There are a few steps to follow to prep surfaces for milk paint. Milk paint (like any water-based paint) adheres best to porous surfaces, such as unfinished wood, very old furniture that the finish has worn off of, lots of flea market finds, rusty metal, etc. If this is the type of project you are working with, there isn't any additional prep to the surface that needs to occur.
On non-porous surfaces, there are a couple of additional steps that can be taken to ensure that the milk paint adheres in the manner you wish it to.
By the way, this is one of the things that I absolutely love about Junkyard Goddess Milk Paint. YOU have creative control over the finished look of the project, not the paint. This is not true with the majority of paints on the market today.
So, If applying milk paint to a non-porous surface, light sanding is an option that will assist in adherence if you want the paint to adhere better. By non-porous, I mean anything that has a finish on it already:
If the finish feels glossy, the surface is non-porous. Because non-porous surfaces have been sealed, their "pores" are closed and they have lost the ability to absorb anything. Just as hair color needs the chemical developer to open the hair cuticle (and make it porous) to allow the color to penetrate, so does milk paint. And that's what sanding does.
There is also another way. Add a bonding agent to the paint. Since Junkyard Goddess Milk Paint does not have any synthetic (and often toxic) glues or adhesives in the formula, adding our non-toxic and naturally-derived bonding agent, essentially makes the paint "stick" to the surface. Since the paint is basically adhering to the surface (similar to a traditional latex paint or a chalk-based paint) without penetrating it, this gives the finished project a different look than if you used the milk paint alone.
The coverage will be more even and consistent without much variance in texture. This can be beautiful, just make sure it's the look you were initially going for. For instance, if you were painting a vintage dresser and you wanted it to look a little used and loved (in lieu of brand-new, squeaky clean) you would likely want the finish to be in the style of shabby-chic or cottage. Both of these styles celebrate the beauty and character of something that has aged naturally.
The nature and ingredients of Junkyard Goddess Milk Paint lend themselves perfectly to this "imperfectly beautiful" style. With light distressing and "chipping" you have a beautiful work of art that can fetch high dollars, if you're selling it.
But if you were to use the wrong type of paint (or added too much bonding agent to the mixture) that created a perfectly opaque, even-toned and consistent finish that adhered REALLY well, you would work twice as hard trying to distress it and chip it up. And once you finished, it likely would LOOK like it was deliberately sanded and chipped up, instead of looking like it aged naturally. This is NEVER a good idea when painting furniture.
So, in order to prepare your piece to paint and determine whether or not to sand and/or use a bonding agent in your milk paint mixture, you first need to decide what style you'd like your completed project to be. Then you'll be ready to move on to the next step, Painting With Milk Paint.