Characteristics of HPMC in construction materials
The workability of the plaster is significantly improved by the addition of HPMC. Mortar without the addition of HPMC was loose and prone to water loss. With the addition of HPMC, however, it seems to have an “oily” quality, giving the wall a full joint and a smooth surface. It makes the tiles or bricks bond tightly to the substrate and extends the workable time for large-scale construction.
Water retention capacity
Cement or gypsum-based products can only gel through a hydration reaction. Water turns the silicates in cement into complex hydrates and the anhydrous calcium sulphate and calcium sulphate hemihydrate in industrial gypsum into dehydrated calcium sulphate, which gives these products their strength. Without water, no reaction can take place and there is no strength. Especially if there is water loss at the interface in contact with cement mortar, plaster and binder. This part would have no strength and almost no bond. Generally, the surface in contact with these materials is the sorbent, which more or less adsorbs some water from the surface, resulting in incomplete hydration of that part. As a result, the strength of the bond between the plaster and the wall may be reduced.
One of the main effects of HPMC is to increase the water retention of the building material, greatly improving its bond strength and shear strength. As the viscosity increases, the water retention of HPMC becomes better.
With the addition of HPMC, the bonding properties of cement mortar, plaster and binder are significantly improved. In particular, the initial bonding force is increased, which ensures that tiles or tiles will not slip off when pasted. The bond between plaster and wall, brick and mortar is firmly established. the amount of HPMC added should not be too large, as too much will, on the one hand, cause the paste to adhere to the construction tools and bring inconvenience to the construction. On the other hand it will cause hollow defects in the plaster and caulking material.
Delaying the setting action
HPMC can be used as a retarder for cement-based building materials (e.g. mortars, plasters, adhesives, caulking materials, etc.). HPMC also has a retarding effect on gypsum-based products.
When HPMC is added, many tiny air bubbles can be created inside the material, like a honeycomb structure. The small bubbles act like “lubricants” and can have very good construction properties. At the same time, the honeycomb structure can also block the capillary action produced by the original cement after hardening and prevent water penetration. This results in good waterproofing of walls, tiles, cracks, etc. The action of the air-entraining agent also improves the frost and heat resistance of the product, increases thermal and acoustic insulation and at the same time reduces the bulk density of the product.
That’s all content about characteristics of HPMC in construction materials
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