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Influence of Cellulose Ethers on the Consistency, Water Retention and Adhesion of Renovating Plasters(6)

3.3. Study of the influence of cellulose admixtures on adhesion to a concrete substrate

The results of the influence of cellulose admixtures, differing in the modification method and viscosity,
on the adhesion to substrates are presented in Figure 5.
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Analysing the results presented in Figure 5a, it can be concluded that with increasing viscosity of

cellulose admixtures, adhesion to substrates increases. The influence depends on the type of cellulose
admixtures. Across the entire range of admixture viscosities, the HPMC and-based admixtures had the
greatest impact on adhesion.

The HEMC effect was slightly lower, although, in this case, the adhesion increases with the increase of the admixture viscosity. Admixtures based on MEHEC influenced theadhesion in a very diverse way. The highest adhesion was obtained for MEHEC with a viscosity of31,000 mPa·s. Further increase in the viscosity of this admixture caused a slight decrease in adhesion.

The standard requirements for the adhesion are mainly determined for repair mortars for concrete

and tile adhesives. In the case of renovation plasters, similarly to the other plasters, a value equal to the

tensile strength of the substrate is assumed to be sufficient adhesion.

Based on the opinion of practitioners, sometimes, despite the fulfilment of mandatory requirements, not all renovation plasters offered by commercial manufacturers show sufficient adhesion. In particular, this applies to the use of renovation plasters on poor substrates which are quite common in the renovation of objects of historical importance.

The author's technological practice shows that for renovation plasters, the adhesion should

not be lower than 0.5 MPa, with the optimal value at 0.8 MPa. In the aspect of the renovation plaster

under consideration, the highest adhesion was obtained for HPMC 52000.

4. Conclusion

The paper presented the influence of cellulose admixtures on consistency, water retention capacity and

adhesion to substrates. As a result of the examination, it was found that due to the shaping of physical

properties of renovation plasters, which were analysed in this paper, the best results can be obtained

with (hydroxypropyl)methyl cellulose HPMC and (hydroxyethyl)methyl celluloseHEMC, particularly:


With the increase in viscosity of cellulose admixtures, the consistency of fresh mortar increases
unevenly. The greatest changes in consistency were observed for HPMC and HEMC when the
viscosity changed, from approx. 6,000 MPa·s to approx. 30,000 MPa·s; further increase in the
viscosity of cellulose admixtures influenced the mortar consistency to a lesser extent.
• There is a relationship between cellulose viscosity and water retention by the mortar. This effect
is uneven, with the greatest intensity observed when the viscosity of cellulose admixtures
changed from 6,000 mPa·s to 15,000 mPa·s. The influence of cellulose admixtures with higher
viscosities on the change in water retention was increasingly lower.
• Adhesion of mortars containing cellulose ethers was higher than that of unmodified mortars.
For the analysed renovation plaster, the highest adhesion was obtained for HPMC 52000.

KEY WORDS:#Cellulose Ethers#Plasters#Water Retention