Abstract. Cellulose ethers such as (hydroxypropyl)methyl cellulose (HPMC), (hydroxyethyl)methyl cellulose (HEMC), methyl ethyl hydroxyethyl cellulose (MEHEC) are currently used admixtures in the production of factory-made mortars. They improve such properties as water retention, workability, adhesion to the substrate, open time etc. in the cement based mortars.
The article investigates the impact of physicochemical properties (molecular weight, methods of modification, viscosity) on water retention, rheological properties and the adhesiveness to the substrates of renovation plasters. The research showed that the cellulose viscosity has a greater impact on water retention despite diversified effects of various derivatives of cellulose.
The influence of viscosity of cellulose ethers is uneven. The greatest growth of retention was observed with the change of viscosity from 100 mPa·s to 15000 mPa·s. The further growth of viscosity of cellulose admixtures influenced the change of water retention with lower intensity. It was also stated that cellulose ethers improve the adhesion of renovation plasters to the substrates. Particularly beneficial results were obtained in the case of plasters consisting (hydroxypropyl)methyl cellulose(HPMC)-based admixtures.
1. Introduction
The walls of historic buildings, depending on their origin, are usually stone, brick or mixed: stone and
brick walls. Lime, lime and clay mortars as well just clay were primarily used as binders [1]. Due to the
long-term impact of environmental conditions: moisture, salts, temperature changes, etc., the absorption
capacity of such walls varies considerably [2]. Renovation mortars are often used in their renovation
[3].
Renovation plasters are a systemic solution that includes renovation rendering coat, plasters that
accumulate salts (base plasters) and hydrophobic plasters. High efficiency in salt removal and drying of
walls is achieved by applying a half-cover rendering coat and two layers of plasters, the first of which
is made of a porous plaster absorbing salt solutions, and the other one - made of a hydrophobic porous
plaster [4].
One of the important characteristics distinguishing the renovation plasters from traditional
cement or cement-limestone plasters is their porosity. In most cases, these mortars are applied in thin
layers, which is why they are particularly exposed to the rapid transfer of water to absorbent substrates.
The time of preserving the mortar working properties is then shortened, the amount of water necessary
for hydration of cement is reduced, which results in lowering the strength and adhesion properties of the
hardened mortars to the substrate [5].
Cellulose derivatives are obtained through a chemical modification consisting in the etherification in
hydroxyl groups present in cellulose with of organic groups. The most important simple ethers are
