Cold Temperature Painting（jotun）

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The optimum environment for application and curing of just about any coating material is 70°F and 50% RH.
However, this set of conditions rarely exists outside of the laboratory for any appreciable amount of time.
We have to understand that the stated curing time shown on a data sheet is an estimate, based on near perfect environmental conditions and the recommended dry film thickness.
Different temperatures, higher humidity’s, film build different then what is recommended, air flow over the surface and the amount of thinner will all effect the cure rate of the coating.

The most common issue our customers face is one of lower temperature and or higher humidity.
This becomes a real problem when using epoxy coatings if the proper precautions are not taken during the storage and mixing steps.
Like most two component paints epoxies cure by solvent evaporation along with molecular changes in the film.
Typically the molecular change in an epoxy will slow down radically at 40°F and stop taking place when the temperature of the film drops below 32°F for standard versions, winter grade mastics will continue curing down to 23°F.
Even though the changes will continue to take place when the film warms back up, the film will remain open and subject to several damaging effects during this extended time frame.

Jotun’s epoxy mastic primers, Jotamastic 87, Primastic AV, Balloxy and Primastic Universal AV are categorized as modified epoxies.
Meaning they contain both a liquid epoxy resin and a hydrocarbon resin.
The liquid epoxy is in there to give good cross linking of the paint film when mixed with the curing agent, while the hydrocarbon is in there to give a superior wetting of the surface.
What does this really mean?
A modified epoxy will outperform pure epoxies when applied on marginally cleaned surfaces, as the modified epoxy will penetrate into the substrate far better than pure epoxies.
This is the major benefit in these types of products and is part of the reason that Jotun’s epoxy mastic’s are accepted, used and praised worldwide. In order to achieve the necessary curing in a relatively short period of time products containing liquid epoxy and hydrocarbon need to be cured with an amine-curing agent, amide-curing agents would be too slow curing.
An amine cured epoxy film, compared to an amide curing epoxy film is stronger, harder, more chemical resistant, more abrasion resistant and more water resistant.
But with the good comes the bad, amine curing epoxies will blush when exposed to moisture and carbon dioxide from the air during the early stages of the cure cycle.
During good conditions, that is when the temperature is above 60°F for the entire cure time it is typically not a problem, unless an unexpected rain shower wets the surface during the first hours of curing.
The real problem shows up when daytime painting is done at 50 to 60°F and that night the temperature drops down to the 30’s and 40’s.
When this happens dew will form on the surface of the uncured epoxy, this will combine with carbon dioxide from the air and blushing will occur.
The blush may be visible; on darker paints it can show up as a white or light colored stain, on lighter colored paints it may not be visible at all.
Normally it can be determined by a simple hand test, wipe your hand across the surface and if it is sticky or feels oily or powdery then it must be cleaned before the next coat is applied.
This cleaning can be a solvent wipe with Jotun thinner no. 7 or it can be removed with warm water and a scrub brush.

Note: if the blush is not removed then the next coat of paint, no matter what type, will delaminate.
This is a known generic type product issue, not just a Jotun issue and is not covered by any warrantee, by us or any other paint company.

Avoiding the BlushAvoiding the blushing issue is not all that difficult.
All of Jotun’s mastics require a 10 minute induction time when mixed at 73°F.
When the temperatures are lower this induction time should to be extended as shown below:

Surface Temperature	Induction Time
75°F to 95°F	10 minutes
65°F to 75°F	30 minutes
55°F to 65°F	50 minutes
40°F to 55°F	80 minutes

• Induction time is the elapsed period between mixing the two components of the epoxy mastic and the subsequent application of it.
• Standard grade epoxies should not be applied when the temperature is below 40°F.
  
• All paints should be stored inside at temperatures above 60°F before application.
• During cold temperatures apply the material as early in the day as possible; avoid paint just before sunset.
• Painting should never be done if rain is expected during the curing cycle.

Jotun does offer a winter cure version of both Jotamastic 87 and Primastic AV.
It is available in five-gallon kits (no ones) in Black, Red and Light Gray.
The winter grade materials can be applied at temperatures as low as 23°F.
The Jotamastic 87 WG kit consists of three cans, one base in a partially filled five and two cans of the cure in partially filled ones.
The Primastic AV WG is a standard two can mix, one partial five and a single one filled to the top.
Winter grade material does cost more as you are using more of the cure – the most expensive part of the kit.


Earl Bowry
Coating Advisor, Jotun Paints, Inc.
757-635-5311
earl.bowry@jotun.com