Granular pumice and method for producing granular pumice

A granular pumice comprising:

• a surface coated with a hydrophobic coating,
• wherein the coating comprises a mixture of a silane and a siloxane;
• wherein the silane is:
• A1) a silane of the general formula:
• R3—Si—(OR2)3;
• where:
• R2 is a methyl or ethyl radical;
• and
• R3 is:
• an alkyl radical having from 3 to 12 carbon atoms;
• or
• an aminoalkyl radical having from 1 to 6 carbon atoms;
• or
• a radical of the general formula
• H2N—(CH2)xR4—(CH2)y—,
• where:
• R4 is an oxygen, sulfur, —NH—, or —NH—CH2—CH2—NH— radical;
• x≧2;
• and
• y≧2;
• or
• a radical of the general formula:
• (R2O)3Si—(CH2)x—NH—(CH2)x—,
• where R2 and x are as defined above;
• where n is an integer from 1 to 5, or
• wherein the siloxane is:
• A2) a siloxanol of the general formula:
• where:
• R5 is a methyl or phenyl radical, with at least 90% of the radicals R5 being methyl radicals;
• and
• m=20 to 250;
• and
• wherein the mixture comprises:
• the silane compound as per A1);
• and
• the siloxanol compound as per A2);
• where a ratio of A1) to A2) is kept so that one SiOH group of the compound A2) corresponds to from >1 to 3 OR2 groups of the compound A1);
• and
• where R2 is an alkyl radical having from 1 to 4 carbon atoms.