Special mortars for fixing ceramic tiles on different substrates, mainly concrete, are very important in house building sector. Besides the binding materials, cement most of all, additives and admixtures that allow to model proper properties of such mortars are used for the manufacture. Methylcellulose is one of the most frequently used admixture for modification of mortars properties. Influence of different admixtures, redispersible powders for instance or other organic compounds containing polymers, on the hydration process of cement and properties of obtained
mortars has been an object of many investigations [1–5].
Results of laboratory experiments concerning influence of water solutions of methylcellulose on chosen physical properties and microstructure of cement based ceramic tile adhesives are pre-sented in the paper.
Methylcellulose is a very important constituent of adhesives despite the fact that its content is very low, normally below tenth of mass percent of dry material. Use of that admixture allow to obtain good performance of mortars. Thanks to methylcellulose mortars are easy to prepare, comfortable in use and easy to handle, which provides obtaining of proper properties and causes that they are most frequently used. Cement based ceramic tile adhesives belong to that group.
Ability to increase of water retention in mortar is a very important property of adhesives with addition of methylcellulose. It provides proper conditions of binding and hardening of a binder.
Some amount of water is bound in the first phase of cement hydration. Simultaneously another amount of water is bound with methylcellulose, added as a powder, to form gel. Formation of gel from methylcellulose results from binding of water molecules by functional groups of cellulose ethers leading to their agglomera-tion. Gel may then give back some water during the progress of cement hydration. Addition of methylcellulose to mortar causes increase of viscosity what reflects in necessity of water to binder ratio increase . Properly chosen addition of methylcellulose allow also to obtain adhesives and besides increased viscosity allow for its longer use.
Methylcellulose is a common name of cellulose ethers. Manu-facture processes of methylcellulose are complex and relay on chemical treatment of finely ground cellulose of high purity, obtained from wood, straw and reed or plants.
One of the important properties of cellulose ethers is viscos-ity of aqueous solutions. According to standard it is determined in solutions (usually 2%) at room temperature, it is dynamic or kinematic viscosity which Pa s and m 2 /s are the respective units. Höppler and Brookfield viscometers are the most frequently used apparatus for determination of methylcellulose viscosity. Methylcellulose powders available on the market are in the wide range of viscosity, measured by Brookfield method, from 200 up to 150 ? 10 3 mPa s. Two types of methylcellulose
(HEMC-hydroxyethylmethylcellulose and HPMC-hydroxypro-pylmethylcellulose) of viscosity in the range of 10–70 Pa s are generally used in ceramic tile adhesives. Typically methylcellu-lose contains additions of starch ethers, polyesters or acrylates . These admixtures improve methylcellulose performance as a result of synergistic effect, mainly due to electrostatic interac-tions between their different functional groups or by the forma-tion of hydrogen bonds or dipole. Use of modifying admixtures have to be based on the knowledge of their influence on the mortars properties, because some of the admixtures may
worsen mortar rheology or even cause agglomeration of its constituents .