Hydrated Lime for Whitewash: Mixing Your Own Lime Paint

Premixed limewash is convenient, but it costs far more than the raw ingredients inside the bucket. Using hydrated lime for whitewash lets you mix a traditional lime paint from a bag of type S lime, clean water and a few simple additives for a fraction of the price. The result is a breathable, matte, slightly chalky finish that has coated barns, fences, masonry and plaster walls for centuries.

The short version: soak type S hydrated lime in water to make a lime putty, let it rest at least overnight, then thin it to the consistency of skim milk and brush on several thin coats. Salt or a small amount of binder improves adhesion and weather resistance outdoors. Each coat looks translucent going on and dries much whiter as it cures.

Lime is caustic, though, so mixing it safely matters as much as the recipe. Gloves, eye protection and good ventilation are not optional.

Why Use Hydrated Lime for Whitewash

Whitewash made from lime is a mineral finish rather than a film. As it dries, calcium hydroxide reacts with carbon dioxide in the air and slowly turns back into calcium carbonate, essentially a thin layer of limestone bonded into the surface. That process, called carbonation, is why lime painted walls feel stony and age gracefully instead of peeling like a failed latex coat.

Lime also breathes. Moisture can pass through it, which makes it a good fit for brick, stone, stucco and old plaster that need to release water vapor. It is naturally alkaline, which discourages mold growth on the surface, and it is inexpensive. A single bag of hydrated lime can cover a large fence or several interior walls.

The tradeoff is durability on the wrong surface. Lime bonds best to porous, mineral substrates. It will not stick reliably to glossy paint, plastic, or sealed surfaces without a mineral primer, and it rubs off slightly when fresh. That chalkiness is part of the character.

Choosing the Right Lime

Type S hydrated lime is the most widely available option at home centers and masonry suppliers. It is fine, dry calcium hydroxide sold in large bags for mortar and plaster. Type S is processed under pressure so it hydrates more completely, which makes it more reliable for DIY lime paint than type N.

Avoid these common mix-ups:

• Garden or agricultural lime is ground limestone (calcium carbonate). It will not cure into a whitewash and simply washes off.
• Quicklime (calcium oxide) reacts violently with water, generating heat. It is not a DIY product.
• Hydraulic lime sets partly by reacting with water, behaves differently and is mainly used for mortars.

Safety First: Working With Caustic Lime

Hydrated lime is strongly alkaline. Dry powder and wet putty both burn skin and can cause serious eye injury. Protect yourself every time you open the bag:

• Wear chemical-resistant gloves, long sleeves and sealed safety goggles, not just glasses.
• Wear a well-fitted N95 or better respirator when pouring dry powder, and mix outdoors or in a well-ventilated area to keep dust down.
• Always add lime to water, never water onto a pile of dry lime, to reduce dust and splashing.
• Keep a bucket of clean water and an eyewash bottle nearby. If lime gets in your eyes, flush with clean water for at least 15 minutes and get medical help.
• Never mix lime with acids or other chemicals beyond the simple additives listed here, and keep children and pets away from buckets and wet surfaces.
• Store bags dry and sealed, away from food and away from pilot lights or ignition sources in shared utility spaces.

Tools and Materials

• Type S hydrated lime
• Clean, cool water
• Optional: plain table salt or a small amount of compatible binder for exterior work
• Optional: lime-safe mineral pigments for tinting
• Two 5-gallon buckets with lids, a drill with a paddle mixer, a fine mesh strainer
• Wide masonry or whitewash brush with natural bristles
• Garden sprayer or mister for dampening the surface
• Gloves, goggles, respirator, drop cloths

DIY Lime Paint Recipe and Slaking Steps

Slaking here means soaking hydrated lime in water so the particles fully wet out and form a smooth putty. With type S hydrated lime there is little heat, but the soak improves workability dramatically.

1. Fill a bucket about one-third with water. Use cool, clean water.
2. Add lime slowly. Gently tip lime into the water while stirring at low speed. A common starting ratio is roughly equal volumes of lime and water to make a thick putty, about the consistency of yogurt.
3. Mix thoroughly. Run the paddle mixer until there are no dry lumps. Keep the speed low to avoid splashing.
4. Cover and rest. Leave a layer of water on top, seal the bucket and let it sit at least 24 hours. Many traditional mixers let putty age for days or weeks; longer aging gives a creamier result. Keep the water layer topped up so air does not start curing the lime.
5. Thin to working consistency. Pour off excess water, stir, and add fresh water a little at a time until the mix is like skim milk or thin cream. For many surfaces that ends up roughly 1 part putty to 1 to 3 parts water. Thinner is better; heavy coats crack and dust.
6. Add salt or binder if needed. For exterior surfaces, dissolve roughly a few cups of salt per 5 gallons of mix in warm water and stir it in, or add a small amount of a compatible binder per the product label. These additions help adhesion and weather resistance.
7. Tint (optional). Pre-mix lime-safe mineral pigments in water before adding, and keep any tint under about 10 percent of the lime by volume.
8. Strain. Pour through a fine mesh strainer to remove grit so the brush glides.

Applying Whitewash Coat by Coat

1. Prepare the surface. Brush off dirt, cobwebs and loose material. Remove failing paint. Lime will not bond over glossy coatings.
2. Dampen the wall. Mist porous masonry or plaster until it is damp but not dripping. A damp surface slows drying and helps the lime bond.
3. Brush thin coats. Work in random crisscross strokes and keep a wet edge. The first coat will look nearly transparent. Resist the urge to lay it on thick.
4. Let each coat cure. Allow at least 12 to 24 hours between coats, misting the previous coat lightly before the next.
5. Build to the look you want. Most surfaces need 3 to 5 coats for solid coverage. Fewer coats give a weathered, translucent effect.
6. Protect while curing. Shield exterior work from rain, hot sun and frost for several days. Avoid applying under about 40°F or in direct afternoon sun.

Coverage: Because the mix is so thin, a gallon of working whitewash typically covers a few hundred square feet per coat on smooth plaster, and noticeably less on rough brick or stone that absorbs more. Plan for multiple coats when you estimate how much hydrated lime for limewash you need.

Troubleshooting Lime Painted Walls

Coating rubs off heavily: The mix was too thick, the surface dried too fast, or there was no binder outdoors. Mist between coats, thin the mix, and add salt or binder for exterior use.

Cracking or crazing: Coats were too heavy. Brush off loose material and apply thinner coats.

Streaky or blotchy finish: Uneven surface dampness causes uneven drying. Mist evenly and keep a wet edge. More coats will also even out appearance.

Will not stick at all: The surface is sealed or glossy. Strip to bare masonry or use a mineral-based primer designed for lime.

Finish looks gray when wet: That is normal. Lime dries much whiter over several days as it carbonates.

Cost Comparison

A bag of type S hydrated lime is inexpensive, generally a modest amount at most home centers and masonry yards, and it can make many gallons of whitewash. Premixed limewash usually costs many times more per gallon. The DIY route also lets you adjust thickness and tint as you go. The main extra costs are a good brush, a mixer paddle and safety gear, which you can reuse.

When to Call a Pro

Bring in a masonry or restoration contractor for historic buildings, tall exterior walls that need scaffolding, or any wall where moisture problems, efflorescence or crumbling mortar suggest deeper issues. Old painted surfaces may contain lead, so test pre-1978 paint before scraping or sanding. A pro can also handle large exterior jobs where weather timing is tight. For a fence, a garage interior, a brick fireplace surround or a single accent wall, hydrated lime for whitewash is a rewarding DIY project with proper protective gear.