Exterior Wall Plastering Construction Technology and Methods - HPMC

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Exterior wall plastering is a fundamental process in the decoration and protection of building exterior walls, and its quality directly affects the waterproofness, durability, and aesthetics of the exterior walls. The main construction process includes: pre-construction preparation → base layer treatment → setting lines and creating plaster spots and screeds → applying the base coat → applying the intermediate coat (whether this layer is needed depends on the design thickness) → applying the top coat and smoothing (or creating a finishing base layer) → curing → quality acceptance.

I. Pre-construction Preparation

1. Technical Preparation: Familiarize yourself with the construction drawings, clarifying the plastering scope, thickness, materials, and special requirements (such as waterproofing, crack resistance, etc.). Provide detailed technical and safety briefings to the construction team.

2. Material Preparation: Prepare qualified cement, sand, admixtures (such as waterproofing agents, crack-resistant fibers, etc.), wire mesh, etc., according to design requirements. Ordinary Portland cement with a strength grade not lower than 32.5 is recommended; medium sand with a mud content not exceeding 3% should be used and sieved before use.

3. Tool and Equipment Preparation: Mortar mixer, wheelbarrow, shovel, trowel board (plaster), wooden trowel, plastic trowel, corner trowel, mortar support board, screed (aluminum alloy or wooden), straightedge, plumb bob, spirit level, measuring tape, sprayer, water pipes, scaffolding or suspended platform, etc.

II. Substrate Preparation

This is a crucial step in preventing hollow spots and cracking.

1. Cleaning: Thoroughly remove dust, dirt, oil stains, residual mortar, and loose particles from the substrate surface. For release agents on concrete surfaces, they must be thoroughly removed with a specialized cleaner or wire brush.

2. Roughening/Spraying Cement (Concrete Surface): Smooth concrete surfaces require roughening, or the "spraying method" (evenly spraying cement slurry onto the wall surface to form a rough bonding layer) to enhance the adhesion between the mortar and the substrate.

3. Wetting: The wall surface should be thoroughly wetted with water the day before plastering. Watering should be even, with a penetration depth of 8-10mm. During plastering, the wall surface should remain moist but without standing water. This step reduces the amount of moisture absorbed by the substrate from the mortar, preventing hollow spots.

4. Wire Mesh Installation: Crack-resistant steel wire mesh or alkali-resistant fiberglass mesh should be laid at the junction of different materials (such as concrete and masonry blocks), in the backfilling of embedded pipe trenches, and in areas with large-area plastering. The mesh should be flat and taut, with an overlap of no less than 150mm on each side, and securely fixed with cement nails or nail guns.

5. Hole Sealing: Inspect and seal all through-wall holes, scaffolding wall tie holes, etc., ensuring a tight seal.

III. Establishing Standards, Creating Mortar Patches, and Applying Mortar Strips

1. Establishing Squareness: First, use a plumb line to hang vertically from the roof downwards, combined with a level, to determine the plaster thickness. Create a standard mortar patch (approximately 5cm square) at each of the upper and lower corners of the wall. Then, using the plumb line, create two more standard mortar patches at the lower corners of the wall, based on these two mortar patches.

2. Creating Mortar Patches: Using the standard mortar patches as a reference, create additional mortar patches at doorways, windows, and corners. The mortar material for the mortar patches is the same as the base coat.

3. Applying Mortar Strips (Marker Strips): After the mortar patch mortar has hardened, apply a trapezoidal mortar strip approximately 80-100mm wide between the upper and lower mortar patches. Smooth it with a screed until its thickness is flush with the mortar patch, serving as the benchmark for plastering. The spacing between mortar strips should generally not exceed 1.5m.

IV. Layered Plastering

Exterior wall plastering must be done in layers, with each layer ideally 5-7mm thick. When the total thickness exceeds 35mm, reinforcement measures are required (such as adding double-layer mesh).

1. Applying the base coat:

On the moistened substrate, first apply a thin layer of neat cement slurry or interface agent, then immediately apply the base coat mortar.

Use a trowel to firmly press the mortar onto the wall, ensuring the thickness is slightly lower than the screed.

This initial leveling ensures a tight bond between the mortar and the substrate.

2. Applying the intermediate coat:

After the base coat has set (approximately 60-70% dry, leaving an indentation but not softening when pressed), begin applying the intermediate coat.

The thickness should be sufficient to fill the screed. Use a screed to smooth the coat from bottom to top, promptly filling any gaps.

After smoothing, use a wooden trowel to roughen and smooth the surface, creating a good foundation for the final coat adhesion.

3. Topcoat Plaster: After the intermediate plaster has set (usually the next day), apply the topcoat plaster.

The mix ratio of the topcoat plaster should be according to design requirements, and it is usually finer.

During application, first use a trowel to apply a thin layer, then smooth and compact the second layer.

The finishing method depends on the desired finish: for paint finishes, use a wooden trowel to create a finely textured surface or a plastic trowel to smooth it; for tile finishes, create a rough, textured surface; for thick paints such as stone paint, create a smooth, finely textured surface.

4. Detail Treatment: Door and window openings, balconies, window sills, awnings: Ensure proper drainage slope and drip lines (grooves). Drip lines should be straight, higher on the inside and lower on the outside, with a depth and width of no less than 10mm.

Inside and outside corners: Use a corner trowel to smooth and straighten them. A straightedge can be used to check their verticality and squareness.

V. Maintenance 

After the plastering layer is completed, moisturizing maintenance should begin 24 hours later. In summer, avoid direct sunlight and use a sprayer or cover with damp burlap sacks or straw mats to regularly sprinkle water for maintenance. The maintenance period should generally be no less than 7 days, especially in dry, hot or windy weather.