Milk paint

Overview

Traditional milk paint is a casein (milk protein) paint with lime and pigment, sold as a powder. Fine Woodworking (Hiller) says casein plus lime react and cure over time. Popular Woodworking says modern "milk paint" typically has casein, lime, pigment and fillers. Wikipedia describes it as a casein paint with a brittle film and ancient history. Not every product sold as milk paint contains casein: General Finishes describes its Milk Paint as a low-VOC, self-sealing, mineral-based paint named for its low-luster sheen, and does not mention casein.

Pros

• Flat, matte, historical look.
• Powder keeps indefinitely when sealed (Fine Woodworking).
• Manufacturer claims (Old Fashioned Milk Paint Co.): biodegradable, non-toxic, odour-free when dry; dry to touch in 30 minutes, recoat after 2 hours.
• Chips and flakes without a topcoat, which suits distressing (Real Milk Paint Co. blog, a manufacturer view).

Cons

• Limited pot life: mix only a day's worth (Fine Woodworking).
• Dries lighter than wet.
• Needs a topcoat for long-term protection (Popular Woodworking); the film is brittle.
• Best on porous wood; not smooth metal or plastic (Popular Woodworking). Extra-Bond helps on non-porous ones (maker).
• Old Fashioned Milk Paint Co. says acrylic sealers may not resist grease, so use an oil or solvent sealer on kitchen cabinets.

Suitability

Bare or scuffed wood, especially softwood and reclaimed pieces (Eastern white pine). For refinishing, use a bonding agent and scuff first (Fine Woodworking). General Finishes says tannin bleed from oak, pine, mahogany and Douglas fir needs a stain blocker or white undercoat under light colours.

Coats and application

1. Sand 120 or 150 (General Finishes product).
2. Mix powder with water; strain as needed. Fine Woodworking: mix a day's worth.
3. 2 coats, with 2 to 4 hours between coats and buff with 220 to 320 (General Finishes product; its paint is thinned 5 to 10% with distilled water).
4. Topcoat with shellac, oil or poly (Popular Woodworking); flaxseed oil is the traditional topcoat. General Finishes says its paint needs no clear topcoat over white or light colours, because of yellowing.

Compatibility

Topcoats include Shellac and Boiled and raw linseed oil. Do not clear-coat white and pale colours with an oil-based product if yellowing matters (General Finishes). Compare Chalk paint.

Care and repair

Rewax or reoil the topcoat. Chips can be touched up with a new mix of paint, though colour may differ.

Safety and environment

Manufacturer claims of non-toxic and VOC-free are claims; the lime in traditional powders is calcium hydroxide, which NIOSH lists as an eye and skin burn hazard and respiratory irritant, so wear gloves, eye protection and a dust mask when mixing. Not stated as food safe.

Related

• Chalk paint
• Distressing and antiquing
• Latex and acrylic enamel paint