In preparation for Nils Ericsons sluss ("Lock of Nils Ericson") he made detailed studies and minute calculations in 1845–1846. He concluded there were insufficient stonemasons in the Stockholm area, and therefore had limestone and granite brought in from other parts of Sweden, quarries Ericson knew well from his earlier projects. He constructed a circular saw turned inwards to cut the head each stock at equal level for the bottom of the caisson, an instrument which was, like virtually all heavy tasks during the project, hand operated by several men. Empty barrels were used as rafts. Ericson gave directions for all sorts of tasks, including dredging, securing the rabbeting of planks, earth fillings, and determining the inclination of the caisson walls in order for them to withstand the pressure from the levees. He had to use an expensive steam dredger, but could avoid a machine for the drainage which saved a lot of money. He also made great efforts to make the extensive piling for the foundation more efficient; the drop forge of the pile driver should hit the pile with a constant effect, why Ericson had the labourers lower the device as the pile sunk. The timbered caisson was built as a huge box on Djurgården, just north-east of the bridge Lilla Sjötullsbron, slightly more than 79 meters long, 16,5 meters wide and 6,2 meters high (266½×56×21 feet), subsequently towed into place before the ends were removed. The temporary drydock on Djurgården is still discernible as a depression in the landscape. The construction work on the caisson began in May 1847 with the construction of barracks for 60 men and a smithy. In the drydock keel blocks tall were then placed and the bottom of the caisson was built upon them — a bed consisting of deal, beams, and 1 inches of boards. The caisson was completed in August, water was let in and the building berth and the barrage were removed. The floating was done in two hours 2-4 a.m., and its dimensions produced enthusiastic comparisons: "larger than the Stockholm Cathedral!", "...could house the entire Swedish Army and its paraphernalia."