Backwater surface waterproofing diagram

The side of the building structure that is in contact with water is called the front surface, and the opposite side is the back surface, also called negative water pressure. Just like a fish tank filled with water, the inner side of the glass is the front water surface, and the outer side is the back water surface. This is easy to understand. The side of the basement retaining wall and foundation raft in contact with the soil is the front surface, and the indoor wall and floor is the back surface.

Building waterproofing first faces the water surface. With the advancement of material technology, even the back surface can achieve the same waterproof effect as the front surface. But after all, the cost of waterproofing on the front surface is much lower than that on the back surface. More importantly, waterproofing on the front surface can also protect the building structure from the corrosion and penetration of groundwater.

Prevention of water on the back surface of the villa basement (Changping)

Grouting and plugging leaks on the back surface of the villa basement (Daxing)

1. After leakage occurs in the building structure, Situations that cannot be handled from the front surface. For example: After a leak occurs in the side wall of the basement of a villa, excavation from the front surface is not only expensive, but also the base plate cannot be waterproofed. Under the action of buoyancy, groundwater will flow from the base plate to between the new waterproof layer of the wall and the concrete over time. , the waterproofing will inevitably fail.

The author personally encountered a villa in Changping District, Beijing. Due to leakage in the side wall, the SBS waterproofing membrane was remade after excavation. The leakage occurred again the following year, and the excavation was carried out for the second time. As a result, there was another leakage before the rainy season was over, causing a huge headache for the owner and the construction company.

This situation is very common. Waterproofing is a whole. Excavation can only deal with the waterproofing layer of the basement exterior wall, but the bottom plate is still unable to do so. Just like a leaking box, only the leaking points on the facade are repaired, but the leaking points on the plane cannot be repaired. The consequences can be imagined.

2. Prevent indoor negative water pressure when decorating the villa basement. Generally, villa owners will invest a lot of money to turn the basement into a multi-functional living and entertainment area during decoration, but they are worried about future leakage in the basement, so they add a negative pressure waterproof layer during the decoration stage to prevent accidents.

This is a wise move. People with a little life experience can understand the prevention of water quality in domestic building structures and civil construction stages. At present, basement leakage has become a very common building quality problem.

Spraying construction of waterproof and impermeable slurry on the back surface

1. The waterproof layer and the concrete have different shrinkage ratios. At the same time, it is difficult to form a gap between the two materials due to insufficient natural bite force. As a dense whole, the negative pressure waterproof coating can easily fall off and crack under the long-term penetration of underground hydrostatic pressure, leading to waterproofing failure.

At the same time, most of the waterproofing and sealing of the back surface is carried out in a humid environment, which has high requirements on the moisture bonding ability of the material. Therefore, qualified back surface waterproofing materials must have strong and stable dry and wet adhesion. At this point, most organic waterproof coatings cannot meet the requirements.

2. Under the long-term action of leaking water, concrete and steel bars will corrode to varying degrees, resulting in a decrease in strength. Therefore, the waterproof material on the back surface must not only be waterproof, but also serve as structural reinforcement, and its compressive and flexural strength requirements are relatively high. Flexible materials obviously don't do the job.

3. Negative water pressure waterproof coatings have been exposed to water for a long time and must have excellent water resistance to resist the plasticization, migration or hydrolysis of waterproof materials by groundwater.

4. Concrete has static cracks, active cracks, development cracks, etc. The waterproof coating on the back surface acting on this basis can easily crack as the base layer cracks, leading to waterproofing failure. A good backside surface waterproofing material must have excellent crack bridging ability and withstand the spread of cracks in the base layer while maintaining the same waterproof performance.

5. The sources of groundwater are complex, and most of them have a certain acidity and alkalinity. The negative pressure waterproof material on the back surface must also be acid and alkali resistant, corrosion resistant and bacteria resistant.

6. Ordinary waterproof coatings or membranes are film-forming waterproofing that adheres to the surface of the building structure, while penetrating crystalline waterproof coatings or aqueous agents provide waterproofing by producing a large number of crystal pores between dense concrete. . Any waterproof material with a single mechanism is unreliable. A good back surface waterproof and impermeable material should have the above two functions at the same time.

The waterproofing membrane is not firmly adhered to the base layer, forming "two skins"

The most common SBS modified asphalt, polyester polypropylene, various synthetic polymer waterproofing membranes, etc. It has poor adhesion with the base layer and has excellent waterproof performance when used on the water surface. However, under the long-term action of underground hydrostatic pressure, leaking water will slowly push it open and cause waterproofing failure.

In a hotel in Shunyi District, the epoxy resin waterproofing reinforcement on the roof caused large-scale leakage

Common JS, polyurethane, modified asphalt-based, and various synthetic polymer waterproofing The coating has good low-temperature flexibility, high elongation and good crack resistance, and is very suitable for use on water surfaces. However, when used as back surface waterproofing, it has poor adhesion with the concrete base layer and has high requirements on the base layer. It is easy to delaminate and fall off in areas where the base surface is moist (moisture content must be less than 9%) and the penetration pressure is high.

Epoxy resin waterproof coatings have high strength, water resistance, acid and alkali resistance, and strong adhesion. However, they have poor moisture adhesion and are easy to powder. At the same time, they are very sensitive to environmental temperature and humidity, grassroots cleanliness, construction technology, The requirements for later maintenance are very high, and it is difficult for the on-site environment and the professional quality of construction personnel to meet the requirements, and problems occur frequently.

The above various organic waterproof coatings are periodic materials with poor durability; the coatings are prone to falling off and cracking, and their impermeability properties are not comparable to those of inorganic materials.

3. Inorganic waterproof coatings/mortars

Cement-based penetrating crystalline waterproofing materials will crack when the foundation cracks

Common penetrating crystalline waterproofing coatings (water-based ), polymer cement-based and various types of rigid waterproof mortar, with excellent impermeability, adhesion, water resistance and durability that are unmatched by organic waterproof coatings, and are most suitable for waterproofing on back surfaces. However, this type of material is rigid and waterproof and is prone to cracking as the structure cracks.

4. Negative water pressure waterproof and impermeable slurry on the back surface

Negative water pressure waterproof and impermeable materials are under construction

Professional back surface waterproofing materials not only have The coating has a waterproof function. It can also react with concrete to form insoluble crystals, dense concrete capillary channels and micro-cracks, and can achieve self-healing for cracks below 0.3mm. It has a dual working mechanism and has more reliable waterproof performance.

The waterproof and impermeable material on the back surface not only retains the high adhesion of inorganic materials, excellent impermeability, acid and alkali corrosion resistance, high compressive strength and good durability. At the same time, it also has certain lateral deformation and crack bridging capabilities, and base cracks below 0.5mm will not have any adverse effects on it.

Can finding a good negative water pressure waterproofing material solve all the problems of basement leakage? The answer is not so. There is a famous saying in the waterproofing industry: "Thirds of materials and seventy percent of construction", which shows that the construction link is far more important than the material in the project. The same waterproof material can often achieve widely different effects when used by different people.

In the waterproof and moisture-proof construction of villa basements, do not rely too much on one construction technology or waterproof material, but should adopt a composite thinking that uses a variety of technologies and materials. For example, areas prone to leakage such as post-cast belts, construction joints, cold joints, deformation joints, settlement joints, and wall pipe fittings need to be reinforced with grouting or grooved and blocked in advance to form multiple layers of defense with the waterproof coating on the back surface.

During the civil construction stage of expanding the basement, it is necessary to set up water-stopping steel plates at the junction of the new and old concrete. During the later waterproofing treatment on the back surface, a self-healing waterproof sealant is slotted here to prevent the negative pressure in the later stage. The waterproof layer implements a sinew-type waterproofing system that combines rigidity and softness. Even if structural settlement causes structural cracks at the junction, the waterproofing function will not fail.

Only good negative pressure waterproofing materials and scientific construction techniques can achieve good later effects. Both are indispensable. This is especially important in waterproofing and moisture-proofing construction in villa basements.