Hydroxypropyl Methylcellulose and Methylcellulose are water soluble ethers with excellent performance, suitable for building coatings as retarders, water-retaining agents, thickeners and binders. HPMC and MC have already been used in plaster, cement, lime and mortar. In cement proportion, it function as a retarder and water-retaining agent; while in concrete composition and mortar, it can improve the viscosity and shrinkage, strengthen the bond force, control the setting time of structural grade cement, increase the initial strength and bending strength. Since it has the function of water retention, it can reduce the loss of water on the concrete surface, avoid cracks on the edge, and improve adhesion and construction performance. Especially in construction, it can extend and adjust the setting time, increase the workability and pumpability of cement and gypsum composition, suitable for mechanized construction to increase the construction efficiency and help prevent weathering of water-soluble salts on the building surface.
I. Roles of Hydroxypropyl Methylcellulose in Building Materials
1. Workability—Plasticity
With the addition of Hydroxypropyl Methylcellulose, the workability of plaster has been significantly improved. The mortar without addition of Hydroxypropyl Methylcellulose is looser and easy to lose water, while after adding Hydroxypropyl Methylcellulose, it seems to have “oiliness” and enables the wall joints full and surface smooth; the ceramic tiles or bricks tightly bonded with the base, and extend the operable time, suitable for large-scale construction.
2. Water Retention—Strength
Cement or gypsum-based product is able to gel only through the hydration reaction. Water makes silicates in cement into complex hydrates, anhydrous calcium sulfate and calcium sulfate hemihydrate in industrial gypsum into calcium sulfate dehydrate, so that these products could have certain strength. If there is no water, the reaction cannot occur, and there will be no strength. Especially if there is loss of water on the interface in contact with cement mortar, plaster and binders, there will be no strength and almost no bonding on this part. Generally speaking, the surfaces in contact with these materials are adsorbents, which more or less adsorb some water from the surface and result in incomplete hydration at this part, so that the bond strength or between plaster and wall will get decreased.
A major role of Hydroxypropyl Methylcellulose is to increase the water retention of building materials, greatly improve its bond strength and shear strength. The water retention of Hydroxypropyl Methylcellulose is getting better and better with the increase of viscosity.
3. Bonding
With the addition of Hydroxypropyl Methylcellulose, the bonding of cement mortar, plaster and binders can be improved significantly, especially for the increase of initial bond force, which can ensure that pasting of ceramic tiles or tiles will not slide down and that the plaster and wall; brick and mortar are firmly bonded. The amount of Hydroxypropyl Methylcellulose added should not be too great, because too much, on the one hand, will make the paste adherent to the construction tool, causing inconvenience for construction, and on the on the hand will cause hollow defects on plaster and caulking materials.
4. Set-retarding effect
Hydroxypropyl Methylcelluloses can be used as set-retarders for cement-based building materials (such as mortar, plaster, binders, caulking materials, etc). If there is no need for particularly long construction time, such a retarding effect is sufficient to satisfy the use needs. Hydroxypropyl Methylcellulose also have certain set-retarding effects on gypsum-based products.
5. Air-entraining agent
After adding Hydroxypropyl Methylcellulose, many tiny bubbles can be produced inside the material, like a honeycomb structure. Small bubbles act like “lubricants” and can have very good construction performance. Also, the honeycomb structure blocks the capillary action generated after original cement hardening and prevents the penetration of water, thus enabling the walls, tiles, cracks, etc. to have good waterproof effects. The effect of the air-entraining agent also improves the frost and heat resistance of products, increases the heat and sound insulation effects, and meanwhile reduces the bulk density of product.
II. Building Materials Able to Use Hydroxypropyl Methylcellulose
1. Cement Mortar
During use of cement mortar, it is very important to ensure good water retention due to strong water absorption of brick and wall, along with a higher sand content of mortar. Otherwise, bricks will be very easy to absorb the water in mortar, leading to partial water loss of mortar and difficulty in adequate hydration of cement. The bond strength of mortar composed of sand, lime and cement is very low, but it will be significantly increased with the addition of Hydroxypropyl Methylcellulose. Even if the eccentric load or horizontal load significantly occurs, the bending tensile strength and shear strength will also be relatively high.
The addition amount of Hydroxypropyl Methylcellulose should be determined experimentally. Too much added, it will produce too many bubbles in the mortar and reduce the compressive strength. But if used properly, it will make a fundamental improvement on the use of cement mortar.
2. Ceramic Tile Adhesive
Since the ceramic tile adhesives must have very high bond strength between the base layer and ceramic tiles, so adhesives are affected by two aspects of absorbed water, the surface of base layer (the wall) and ceramic tiles. For ceramic tiles, there are large differences in the quality. Some have large pores, and the water absorption of ceramic tile is high, so that the bonding properties of ceramic tile adhesive will get damaged. In this case, water-retaining agents appear particularly important, and addition of Hydroxypropyl Methylcellulose can well satisfy this need.
3. Plaster
For plaster (plastering paste), the workability, plasticity and initial viscosity are several important properties. Even adding a very small amount (a few thousandths) of Hydroxypropyl Methylcellulose will also make these properties significantly improved. In cement- and gypsum-based plaster, water is essential for final hardening. Just like cement mortar, the water retention of cellulose will enable the plaster after curing to have relatively high bond strength.
4. Bonding Gypsum, Caulking Gypsum and Gypsum-based Finish Materials
Gypsum products are more and more popularly used, with such advantages as light weight, thermal insulation, fire resistance and ability to adjust the indoor humidity. The consumption of matching bonding gypsum and caulking gypsum has already been very large. Preparation of these materials all requires adding an appropriate amount of Hydroxypropyl Methylcellulose as water-retaining and binding agents to achieve full hydration of gypsum, ensure adequate adhesion and to prevent the occurrence of cracks. Currently, gypsum-based finish materials (finish gypsum or render gypsum) have gradually replaced other finish materials. Usually 0.2% of Hydroxypropyl Methylcellulose is added into these materials to greatly improve the construction performance, prevent the occurrence of cracks, make the wall plastered flat and smooth.
5. Other Building Materials
Hydroxypropyl Methylcellulose have been widely used in colorful coatings, greatly improving the performance and decorative effects of these products. Hydroxypropyl Methylcellulose can play a significant role where there is a need for bonding, water retention and improvement of construction performance. Hydroxypropyl Methylcellulose have now been applied in many domestic building materials, and have achieved very good economic and social benefits. With the increase of production capacity and variety, the improvement of product quality and the decrease of price, there will be a wider application in building materials.
III. Uses of Hydroxypropyl Methylcellulose in All Aspects
Mortar: The use of cement mortar as a coating for interior and exterior wall can increase the adhesion of sand grains onto the wall and improve the construction performance of mortar. The construction method is similar to that of gypsum coating for interior wall.
Bonding ceramic tiles: For construction, ceramic tiles do not need to be soaked with water in advance. The construction method is similar to conventional methods, and the wall requires no water spray. With the use of HPMC, the bonding fastness of ceramic tiles can be significantly improved, and the slurry is longer in the construction period, fine and smooth in appearance, uniform and convenient for construction.
Concrete: HPMC can be used as a drag-reducing agent in pipeline and a water-retaining agent on surface, and can greatly improve the initial setting strength.
Binders and rubber powder used in buildings: For the binder and RDP (redispersible polymer powder used in buildings, the use of HPMC as an auxiliary bonding material not only improves the bonding properties, but also enhances its mildew resistance.
Cement products: In the production process of pipes or plates made of gypsum cement, the addition of a small amount of HPMC, MC or series as a water regulator, water-retaining agent, set retarder or binder enables the products without dehyration in the case of pressure and shear force, while improving the compressive strength of product.
Coatings industry: Due to excellent performance, HPMC and MC have a wide range of uses in coatings. For instance, it can be used as a film-former, thickener, emulsifier, stabilizer, etc. in latex paints and water-soluble resin coatings, enabling the coating film with good abrasion resistance, leveling and adhesion, and also improving the surface tension, PH stability as well as the compatibility with metallic pigments. HPMC and MC have water retention, so have good brushing and leveling, as well as good storage stability and relatively good blending performance with organic solvents.
Building adhesives: The cold-water instant soluble product of high viscosity produced has good dispersion in cold water and high viscosity. Its gelation time can be customized according to customers’ needs. After you let it sit, there will be no layering or decrease in the viscosity, which is very suitable for the production of building adhesives.
