*3.1. Chemicals*

Tetraethoxysilane (98.5%), triethoxymethylsilane (98.5%), CDCl3, DMSO-d6, CH3COOD, D2O, and chitosan (72% deacetylation) were obtained from Sigma Aldrich. The ethylene glycol (JT. Backer, 99%) was distilled prior to its use in each reaction.

#### *3.2. Synthesis of THEOS and Preparation of THEOS/MeTHEOS–Chitosan Formulations*

The synthesis of THEOS and MeTHEOS by transesterification reactions was performed in a dry nitrogen atmosphere using Schlenk techniques. The reaction system used a three neck round bottom flask, a Vigreux column, a condenser, and a collector flask.

#### 3.2.1. Synthesis of THEOS by the Transesterification of TEOS

Into a three neck round bottom flask purged under N2 flow, 4.3 mL of freshly distilled ethylene glycol (4.76 g, 0.0768 moles) was added. After 30 min under magnetic stirring, 4.3 mL of TEOS (4 g, 0192 moles) was added drop by drop. The first drop of ethanol collected was considered the reaction initiation. The reaction temperature was 140 ◦C and was stable until the reaction ended (15 h). The reaction crude was concentrated under the vacuo line.

#### 3.2.2. Synthesis of THEOS–Chitosan and MeTHEOS–Chitosan Solutions

Formulation solutions were prepared by the addition of 0.5 g of THEOS or MeTHEOS to 10 mL of an aqueous solution of chitosan (0.5%) in acetic acid (1%) under magnetic stirring until complete dissolution. The % of DDA of chitosan was 72% (Sigma Aldrich Química, S.L., Toluca, Mexico). The described solutions were used to obtain hybrid films that were characterized by FTIR, SEM–EDX, and solid state NMR and regarding their thermal stability, and then used in consolidation and hydrophobic treatments of the stones. The formulations named 1, 2, and 3 were prepared using chitosan obtained from the extraction of shrimp exoskeleton with three different degrees of deacetylation (%DDA): 62%, 66%, and 70%. Formulation 1 (0.5 g of THEOS or MeTHEOS and 10 mL of 0.5% aqueous solution of chitosan), formulation 2 (1 g of THEOS or MeTHEOS and 10 mL of a 0.5% aqueous solution of chitosan), and formulation 3 (0.5 g of THEOS or MeTHEOS and 10 mL of a 1% aqueous solution of chitosan) were applied to the stones and used in the hardness and contact angle determinations.

#### 3.2.3. Synthesis of THEOS–Chitosan and MeTHEOS–Chitosan Films

The formulation solution obtained in each case was dispersed on plastic Petri dishes and left to dry at room temperature. Further characterization was performed by FTIR and solid state NMR (29Si and 13C).

#### *3.3. Analytical Methods*
