This post covers sealants that you can (or should) use over Milk Paint, water-based acrylic paint, Chalk Paint, and clay paint to make them more durable to liquids, stains, and general wear.
Some sealants would change the look of the paint (the sheen level or even the color) and others will look invisible.
Different sealants would be used for interior versus exterior projects.
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1. To Seal Milk Paint on the Interior
Depending on where you are applying the Milk Paint and how durable you need it to be, you can choose from a number of topcoats including:
Natural oils: hemp oil, walnut oil (with wax), and the most durable penetrating oil, tung oil can all be used to seal Milk Paint. The oils tint the color – they darken it making the Milk Paint look richer, less pastel, not matte and chalk-like, and they add a slight yellow tint which you would only be able to see on some whites. Make sure the oil is compatible with the paint color. (See picture below).
Tung oil has the strongest (natural) odor of the three. Hemp and walnut oil are both quite mild in odor.
I did not have good luck with polyurethane or other acrylic coatings that are intended for wood floor finishing over Milk Paint
Alcohol-based coating: Shellac does work over Milk Paint but it looked uneven when applied directly onto the Milk Paint. It worked better when applying a natural oil first, then shellac (see photo below, but make sure you put enough coats of milk paint on before the oil as the oil will bring out the imperfections!). This leaves the Milk Paint very durable! It would be a good combo on toys and I would consider it for cabinets as well.
2. To Seal Milk Paint on the Exterior
Tung oil is the best sealant for Milk Paint that I know of. Be sure to put on enough coats of Milk Paint before the oil. As you can see above, my one coat of Milk Paint looked fine when it was just the paint, but once I added the tung oil it was clear that the paint was not applied thick enough.
Note, don’t use the shellac on exterior applications, that is just for the interior.
The color is Federal Blue from Old Fashioned Milk Paint
Synthetic polyurethane sealants didn’t work well over Milk Paint in my trials.
3. To Seal Water-Based (Acrylic) Paint on the Interior & Exterior
You don’t need a sealant on interior acrylic paint. If you used a paint that is too matte to hold up to what you need, you can go over with the same paint in a higher sheen. That will give it more durability and the ability to wipe it down easily.
AFM Polyureseal EXT is a clear low VOC polyurethane that can be applied over painted surfaces (usually this is used on the exterior).
You can also use other polyurethane or acrylic coatings over paint to make it more durable or to seal in a paint that is offgassing or toxic. See the post on remediating offgassing for more options.
4. To Seal Chalk Paint
I tried the Annie Sloan Wax which smelled like petroleum products to me and I did not tolerate it at my level of chemical sensitivity.
With Annie Sloan wax over Chalk Paint, it held up extremely well to mustard and mayo. Wax is actually the most durable coating over Chalk Paint.
You don’t have to use this type of wax, you can use a wax from The Real Milk Paint Company that is made with safer solvents or no solvents.
If you are waxing Chalk Paint, this large wax brush can be used to apply it to the walls. Remove the excess with a cloth.
I also tried the BioShield Glaze and that helped it hold up perfectly to mustard and mayo as well.
AFM Penetrating Waterstop did not help it hold up to mustard or mayo even though I had great results using this over clay plaster.
Acriglaze does not work over chalk paint either.
5. To Seal Clay Paint
Over BioShield Clay paint you can use Wall Glaze or AFM Penetrating Waterstop to add more water resistance and cleanability – I tested both of these. They recommend the wall glaze for areas like the kitchen and hallway.
The ingredients of the wall glaze are cellulose, alcohol ester, silica, carnauba wax, clay, water, and preservative.
BioShield Solvent-Free Paint worked the best with AFM Penetrating Waterstop as the sealant. It helped it hold up with no staining from either mustard or mayo and the clay paint retained the same color and sheen.
Wall Glaze also worked well on BioShield Solvent-Free Wall Paint but there is an ever so slight mustard stain.
Their basic Clay Paint held up best with their Wall Glaze. With also an ever so slight stain from my tests that cannot really be seen from a few feet away.
AFM Penetrating Waterstop did not help the basic Clay Paint hold up well.
Acriglaze works perfectly over clay paint as well, but I didn’t test this one.
Corinne Segura is a Building Biologist Practitioner with 8 years of experience helping others create healthy homes.
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