With the acceleration of industrial upgrading in China's construction industry, assembly building has shown a rapid development trend in recent years. As the first line of defense against waterproofing of external wall joints, the performance of assembly building sealant has a direct bearing on the waterproofing effect of the project, and it has also attracted more and more attention. At present, there are many manufacturers of building sealant on the market. According to the difference of basic polymer, it can be roughly divided into: silicone gel (SR), polyurethane gel (PU), silane modified polyether gel (SMP), also known as MS gel abroad.
Types and characteristics of assembled building sealants commonly used on the market at present
Silicone gel (SR) is a sealant made of polydimethoxysiloxane as the main raw material. The sealant has excellent elasticity and good weather resistance, but it also has some defects, such as poor coating ability.

Polyurethane adhesive (PU) is mainly made of polyurethane prepolymer. This kind of sealant has high tensile strength and excellent elasticity, but its weatherability, alkali resistance and water resistance are poor. It can not endure long-term heat and its storage stability is greatly affected by the outside world. Bubbles and cracks may occur when it is used in high temperature and heat environment.

Silane modified polyether sealant (SMP) is a kind of sealant based on silane terminated polyether. This kind of product has excellent elasticity, low pollution and other characteristics, and good bonding effect with concrete slab, stone and other building materials.
Performance Requirements and Selection of Assembled Building Sealant
Assembled building exterior wall panels are located on the exterior facade of the building, directly in the atmosphere environment, including temperature, humidity, building load, seismic load, sunshine and other factors, which will affect their performance. This requires that the sealant for assembling building should also have many requirements, the comprehensive performance should be strong, the main performance requirements. As follows:

1. Mechanical properties
Prefabricated exterior wall panels will produce relative displacement between the exterior wall panels under the action of load and temperature. Therefore, the sealant for assembly building must have certain elasticity, certain free expansion and deformation ability, and excellent recovery ability. The mechanical properties of assembled building sealants should include displacement ability, elastic recovery rate, tensile modulus and elongation at break.
2 Weatherability
JGJ1-2014 "Technical Regulations for Assembled Concrete Structures" clearly stipulates that the waterproof and sealing materials for building joints should be weatherproof materials. If the materials are not properly selected, it will affect the sealing performance and life of assembling construction, thus causing sealant cracking, causing leakage, and even making seals appear shortly after assembly. Rubber failure affects building safety.
There are a lot of C-N bonds in the main chain of polyurethane adhesive. Compared with silicone rubber and modified polyether rubber, the bond energy of polyurethane adhesive is the lowest. Under long-term sunshine, the C-N bond in the molecular chain of polyurethane rubber is easy to break, and the phenomena of powdering and cracking occur. This is also the main reason why the weatherability of polyurethane rubber is worse than that of silicone rubber and modified polyether rubber.

3. Environmental protection
Green environmental protection is the demand of economic and social development. According to GB18583, TVOC of PU, SR and MS sealants is tested. The test results show that TVOC of PU sealants is 80mg/L, while TVOC of SR and MS are lower than the limit value of equipment detection (50mg/L), and the environmental protection is obviously better than that of PU sealants.

4. Finishing property
In this paper, waterborne waterproof latex paint was applied on the surface of cured sealant. The results are shown in Fig. 1.

5 Curing Rate
The curing thickness of 24 h and 15 d were measured. The results are shown in Table 4.