Masonry paint can be used on outdoor brick or stone walls to get a clean look that's easy to maintain. However, exterior paint should be redone or touched up every so often, and most people make the mistake of just going over older paint with new paint, which results in flaking and peeling over time. You can have the wall professionally re-rendered or follow the steps below to effectively strip masonry paint off your wall before you give it a new coat.
Step 1 - Take Appropriate Precautions
Wear elbow-length gloves and old clothes when working with caustic mixtures like those needed for this project as they can severely burn your skin. Also, use a wooden stick to mix to keep the solution away from your skin and clothing.
Step 2 - Scrape Flaking Paint
If masonry paint is not properly applied—such as if the wall was not properly rendered or not allowed to dry, or if coat after coat of paint was layered on—the top coat of paint will start peeling and flaking, and you are likely to have bubbles in the surface.
Take a putty knife or scraper to this peeling layer to remove loose bits. Many people use sandblasting and wire brushes, but while these methods provide a quick fix, they can damage the wall beneath the paint, leaving the surface porous.
Step 3 - Remove Fungus and Algae
You can get rid of fungus and algae on the surface by preparing a cleaning solution with one cup of bleach in one gallon of water. Apply this to the wall using a long-handled scrub brush, and then rinse with clean water.
Step 4 - Prep the Chemical Treatment
Once you have removed the top layer of the paint and fungus, let the wall dry. Prepare a caustic mix for stripping the remaining layers of paint while you wait. The easiest solution to work with will be a ready-made, peel-off mix you can purchase from your local home improvement stores.
However, if you'd rather create a mixture, just add about 300 grams of caustic soda to a liter of water. Then, add flour to the solution and mix until you reach porridge-like consistency.
Step 5 - Apply the Chemical Stripper
Apply the chemical stripper using an old flat brush or a scraper. You can mark out areas and do the job in square foot increments; if you need to, you can make the mix in batches so you don't have to worry about the solution drying out. Once applied, leave the mix on for two days before you remove it.
With ready-made, peel-away mixes, just follow the instructions on the product packaging.
Step 6 - Peel Away old Paint
Use a pressure hose with hot water to wash your homemade caustic off the wall. Your masonry wall will reveal itself as you rinse.
Your peel-away option will direct you to lay peeling strips on top of the mix. Let the strips sit for the directed amount of time, and then simply pull them off to take the paint with. Once you're done, give the wall a quick rinse. and make sure you dispose of the strips properly.