Questions about cementboard underlayment
bwd
| Posted in Construction Techniques on
I am renovating a bathroom using Hardibacker cement boards over the subfloor in preperation for tile.I plan on screwing the backer board down without thinset between it and the subfloor. The instructions say to install with smooth side up, but it seems that the rough side would adhere better to the tiles. Is therea good reason not to install this way and what about using Mastic on the floor instead of thinset??
Replies
Ummmm..... I'm betting that Hardie probably knows which side the tile adheres to best. I'd stick with their instructions. Mastic is for wall tile that won't see any stress, thinset for floors.
lol
Hi ... my name is Jeff.
I'm planning on buying a product and going against the manufacturers installation instructions. I'm hoping if enough people reply to my post ... another idgit will tell me it's ok ...
like not using TSet under the backer ...
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Hallelujah brother!!
I just re-read your post again..... you said you are not planning on using thinset between the backerboard and the subfloor. Why are you trying to reinvent the wheel? Follow the directions and you'll have a nice floor. Decide you're smarter than the manufacturers and you'll end up with crap. Do yourself a favor and use thinset to set the backerboard down, don't lay the Hardie upside down despite that lightbulb that went off, and spring for some more thinset to give your tile a fighting chance.
Oh... and welcome to the forum.
What diesel said. Your plan of action as outlined in the first post is a receipe for disdaster. And you're going to waste your time and money.
Why are you adding a layer of hardie on the floor? If you're doing it to make the floor stronger, it won't work. If you're doing it to provide a good bonding surface for the tile, you're on the right track.
"When asked if you can do something, tell'em "Why certainly I can", then get busy and find a way to do it." T. Roosevelt
You can screw the hardibacker down onto the subfloor IF the subfloor is sound and flat and solid.
We ripped out finished pine flooring in our five year old kitchen two years ago and screwed hardibacker directly onto the subfloor with no thinset underneath. Screwed six inch on the edges and one foot in the field. This over 3/4" T&G subfloor over Boise Cascade four star rated I-joists/span length. You could bring in the Denver Broncos and have them jump up and down in unison and the dishes won't rattle.
Over the hardibacker went a coat of thinset and 3/8" thick porcelain tiles. Nary a crack to be found to date.
Do go smooth side up. The thinset does not need a rough surface to adhere to, and getting a nice smooth level coat on the rough side is simply making things harder than they need to be.
Chris
Thinset the board down - the last think you want is popping and flexing 1 year down the road.
Either side of the harti board will work fine. the smooth side is easier to deal with. When you trowel the thinset, you have less chance of scraping up bits of it.
Mastic - yuck. It smells and has a shorter open time. Thinset is made for what you are doing.
You could use liquid nails and staples. Thinset will stick well to either side. Wonder board has a sticker on it that says either side but if you put the label side up, remove the label. Label is on smooth side. Some brands have dots to indicate fastener placement. So its ok not to use thinset.
Liquid nails is not a good material to use under cement board. It creates hollow spots between the beads, then when the floor is walked on the board flexes and the tiles pop off.
Hollow spots? Not really. The glue gets compressed by the staples
You must use thinset under the backer board.
Here's a tip for setting the tile. There will be a fine layer of dust on the board which has to be removed before applying the thinset on top for the tile. Otherwise the thinset rolls up without adhering to the board unless you apply lots of pressure to overcome it. Vacuum the board, then wash it down with plain water on a fairly wet rag. An old hand towel works nicely. Rub some to get the dust off. You can leave the backer wet. Then during the last few minutes of slaking the thinset wipe the board down again to dampen it. The clean, damp board will accept the thinset much better.
When I was in Engineering school (Oregon State - go Beavs!), they taught all of us a simple saying: "When in doubt, make it stout, out of things we know about".
Follow the directions!
Also, I have spread a lot of thinset and some mastic (liquid nails, etc.) I will take spreading the thinset any day.