How to Properly Prime Engineering Blocks for Painting, Low-Suction Surfaces

You are painting the exterior of a property. You roll the masonry paint onto the main red brick walls, and it sticks perfectly. Then you get to the "DPC" (Damp Proof Course) - those bottom three rows of dark, shiny blue or red bricks near the ground. You paint them. A week later, the paint on those specific bricks is hanging off in large plastic sheets.

Why did the paint stick to the wall but fall off the base? Because those aren't normal bricks. They are Engineering Bricks. They are designed to be waterproof, chemically resistant, and incredibly strong. In painting terms, they are essentially glass.

Standard masonry paint relies on soaking into the brick to hold on. Engineering bricks don't let anything soak in. If you want to change the colour of these stubborn bricks, you have to stop treating them like masonry and start treating them like tiles.

1. Identification: Spotting the "Class A" Brick

Engineering bricks (like the famous Staffordshire Blue or Accrington Nori) are fired at extremely high temperatures until the clay vitrifies (melts).

• The Look: They usually have a metallic sheen or a smooth, shiny face. They are often Blue, Black, or Dark Red.

• The Sound: Tap one with a trowel. A normal brick goes "thud." An engineering brick goes "ring" (a high-pitched metallic clink).

• The Location: They are used where strength and water resistance are needed: Damp Proof Courses (bottom of wall), Window Cills, Archways, and Bridge Cappings.

2. The Science: Zero Suction

We talk a lot about "High Suction" surfaces (like Flettons) sucking the water out of paint. Engineering bricks have Low to Zero Suction. They are classified as Class A (< 4.5% water absorption) or Class B (< 7%).

The Failure Mode: When you apply standard masonry paint:

• The paint sits on the surface.
• It cannot send "roots" into the pores because there are no pores.
• It dries into a film that is merely resting on the brick, held only by weak surface tension.
• As soon as rain or frost hits it, the film delaminates and falls off.

3. The Preparation: Mechanical Key

You cannot skip this step. Because the surface is chemically inert and smooth, you must create a Physical Key. You need to roughen the surface to give the primer something to grab.

• Wire Brush: A hand wire brush is rarely enough.
• Angle Grinder / Drill: Use a cup brush attachment or coarse sanding disc (40–60 grit).
• The Goal: You are trying to take the "shine" off the face of the brick. You want to scratch it until it looks dull and matte.

Warning: Wear a mask. Silica dust is extremely dangerous.

4. The Primer: The "Bridge" Coat

Do NOT use a "Mist Coat" (diluted paint). Diluting paint is for absorbent surfaces. If you put watery paint on an engineering brick, it will just run down the wall and pool on the floor.

You need a High-Performance Adhesion Primer. You are looking for a product designed for "Difficult Surfaces" or "Dense Masonry."

Option A: Solvent-Based Stabiliser (The Traditional Way)

A high-quality, penetrating solvent primer can sometimes find enough microscopic grip to hold, but it is not the strongest option for vitrified surfaces.

Option B: Specialist Adhesion Promoters (The Modern Way)

This is the gold standard. Look for "All Surface" primers (often water-based, but reinforced with epoxy or acrylic resins) that claim adhesion to Glass, Tile, and PVC.

• If it sticks to glass, it will stick to engineering brick.

• Bedec MSP (Multi Surface Paint) or Zinsser Bulls Eye 1-2-3 are common examples of primers that can grip shiny surfaces.

5. The Application Process

1. Degrease: Engineering bricks near the ground often have splashes of oil from driveways or algae slime. Wash with a strong detergent and rinse. Dry thoroughly.

2. Abrade: Scuff the surface with your power tool.

3. Prime: Apply one thin coat of your Adhesion Primer. Do not put it on thick. You want a tight bond, not a thick skin.

4. Test: Wait 24 hours. Stick a piece of tape on the primer and rip it off. If the primer stays on the brick, you have adhesion.

5. Topcoat: Now you can apply your standard exterior masonry paint over the primer.

Conclusion

Painting engineering bricks is like painting a bathroom tile. If you just slap emulsion on it, it will wipe off. You have to accept that the brick does not want to be painted. You have to force it to accept the coating.

• Scratch the shine off

• Use a "Tile and Glass" grade primer

• Don't rely on standard masonry paint alone

Shop our Specialist Masonry Paints and Masonry Primers now.