*2.6. Bond Strength*

For bond strength tests, substrate in accordance with point 2.3 was used. Five series of samples were prepared, in different thermal and moisture conditions—in laboratory conditions (23 ± 2 ◦C, 50 ± 5%), at high temperature and low relative humidity (25 ± 2 ◦C, 30 ± 5%), at high temperature and high relative humidity (25 ± 2 ◦C, 90 ± 5%), and at low temperature (5 ± 2 ◦C) and the resulting RH (Table 3). The abovementioned adhesive application conditions were adopted based on the product manufacturer's guidelines on the permissible boundary conditions for its use, which fit the concept of ETICS-dedicated polyurethane adhesives tests [5,23].

Prior to sample preparation, OSB, FGB, CPB, and concrete and MW boards were stored for 24 h under conditions programmed for adhesive application. The adhesive itself was stored for 24 h in laboratory conditions. The adhesive was applied to the mineral wool in the serpentine pattern (Figure 2b). The mineral wool was bonded to the substrate with an open time of 180 ± 10 s., creating 8 ± 1 mm thick bonds with the use of spacers. In laboratory conditions, series with 15 ± 1 mm thick bonds were also prepared. Samples were cured for 24 h under adhesive application conditions. To ensure that the bond thickness remained constant during curing, spacers were maintained, and a load of 15 kg was applied (Figure 2c). At the end of curing, the excess adhesive in the form of squeeze out was cut off, forming 200 mm × 200 mm × 8 mm or 200 mm × 200 mm × 15 mm adhesive bonds (Figure 3a).

**Figure 3.** Bond strength test: (**a**) sample scheme, (**b**) sample from OSB/23/50/8 series under load in the testing machine.

Bond strength test involved determining the maximum tensile stress of an adhesive bond with a force acting perpendicular to its face. The method is often used in the testing of construction adhesives [44]. It was derived from TR46 [23]. Tests were conducted under laboratory conditions immediately after the samples were cured under specific conditions (Table 3). The test was carried out using a computer-controlled class 1 testing machine (Instron, Darmstadt, Germany), with a constant speed of 10 ± 1 mm/min. (Figure 3b). The samples were glued into 200 mm × 200 mm metal holders. The tension force values were recorded until damage. Bond strength *σ<sup>T</sup>* was calculated according to (1) and expressed in kPa. In each series, ten samples were tested, and the total was 160 samples.

$$
\sigma\_T = \frac{F\_{Tmax}}{A} \tag{1}
$$

where: *FTmax*—maximum tensile force, in kN; *A*—bonded area, expressed in m2.
