Replies

1. 
   onslow | Jun 05, 2020 02:51pm | #1

   7709325,

   I don't know much of anything about east Texas other than Bigfoot supposedly lives in the part near Louisiana. Are you perpetually humid like Houston? Are you in a flood plain? Is air conditioning used a big part of your year.

   You seem to well under way with construction if you have already spray foamed under the deck. I don't seem moisture transport through the floor joists as a huge factor, but perhaps. If you are really concerned about being vapor open on the main floor areas then I would guess sheet vinyl would not be a good idea. I kinda suspect it is not an issue. I have a home with sheet vinyl in the kitchen and master bath. The floor is over a crawlspace in a relatively dry environment and AC is about 6 months a year here. I only have batts under the floor, so I would think you are ahead of the game if you used closed cell foam. If not, then maybe be cautious. Anyway, my few sojourns into the spider zone under my house has not revealed mold or other signs of excessive moisture. Mice and spiders, yes.

   If your pier construction allows for reasonable free air exchange, which my crawlspace does not have, then I would think you are again safer than not. The bottom of the deck is presumably sealed with foam and not subject to air flow. You did note 1 1/8 TG, is that 4x8 sheets or boards? I ask because the boards might be prone to expansion more than the sheet goods. But only if you have wide swings in humidity externally or internally.

   Any of the engineered woods once locked together or nailed down are not going to provide much if any air exchange with the interior air. The modern coatings of aluminum oxide are most likely impervious. Pergo would behave much the same with an entirely synthetic surface. I don't see how anything other than wide solid boards would show bad behavior.

   The tile floors will be not subject to air exchange from above or below. They will be subject to water and high moisture during showers and baths. Cement board would not be my choice, I would go with the Hardibacker properly set with the right screws not drywall screws. Use RedGard on top and seal the edges at the walls with a good sealant. NOT silicone.

   Then set your tile and use a sealer on the grout, mostly to keep it cleaner. Whatever water makes its way through the grout (and it does) will then be unable to go further than the thinset bed holding the tiles. Unless you have 20 splashy kids taking baths, most of the moisture will come back out the grout lines and be of no harm. The thinset will be a small reservoir risk if lots of water is splashed about frequently, but the RedGard is there to keep it from soaking any further. Not that the Hardiboard would take up water, like cement board does in my experience. Its just my belt and suspenders attitude.

   Other than saltillo tile and some expensive hand made tiles and certain stones, tile will be essentially impervious to water. You can seal the whole floor tile and grout with various products, but it will create a maintenance issue. I know, I have just put down a painful amount of quarry tile on my stairs, which is technically impervious. I went with sealer because it simply looks better sealed than dry. I will now have to re-seal as the dog wears it off with its claws. Better than having the dog ravage oak treads, which I have also been through.

   Say hi to Bigfoot for me, if you see him.