Hi all, So I've done my research and have decided to build a raised hearth that has two layers of 1/2" Hardibacker. The hearth measures 48" by 60"; since Hardibacker ('HB") only comes in 35" x 60" sheets, that means each of my layers must have a seam in it where the full 36" sheet butts against a 12" sheet. Do I lose R-value from the resulting joint? If so, is there a tape or any other kind of material I can use to fix this? Thanks in advance. I have scoured the search engines and not found this issue addressed. The two main hearthbuilding documents on this site's "Resources" sections were very helpful for all my other questions.