Curiosity always gets me in trouble. When a question comes up, that piques my interest, I just have to find the answers, especially when they aren’t obvious and are hard to find on google. As I started to wonder about the properties of various chalk paint recipes, my curiosity about paint itself came up. So what then is chalk paint? How is it different than regular paint?
To answer these questions, I guess the place to start is to discuss paint itself. Many brand name ‘chalk paints’, including Annie Sloan, are very protective of their formulas and don’t list ingredients, so it’s hard to tell exactly what is in their paint. Whatever their formulations may be, basic paint is essentially comprised of four components: pigments, binder, liquid, and additives. How companies combine these components is what gives paint its character and distinction. So let’s look at the components that make up latex paint:
Pigments – provide colour and coverage power
White – Titanium dioxide (TiO2)
-predominate white pigment that provides exceptional whiteness by scattering light
-provides whiteness and ‘hiding’ in flat or glossy paint
-requires extender to ensure proper spacing of particles to avoid crowding and loss of hiding
-has more chalking tendency in exterior paints than most colour and extender pigments.
-provide colour by selective absorption of light
-compounded into liquid dispersions called colorants
-added at point of sale to tint bases
-added to white paints designed for tinting
-used in factory as dry powders and in liquid colorant form to make prepackaged colour paints
-provide bulk at relatively low cost, but with much less hiding than TiO2 and can impact other properties
-combination of using different percentages of primary and extender pigments determines the price of the paint and the ability of certain paint properties
** calcining -heated to drive off water and create air-particle interfaces
-resinous material that binds the pigment and provides adhesion, integrity and toughness to the dry paint film
-as the wet paint is put on the wall, the binders control how the paint dries and/or cures
-as the water part of the paint evaporates, the binder forms a solid film on the top layer of the paint
Affects all properties of the coating:
Adhesion – i.e. resistance to blistering, cracking and peeling
Resistance – i.e. scrubbing, chalking and fading
Application – i.e. flow, leveling and film build, and gloss development
100 percent acrylic
-provides better overall adhesion on a wider variety of surfaces
-very durable, especially when applied to fresh masonry surfaces
-resists the effects of alkaline surfaces
-offers better stain protection, greater water resistance, and greater resistance to cracking and blistering
-preferred for outdoor application, but used indoors as well
-more expensive than vinyl acrylics
Vinyl acrylic (PVA – polyvinyl acetate=glue)
-polyvinyl acetate is a thermoplastic polymer commonly used in glues, paint, and several industrial adhesives.
-tends to be quite flexible and has a strong binding capability, which is one of the main reasons it’s so popular in products like glue and paint
-helps to form a tough coating and a supportive film.
-used to primarily reduce cost
-used for enhanced water resistance, gloss development and cost reduction
-the liquid in latex paint is water
-provides the desired consistency to make it possible to apply the pigment and binder to the surface being painted.
-additives are anything else that is added to the paint to add properties like mildew resistance, defoaming, leveling, and flow
As you can see, paint may have the four components of pigments, binders, liquid and additives in common, but the formulations can vary depending on how the paint is going to be used. It is easy to see how paint usage and application would change the component ratios. For example, an exterior paint would require more water proofing properties to defend against rain and snow, vs a living room paint that needs no such protection.
That brings me to “chalk” paint. What makes this paint so special? While researching paint ingredients, there is a common denominator: Calcium carbonate (chalk) already seems to be a common ingredient in latex paint as an extender. It essentially maximizes the paint pigments so you don’t need as much to get the desired colour and fills up the volume in the paint so you don’t need to use as much (resin) binder. So when making DIY chalk paint, it makes sense to start with a basic latex paint. What you end up with depends on which chalk paint additive you add to the paint.
DIY Chalk Paint Additives
Plaster of Paris – 2CaSO4·H2O
Many people complain that when they use Plaster of Paris to make their chalk paint, it starts to dry up and harden and needs water to moisten it again. If you check out what Plaster of Paris is, you will learn that it is a quick setting gypsum plaster that is a fine powder consisting of calcium sulfate hemihydrate that hardens when moistened and allowed to dry. It is commonly used to precast and hold parts of ornamental plasterwork placed on ceilings and cornices as well as being used in medical facilities to make plaster casts to immobilize broken bones. It stands to reason then why it hardens when mixed with water and wet paint.
Baking Soda – NaHCO3
Baking Soda, aka sodium hydrogen bicarbonate, is a chemical salt that is composed of sodium and bicarbonate ions that form a white solid that is crystalline, but often comes as a fine powder. It has a slightly salty, alkaline taste and has been found to have many good uses from food to medicinal applications. I can’t explain how it came to be added to paint, but it does leave a grainy texture that some painters like to work with.
Lots of people like to use non-sanded grout as their chalk paint additive. This grout is a mixture of Portland cement, powdered pigments and water. Portland cement hardens when it reacts with water and is mostly made out of calcium silicates, aluminum and iron-containing clinker phases, and other compounds. It is also caustic, so it can cause chemical burns. Since this is grout and is supposed to harden, it is no wonder that it also hardens when it is mixed in water-based paint.
Calcium Carbonate – CaCO3
Calcium carbonate is mined as limestone, chalk, and marble. It is the most widely used mineral in the paper, plastics, paints and coatings industries both as a filler – and due to its special white color – as a coating pigment. It is also sold as “whiting powder”, “lime powder”, and “marble dust”. Since calcium carbonate is already an ingredient in paint (as discussed above) and is actually “chalk”, it only makes sense to add more to latex paint to increase the ‘”chalky” effect of the paint. This is my personal favourite additive! My go-to recipe can be found here.
Other Additives Worth Looking At
So in conclusion, whichever chalk paint you end up using, it all comes down to personal preference. For me, painting is one of my many hobbies that gives me pleasure as I experiment with different techniques and recipes to rehabilitate tired furniture. I hope to start sharing my projects soon (still organizing photos). Happy painting!
These are some of the sources I stumbled upon in my quest to answer: What is in chalk paint?
Binder: The ‘Glue” That Holds Paint Together
The Ingredients of Paint and Their Impact on Paint Properties
Liquid and Additives
How Color is Affected by the Ingredients of Paint
Interior Paint, Exterior Paint, Architectural Paints