▁ ▁The ▁appeal ▁of ▁Form stone ▁was ▁that , ▁once ▁installed , ▁it ▁required ▁virt ually ▁no ▁maintenance . ▁Sales men ▁bo asted ▁that ▁the ▁ins ulation ▁last ed ▁forever ▁and ▁that ▁the ▁first ▁cost ▁was ▁also ▁the ▁last ▁as ▁no ▁up keep ▁or ▁repair ▁was ▁required . ▁Sales men ▁also ▁pointed ▁out ▁that ▁Form stone ▁was ▁also ▁about ▁one - third ▁the ▁cost ▁of ▁other ▁fa ç ade ▁improvement ▁solutions . ▁Its ▁color ful ▁st u cco - ven e er ▁gave ▁a ▁stone - like ▁appearance ▁that ▁could ▁be ▁sh aped ▁into ▁different ▁text ures . ▁Form stone ▁was ▁particularly ▁popular ▁in ▁East ▁Baltimore , ▁where ▁residents ▁believed ▁that ▁the ▁stone ▁im itation ▁made ▁their ▁neighborhood ▁res emble ▁that ▁of ▁an ▁Eastern ▁European ▁town , ▁which ▁some ▁thought ▁had ▁an ▁appearance ▁of ▁aff lu ence . ▁ ▁Pat ented ▁in ▁ 1 9 3 7 ▁by ▁L . ▁Albert ▁Knight , ▁Form stone ▁was ▁similar ▁to ▁a ▁product ▁that ▁was ▁invent ed ▁eight ▁years ▁earlier ▁in ▁Columb us , ▁Ohio , ▁and ▁called ▁P erman ent ▁Stone . ▁P erman ent ▁Stone ▁was ▁also ▁a ▁v ene er . ▁In ▁the ▁ 1 9 7 0 s ▁pres ervation ists ▁and ▁re hab bers ▁felt ▁that ▁Form stone ▁took ▁away ▁from ▁the ▁historic ▁and ▁architect ural ▁value ▁of ▁the ▁homes ▁and ▁many ▁had ▁it ▁removed . ▁This ▁can ▁be ▁a ▁cost ly ▁and ▁time - consum ing ▁process . ▁Once ▁removed , ▁the ▁brick ▁requires ▁a ▁thorough ▁acid - w ash