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The effective porosity of all analyzed tuffs varies from 12 % (MG) to 41 % (CAO). The Mitla tuffs show the lowest values (12–15 %). The sample with the highest matrix density is MR with 2.6 g/cm3, while MG has the lowest density with 2.2 g/cm3 (Tab. 1). The saturation degree S of the samples ranges from 0.59 (MG) to 0.92 (MR, CVO). After Hirschwald (1912) most samples are weathering and frost resistant except MR and CVO. The pore size distributions were measured for all samples (Fig. 3). It is noticeable, that CVO and MR have almost no capillary pores, but a high share of micropores.

Figure 3: Comparison of the ratio of micropores and capillary pores.

The samples from Mitla show the lowest capillary water absorption (0.7 kg/m2√h–1.7kg/m2√h). The samples from Oaxaca show moderate w-values ranging from 1.0–2.8 kg/m2√h (CV ) to 6.4–8.5 kg/m2√h (CAO). CVO has the highest water vapor diffusion resistance factor μ with 21.9, followed by MR with 19.0. The sample with the lowest water vapor diffusion resistance is CAO with 7.4. Hygroscopic water sorption was measured from 20–95 % rh. The highest sorption value was measured for CVE with 7.75 wt.-% at 95 % rh. The lowest sorption at 95 % rh was measured for CRO with 1.74 wt.-%. Between 20 and 75 % rh all samples show a linear weight increase with varying gradient. Above 75 % rh the curves show a sudden increase in slope. The highest ultrasonic velocities were measured for MR (3.7–3.8 km/s) and CVO (3.2–3.6 km/s). The lowest ultrasonic velocity was measured for CRE (1.6–2.3 km/s).

The tensile strength of all samples varies between 1.3–1.7 MPa (CRE) and 6.4–6.9 MPa (CVO). MR has the highest surface hardness with 528–604 HL followed by CVO (603–632 HL). The lowest surface hardness was measured for CAO with 330–337 HL.56

Table 1: Petrophysical properties and weathering behaviour of the studied samples.