Anyone who played with building blocks knows the technique: the blocks have to be offset to build a stable structure. This is also true for a real building site. The building workers know just how to bond the stones in each individual place to create a bearing structure from the building plan. In addition the joint thickness and the mortar quality must be defined and complied with. In the Frauenkirche this was particularly difficult on the piers, the dome and other curved areas as well as where old and new stones were joined.
 
The ashlars were first laid on small spacer plates of lead to produce uniform joints. These plates were exactly the same height as the specified joint, i.e. normally 6 mm. A gap was thus created between the lower and upper rows of stones which was filled with liquid mortar. A special ‘pouring mortar for thin joints’ was developed for this purpose. To prevent the mortar from escaping at the other end, this was sealed with hemp rope. The rope was removed after the mortar had set and the joint then closed with joint mortar.
 
Special attention was paid to the eight inner piers. Bähr knew that these piers were of paramount importance for his bearing concept. But he had to estimate the flow of forces intuitively in the absence of scientific findings. Considering these prerequisites, his assumptions were remarkably true but not absolutely accurate. The flow of forces partially deviated from his predictions. Furthermore, the methods for testing materials were not nearly as sophisticated as those of today so that less suitable sandstone blocks were also used. Finally, the blocks could not be laid in Bähr's time with today's precision. This unfortunately led to severe building damage which became apparent through cracks in the piers, for example. 
 
These mistakes had to be avoided in the rebuilding project. Complicated calculations with regard to the bearing concept were carried out to correct the flow of loads in bearing structure planning. Only high quality sandstone ashlars whose strength had been tested and whose dimensions had to be within a tolerance of not more than 1.5 mm (!) were used for the piers. The pier base planes were enlarged and fewer (but bigger) individual ashlars were used per layer to reduce the number of joints. Finally, a very close eye was kept on compliance with the joint thickness and mortar quality so that the bearing capacity of the piers' stone work could be doubled as a result.