Workable cementitious compositions

A process of modifying the slump of a cement mix which is applied by spraying said cement mix onto a substrate from a spray nozzle, comprising the steps of adding a water-soluble poly(alkylene oxide) of molecular weight from 100,000-8,000,000 and a plasticizer or superplasticizer selected from the group consisting of lignosulphonates, melamine sulfonate-formaldehyde condensates, carboxylates and styrene-maleic anhydride-based copolymers in free acid or salt form, said styrene-maleic anhydride-based copolymer selected from ##STR3## in which R is an C.sub.2-6 alkylene radical

• R.sub.1 is a C.sub.1-20 alkyl-, C.sub.6-9 cycloalkyl- or phenyl group,
• x, y, and z are numbers from 0.01 to 100
• m is a number from 1 to 100 and
• n is a number from 10 to 100
• with the provisos that
• i) the ratio of x to (y+z) is from 1:10 and 10:1 inclusive,
• ii) the ratio of z:y is from 3:1 to 100:1 and
• iii) m+n=15-100
• and ##STR4## in which M is hydrogen or the residue of a hydrophobic polyalkylene glycol or polysiloxane, R, R.sub.1, m and n are as hereinabove defined,
• a, b, and c are numbers from 1 to 100
• with the provisos that
• i) the ratio of a to (b+c) is from 1:10 to 10:1 inclusive,
• ii) the ratio of c:b is from 5:1 to 100:1 and
• iii) m+n=15-100
• to the cement mix prior to the cement mix reaching the spray nozzle and injecting a .beta.-naphthalene sulfonate-formaldehyde condensate into said cement mix at the spray nozzle optionally together with a conventional accelerator.