Hello fellow spooky villagers! We are under 150 days til next Halloween!
I am TheChemFreak and started my Spooky Town villaging with Grisley’s Greenhouse in 2010 but my love of Halloween started 31 years ago!
Here I am in Kindergarten making an awesome Leonardo with a killer homemade hair barrette.
Fast forward to the present and I still enjoy dressing up for Halloween and terrifying people.
I am a chemist by day, specializing in polymer synthesis and paint formulation. In my articles to you I would like to present a healthy mix of fun, science, and spooky. I am continually interrogated by family and friends for the appropriate coating for a particular surface. The most common paint you will encounter is latex.
Latex paint is actually a misnomer; true latex is extracted from a Brazilian Rubber Tree Plant. Latex paint actually contains NO latex! Latex paint is actually an emulsion of synthetic polymers such as acrylic, vinyl acrylics, styrene acrylic, etc. Latexes are waterborne, meaning it has minuscule volumes of harsher solvents like acetone, methyl ethyl ketone, and xylene. Generally compared to other paint types, latexes are less durable though environmental concerns have pushed great advances in latex technology.
So if latex is not the “best” paint available why can’t I use solvent borne on my Styrofoam to strengthen it?
Solvent borne paints, especially spray paints not specifically formulated for plastics, use harsh solvents to carry the polymer resins that provide the durability. So if the solvent can dissolve a hardy polymer it makes sense that it will also dissolve your Styrofoam/PVC!
Oh yeah TheChemFreak? If a latex is waterborne how come water doesn’t dissolve the paint off my walls when I clean it?
That is the magic of latexes! The polymer is not actually dissolved in the latex paint! Try to think way back to science class. Micelles. Micelles are spheres of molecules that use the hydrophobic/hydrophilic properties to form balls. The molecules form a ball because that is the lowest energy configuration available at the time. Think about bacon fat being dropped into soapy water. Those grease balls are micelles. Polymer resins that make up latexes use that same technology. Drop the polymer resin into water and it forms a micelle. Also, that is why latexes aren’t usually put through a spray can, too big!
Well, if latex paint is just a bunch of micelles, how in the world does it form a single coating?
This is where the little bit of solvent comes into play. Latex paints are full of additives; one of the additives is a coalescent agent. Coalescent agents evaporate slower than water. Basically, after you paint the latex paint on the wall the water starts to evaporate. As the water evaporates, the concentration of the coalescent agent increases, causing the micelles to “glue” together.
Luckily for us villagers, paint chemists have been busy! A fairly new product has reached the shelves of our local department stores. Plastic primers in a spray can. This technology takes advantage of modifications that allow the polymer to be dissolved in less harsh solvents like acetone, acetates, and ethers. As I mentioned before, acetone is harsher than water, but not nearly as destructible to plastic as xylene. So actually the plastic primer does damage the surface on a microscopic scale but visibly. The polymer coating left behind is durable enough for solvent borne paints if adequate drying time is allowed. Both Valspar and Rustoleum have a line of plastic primers. I would recommend using the same brand that you favor for your traditional spray paints.
Personally, I use acrylic latex paints and an acrylic topcoat for my Spooky Town and solvent borne paints for anything used outdoor or would need excessive cleaning. In my experience baked polymer clay can handle solvent borne paints. A general rule of thumb, latex can go on top of solvent borne, solvent borne cannot go on top of latex. If you have specific questions regarding coatings feel free to leave a comment or contact me!