Acid etch resistance for calcareous substrates

A method of providing acid etch resistance, water repellency, oil repellency and stain resistance to a substrate surface comprising contacting the substrate surface with a copolymer of formula (I)

• wherein
• Rf is C1 to C10 linear or branched fluoroalkyl, optionally interrupted by one or more —O—, —CH2—, —CFH—, or combinations thereof;
• Q is an alkylene of 1 to about 15 carbon atoms, hydroxyalkylene of 3 to about 15 carbon atoms, —(CnH2n)(OCqH2q)m—, —(CnH2n)(NR′)z—SO2—NR′(CnH2n)—, or —CONR′(CnH2n)—, wherein each R′ is independently H or an alkyl of from 1 to about 4 carbon atoms, n is independently 1 to about 15, q is 2 to about 4, m is 1 to about 15, and z is 0 or 1;
• Ra is a C3 to C4 branched alkyl;
• M is H, NH4, Na, Li, Cs, K, HNR3 or mixtures thereof;
• R is C1 to C4 linear or branched alkyl;
• a is an integer from about 20 to about 50 mol %;
• b is an integer from about 5 to about 35 mol %;
• and
• c is an integer from about 15 to about 60 mol %;
• wherein the sum of a+b+c is equal to 100%.