Abstract
In the article, the value of compressive stress defined according to the flat jack method with a theoretical value of the stress was compared. The test was performed in a laboratory using part of the 38 cm thick masonry wall according to the procedure described in the ASTM C1196 – 14a Standard. Significant correspondence between the obtained results confirms that this diagnostic method is useful in Polish conditions as well as it allows one to estimate approximately how accurate it is.