Mortar (masonry)
Mortar was a substance, consisting of sand and cement, used in masonry to bind construction bricks or blocks, such as those made out of , together and fill the gaps between them. 

In 2373, Captain Sisko marveled at a painting containing a Bantaca spire, noting that the structure was made of hundreds of stones carved and fitted together so tightly that they didn't require mortar. ()

See also 
 Bricklayer

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Materials