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Moisture barrier questions...

16 years ago

I am installing a tile floor in a 2nd floor bathroom (not up the walls). The Hardie board website makes no mention of installing a vapor barrier but after reading a few posts, it sounds like I should. However, I have a few questions:

1.) What product do you recommend? I heard reference to 'roofing felt'... is this the same as 'tar paper'?

2.) How should it be installed? Do I use thinset (or some other adhesive) between it and the plywood subfloor? Do I nail/tack it down? I assume the Hardie board is then layed directly on top using thinset and screws?

3.) I have not decided yet if I will use tile or wood baseboards where the floor meets the walls (depends if I can find matching base tiles). In either case, should the moisture barrier extend a few inches up the walls (but behind the base board) or just lay flat?

Thanks in advance!

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Comments (3)

bill_vincent
16 years ago
For a floor, there's no need for a vapor barrier. That's only for behind walls of a shower, or tub/ shower combo.
lmhall2000
16 years ago
With all the looking I've done...it is recommended that you put a layer of thinset between the plywood and your hardibacker...I was told to just slap some thinset on the back of your hardibacker as you lay it down...it's mainly used to hold it in place...another tip was to leave 1/8 inch between boards and put your boards in a brick pattern..meaning don't have four corners meet. The recommendations for nailing it down are excessive..I think going by the nail slots on their boards they'd have you put over 40 screws in a 3x5...that's a lot of screws!

If you were doing a large area, I would definitely use the thinset...I put about 30 screws in a 3x5 in bathrooms that were smaller than 5x8 feet..I used the hardibacker brand and then I used the cheaper screws that are made for roofing...both worked well..I did not put thinset between my boards...for two reasons...they were small bathrooms...I found out my builder (500k + houses) tiles directly on the plywood! So I figured going the extra step of putting in the hardibacker on top and screwing all those in each board...that board wasn't going anywhere...and by the time it does..I'll be ready for a new floor...

No vapor barrier is needed like Bill said...so do what you think is best for your application....if you're doing an area greater than 100 sq. feet I would definitely use thinset between each board....and make sure you screw the nails down flush with the hardibacker and that the floor is solid and firm before tiling...

Have fun!!
Tara
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bill_vincent
16 years ago
If you're doing 10 square feet, the thinset needs to be between the backerboard and subfloor. It's not there to hold it in place. It's there to fill the paper thin void that would exist otherwise, and take the minute vibration out of the floor that it would cause, shortening the life of the floor.

I'm sorry-- I didn't see that last night when I initially answered.

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