Analysis on problems of exterior wall insulation system

1 base course (masonry)

Uneven settlement and deformation may occur in the later stage of the main structure of the building, which may lead to the deformation of the wall and then transmitted to the insulation layer. In addition, the dry and wet state of the base surface, foreign matters and pollution may lead to the destruction of the vitrified bead insulation system. In addition, the elastic modulus between the two media of concrete structure and masonry is different, which is easy to cause cracking and hollowing of the insulation layer in case of deformation. Alkali resistant glass fiber grid cloth shall be used to pave the surfaces of different media conversion points to improve the ability of the insulation layer to resist stress and deformation.

(1) The cleaning of wall surface shall remove pollutants, foreign matters and loose parts. (2) after the interface isolation of the wall surface is cleaned, the wall base course shall be treated with interface agent. The interface agent, sand and cement can be mixed into mortar and coated or sprayed with roller brush.

2 insulation layer

The single plastering of thermal insulation mortar is too thick, which is easy to produce hollowing and cracking; In the process of on-site configuration, if the water content is not well controlled, the mixing method and time are unscientific, the workability of the thermal insulation mortar will become poor, and there will be dry shrinkage or sliding. Therefore, the following measures shall be taken during construction to reduce the cracking of insulation layer:

(1) The forced mixer shall be used for mixing, and the mixing time shall be controlled within 3 ~ 5min. The slurry mixed according to the design mix proportion shall be used up within 1h, and water shall not be added halfway.

(2) Control the thickness of single plastering. Too thick plastering will increase the shrinkage stress, and it is easy to cause the mortar to fall due to its own weight before initial setting, resulting in inconsistent density up and down, resulting in hollowing and cracking. The screeding shall be made on the wall base layer in sections, and the thickness of single plastering shall be controlled within 20mm. If there is layered plastering, it shall be carried out after the last plastering layer is hardened and consolidated, and the thickness of the last plastering shall be controlled within 5 ~ 10mm. The surface course shall be rubbed with a large bar, and the water shall be collected on the mortar surface. When the iron plate plastering is not plastered, it shall be pressed with an iron plate for 1 ~ 2 times to press the surface particles into the mortar.

(3) Watering and curing shall be done within 24h after the construction of insulation layer, and the curing time shall be ≥ 3D. The anti crack mortar protective layer can be constructed only after the insulation layer meets the curing conditions.

(4) Dividing joints shall be set when necessary, and horizontal dividing joints shall be set according to the floor; The vertical dividing joint shall be set according to the wall area, and the dividing joint area should be controlled within 36m2. The method is to cut grooves and blocks on the insulation layer after construction. When the anti crack layer is constructed, the groove shall be filled with anti crack mortar, and the alkali resistant grid cloth shall be continuously opened at the division joint.

3 anti crack mortar protective layer

The anti crack mortar protective layer is composed of anti crack mortar and reinforcing mesh. The anti crack mortar is composed of mortar mixed with polymer anti crack fiber and hydroxypropyl methylcellulose, redispersible latex powder, etc. the reinforcing mesh generally adopts alkali resistant glass fiber grid cloth. Under the joint action of the two, it can strengthen the anti crack effect, resist dry shrinkage stress and temperature difference stress, and restrict the deformation of the insulation layer. During construction, construction in rainy days and construction with strong wind above level 5 shall be avoided. The reinforcing mesh shall be flat and tight and close to the mortar on one side of the facing layer; The stress at the corner of the door and window opening is concentrated and easy to crack, so the reinforcement mesh shall be set around the opening. The reinforcement mesh at the external corner of the opening shall be turned out by 100mm, and 300mm shall be added at the four corners ×  300mm mesh cloth. The lap length of alkali resistant glass fiber grid cloth shall not be less than 100mm, and the lap joint shall be filled with mortar.

4 crack control of finish layer

(1) Flexible coating and flexible putty shall be selected for the coating finish layer, and the construction quality acceptance shall meet the relevant requirements of code for quality acceptance of Building Decoration Engineering (gb50210).

(2) It is strictly forbidden to select face bricks with high water absorption for face brick facing layer, and the construction quality acceptance shall meet the requirements of building decoration

Relevant requirements of code for acceptance of repair engineering quality (gb50210).

To sum up, it is extremely necessary to make good preparations for the construction of external wall insulation system, because it can ensure good construction quality in the later stage. In addition, it is also necessary to do a good job in the construction quality control of external wall inorganic insulation mortar and grasp various technical operation points in the construction process.