Waterproofing Methods: Brushing, Rolling, and Troweling!

Waterproof coating application methods include brushing, rolling, spraying, and troweling. In actual construction, the method should be selected based on the type, performance, thickness of the material, and specific work locations.

For rigid waterproof coatings, use steel trowels or wooden floats for troweling; for flexible waterproof coatings, manual brushing with a brush (such as a flat brush, long-handled brush, or round brush) or mechanical rolling can be used.

Use a brush to apply coating generally using the 'back-brush' method, or apply it along the edge of the coating using a brush to level it. For vertical surfaces, the back-brush method is recommended. The coating must be applied evenly and consistently. When applying, control the amount spread to avoid excessive accumulation in one area, which may cause difficulty in leveling and result in uneven thickness. Avoid trapping air bubbles within the coating layer—remove any bubbles immediately if detected. The number of passes must follow pre-test results to ensure proper coverage. Never rush through the process just to save time or effort—do not over-apply in a single pass. After the first coat dries completely, proceed with the next layer. After drying, clean off any residue or contaminants before applying the next coat. Prior to each subsequent layer, inspect the previous layer carefully for defects such as air bubbles, pinholes, leaks, cracks, or foreign materials. Repair any issues before proceeding.

Apply coating to vertical surfaces first, then horizontal ones. When applying vertically or horizontally, use either segmented or sequential methods. When segmenting, each section's width should match the width of the reinforcing material to prevent stepping on freshly coated areas. For coatings with poor flow properties, to facilitate rolling and speed up progress, segmented intervals can be used. After the first layer dries, roll and smooth the surface. Segments are typically 0.8–1.0 m wide to allow easy rolling operations and align with the width of reinforcing materials.

Apply the coating to vertical surfaces before horizontal ones. The number of applications depends on the coating’s flow quality—coatings with good flow should be applied multiple times to avoid sagging. This prevents upper layers from becoming thinner and lower layers thicker, which could compromise the waterproofing performance. Ensure even, consistent application across all layers, with perpendicular directions between passes to enhance overall integrity and uniformity. Overlap joints by 50–100 mm during each pass, extending beyond the joint by at least 50 mm to prevent leakage.

Achieving consistent coating thickness is critical for quality. After brushing, the coating should be applied uniformly according to the specified thickness (based on the material’s per-square-meter usage). Apply evenly and precisely. The brushing direction between layers should be perpendicular to ensure structural integrity and uniformity. Overlaps should be maintained at 50–100 mm, extending beyond the joint to avoid leakage.

For rigid waterproof coatings with poor flow characteristics, rolling is typically used. Due to the relatively thick layer produced by rolling, stricter workmanship standards are required. Therefore, operators must have solid experience in rolling techniques and a thorough understanding of the material’s properties and requirements.

1) Rolling Work Process. Rolling typically includes two steps: base layer application (bottom layer coating) and waterproof membrane rolling.

① Base Layer Application. Use mechanical rolling or manual brushing to apply a single layer of waterproof coating onto the substrate. The goal is to fill micro-pores and fine cracks while enhancing adhesion between the base and the waterproof layer.

② Waterproof Layer Rolling. After the base layer has dried, proceed with rolling the waterproof coating using tools such as trowels, rollers, or corner scrapers. Typically, one pass is sufficient.

For wall corners, roll from top to bottom and left to right, starting from one side and smoothing the edge. Achieve a smooth, tight finish. Leave a small margin (rough surface) to prepare for the next coat. When repairing wall surfaces, form the junction between walls and floors into a rounded shape.

When rolling the floor waterproof layer, pay attention to the junction with walls. This area should be formed into a rounded shape to increase thickness. Roll from the wall base toward the center of the floor in one direction, pushing and smoothing the edges evenly. Leave a rough surface to aid in subsequent work. Complete the entire floor in one continuous pass—do not leave gaps or unfinished sections. If there are joints or overlaps, treat them properly with waterproofing measures.

When the base surface is uneven, add an extra trowel pass. Apply another layer of coating over the existing base layer to improve flatness and strengthen the bond between the base and surface layers. This improves both surface flatness and adhesion.

② Rolling Protective Layer. After the waterproof layer has dried, apply the protective layer according to design requirements.

2) Rolling Work Precautions

① Do not collect spilled coating on the ground to avoid contamination and potential impact on waterproofing effectiveness.

② The coating thickness must be determined based on design specifications and must be even and consistent.

③ Tools and coating materials should be checked promptly. If contamination or debris is found, clean or discard immediately.

④ After troweling, wait until the surface is no longer wet before using a steel trowel to press and smooth. Timing is crucial—rolling too early has no effect; too late causes the coating to adhere to the trowel, resulting in crescent-shaped marks.

⑤ After rolling the waterproof layer, wait for it to dry before applying the protective layer.

Troweling involves using a trowel to evenly spread rigid waterproof coating onto the substrate to form a coating layer that meets design thickness requirements. Common tools include angle trowels, oil trowels, and curved trowels.

1) Troweling Work Process. During troweling, first spread the coating directly onto the substrate, then use a trowel to level and smooth it, ensuring even thickness, no sagging, no air bubbles, and a smooth surface. Allow it to dry. For coatings with poor flow, after the surface is no longer wet, use a steel trowel to press and smooth.

① Apply force evenly when troweling. Maintain a 50°–60° angle between the trowel and the surface. Apply consistent pressure.

② Control coating thickness using pre-marked metal rods (or wooden strips) placed on the trowel or directly on the substrate. The rod height must match the required thickness. Typically, 2–3 passes are needed, with a total thickness of 4–8 mm.

③ Only perform 1–2 back-and-forth troweling passes. Do not repeat more than twice, or it will lead to 'dry skin not drying' (a condition where the surface hardens while the interior remains soft).

④ For circular or irregular surfaces, use a curved trowel for troweling.

⑤ To accelerate work progress, use segmented intervals. After the first layer dries, roll and smooth the area. Segment width is usually 0.8–1.0 m, matching the width of reinforcing materials for ease of operation.

⑥ Proceed to the next layer only after the previous layer has fully dried (typically at least 12 hours). Wait until the coating is firm enough to avoid footprints or sinking before continuing.

⑦ If defects such as air bubbles, uneven surfaces, cracks, or trowel marks appear, repair them immediately before proceeding to the next layer.

2) Hot-Melt Troweling Process

The hot-melt troweling method is suitable for high-performance, modified asphalt waterproof coatings. First, mix the coating with a heating agent in a container and gradually heat it to around 190°C. Keep it warm for use. Before application, spread the heated coating onto the substrate, then quickly use a trowel with a sharp edge to level it. Work swiftly and accurately, ensuring the coating is evenly leveled before it cools. If it hardens prematurely, it cannot be leveled effectively.

Controlling coating thickness is key in hot-melt troweling. Use a trowel with a sharp edge and push it forward at a consistent angle. Maintain a stable angle and move smoothly. Complete the troweling before the coating begins to harden. In cold environments, the coating cools rapidly—especially on flat surfaces where heat dissipates quickly and is absorbed by the substrate. It’s easy to start troweling before the coating is fully hardened. Adjust material quantity and minimize the interval between spreading and troweling. If temperatures are too low, preheat the substrate with a heat lamp before applying and troweling. If the coating starts to harden prematurely, use a heat lamp to reheat the surface until it turns dark gray, then re-trowel for a smooth finish.

When applying waterproof coatings on reinforced concrete structures, control the thickness of each troweled layer at 1–1.5 mm. For reinforced concrete elements, use segmented troweling. After leveling the first layer, immediately install the reinforcement, then trowel the second layer to the design thickness. When applying a cement-based protective layer, apply it simultaneously with the final trowel pass. When applying a protective layer over the waterproof membrane, do so only after the membrane has fully cured.

Combining hot-melt coatings with reinforcing mesh significantly enhances the reliability of the waterproof layer. The mesh ensures consistent thickness, while the coating forms a continuous waterproof barrier, preventing leaks caused by mesh joints. Especially with pressure-sensitive, thermoplastic modified coatings, this combination eliminates stress-induced cracks from structural layers and substrate cracking, containing leaks within localized areas without compromising overall waterproof performance. Before combining, mark the mesh width and overlap width on the substrate. During work, spread the heated coating in a flowing pattern onto the substrate, then immediately use a trowel with a sharp edge to level it. Then, one person follows the line to lay the mesh, while another uses a long-handled roller to press from the center outward, expelling air beneath the mesh and ensuring tight adhesion. After the coating cools, treat the mesh joints.