Hello,

I am planning to install 4x8' hardibacker sheets (1/4") to a cinder block wall. They will become supports for a combination tile and painted mural. I understand I should use an acrylic modified thinset and the right size screws. This work is sited in Southern California next to the coast and there is abundant humidity and marine layer though comparatively little rain. Shadier parts of the wall hold the morning dampness. Do you think I should use a moisture barrier? If so, how is it installed?

I plan to abutt the sheets and use an acrylic dispersion medium to fill the gaps. Thanks so much!

Is this a exterior block wall of a building or is it a retaining wall or something. Hardiebacker comes in 3x5 or 4x8 sheets. The seams should be covered with fiber mesh tape and thinset. Its best to follow manufacturer installation instructions. http://www.jameshardie.com/homeowner/pdf/backer-install-us.pdf How flat do you need to get this finished wall?