Self Leveling Underlayment over OSB
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Self Leveling Underlayment over OSB
I am planning to tile my master bathroom floor. I've stripped the floor down to the 5/8" OSB subfloor. There are some real level issues with this room. The difference between the floor height at the door and that at the far wall is about 3/4". It's not just a slope issue either there are floor height variances through this small (7.5' x 7.5') room that are pretty significant.
I'm thinking of using self-leveling underlayment. I realize that there will be somewhat of a step up at the door, but I'm thinking it might be better to deal with the doorway height issue than not to level the floor.
Some of the things I've read recommend against pouring the SL mortar over OSB board. In my other tile projects, I've used RedGard over the OSB then thinset (with latex) then hardibacker or Durock or some other cement board with pretty good results. The RedGard seals the OSB.
Would the following work...
----Tile---------------------------
----Thinset------------------------
----Self Leveling Mortar ----------
----Mesh ?-------------------------
----RedGard------------------------
----OSB----------------------------
Some questions:
Any input is greatly appreciated.
Thx
John
I'm thinking of using self-leveling underlayment. I realize that there will be somewhat of a step up at the door, but I'm thinking it might be better to deal with the doorway height issue than not to level the floor.
Some of the things I've read recommend against pouring the SL mortar over OSB board. In my other tile projects, I've used RedGard over the OSB then thinset (with latex) then hardibacker or Durock or some other cement board with pretty good results. The RedGard seals the OSB.
Would the following work...
----Tile---------------------------
----Thinset------------------------
----Self Leveling Mortar ----------
----Mesh ?-------------------------
----RedGard------------------------
----OSB----------------------------
Some questions:
- Would the SL concrete flow OK over the RedGard? Do I need to use an SL primer?
- If I need to use a primer can I put it directly on the OSB? Will it give me the same protection as the RedGard?
- Since the differences in height of the floor between the wall an the door are pretty significant, how thin can I go with the SL concrete before it risks cracking?
- Should I do the SL concrete over a mesh? If so, recommendations?
Any input is greatly appreciated.
Thx
John
Last edited by jmpdiy; 01-10-09 at 09:19 AM. Reason: fix title
#2
Not a good approach.
If your joists are good, I would do the following.
OSB
Cement backer board (laid in a bed of thinset and screwed per manu. instructions)
SLC
Thinset
Tile
If your joists are good, I would do the following.
OSB
Cement backer board (laid in a bed of thinset and screwed per manu. instructions)
SLC
Thinset
Tile
#3
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OSB
Cement backer board (laid in a bed of thinset and screwed per manu. instructions)
SLC
Thinset
Tile
Cement backer board (laid in a bed of thinset and screwed per manu. instructions)
SLC
Thinset
Tile
Also, I think that TEC makes an slc that they claim can be used over osb. Check out the Tec Specialty Products website.
Yes you will need a primer, and lath as well. Read and follow all the instructions for the slc.
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Thanks for the quick replies.
If I followed HeresJohnny's recommendation substituting plywood for the cement board could I go thinner? My concern with the cement board was overall thickness causing me an even greater height differential at the door.
My other idea is to skip the SLC and just go with the cement board as I have in the past, leveling as much as I can with the layer of thinset between the OSB and cement board. Thoughts?
Is tiling directly over SLC a bad idea? A contractor friend of mine does this as normal practice.
I'll check out the TEC offerings.
Thx
John
If I followed HeresJohnny's recommendation substituting plywood for the cement board could I go thinner? My concern with the cement board was overall thickness causing me an even greater height differential at the door.
My other idea is to skip the SLC and just go with the cement board as I have in the past, leveling as much as I can with the layer of thinset between the OSB and cement board. Thoughts?
Is tiling directly over SLC a bad idea? A contractor friend of mine does this as normal practice.
I'll check out the TEC offerings.
Thx
John
#5
Member
could I go thinner?
My other idea is to skip the SLC and just go with the cement board as I have in the past, leveling as much as I can with the layer of thinset between the OSB and cement board. Thoughts?
Is tiling directly over SLC a bad idea? A contractor friend of mine does this as normal practice.
#6
Definitely add more plywood, I don't know of any method that allows 5/8" OSB as the subfloor. Are you sure it's only 5/8" thick? Did you remove another layer from the floor? Don't know of a jurisdiction that would allow that.
Jaz
Jaz
#7
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Woops, missed the 5/8". Jazman is right about that. Tec EZ-Level claims it can be used over 3/4" osb. We're dealing with 5/8" here. I'm not sure I'd be comfortable with slc over osb anyway. Most self levelers can't be used with osb.
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And to add to what Johnny said about the thickness of slc, yes, at it's thinnest it needs to be 3/8" or more over ply, not osb, but 5/8" isn't 3/4 so...
But, over properly installed cbu, you can use slc as needed to a feather edge. You need the slc primer. Don't blow your money on redgard on the osb before thinsetting down the cbu. The small amount of moisture in the thinset is not going to damage the osb. Driving 60 screws or nails per sheet through your redgard is just a wasted $1/sf. If you want waterproofing, do it over the cbu and slc.
5/8" is very much as minimum as you can get. I vote the adition of plywood, nothing less than bc sanded in quality and nothing thinner than 3/8".
Transitions can be made to go from one height to another and transition height should not be a greater consideration than rigidity and stability.
But, over properly installed cbu, you can use slc as needed to a feather edge. You need the slc primer. Don't blow your money on redgard on the osb before thinsetting down the cbu. The small amount of moisture in the thinset is not going to damage the osb. Driving 60 screws or nails per sheet through your redgard is just a wasted $1/sf. If you want waterproofing, do it over the cbu and slc.
5/8" is very much as minimum as you can get. I vote the adition of plywood, nothing less than bc sanded in quality and nothing thinner than 3/8".
Transitions can be made to go from one height to another and transition height should not be a greater consideration than rigidity and stability.
#9
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Brian
Tec claims their slc can be used over 3/4" osb. I would not be comfortable with this but Tec makes this claim.
Link below
http://www.tecspecialty.com/content/...x?product_id=8
select "PDS - EZ Level" in the drop down box.
Tec claims their slc can be used over 3/4" osb. I would not be comfortable with this but Tec makes this claim.
Link below
http://www.tecspecialty.com/content/...x?product_id=8
select "PDS - EZ Level" in the drop down box.
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Like you, I wouldn't do it over OSB either but looking at the data sheet, I suppose it's like liquid Hardibacker at 6000 to 7000 psi, with wire reinforcement. Custom lets you go with single layer t-g ply up to 24" oc with 1/2" pour of wire reinforced Level quick. At the price of slc's, it would be cheaper to go with 3/8" ply and Ditra. Easier on the back as well.
#11
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At the price of slc's, it would be cheaper to go with 3/8" ply and Ditra. Easier on the back as well.
................................
#13
Ditra is great stuff. You basically mix up a loose thinset, lay the Ditra down, and use the flat side of your trowel to set it in the thinset bed. Immediatly after that, you can start tiling if you'd like.
#14
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Go here and read as much of this as you can. Follow there instructions. Come back and ask about anything thats not clear.
Schluter-DITRA - Schluter-Systems
Schluter-DITRA - Schluter-Systems
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Very slow moving project. Still planning... We're getting by with one batchroom upstairs for now.
Thinking of going with the Ditra. One question though, since the subfloor is only 5/8" tongue-and-groove OSB, and while most of the floor is 16" oc, there is one set of joists that are 24" oc (accommodating duct work). The Ditra handbook specifies min 5/8" over 16" oc, and 3/4" min. over 24" oc. (Ditra-XL). Should I put a layer of plywood (min. thickness?) or a layer of cement board over the OSB? I was thinking plywood, but not sure what would be best.
On the level issue, I think since the real problem is that two adjacent joists are a 1/2" different in height, I think I can put 1/2" plywood over the OSB in the lower section , feather thinset at the point of the drop off, and take the hit on the height transition at the doorway. Seems to be the best approach to getting the smallest transition.
BTW. Thanks to all for all the good advice.
Thinking of going with the Ditra. One question though, since the subfloor is only 5/8" tongue-and-groove OSB, and while most of the floor is 16" oc, there is one set of joists that are 24" oc (accommodating duct work). The Ditra handbook specifies min 5/8" over 16" oc, and 3/4" min. over 24" oc. (Ditra-XL). Should I put a layer of plywood (min. thickness?) or a layer of cement board over the OSB? I was thinking plywood, but not sure what would be best.
On the level issue, I think since the real problem is that two adjacent joists are a 1/2" different in height, I think I can put 1/2" plywood over the OSB in the lower section , feather thinset at the point of the drop off, and take the hit on the height transition at the doorway. Seems to be the best approach to getting the smallest transition.
BTW. Thanks to all for all the good advice.