surface be sanded lightly before applying two coats of an
appropriate exterior primer. They also recommend sealing and priming any raw edges.
The manufacturers of exterior primers also recommend using two coats for optimum
performance.
Adverse conditions during the paint's drying & curing time can interrupt the
polymerization process which determines the film integrity and bonding properties of
the paint. In order for acrylic paint to cure, water and other volatiles contained in the
paint must be allowed to evaporate. Humidity greatly hinders this process, and makes
the paint vulnerable to damage before it cures.
In a test performed between 3 types of paint and left out in the rain - True Colour
clearly suffered the most failure compared to Golden and Rheotech (Museum) paints.
The question was raised regarding Museum's performance being attributed to its
lesser pigment load, but to be equitable, a more controlled test using the same
pigments and paint coverage should be undertaken, as different pigments use varying
pigment-to-binder ratios.
From Golden Paints' website, their technical information page on Painting Exterior
Murals: “Avoid painting in adverse weather conditions, such as rain and fog. This
addition of moisture can effect the drying times and will re-introduce water back into
recently dried paint films. It is especially important to allow proper drying/curing time
between the (paint) and the varnish layer. Trapped moisture can severely hinder
adhesion, and can cause clouding of a clear layer. High humidity can also effect the
mural’s drying times similar to the conditions cited above for precipitation. As the
relative humidity climbs above 70%, more caution needs to be taken.”
Conclusion
At this early time, it's difficult to foresee if any or all of the 2009 murals will suffer any
failure. It would be wonderful to guarantee their success, but there are many variables
between murals - paint application, protection from rain, paint thickness, retained
moisture in both the paint and substrate - and still more variables to endure.
One problem we can avoid is varnishing too soon. The Community mural is especially
vulnerable to any moisture still retained in the paint and substrate from its lengthy
exposure to rain and humidity. According to the technical information available,
varnishing before the paint has cured (which could take a few weeks, perhaps longer
for some of these murals) could result in lost adhesion between the paint and
substrate.
Bringing the murals indoors will definitely prevent any further damage to the paint
surface and help speed the drying of the underlying layers. Allowing the finished
murals to cure indoors before varnishing will certainly increase the murals' chances of
surviving well into the future.
If you have any questions or further information to add to this subject, please feel free
to contact me here.
The durability and permanence of an outdoor mural is dependant on many factors.
These factors are: Substrate, preparation of the substrate, type of paint, method of
applying paint, conditions during the paint's drying & curing time, final protective
coating or varnish, and weather extremes during painting as well as after completion.
2007 Mural Project
Substrate - Crezon (Trademark) Panel [from their product specifications sheet: “...
constructed of an MDO overlay on plywood... “The working face consists of resin
impregnated MDO cellulose overlay.”]
Preparation - single coat of Zinsser BIN primer [An alcohol/shellac-based
primer/sealer]
Paint - Tri-Art True Colour artists' acrylic paint
Method - It is not known if water was used extensively to reduce paint viscosity
and/or opacity in most of the murals.
Conditions - Seven murals were painted indoors, three outdoors (2 on the Algonquin
Theatre, facing South, plus the Community mural facing North), in mostly fair weather
except for 2 or 3 days of rain, without overall excessive humidity. They were left to cure
before varnishing.
Final Varnish – Speed Dry UV Acrylic 4005 Gloss by 1-Shot
Weather - as with all our murals, they are exposed to extremes of sun, heat, humidity,
rain & snow, cold & freezing throughout the year.
Observations - none of the 2007 murals appear to have suffered any deterioration
at this time. A closer examination and photos will follow.
2008 Community Mural
Substrate - Plum Creek MDO Sign Grade Plywood [from their website: “A quality
Medium Density Overlay plywood product, "B" grade veneer under paper”]
Preparation - single coat of Zinsser BIN primer [An alcohol/shellac-based
primer/sealer]
Paint - Tri-Art True Colour artists' acrylic paint
Method - water was used to reduce paint viscosity and opacity, mainly in the
preliminary layers.
Conditions - This mural was painted entirely outdoors. It underwent painting during
intermittently rainy and humid weather. The surface and back of the substrate were
sometimes exposed to heavy rain. Some blistering of the paint surface was apparent
after exposure to the rain.
Final Varnish - Speed Dry UV Acrylic 4005 Gloss by 1-Shot
Weather - as with all our murals, extremes of sun, heat, humidity, rain & snow, cold &
freezing
Observations - the 2008 community mural suffered complete failure. The blistered
areas peeled away first from the substrate, and other areas later flaked and/or peeled
off. In some areas, the paint separated from the primer, yet in other areas the primer
was visible adhered to the removed paint, leaving the substrate surface bare. The
peeling was first observed next to a central seam in the panel.
2009 Mural Project
Substrate - Crezon (Trademark) Panel
Preparation - single coat of Behr Acrylic/Latex Primer [the manufacturer's
recommendation for this product is for interior use]
Paint - Tri-Art True Colour artists' acrylic paint
Method - water was used in most of the murals to reduce paint viscosity and opacity
in preliminary layers. Subsequent layers of most of those murals included polymer
acrylic medium and not water.
Conditions -
1. The Community mural was painted outdoors (facing North). For the first 2 days,
painting took place in fair weather. For the subsequent 6 days, the mural was exposed
to direct rain and humid weather. Much of the time the painted surface was covered
closely with a tarp, though some rain leaked onto the surface, causing previously dry
paint to re-hydrate and run. Some blistering of the paint surface was apparent after
exposure to the rain.
2. Varley mural - this mural was attached to a South-facing wall. A lesser amount of
running and blistering occurred compared to No.1. Once dry, blistered areas were
sanded and painted over. At this point, Polymer medium was used with the paint, and
the surface was generally, though not always, protected from the rain with a tarp.
3. Carmichael mural - as with the Varley, attached to a South-facing wall. This mural
was moved indoors after 3 days of rain exposure. Slight blistering was sanded when
dry and painted over. No apparent failure noted at this time.
4. Jackson mural - attached to a West-facing wall. Severe blistering & running
occurred and it was moved indoors after 3 days of rain. Blistering was sanded when
dry and painted over. No apparent failure noted at this time.
5. MacDonald mural - attached to East-facing wall. Blistering & running occurred and
it was moved indoors after 3 days of rain. Blistering was sanded when dry and painted
over. No apparent failure noted at this time.
6. Harris mural - attached to East-facing wall, with a considerable overhang protecting
it from direct rain exposure. It was protected under a tarp with air circulation for most
of the time. No apparent failure noted at this time.
7. Johnston mural - attached to a West-facing wall. This mural was continually
protected under a tent-like tarp with air circulation. One corner was exposed to direct
rain, and blistering occurred in some areas of dry paint. It was sanded when dry and
painted over. No apparent failure noted at this time.
Other Murals
Two additional murals were completed in 2008, using the same substrate and paint as
the 2008 community mural, under similar rainy weather conditions. One of those
murals had suffered some repeated severe blistering, notably one particular area.
A number of previous murals have been painted here over the years, under varying
weather conditions. Those murals, mostly painted with Tri-Art Rheotech (Museum
label) paint have weathered very well, including those painted in rainy weather.
In October 2008, three murals were painted on Bell switching boxes. The painted
surface was first sanded then given 2 coats of Zinsser exterior-grade primer. All 3
murals used a combination of Tri-Art HV, True Color, Golden and M. Graham acrylics.
1. The mural on High Street was painted using True Colour plus polymer medium, in
fair weather, then covered loosely with a tented tarp as the weather changed to cool &
rainy. It cured for 10 days under a tented tarp before being varnished. No apparent
failure noted.
2. The West St. mural was painted during rainy cool weather, but the entire project
was protected by a waterproof tent, with an added heat source. It cured for at least 10
days under the ventilated tent before being varnished. No apparent failure noted.
3. The mural at Huntsville Place Mall was also painted using assorted acrylics with
polymer medium, during rainy cool weather, but the entire project was protected by a
waterproof tent. A small area of blistering occurred after exposure to rain, snow, and
freezing temperatures when the tent blew off. The blistering settled back as the area
became dry from circulating air. It cured for at least 5 days under a ventilated tent
before being varnished. No further failure noted.
Additional information
The method of applying paint would address the thickness of paint films, or the use of
water, a painting medium, or some other material or additive mixed with the paint. For
example, any ratio of an appropriate acrylic medium will have no ill effect, but excessive
use of retarder or water can alter the paint's binding properties. Any other additive not
recommended by the manufacturer can reduce the paint's film integrity as well.
Preparation can be as important as the method of painting. The manufacturers of sign
boards all recommend the surface be sanded lightly before applying two coats of an
appropriate exterior primer. They also recommend sealing and priming any raw edges.
The manufacturers of exterior primers also recommend using two coats for optimum
performance.
Adverse conditions during the paint's drying & curing time can interrupt the
polymerization process which determines the film integrity and bonding properties of
the paint. In order for acrylic paint to cure, water and other volatiles contained in the
paint must be allowed to evaporate. Humidity greatly hinders this process, and makes
the paint vulnerable to damage before it cures.
In a test performed between 3 types of paint and left out in the rain - True Colour
clearly suffered the most failure compared to Golden and Rheotech (Museum) paints.
The question was raised regarding Museum's performance being attributed to its
lesser pigment load, but to be equitable, a more controlled test using the same
pigments and paint coverage should be undertaken, as different pigments use varying
pigment-to-binder ratios.
From Golden Paints' website, their technical information page on Painting Exterior
Murals: “Avoid painting in adverse weather conditions, such as rain and fog. This
addition of moisture can effect the drying times and will re-introduce water back into
recently dried paint films. It is especially important to allow proper drying/curing time
between the (paint) and the varnish layer. Trapped moisture can severely hinder
adhesion, and can cause clouding of a clear layer. High humidity can also effect the
mural’s drying times similar to the conditions cited above for precipitation. As the
relative humidity climbs above 70%, more caution needs to be taken.”
Conclusion
At this early time, it's difficult to foresee if any or all of the 2009 murals will suffer any
failure. It would be wonderful to guarantee their success, but there are many variables
between murals - paint application, protection from rain, paint thickness, retained
moisture in both the paint and substrate - and still more variables to endure.
One problem we can avoid is varnishing too soon. The Community mural is especially
vulnerable to any moisture still retained in the paint and substrate from its lengthy
exposure to rain and humidity. According to the technical information available,
varnishing before the paint has cured (which could take a few weeks, perhaps longer
for some of these murals) could result in lost adhesion between the paint and
substrate.
Bringing the murals indoors will definitely prevent any further damage to the paint
surface and help speed the drying of the underlying layers. Allowing the finished
murals to cure indoors before varnishing will certainly increase the murals' chances of
surviving well into the future.
If you have any questions or further information to add to this subject, please feel free
to contact me here.
| Report on Mural Durability Group of Seven Outdoor Gallery, Huntsville, Ontario |
Close-up of failed acrylic paint surface which
was directly exposed to rain.
Even though the paint appeared dry, it had
not cured due to the extremely high
atmospheric humidity. This area was allowed
to thoroughly dry, then it was sanded and
repainted. The mural was allowed to cure
further, under protection of a tarp, for a
number of weeks before varnishing.
No failure has been noted since varnishing.
was directly exposed to rain.
Even though the paint appeared dry, it had
not cured due to the extremely high
atmospheric humidity. This area was allowed
to thoroughly dry, then it was sanded and
repainted. The mural was allowed to cure
further, under protection of a tarp, for a
number of weeks before varnishing.
No failure has been noted since varnishing.