Why Painting and Gluing in Cold Weather is Tricky
or: A man’s got to know the limitations of his materials.
It is sometimes necessary to work in cold weather, and the work may include gluing and painting things. Glues may or may not contain volatile components including liquids that dissolve resins (“solvents”), and paints often do. It is vital to know the nature of the adhesives and coatings that are being used and their limitations, and doubly so if one is working in adverse weather conditions.
Solvents evaporate more slowly in cold weather.
Water freezes when its temperature gets below 32F; that is generally considered “cold weather”. Latex (water-borne) paints are resin-in-water emulsions and will coagulate and separate if the water-phase freezes. If that happens they are no longer useful, as they will not behave correctly.
The “drying” of many paints involves chemical reactions. The “curing” of many one-component adhesives and all two-component adhesives and coatings involves chemical reactions. The chemical reactions of atoms and molecules of a liquid or mixture to make bigger molecules, becoming a solid and sticking to other things is called “curing”
All chemical reactions go faster at higher temperatures and more slowly at lower temperatures. It is a chemist’s rule-of-thumb that a reaction rate doubles as the temperature increases another ten Centigrade degrees (that’s eighteen Fahrenheit degrees). In fact the temperature increase for a doubling of rate varies depends on the particular atoms and molecules involved; the doubling may be every six centigrade degrees or every fifteen centigrade degrees or anywhere-in-between. Thumbs vary!
Why Glue Doesn’t Set, or Paint Dry, When It’s Cold – The Science
There is a temperature at the low end, at which a chemical reaction just basically quits.
Chemical reactions have Activation Energies. That means below about a certain temperature there is not enough thermal energy (molecular-energy-of-motion-of- molecules) to get things over the potential-energy-barrier of their own molecular structure such that the atoms can then come together on the other side of the energy-barrier and stick-together. So, a chemical reaction may get slower and slower at some rate or slope, and at a minimum-temperature-stated-by-the-manufacturer the “slower-and-slower” becomes “a-LOT-slower” because it’s in the process of quitting. The minimum-use temperature specified by the manufacturer for application and cure of their product is specified at that minimum because that’s as cold as you can safely get, using their product, and still have everything-work-properly.
Some single-component glues do contain solvents, and rely on solvent-dissipation into the wood and eventual diffusion out-and-away into the atmosphere as part or all of their adhesion-development process. The manufacturer of these products will have applications-information and an acceptable-for-use temperature range that must be adhered to (pun entirely unintentional), if their product is to perform correctly.
Some single-component glues and most two-component glues do not contain solvents, but their manner of adhesion-development has some dependence on temperature.
Solvents have a “vapour pressure” which is related to how fast they evaporate. As the weather gets colder, the vapour pressure of everything including water, gets less. Vapour pressures never get to zero, but in cold-enough weather the vapour pressure of a solvent or mixture may get so low that the product does not work as the manufacturer intended, and that is another factor that may determine the lowest-use-temperature of a product. Again, it is something the manufacturer specifies.
So, we have to use products within a temperature-range specified by the manufacturer, but Mother Nature is not always cooperative.
What Sets The Temperature We Work At
Skipping the Global warming / cooling arguments…
Everything radiates heat, depending on how hot it is, meaning how far above Absolute Zero. Hotter things radiate more per unit area, and colder things less. Heat energy, or “heat” for short, always flows by its own nature from hotter things to colder things, never the opposite.
When there are clouds overhead at night, the surface of the earth radiates about as much heat upwards as the clouds above radiate downwards, since they are about at the same temperature and therefore are radiating about equal amounts of energy. Thus, the clouds act as a heat-mirror, keeping the planet surface from getting really cold at night. It is the backside of the cloud that gets really cold, since the backside is facing Deep Space, where it is REALLY cold, at the temperature of the space between stars, Near Zero Kelvin (-273 degrees centigrade, or, about 450 degrees Fahrenheit below zero in old money), or absolute zero as it is also known.
When there are no clouds overhead, the earth radiates its heat away to the night sky.
So, cloudless nights are colder.
When cars, buildings and anything on the surface gets cold enough at night, moisture in the air condenses on those cold surfaces. That is where dew comes from. The temperature at which dew condenses onto a surface is called the dew point. It varies with the humidity (moisture content) of the air.
During the day, the sun shines on the “day-side” of this planet and the energy from the sun warms everything on the surface. Energy from the sun comes to us as radiated energy. Once received, the radiated energy heats the air, the oceans and the land, and we have additional heat-transfer means driven by wind, rain and snow. In the middle of all this, folks are trying to get things done.
So How Do I Work With Glues and Paints When It’s Cold
Latex paints freeze (the water-part, any ways) at around Zero centigrade (32 degrees Fahrenheit in old money). That’s one hard limit. Other products have other lower-temperature limits. Storage-temperatures may not be as cold as minimum-use temperatures. All pure compounds freeze, and epoxy resins are no exception. Our Oak and Teak Epoxy Glue, for example, may be applied near freezing and will actually cure as low as -2 °C, 28F, but if stored at that temperature for days or weeks it may well freeze solid, and need to be warmed gently to melt the resins back into their normal liquid states.
You have to find a way to stay within the working temperatures of the products during application and cure. After curing, most wood-related products will survive temperatures far below freezing; it’s just during the application/drying/curing process that things need to be a bit on the warm side, usually 0°C / 32F or above.
The best solution to working in cold weather is to do it indoors; at least, sheltered from the wind and rain/snow, one has half-a-chance of warming something at least a little. But, what if you don’t have an indoors, or if the-thing-you-are-working-on is too big to fit indoors, even if you had one?
There is some solar-heating technology that can be used to ease your pain, and may allow you to get work done even in adverse weather conditions.
Heat Your Work With Solar Heating
What Is Solar Heating
For years a friend of mine had his rather-huge backyard swimming-pool heated by sunlight and nothing else. No solar-collectors, just the pool soaking up sunlight. But, why did it work?
The sun sends us all of its energy as radiated energy, but there are different kinds of radiated energy. The units (packages) of radiated energy are called photons, and there are really big ones, fair-size ones, medium-size ones, small ones, really teensy ones and on down to almost zero-size ones. The difference depends on the amount of energy each photon carries, and here we just used the word “energy” in a different way. I need to take a sidebar to explain about this.
There are many forms of “energy”. Technically, “energy” is the capacity to do work. In this universe it manifests in different ways. There are little packages of electromagnetic energy; these are called photons. Electric and magnetic fields both have fixed locations, but can get involved together in a special way and then as a unit, propagate (at the speed-of-light, 186,000 miles per second); this unit-of-energy-in-motion is called a photon. Very high-energy photons are called X-rays or Gamma-rays. Ones of progressively lesser energy are light, or heat (infra-red radiation), or microwave power, or radio waves. All these are photons, carrying different amounts of energy.
There are other forms of energy; there is the energy-of-motion of a moving mass (a falling rock, or a speeding bullet); there is also the energy stored in mass itself (Einstein’s E = MC² equation), the release (conversion) of which happens in an atomic bomb. The universe contains all these different forms of energy, but they are all forms of the same thing; they can all do work, and they can all heat a cup of water, of which there are quite a few in that swimming pool.
Photons of light or heat from the sun (sunlight feels warm, right? Your skin is absorbing that energy and becoming warmed.) are absorbed by the water of the swimming pool, and the energy of the photon becomes heat-energy of the mass of water in the pool. The pool becomes warm. With the average outdoor swimming pool or lake, it warms up during the day, and cools off at night. The average temperature depends on how many warm days or cold days there are in a row. You all know this. What you may not know is why the pool cools off so much at night, if there is no swimming-pool-heater. The reason is that it loses its heat-energy to the night sky by radiation, as we discussed earlier. You can see that there is an energy-balance, as solar-energy in, and radiated energy out. But the pool is not glowing at night; how does it lose that heat by radiation?
Make A Personal Green House To Heat Your work
Use The One-Way Heat Mirror For YOU
Here’s the trick: objects at different temperatures radiate different energies of photons. We are going to describe the energy of a photon by its wavelength; the longer the wavelength, the lower the photon’s energy. The sun is super-hot; tens of thousands of degrees (Fahrenheit or centigrade, it doesn’t matter. It’s a hundred million miles away and over fifty thousand degrees.) and the portion of its energy that makes it into and through the atmosphere has a wavelength of some few-tenths of a micron (a millionth of a meter, smaller than a human hair), and a whole spectrum of wavelengths, from that on down to a few microns. That’s what we get from the sun, a super-hot thing. At about room-temperature or freezing-water temperature, things radiate at MUCH longer wavelengths, around thirty to a hundred microns. Why? It’s technical. I have simplified a lot of stuff to get down to these basics. There are books on physics if you really want to know what’s-behind-the-curtain, but this is how things work in this Physical Universe.
You’re probably beginning to suspect by now that you know how that swimming pool loses its heat at night, and you’re probably right. It loses its heat by radiation, but at its natural radiating wavelength, because it’s not as hot as the sun. That’s right.
So, how did my friend heat his pool? He used a one-way mirror. The very short wavelength solar energy came in through the mirror, but the very long-wavelength radiated-energy from the swimming pool bounced off the mirror and went back into the pool. Clever, eh?
How did he make a one-way mirror? He used a common plastic material that would pass visible light and heat from the sun, but reflect the very-long-wavelength energy of the pool. Mechanically, it was simple. The material he used was polyethylene. You can buy it in sheets and rolls in the paint departments of most stores, and it is what bubble-pack is made of. It reflects heat from things around room temperature, just because the molecular structure of polyethylene passes short-wavelength photons (visible light) and reflects very-long-wavelength photons (called infrared). Between the air pockets that act as physical air-space insulation and the energy-reflecting molecular structure of the polyethylene itself, it greatly reduces heat-loss from the thing being warmed. I use a couple sheets of the quarter-inch-bubble-size in my microwave above and below something I am warming up. It takes about half the time to warm something, as the food does not lose its heat by radiation while it is being heated by the microwave energy, a different wavelength (a few centimetres) that happens to be absorbed very efficiently by the water in food, which is why microwave ovens work. This might also now be giving you an idea of how to glue wood outside in really cold weather.
Warm The Wood With The Sun Itself, So Your Paint Or Glue Works
Let’s start with the supplies: You will need enough of the quarter-inch bubble-pack to cover the wood or wrap it, with about four layers. You will need some clear packaging-tape to hold the bubble-pack in place when the wind is blowing. You will also need a means of measuring wood temperature (such as a thermocouple–reading meter and a thermocouple, with that thermocouple fastened to the underside or between a few layers of the wood. A dial-thermometer could be used, but is not as accurate. There is a company called Omega, that sells temperature-measuring equipment. Digital Thermocouples are readily available on eBay for around £10, just search ‘digital thermocouple’.
On small projects an electric blanket could be used under the bubble-pack to warm things, but for physically larger projects that is not always practical. The sun will heat everything, and if you have good enough insulation the daytime heat will accumulate under the bubble-pack insulation, and eventually the wood will warm up enough to get the work done.
The whole idea is to know when the wood temperature has warmed up enough to be able to glue it and keep within the manufacturer’s design limits for their glue.
There’s another reason to want the temperature of the wood to be above freezing when applying the glue. If the wood surface is below freezing, water vapour in the air can condense on the wood surface as a film of ice. The glue won’t then stick to the wood because the film of ice acts as mould-release and prevents adhesive bonds between wood and glue from ever forming.
How long it will take depends on the mass of wood and the weather. Remember that energy is coming in based on the area of material looking at the sun, and that it takes more energy to warm more mass. Warming a large thing may take a couple weeks or more, and there’s not a lot of sunlight on a cloudy day. That is why you need to have a means of measuring the daily wood temperature without unwrapping everything. The thermocouple is a small thing on the end of a wire, and the meter can be plugged-in, a reading taken, and disconnected for the day. After a few days to a week you should have an idea of how things are going. You will still have the limitation of not getting much warming-help in a blizzard, but if you have some decent weather-windows in-between the blizzards, you can get some work done.
Copyright Steve Smith 1993 – 2014, All rights reserved