Walls are the primary barrier between the indoors and outdoors. Once wall waterproofing fails or structural gaps appear, outdoor moisture can seep in, leading to damp walls and mold. The common causes include:
1. Damaged exterior wall waterproofing:
Exterior walls are constantly exposed to wind and rain, causing materials like paint, tiles, and insulation layers to age, crack, and peel over time. Rainwater seeps into the wall through these damaged areas. Older houses are especially prone to this, as their waterproofing layers may have expired or were poorly applied during initial construction (e.g., uneven paint coating or loosely attached tiles). Additionally, if the exterior insulation layer develops hollows or cracks, rainwater can pool between the insulation and the wall, slowly seeping indoors. This creates “invisible seepage,” where there are no obvious water stains on the surface, but the wall remains constantly damp.
Exterior walls are constantly exposed to wind and rain, causing materials like paint, tiles, and insulation layers to age, crack, and peel over time. Rainwater seeps into the wall through these damaged areas. Older houses are especially prone to this, as their waterproofing layers may have expired or were poorly applied during initial construction (e.g., uneven paint coating or loosely attached tiles). Additionally, if the exterior insulation layer develops hollows or cracks, rainwater can pool between the insulation and the wall, slowly seeping indoors. This creates “invisible seepage,” where there are no obvious water stains on the surface, but the wall remains constantly damp.
2. Structural gaps in the wall:
During construction, minor gaps are inevitable in masonry and concrete pouring. Later house settling can also widen these gaps. These gaps act as “channels” for rainwater to penetrate the wall and spread to the interior. Common high-risk areas include the joints between window sills and walls, balcony railings and walls, air conditioning holes, and where pipes pass through the wall.
During construction, minor gaps are inevitable in masonry and concrete pouring. Later house settling can also widen these gaps. These gaps act as “channels” for rainwater to penetrate the wall and spread to the interior. Common high-risk areas include the joints between window sills and walls, balcony railings and walls, air conditioning holes, and where pipes pass through the wall.
3. High water absorption rate of wall materials:
Some older homes use red bricks or aerated concrete blocks, which are highly absorbent. If the exterior wall lacks effective waterproofing, rainwater is absorbed by the wall. When the indoor and outdoor temperature difference changes, the moisture vapor exudes from the wall, causing dampness. This is particularly common in rainy southern regions; even without obvious exterior damage, walls may appear to be “sweating.”
Some older homes use red bricks or aerated concrete blocks, which are highly absorbent. If the exterior wall lacks effective waterproofing, rainwater is absorbed by the wall. When the indoor and outdoor temperature difference changes, the moisture vapor exudes from the wall, causing dampness. This is particularly common in rainy southern regions; even without obvious exterior damage, walls may appear to be “sweating.”
Wall Dampness and Seepage: Identify the Source First, Then Treat Accordingly
Wall dampness is the most common issue. First, determine whether it is caused by “exterior penetration,” “internal pipe leaks,” or “condensation,” and then treat it accordingly.
1. Methods to Identify the Source
- Exterior penetration: Water stains or dampness appear on the wall during rain and gradually dry up when the weather clears.
- Pipe leaks: Localized dampness on the wall, especially near water or AC pipes, usually indicates a pipe leak or poor sealing around the pipes.
- Condensation: No obvious water stains, but the wall is overall damp and moldy, worsening when ventilation is poor.
2. Wall Dampness Caused by Exterior Penetration
If the exterior wall is accessible (e.g., a standalone house or if the community allows exterior work), treating it from the outside is the best permanent fix. If exterior work is impossible (e.g., high-rise apartments or restricted by property management), you must apply an indoor remedial treatment.
If the exterior wall is accessible (e.g., a standalone house or if the community allows exterior work), treating it from the outside is the best permanent fix. If exterior work is impossible (e.g., high-rise apartments or restricted by property management), you must apply an indoor remedial treatment.
Exterior Treatment Plan:
- Step 1: Clean the damaged areas on the exterior wall. Scrape away aged, cracked paint and tiles. Hollow insulation layers must be removed and relaid.
- Step 2: Use BANDě repair series materials to fix wall gaps. Fill gaps around doors, windows, and pipe penetrations with sealant and expanding foam, then level the surface with BANDě inorganic powder.
- Step 3: Reapply the exterior waterproofing layer. Use BANDě exterior-specific waterproofing materials (such as inorganic rigid waterproofing agents or cement-based waterproof coatings) or waterproofing membranes. Apply evenly, paying special attention to window sills, balcony railings, and drains.
- Step 4: Restore the exterior decorative layer by applying BANDě exterior inorganic paint or retiling to ensure a flat, sealed surface.
Indoor Remedial Plan:
If exterior work is impossible, you must apply “negative-side waterproofing” from the inside. While not as effective as exterior treatment, it will alleviate the problem.
If exterior work is impossible, you must apply “negative-side waterproofing” from the inside. While not as effective as exterior treatment, it will alleviate the problem.
- Step 1: Remove the decorative layer (paint, wallpaper, putty) from the damp interior wall until the base wall is exposed.
- Step 2: Clean the wall surface. Once dry, apply a negative-side specific waterproof coating (such as BANDě penetrating crystalline waterproofing). This type of coating penetrates the wall to form waterproof crystals that block the seepage channels.
- Step 3: After the waterproof coating dries completely, use moisture-resistant putty to level the wall, then apply BANDě inorganic anti-mold paint.
- Step 4: Restore the decorative layer.
Note: Negative-side waterproofing requires specialized materials; regular waterproof coatings are ineffective. Also, ensure the base wall is completely dry during application.
3. Wall Dampness Caused by Seepage Around Pipes
- Step 1: Locate where the pipes pass through the wall or floor slab. Scrape away the surrounding decorative layer and old sealant.
- Step 2: Check if the pipes are damaged. If leaking, replace the pipe or repair the joints.
- Step 3: Fill the gaps between the pipes and the wall/floor slab with expanding foam, then seal with sealant to ensure there are no voids.
- Step 4: Apply BANDě waterproof coating to the surrounding wall, extending at least 10 cm beyond the pipe, and then restore the decorative layer.
4. Wall Dampness Caused by Condensation
The core solution for this issue is “ventilation/dehumidification + reducing temperature differences.”
The core solution for this issue is “ventilation/dehumidification + reducing temperature differences.”
- Step 1: Improve indoor ventilation. Open windows frequently on sunny days. During the plum rain season or winter, use fresh air systems or exhaust fans to promote air circulation.
- Step 2: Control indoor humidity. Use a dehumidifier or the AC’s dehumidification mode to keep indoor humidity between 40% and 60%. Reduce indoor moisture generation during humid weather (e.g., turn on the range hood while cooking, close the bathroom door and turn on the exhaust fan while showering).
- Step 3: Improve wall insulation. If the wall lacks insulation, install insulation boards on the interior wall before applying the decorative layer. This reduces the temperature difference between the wall and the indoor air, preventing condensation.
- Step 4: Treat the wall. Scrape away moldy areas, wipe and disinfect with an anti-mold agent. Once dry, apply BANDě inorganic anti-mold paint to prevent future mold growth.
