Limewash and whitewash are two techniques used to give brick a light, matte finish, but they differ in composition, application, and permanence. The best choice depends on your aesthetic goals and the specific surface.

Composition

• Limewash: A natural and environmentally friendly option made from limestone, water, and sometimes pigments. It is breathable and soaks into porous surfaces like brick.

• Whitewash: Traditionally made from lime, water, chalk, and binders, but a similar look can be achieved with watered-down white paint. It is paint-based and sits on top of the surface.

Appearance and Finish

• Limewash: Provides a natural, textured appearance that allows the brick's character to show through. It offers a more traditional finish.

• Whitewash: Creates a softer, more opaque finish, often used for a rustic or shabby-chic style.

Application and Permanence

• Limewash: Is semi-permanent and can be removed, making it a good choice if you might want to change the look in the future. It requires more skill to apply and cannot be used on previously painted brick.

• Whitewash: Is a more permanent solution. It is more forgiving to apply and can be used on painted brick. However, because it sits on the surface, it can trap moisture.

Ultimately, if you want a breathable, natural, and reversible finish for unpainted brick, limewash is a great option. If you need a more permanent, opaque coating that can be applied over painted surfaces, whitewash is the better choice. Whitewashing may also be more economical, costing approximately $1.40 to $4.20 per square foot.

The number of coats you need to apply when whitewashing a surface depends on how opaque you want the final product to be. If you're going for a transparent, barely there look, a single coat or two may suffice. For fuller coverage, you'll want to use multiple coats. Another option is to use a less diluted paint to get a thicker coverage. 

Various kinds of substances and deck preservatives act as protective coatings for wood to prevent rot, which is caused by water getting into the wood and creating cracks and splits. Stains, paints, and sealants are the three best options to protect your wood, but there are also oils, varnishes, and waxes available. You’ll need to reapply sealant at least once per year, and you should inspect your wood deck regularly to look for signs of damage or general wear and tear.

It’s a good idea to sand your porch before painting. This will remove loose or chipped paint and debris, and give you a cleaner surface so that your new paint goes on smoothly. But if the existing surface is in good condition, it’s not necessary to sand your porch before you paint.