Wall damp keeps coming back after scraping. What should I do?
The short answer
Wall damp (salt efflorescence) is what's left behind when moisture moves through a wall, carries salts to the surface, evaporates and leaves crystals. The order never changes: find where the water comes from and stop it, confirm the wall has actually dried, and only then install boards and finishes. If you only scrape, patch and apply anti-mold paint while the water source is still there, it will come back.
Key points
- Wall damp is a symptom, not the cause. What needs fixing is where the water comes from and whether the wall has dried.
- Moisture has four sources: wet only after rain, constantly damp, wet only after water use, and seasonal condensation. Each is handled completely differently.
- Where the white powder appears is where moisture evaporates. The entry point is often above or to the side, not necessarily directly below.
- V-CORE vacuum-layer double-wall wall damp repair adds an independent functional layer on the indoor side after the water is stopped and the wall is confirmed dry. V-CORE itself does not stop water.
- If the exterior source is still letting water in and can't be fixed, we will tell you plainly not to board over the wall yet.
Why does wall damp keep coming back?
You scraped it, patched it, repainted it, and six months to a year later white powder appears in the same spot again, a little larger than last time. This is the most common story in older Taiwanese homes.
The cause isn't complicated. Moisture seeps through the pores of concrete or brick and carries free calcium and soluble salts from the cement with it. When the water evaporates at the wall surface, the salts stay behind and crystallize. That's the efflorescence, powdering, bubbling and peeling paint you see. As long as water still has a way in, the cycle repeats.
Conditions in Taiwan make this happen more often: hairline cracks from earthquakes, the high humidity and temperature swings of an island climate, the natural porosity and aging of concrete, and, in apartment buildings, water sources outside your own unit, such as the unit upstairs, pipe shafts, exterior walls and window frames.
Where is the water coming from? How to tell the four sources apart
| Type | When it gets wet | Common locations |
|---|---|---|
| Rain-driven | Appears only after heavy rain or wind from a certain direction, then slowly dries | Exterior wall cracks, tile joints, around window frames |
| Constant | Unaffected by weather; the damp patch keeps growing | A broken supply pipe or a loose fitting |
| Usage-linked | Noticeable only after showers, laundry or washing the balcony | Walls outside bathrooms, ceilings, pipe shafts |
| Condensation | Seasonal, large area, evenly spread | Cold wall surfaces, the inside of west-facing or north-facing exterior walls |
These four sources need completely different treatment. Mixing them up is where recurring wall damp begins.
Before you call anyone, note these three things
- Location: The bottom of the wall, by a window, the side next to the bathroom, or the side facing outdoors?
- Timing: Only noticeable after rain or during the plum rain season (May–June), or there all year round?
- The last repair: When was it done, what method was used, and how long before it came back?
If you can, take one photo on a sunny day and one after rain. These records help sort out what's going on, and they're more useful than any promise of a "guaranteed permanent fix."
Common mistakes
- Only scraping, patching and repainting: If the water source isn't dealt with, salts will migrate to the surface again with the moisture.
- Only removing mold or spraying anti-mold products: That clears the result, but the conditions that keep the wall damp are still there.
- Boarding over the wall before it has dried: It may look fine, but problems can show up one to three years later: the board's adhesive bond fails, boards bulge, or damp creeps out from board edges or around windows. And whatever is sealed in is hard to inspect later.
How 1618 天地牆 handles it: assess first, then build
We sort wall conditions into three situations, each handled differently:
- The source has been stopped, or it was condensation all along: We can go straight to indoor-side work. Condensation is the best-suited case: the functional layer raises the wall surface temperature, so condensation is less likely to form.
- The source is largely under control, but the wall still holds residual moisture: We first remove loose old plaster and reinforce the water-stopping, wait until a re-test shows the moisture level meets the target before boarding, and leave a removable access panel.
- The source is traced to the exterior wall, which hasn't been repaired yet: Fix the exterior wall first, and do the interior only after the wall has truly dried.
Layers of V-CORE vacuum-layer double-wall wall damp repair:
- Existing wall: Inspection, substrate preparation, water-stopping
- V-CORE vacuum-layer fire-resistant board: One composite board that handles thermal insulation, vapor blocking, and sound insulation and vibration damping
- Skim coat and paint: Back to a wall you can use normally
The V-CORE vacuum layer doesn't absorb water and has low vapor permeability, but it is not a waterproofing layer and does not stop water. Water-stopping is a separate step, and whether the workmanship and curing are done properly directly decides success or failure.
When is boarding over the wall not recommended?
- A supply or drain pipe is actively leaking.
- The wall's moisture content is high, meaning liquid water is still feeding in.
- The exterior source can't be fixed, for example because it's in another unit and the owner won't cooperate.
Forcing a board installation in these cases just seals the water inside the wall. The more honest approach is to first help work out what can be done about the source, or switch to a breathable repair that lets the wall keep drying, then come back to add the board once the source is fixed.
How to think about long-term cost
Don't just compare this one quote. How many times have you repaired this over the past few years? How much time went into moving furniture, closing off the room, cleaning up dust and repainting each time? And when will the next round be?
The value of the V-CORE vacuum-layer double-wall system is less demolition, faster installation, stable performance and low maintenance. The work is done from the indoor side, with no large-scale work at height on the exterior wall. Thermal insulation and vapor blocking come from how the build-up itself works, not from a coating that needs to be reapplied regularly.
How is the quote put together, and how are timing and handover judged?
We don’t quote without seeing the site. The inspection first establishes where the water comes from and how wet the wall is; only then does a quote mean anything. The quote lists the actual work item by item. Typical items:
- Preparation and removal: stripping loose old plaster, debris removal, dust protection and moving furniture.
- Water stopping and substrate: water-stopping treatment, crack repair, levelling and bond reinforcement. How many water-stopping coats are needed depends on the assessment, and the quote lists them separately.
- Functional layer and finishing: V-CORE vacuum-layer fire-resistant boards and fixings, edge sealing, access panels, skim coat and paint.
- Exterior wall: if the exterior wall has to be dealt with first, it gets its own quote, separate from the interior work. Where the exterior wall is a common part of the building, the work may need the building community’s consent.
How much space you lose: the functional layer adds thickness, so the quote states the finished net dimension of each wall. Moving sockets or switches is arranged separately with an electrician.
What drives the schedule: the biggest variable is waiting for the wall to dry. Exterior work that must come first, a wall that is still wet, and curing time after water stopping all extend the schedule. We explain this after the inspection rather than promising a fixed number of days.
What counts as handover: before boarding, we confirm the wall’s moisture condition and substrate bond; if it doesn’t pass, we don’t board, and this check is photographed. At completion we check board fixing, edges and the paint finish, re-check moisture around the area, and hand over the work record. Warranty scope and exclusions are written in the quote.
FAQ
Is wall damp always caused by a leak?
Not necessarily. Humid indoor air meeting a cold wall can also condense, leaving similar efflorescence and damp marks. Condensation and leaks are handled completely differently, so the cause has to be determined first.
Can a dehumidifier or anti-mold paint solve wall damp?
Dehumidifying and mold treatment deal with the result. If the moisture source isn't addressed, they usually only slow it down.
Can wall damp be fixed for good?
It depends on where the water comes from. Only if the source can be stopped and the wall can dry is there a chance it won't come back. Some sources are beyond what a resident can control, and in those cases we'll tell you honestly.
Water is seeping in through the exterior wall. Can I just fix the inside?
If the exterior source is still letting water in, an interior-only fix won't last. We'll recommend fixing the exterior wall first, then doing the interior once the wall has dried.
What if something goes wrong after the wall is boarded over?
Where needed, we add an access panel so future checks and spot repairs are possible, instead of sealing everything shut.
How long is the warranty?
Warranty scope and terms are based on the actual site assessment and the material's technical data, and are stated clearly at the quotation stage. We don't give a fixed number of years before it has been confirmed.
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