▁German ▁building ▁materials ▁company , ▁Kn auf . ▁The ▁deal ▁closed ▁in ▁April ▁ 2 0 1 9 . ▁ ▁History ▁In ▁the ▁ 1 8 9 0 s , ▁gy psum ▁manufact ur ers ▁perfect ed ▁a ▁method ▁of ▁strength ening ▁pl aster ▁by ▁adding ▁a ▁ret ard er , ▁which ▁controlled ▁the ▁setting ▁time , ▁thus ▁creating ▁a ▁vi able ▁compet itor ▁to ▁traditional ▁l ime ▁pl aster . ▁Because ▁gy psum ▁was ▁pl ent iful , ▁and ▁available ▁at ▁a ▁relatively ▁low ▁price , ▁and ▁because ▁the ▁manufact uring ▁process ▁was ▁so ▁simple , ▁new ▁fir ms ▁flo oded ▁and ▁fragment ed ▁the ▁market , ▁placing ▁constant ▁down ward ▁pressure ▁on ▁prices . ▁ ▁On ▁December ▁ 2 7 , ▁ 1 9 0 1 , ▁ 3 0 ▁gy psum ▁and ▁pl aster ▁companies ▁merged ▁to ▁form ▁the ▁United ▁States ▁Gy psum ▁Company , ▁resulting ▁in ▁the ▁creation ▁of ▁the ▁first ▁nation wide ▁gy psum ▁company ▁in ▁the ▁United ▁States . ▁The ▁new ▁company ▁combined ▁the ▁operations ▁of ▁ 3 7 ▁min ing ▁and ▁calc ining ▁plants ▁producing ▁agricult ural ▁and ▁construction ▁pl aster . ▁ ▁In ▁ 1 9 0 9 , ▁US G ▁purchased ▁the ▁S ack ett ▁Pl aster ▁Board ▁Company , ▁invent or ▁of ▁S ack ett ▁Board , ▁which ▁was ▁a ▁panel ▁made ▁of ▁multiple ▁layers ▁of ▁pl aster ▁and ▁paper . ▁By ▁ 1 9 1 7 , ▁a ▁new ▁manufact uring ▁process ▁produced ▁bo ards ▁with ▁a ▁single ▁layer ▁of ▁pl aster