[Acceptance of mud work details] Will the tiles become "bulging" after they are hollowed out? Popular science on the "five-point percussion method" of telescopic drum sticks and regulations and standards for builders to replace hollow bricks

Invisible landmines in the new home: Why do the newly installed tiles make a hollow sound when you walk on them?

In the greater Taipei area, after many homeowners have worked hard to complete interior renovations that lasted for several months, or happily bought a pre-sale house, when they walk barefoot on the new polished quartz tiles in the living room, or touch the beautiful tiles on the bathroom wall, they sometimes feel that the sound of certain tiles is "hollow" and "crunchy", which is completely different from the sound of other solid tiles. This is called "tile hollowing (hollow brick)" in mud work. Many homeowners find it troublesome and think that as long as the tiles are not cracked, it doesn't matter. This is actually a very dangerous misunderstanding. Taiwan is located at the junction of tectonic plates, with frequent earthquakes and drastic temperature changes in winter. If the mud mortar at the bottom of the tiles is not full enough and there is an air layer between the tiles and the structural wall, once it encounters severe thermal expansion and contraction, the tiles will suddenly bulge over a large area late at night because there is nowhere to release the expansion stress, burst and fly away. This is a common tragedy of "bulging arch" of tiles in Taiwan, which can easily injure family members.

Popular science on physical causes: Why do tiles produce hollows?

There are three main reasons for the hollowing out of tiles in terms of physics and clay work practices:
1. The clay tile laying method is not practical (single-sided adhesive): Traditional clay craftsmen are laying large quartz tiles (such as 60x60 or 80x80), sometimes in order to save labor, only cement mortar (or tile adhesive) is applied to the wall or floor, and the back of the tile is not applied (single-sided adhesive). This will result in insufficient contact area between the tiles and the mortar to form a continuous physical bonding surface.
2. The adhesive dries too quickly: When applied in hot summer, if the structural floor or wall is not wetted with water in advance, the floor will quickly absorb the moisture in the cement mortar, causing the mortar to lose its hydration reaction (Hydration) activity, and the tiles will dry out and fail before they are firmly adhered.
3. Starting the joint filling project too early: The 48-hour cement initial setting period has not passed after laying the tiles, and the moisture in the mortar has not yet completely evaporated. If the tile joints (sealant) are filled too quickly, the moisture will be locked under the tiles, and the air pressure generated by evaporation will push the tiles apart to form a hollow.

Telescopic drumstick "five-point tapping test method" and national acceptance standards

In the professional home inspection process, there are strict physical inspection methods to check the hollowness of tiles:
1. Drumstick tapping method: The home inspector will hold a "telescopic drumstick (Inspection)" with a solid stainless steel ball at the front. Hammer)" on each tile (i.e. the four corners of the tile's upper left corner, upper right corner, lower left corner, lower right corner, and the center point). Corners are the areas most likely to cause hollowing due to insufficient mortar.
2. Acceptance and return standards for builders and decorators in Taiwan: Although Taiwan currently does not have a uniform mandatory return empty rate under the Civil Code, based on the acceptance practices of pre-sale houses of the Department of Lands of the Republic of China and the negotiation standards of various construction technicians associations, there are the following three hard red lines for evaluation:
- The tile must be replaced.
- It is deemed to be unqualified and the builder should eliminate it and re-submit it.
- Because the ground bears the weight of the human body and the pressure of heavy objects, hollows on the ground are more likely to break than walls. Usually, if there are more than 3 consecutive hollow floor tiles in a room, the builder must eliminate duplicate ones in the entire area, otherwise the tiles will not pass the re-inspection.

Budget price for partial removal and replacement of tiles in Shuangbei

In the greater Taipei area, the cost of partial removal and repaving of hollow bricks is mainly affected by the "tile specifications" and "construction scope":
* The master needs to use a stone cutter to carefully cut the grout, remove the old tiles, remove the old cement mortar layer, and re-apply the adhesive for paving. The replacement cost of a single piece is about NT$ 3,000 to NT$ 5,000/piece. If the quantity is only 1 piece, the master will usually charge a basic half-day wage of about NT$ 2,500 - NT$ 3,500.
* The replacement price of a single piece with materials (excluding special imported brick fees) is about NT$ 800 to NT$ 1,800 / piece.
* Drill tiny holes in the joints of the tiles, use a high-pressure infusion machine to inject epoxy or special adhesive glue under the tiles to fill the hollows. The cost is about NT$ 800 to NT$ 1,500 per piece.

Commercial acquisitions and businessmen’s long-term asset thinking: empty talk is a hidden time bomb for future CapEx expansion

For real estate commercial investors who specialize in buying second-hand houses for renovation and resale (Flip) or operating long-term rental apartments in Shuangbei, Ceramic tile "penggong" is the most common after-sales maintenance dispute encountered in the decoration of old apartments in Taiwan. Once the tiles burst within 1 year after being resold to the buyer, according to the property defect warranty liability under the Civil Code, the merchant must bear the full cost of removal and resurfacing, and even need to compensate the buyer for the loss caused by the relocation of furniture. This will directly cause the CapEx (capital expenditure) of the investment property to get out of control and erode profits. When businessmen purchase mud for renovation of old houses for project acceptance, they insist on using telescopic drumming sticks to tap each piece for acceptance, and remove the hollow bricks before handing over the house, which can effectively eliminate the risk of arching in the next 5-10 years. This kind of sophisticated quality control of concealed mud work is an intangible asset that guarantees the long-term value-added space of the property and the buyer's willingness to take over.

Decoration and renovation contract specifications and project budget risk prevention (2025-2026 practice)

Residential interior decoration and water and electricity renovation involve huge financial and professional technical requirements, and are also one of the areas with the highest incidence of consumer disputes. According to the "Regulations on Interior Decoration of Buildings" announced by the Ministry of the Interior's Land Management Bureau and the "Interior Decoration Contract Template" of the Consumer Protection Agency of the Executive Yuan, when signing any decoration or water and electricity project contract, homeowners must adhere to the principles of "item detailing (pointing of work and materials)" and "staged acceptance payment", strictly reject vague estimates that "complete the whole room project in one go", and eliminate common disputes from the source of malicious additional payments after the start of construction.

In terms of budget preparation, industry standards recommend that the overall water and electricity project be disassembled into: foundation removal and stone removal, water supply and drainage pipes and outlet piping, electrical box and circuit configuration, switch and socket panel installation, mud backfilling and waterproofing, and general acceptance of the installation of electricity and water for all room equipment. It is recommended that the contract payment adopt a healthy payment ratio of 10% signing deposit, 30% completion of water and electricity pipeline slotting and piping, 30% completion of wood and cement structure, 20% completion of equipment installation, and retaining 10% of the final acceptance payment. The final payment will be allocated after confirming that the water and electricity functions are operating correctly.

Key points of pit prevention inspection during project construction and acceptance

1. On-site setting out to confirm positioning: Before water and electricity enter the site to cut stones and troughs, the homeowner should check the height of the switch socket, the height of the air-conditioning drain hole and the drainage slope one by one to avoid the dilemma of finding that the socket is blocked by the cabinet after the woodwork or system cabinet comes in.
2. Pipeline archiving, photography and storage: Before the water and electricity piping is completed and the pipes are sealed, it is necessary to take high-resolution photos and laser ranging marks of the ceiling, wall and ground pipeline directions of the whole house and archive them as a key basis for avoiding hidden water and electricity pipes when drilling holes in the wall to install paintings and hanging cabinets in the future.
3. Inspection of brand specifications of incoming materials: Confirm that incoming wires (such as Pacific, Walsin Lihua), circuit breakers (such as Shihlin Electric, Panasonic) and water pipes (Nanya PVC, SUS304 stainless steel) have CNS markings and factory inspection certificates to prevent inferior sub-brand materials from being mixed.