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[Second pouring seams in window frames are waterproof] Does water seep from the window when it rains? "Second pouring joint" seismic and anti-cracking grouting and non-shrinkage cement mortar construction method at the joints of exterior wall window frames

✍️ SOSfix Technical Engineering Team⏱️ 5 min read📅 Published: 2026-09-09T09:29:46+08:00

The culprit of water leakage on the windward side: cracking of the "secondary pouring joint" between the window frame and the concrete shear wall

In Taiwan's climatic environment with many typhoons and earthquakes, many windward houses in the greater Taipei area often face an annoying problem: whenever a strong typhoon or heavy rain strikes, the walls around the windows and even under the window sills begin to seep, which can even cause the paint walls to turn into powder. Many homeowners intuitively think that the window is not airtight or the window frame is deformed, but even if they replace expensive airtight windows, the water leakage still remains. The source of this type of leakage is usually hidden inside the cement wall, that is, the "Construction Joint" between the metal edge of the window frame and the concrete shear wall. During construction, the exterior shear wall (R.C. Wall) is grouted first, and then the window frame is installed and cement mortar is filled around the periphery. The interface between the two cements poured at different periods lacks continuity. Coupled with the drying shrinkage characteristics of the cement and frequent earthquake pulls, the joints are prone to fine cracks that are invisible to the naked eye, becoming a blind spot for rainwater to penetrate.

Seismic grouting construction: the correct proportion and water blocking principle of non-shrinkage cement mortar

To eradicate the leakage of secondary pouring joints, the most critical mud work method is "flood prevention and anti-seismic grouting (frame joint caulking project)". Traditional cement builders mostly use ordinary cement mortar to seal joints. However, ordinary cement will produce "drying shrinkage" during the curing process. After curing, a small gap will be drawn between the metal of the window frame and the cement. Modern high-standard construction always specifies the use of "Non-Shrink Grout":
*Non-shrinkage cement has special expansion agents (such as aluminum powder or calcium sulfoaluminate) added to it. In the early stages of cement hydration and solidification, it will produce a slight volume expansion, which just offsets the drying shrinkage stress of the cement itself. In this way, the cured cement mortar will tightly hold against the metal window frame and the existing concrete wall, squeezing the gaps until water is leaking, forming a rigid water-blocking barrier without gaps.
* The water-cement ratio must be strictly controlled in the preparation of caulking mortar. Use a special manual or electric "caulking gun (grouting gun)" to fill the entire cavity around the window frame from bottom to top, from deep to shallow, and compact it repeatedly with hand tools. It is strictly forbidden to allow air bubbles (honeycombs) to remain inside.

Selection and production process of silicone material for "blocking waterways" around the window frame

In addition to the non-shrink cement grouting on the inside, the "elastic waterproof seal (commonly known as water blocking)" at the junction of the exterior wall and the window frame is the second line of defense. The material selection and process of waterway plugging are related to the service life of exterior wall waterproofing:
1. Traditional acidic or neutral weather-resistant silicone will pulverize and debond from the cement surface in about 2 to 3 years when exposed to strong outdoor ultraviolet rays and acid rain. Modified polyurethane or MS glue has excellent UV resistance and elongation (up to more than 50%), and can withstand the slight displacement of the window frame caused by earthquakes without cracking or degumming.
2. Before application, the aged and old silicone must be completely scraped off with a utility knife. The cement surface should be painted with a "special primer for stone/cement" to seal the free alkali on the cement surface, enhance the adhesion strength of the new caulking agent, and prevent the new glue from degumming due to alkaline hydrolysis.

Inspection standards for second-hand house sales and high-end residential exterior wall leakage prevention

For second-hand house sellers, old house flip investors or high-end residential buyers, the waterproof quality of window frames is the "touchstone" to test whether the concealed construction is solid.
When renovating an old house or submitting it for home inspection, it is strongly recommended to entrust an inspection agency to conduct a "Water Spray Test": use a nozzle on the outside of the window frame with a water pressure of more than 2 bar to continuously spray the joints of the window frame for at least 30 minutes, and use an infrared thermal imaging camera indoors to observe whether the temperature of the wall around the window frame has dropped (representing moisture penetration and cooling). A window frame that has passed the water spray test, is grouted with non-shrinkage cement on the inside, and has a solid waterway on the outside can ensure that there will be no worries about leaks in the window side wall for the next 10 years. This not only saves you the trouble of repeated injections to catch leaks and repaint, but it is also a key technical detail to show buyers the quality of construction, maintain high unit prices, and sell quickly when properties are for sale in the greater Taipei area.

🇹🇼 Expat Living Note: Home Repairs in Taiwan

If you are an international resident renting an apartment in Taipei, New Taipei, or anywhere in Taiwan:

Voltage & Electrical Safety: Taiwan standard household voltage is 110V (60Hz). Do not plug 220V imported European/UK appliances directly without a certified step-up transformer.
Plumbing Terminology: Local plumbers are called 水電 (Shuǐdiàn) and handle both water and electrical repairs.
Landlord Obligations: Under Article 429 of Taiwan Civil Code, landlords are legally responsible for repairing natural wear and tear (such as hidden wall pipe leaks, water heater faults, or booster pump failures) unless explicitly waived in your lease.

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