Water-soluble phenoplasts (I), are ued for thinning concrete. (I) may be (1) resols, partic. phenol-HCHO resols, consisting, entirely or appreciably, of phenol-alcohols; (2) sulphonated novolacs contg. -SO3H gps., or (3) hydroxydiphenyl-sulphones having tanning properties. W.r.t. Ca lignin sulphonate and sulphonated melamine resin, as controls, when using phenoplasts (i) start of setting is shortened less with increasing concn., (ii) false setting is prevented, (iii) air pore content in mortar can be reduced by mixing phenoplast and Ca lignin sulphonate, (iv) sweating with hydration is reduced.
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