What if the tide comes back from the foundation?

Indoor moisture regain mainly occurs at the bottom of the house. Generally speaking, there are two reasons: first, humid air with high temperature (relative humidity above 90%) meets the ground with low temperature, and the ground is smooth and does not absorb water, so it is easy to produce condensed water on the ground (usually it will be produced when the temperature is around 2℃). This happens mostly in the rainy season, with much rain, high temperature and high humidity. Once the climate turns fine and dry, the phenomenon of moisture regain can be eliminated. Second, the water in the foundation soil under the ground cushion rises by capillary action, and the vaporous water permeates upward, which makes the ground material wet, and then worsens the humidity of the whole room. This kind of situation often happens all the year round, which is difficult to deal with, with poor outdoor drainage and poor indoor ventilation. The surface layer in most parts of South China is mostly clay and loam. The water level of clay capillary can rise to 2-2.5m, and that of loam can rise to1-1.3m. When building materials with poor compactness are used as indoor floors, capillary action will be increased, and the ground moisture regain will be serious.

Second, the inspection and treatment of wet ground

1. Check. First, check whether there are cracks on the ground, which is the main channel for groundwater to penetrate upwards. Cracks with a width greater than 0.05MM are generally visible cracks in cement mortar or the whole poured concrete floor. Regular cracks usually appear along the longitudinal or transverse direction of the room, which is formed by shrinkage and cracking of materials. Then check whether there is an empty drum on the ground. The inspection method can be tapped vertically along the ground with a wooden stick. If the tapping is free, then there is an empty drum.

2. Treatment of cracks and hollowing. For regular cracks, V-shaped cracks should be chiseled, and the inside of the cracks should be cleaned and sealed with drainage ointment. If it can be baked with flame, the cracks will be fully dried and the effect will be better. Generally, hair cracks will be closed in a large area. Where there is an empty drum, the surface layer should be knocked off, the cushion layer should be chiseled off, a cement slurry should be brushed on the cushion layer, and then the surface layer should be repaired and leveled with the same material.

3. Moisture-proof treatment. After the local treatment of cracks and hollows, the surface layer should be fully moisture-proof and closed. The principle of treatment is to block the capillary permeation channel in cement mortar or concrete. Generally, waterproof coating or waterproof agent can be applied. Before painting, the surface should be chiseled and cleaned, and the second waterproof coating should be painted. The first brush should be forced to penetrate into the capillary hole. After the coating is dried for the first time (generally about 24 hours), it is brushed for the second time to form an integral waterproof coating. At the corner between the ground and the wall, paint should be brushed to the height of the wall skirting board.

After the original ground is moistureproof, make a new surface layer. The selection of new surface materials should consider the high strength, wear resistance, strong moisture-proof ability, easy cleaning, practical and beautiful appearance of ground materials, and cement mortar can also be used as surface materials.

For air humidity, it is a widespread natural phenomenon. Except for special needs, the equipment can be used to control humidity. Generally, buildings should not open windward windows and doors, so as to reduce the influx of humid air into the room.

In several residential projects, we tried to treat wet ground with plastic film and achieved good results. Specifically, a 3cm thick 1: 3 cement mortar leveling layer is made on the original cushion layer to flatten the surface. Can not have sharp corners, uneven, in case of plastic film puncture and water seepage, two layers of plastic film are laid on the leveling layer, paving and compacting, and the lap joint shall not be less than 10cm. Pouring a 6cm thick C20 fine stone concrete integral surface layer on the paved film, tamping and leveling, adding slurry and calendering. After doing this, there is no moisture regain on the ground and walls.

Third, how to prevent the ground moisture regain

In order to prevent the resurgence of the ground, it is very important to strictly control the construction quality besides strictly following the drawings.

1. Pay attention to the construction quality of plain fill layer. This is the first line of defense against moisture on the ground. Clay (yellow) soil should be used for filling the damp-proof ground, and 3: 7 or 2: 8 lime soil can be used for filling when conditions permit. Construction waste or miscellaneous rammer should not be used for filling, and the fill should be compacted by layers, with the thickness of each layer being 20 mm Loose filling and soaking method should not be used for filling moisture-proof ground, so as not to increase the water content of foundation soil.

2. Construction of moistureproof layer. In a residential building, a pilot project was carried out to isolate moisture through mats. Dry cushion adopts 25cm thick compacted blue gravel, and surface joints are filled with coarse yellow sand or flaky. 6cm thick fine stone concrete; 1: 2.5 cement mortar surface. After three years of observation, there is no moisture regain on the ground. After many engineering practices, it is proved that this cushion is an effective moisture-proof measure.

The following problems should be paid attention to in overhead ground construction:

(1) The foundation soil under the overhead slab should still be compacted to minimize water infiltration into the space under the slab.

(2) There should be enough space and ventilation under the overhead slab. Because although the foundation soil under the overhead slab is compacted, there will still be water seeping upwards and silting into the slab. After the ventilation holes are set, it is very beneficial to dry the ground.

(3) The ridge wall where the overhead slab is located shall be built with cement mortar, and the top surface shall be covered with a layer of waterproof mortar.

(4) Pay attention to the flat-fell seam quality of overhead slab. Flat-fell seam of overhead slab is the weak part of ground moisture-proof. If it is not handled properly, the moisture under the plate will take advantage of it. When laying boards, there should be a certain gap between boards. Before caulking, it should be carefully cleaned and moistened. When caulking, it should be carefully embedded with fine stone concrete. When the plate is thick, it should be embedded in layers and carefully maintained before it can be used normally.

(5) If conditions permit, a layer of hot asphalt should be brushed at the bottom of the slab before paving to block the capillary holes at the bottom of the slab, which can effectively improve the moisture-proof effect of the overhead ground.

Attention should also be paid to the construction of moisture-proof ground: the moisture-proof ground should be combined with the moisture-proof wall foundation, the wall foundation should have a waterproof mortar moisture-proof layer, and the inner wall surface of the contact part with the ground should also be plastered with waterproof mortar.

The height difference between indoor and outdoor of moisture-proof ground should not be less than 30cm, and a aproll slope should be set outdoors to timely eliminate accumulated water such as rain and snow, prevent rainwater from infiltrating indoors and increase the water content of foundation soil.