b'ASK THE EXPERTSAsk the Experts Q&As are culled from member inquiries to NTCAs Technical Support staff. To become a member and make use of personal, targeted answers from Technical Support staff to your installation questions, contact Jim Olson at jim@tile-assn.com.QUESTION PVAsareusedinglueslike I need some help in understand- Elmersandarewatersoluble. ing PVA/Polyvinyl Acetate. I under- Previously PVAs were used on some standcontractorssometimesaddthin-set mortars, but carried a dis-PVA believing that it will strength- claimer that they were for interior enbond.However,inwetareas,dry use only, and are seldom used PVAisknowntore-emulsifyandany longer. SBRs are are not water weaken the bond. Do you have anysoluble and can be used in exterior knowledgeofPVAyoucanshare(wet) environments.with me, such as failures from usingPVAs are generally less expensive PVA as an admixture, and can youthan SBRs, but they are not created helpmeunderstandifthereareequal. anyplausiblereasonstoaddittoI hope this is helpful. cementitious tile setting materials?Scott Carothers, CTEFANSWER 2Ireachedouttosomemanu-facturersandtheywereextremely helpful, and sent me a lot of infor-mation. Following is a summary of this information: n PVA (polyvinyl acetate) not to be confused with polyvinyl alcohol is stillcommonlyusedasageneral purpose adhesive in interior or non-water immersed applications.Frequentlyitisusedasabond-ANSWER 1 ingagentorprimerpriortothe I am not a chemist,applicationofnon-modifiedplas-butinthepastthereters and mortars to a cementitious were two additives forsubstrate.Anattractivefeaturein thin-setmortars.Onethis application is the rewettable was the PVA you askednature of the bonding primer when about and the other isitcontactsthefreshalkalinemor-anSBR(styrenebuta- tar, allowing some inter-diffusion of diene rubber). the polymer that can help bind the 20TileLetter | August 2020'