Carboxymethyl cellulose (CMC) or cellulose gum is a cellulose derivative with carboxymethyl groups (-CH₂-COOH) bound to some of the hydroxyl groups of the glucopyranose monomers that make up the cellulose  backbone.

In the construction industry, CMC is used as a thickener and rheological modifier of cement, mortar, and tile adhesive mixtures. It is very compatible and easily dispersed in many kinds of mixture recipes.