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Influence of Cellulose Ethers on the Consistency, Water Retention and
Adhesion of Renovating Plasters(1)

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


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].

In order to limit this phenomenon, admixtures increasing water retention, produced on the basis of
cellulose derivatives, can be added to mortars [6-9].

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

methylcellulose (MC), ethylcellulose (EC) and benzylcellulose (BC). Mixed ethers include
ethylbutylcellulose (EBC), methylethylcellulose (MEC), Hydroxypropylmethylcellulose (HPMC), etc.
Cellulose ether structures used in the studies are shown in Figure 1.
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