Hi guys,
I am in the process of finishing my basement and have become really confused about what I need to do for the bathroom subfloor.
I live in Montreal Canada and we built our house 7 years ago. The house is well built and the land is 98% plus sand and we have never had any moisture issues. There is poly sheet underneath the slab and my slab is at least 4-5 thick. I have installed 1 XPS rigid foam (staggered joints) everywhere in the basement and taped the joints. Then tapconed 5/8 T&G plywood to the slab (at least 10-12 per sheet) perpendicular to the foam boards. I am installing 8mm floating vinyl flooring everywhere but now have reached the bathroom which will be tiled and I am stuck.
I have to match 1.94 of height difference between slab and the rest of the basement (1 xps+.625 plywood+.315 vinyl flooring).
I do not want to build it up with cement and tile over it because it will still feel very cold specially in the winter and installing heated floors is out of question because in my area all you will be doing is pay to heat the slab and floor.
Everywhere I read they suggest 1 thick subfloor under the tile (2 rows of 5/8 T&G ply). The thinnest XPS foam I find is .8 . This plus .5 -9/16 for tile (thinset+ditra+thinset+tile) equals 2.6 . This is more than 5/8 of transition.
Since I am on the slab do I still need 1 subfloor under tile to prevent future cracks? Or can I just use one sheet of plywood?
How can I match the height? I would love to have a flat transition or maybe 1/8 difference Max.
I was thinking of using Kerdi board instead of rigid foam since they have different thicknesses but Schluter suggests Kerdi board for walls only.
Any help or idea would be greatly appreciated.
Best thing to do is find out the manufacture
Specs on the floor that you are using .
And suggest to them your options ,
And see if they will expect the scope of work
So you don't void your warranty of the product you are using
Hi there,
There is a great product on the market called Wedi Board. It comes in 1/2 and 1/4 thicknesses.
You could probably use kerdi board then detri on top of that. Making sure all are cemented down properly.
Thanks for the replies. Kerdi board is not approved for floors and I confirmed that with their sales rep.
Darcy,Wedi boards seem like a really nice option. They even come in 40mm thick which means I may not even need to put down plywood. I will contact them to see what they recommend and if it is available and reasonably priced in my area. Thank you for your great suggestion.
In the meantime any other suggestion would be greatly appreciated.
Hi Mike
You can mortar your ditra directly to your concrete slab floor if that is an option.
There are a few thicknesses of ditra available 1/8" and 5/16"and in ditra heat -1/4" and 5/16".
Although not heating your floor you could still use the ditra heat if that thickness works to your advantage. As well it provides the thermal break so you can skip the XPS.
One layer of 5/8ths then the ditra might give you the height required?
Schluter has a huge selection of transitions such as Reno-U and Reno-TK which might alleviate and soften the transition issue. Check their web site.
Dave
Hi Dave,
I had not considered that but I'm not sure that combo is enough to compensate for my height difference. I have to make up at least 1 3/8". Unless I misunderstood your post 5/16" Ditra +5/8" plywood on top = 15/16"
Also how do you suggest I install the entire system? Thinset+Ditra+Tapcon 5/8" plywood through all+thinset(+another layer of ditra?)+thinset+tile?
Those transitions from Schluter look pretty neat. I might use it in my hearth under the stove.
You may want to reconsider and use leveling cement to get your slab floorheight higher in the bathroom. I don't recommend putting plywood directly on the sub-floor even with a vapour barrier. You will have problems in the future.
Fix your drain lines and toilet flange to the correct height, install leveling cement as necessary, install mortar and ditra heat duo and then mortar and tiles. You will have a thermal break with the ditra heat duo.
Dave
Mike,
Just a quick observation. A double layer of 5/8" plywood is usually recommended as a tiling base in a wood framed construction where floor joists are on 16" centers. This serves to stiffen the flooring to a deflection of 1/360 or less for tiles. (natural stone requires more stiffness)
When applying tile to a slab, the deflection of your floor is essentially 0 and plywood serves to build thickness rather than stiffness. However, introducing compressible elements to the floor construction can produce flex due to compaction (Kerdi board or foam insulation compress under load - That's why their use is not recommended as part of a floor meant to support tile)
When you try and make a "sandwich" a variety of different elements to achieve a give thickness you really have to be careful to accomodate many different factors regarding each item's performance and the suitability for your intended purpose (in this case as a base for a heated tile floor)
I might suggest that you consider a mortar bed screeded to the required thickness to support the balance of systems and finishes. Mortar can serve as a solid base for tile as well as adding thermal mass to your heated floor which, once warmed up, contributes to a feeling of comfort underfoot.
There are many ways to skin a cat, and many suggestions here will achieve your intended results. I prefer a simpler approach, which is to install a mortar layer of appropriate thickness which then controls the number of elements in use for your floor.
I hope this helps
Jacques Bouchard
Stellium Renovations
Montreal
Thanks for all the support guys. It seems like the most common suggestion is to build it up with mortar bed. I was hoping to avoid that for several reasons, the first two that come to mind are labour and cold feet.
Jacques, I am glad you mentioned the difference between building on slab and on top of joist leading to deflection. I do not have enough experience to know what would be the minimum required plywood thickness when used on slab to raise height. To be honest with you, I am not at all concerned about compressive forces over the xps foam. They are rated at 15-25 PSI depending on brand. That is 2160-3600 pounds a square foot. Now add 5/8" plywood on top to distribute the load and you have nothing to worry about. As mentioned in my first post, it would all be tapconed to the floor to avoid flex. To be able to use this method, I have to use .8" XPS+3/4" plywood but I am not sure it would be enough under the tile. My assumption so far was that I need 1 - 1 1/4" just like on top of joists.
I am also looking at Wedi boards as suggested by Darcy. It seems like a really good product but I am having a hard time getting it in my area.
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