The addition of 1% chlorhexidine diacetate to COE Hydrophilic Gel Alginate has decreased its compatibility with the dental stones and disinfectants tested when compared with its nonantimicrobial counterpart. In terms of gypsum compatibility, the nonantimicrobial COE Alginate was compatible with all disinfectant and gypsum combinations tested. The addition of 1.70% didecyldimethyl ammonium chloride to Jeltrate Plus Antimicrobial Alginate has increased its compatibility with all the dental stones tested. A strong positive correlation (r = 0.7398) was found between visual gypsum compatibility evaluation scores and surface roughness of gypsum casts.