Tile over Radiant Question?
#1
03-06-05, 10:52 PM
Tile over Radiant Question?
I have a question about my installation. I'm sorry about the length but I'm thoroughly confused at this point.
I have a 3/4" Advantech subfloor with I-Joists every 16". I have staple-up radiant under the subfloor using heat transfer plates.
I was in the process of laying down 1/4" Hardibacker EZ Grid using Versabond Fortified Thin-Set Latex Mortar (polymer modified).
http://www.custombuildingproducts.co...er=arc&lang=en
As to the thickness of the floor, I would have done more but I'm trying to keep the R-value down because of the staple-up radiant. It is a catch 22. I would like a stronger floor but it would reduce the efficiency of the radiant system. Otherwise, I would have done the 1/2" plywood with 1/4" hardibacker or a 1/4" multiply with 1/2" hardibacker.
I am screwing it down but I can only use a 3/4" screw because of the staple-up radiant. I tested a 1" screw but it still pokes through so I couldn't risk it. Because of this, I am screwing on a 4" grid instead of the typical 8". I'm also using a standard wood screw instead of the backer screw since it's not available in a 3/4" length. I was even thinking about hitting it with an air stapler using 3/4" staples.
One tile guy I talked to said I should be using an acrylic admix mortar to lay down the hardibacker instead of the latex mortar I'm currently using. He said I needed the better adhesion for the Advantech. I was under the impression that the layer of thinset beneath the hardibacker was more of a filler than a bonding agent.
I talked to another tile guy who said I was doing it all wrong and that the tile will be breaking loose within a couple of years. He said I should have used a crack isolation membrane such as Schluter's Ditra product. He said that my only hope now would be to use a crack isolation membrane over the hardibacker, such as Mapei Mapelastic HPG.
If I would have remembered previous advice, I would have probably used ditra instead of hardibacker. However, I completely forgot about ditra and began laying down the hardibacker. A good portion is already installed, so it is too late for ditra at this point. Unless you know of an easy way of removing hardibacker that has been put down with thinset and screws on a 4" grid?
I talked to yet another tile guy who said I should use a better thinset for adhering the tile to the hardibacker. He said the Versabond was OK for the hardibacker to Advantech but I should be using the Mapei Kerabond+Keralastic for the tile.
My questions are as follows:
1. Should I be using an acrylic admix mortar to lay down the hardibacker instead of the latex mortar I'm currently using?
2. Are the 3/4" screws on a 4" grid enough or should I also hit it some more with an air stapler using 3/4" staples?
3. Do I really need to tape off the hardibacker seams using a glass fiber tape as recommended by hardibacker?
4. Do I need to use a crack isolation membrane over the hardibacker because of the radiant? If not required, is it recommended?
5. Is Versabond a suitable thinset for the tile or should I be using the Mapei Kerabond+Keralastic product instead?
I'm not trying to take the cheap way out. I want a floor that lasts while maintaining the efficiency of the radiant. I'm willing to do what it takes as long as I know it's going to make a difference.
Thank You
I have a 3/4" Advantech subfloor with I-Joists every 16". I have staple-up radiant under the subfloor using heat transfer plates.
I was in the process of laying down 1/4" Hardibacker EZ Grid using Versabond Fortified Thin-Set Latex Mortar (polymer modified).
http://www.custombuildingproducts.co...er=arc&lang=en
As to the thickness of the floor, I would have done more but I'm trying to keep the R-value down because of the staple-up radiant. It is a catch 22. I would like a stronger floor but it would reduce the efficiency of the radiant system. Otherwise, I would have done the 1/2" plywood with 1/4" hardibacker or a 1/4" multiply with 1/2" hardibacker.
I am screwing it down but I can only use a 3/4" screw because of the staple-up radiant. I tested a 1" screw but it still pokes through so I couldn't risk it. Because of this, I am screwing on a 4" grid instead of the typical 8". I'm also using a standard wood screw instead of the backer screw since it's not available in a 3/4" length. I was even thinking about hitting it with an air stapler using 3/4" staples.
One tile guy I talked to said I should be using an acrylic admix mortar to lay down the hardibacker instead of the latex mortar I'm currently using. He said I needed the better adhesion for the Advantech. I was under the impression that the layer of thinset beneath the hardibacker was more of a filler than a bonding agent.
I talked to another tile guy who said I was doing it all wrong and that the tile will be breaking loose within a couple of years. He said I should have used a crack isolation membrane such as Schluter's Ditra product. He said that my only hope now would be to use a crack isolation membrane over the hardibacker, such as Mapei Mapelastic HPG.
If I would have remembered previous advice, I would have probably used ditra instead of hardibacker. However, I completely forgot about ditra and began laying down the hardibacker. A good portion is already installed, so it is too late for ditra at this point. Unless you know of an easy way of removing hardibacker that has been put down with thinset and screws on a 4" grid?
I talked to yet another tile guy who said I should use a better thinset for adhering the tile to the hardibacker. He said the Versabond was OK for the hardibacker to Advantech but I should be using the Mapei Kerabond+Keralastic for the tile.
My questions are as follows:
1. Should I be using an acrylic admix mortar to lay down the hardibacker instead of the latex mortar I'm currently using?
2. Are the 3/4" screws on a 4" grid enough or should I also hit it some more with an air stapler using 3/4" staples?
3. Do I really need to tape off the hardibacker seams using a glass fiber tape as recommended by hardibacker?
4. Do I need to use a crack isolation membrane over the hardibacker because of the radiant? If not required, is it recommended?
5. Is Versabond a suitable thinset for the tile or should I be using the Mapei Kerabond+Keralastic product instead?
I'm not trying to take the cheap way out. I want a floor that lasts while maintaining the efficiency of the radiant. I'm willing to do what it takes as long as I know it's going to make a difference.
Thank You
#2
03-07-05, 07:37 AM
Well to answer all your questions
1) thinset under the backer is only to support and fill voids so using the admix and unmodified is not the way to go. Osb does not lend itself to being a good bonding substrate for thinsets, so even a more expensive thinset won't bond well and would shear off.
2) 3/4" screws won't get you any warranty on your materials. As a matter of fact, the amount of thread in the osb will be minimal as the tapered point doesn't really count. You've also probably came close to popping the screws in half trying to countersink them into the backer, so consider them to have only half the strength they started with, if not even less than that.
3-4)You should have used Ditra for this installation or Wonderboard/Durock as they have better thermal mass for holding the heat than hardi. You could also have just used the Ditra. An easy way to pull up Hardi that has been thinsetted and screwed is just to unscrew it. You'll be pleasantly surprised how easy thinset will shear from osb. The fleece on the back of Ditra will allow for the tow substrates to move independantly which is why it is ok to thinset ditra to osb. Hardi must be taped and thinsetted at the joints. It makes the surface act as one continuous sheet of underlayment and strengthens the joint between boards.
5) Versabond on backer board works fine. Unless you have a really hard to bond porcelain tile and need the extra adhesion that the Kerabond/Keralstic would provide.
You could continue as you are doing and put Ditra over top, but I would expect problems just from issues associated with improperly installed Hard under the Ditra. Crack isolation membranes won't help anything if the Hardi pops a few screws and creates a verticle movement problem. Is there any way to map out the heating tubs with a couple holes drilled up along side the tubes through the floor to use a reference points for chalk lines to know where to hit the board with the proper screws? You will be able to get some areas with the 8" oc spacing and then some others with more conservative spacing such as 4-6" for the rows and back to 8" oc within the rows.
1) thinset under the backer is only to support and fill voids so using the admix and unmodified is not the way to go. Osb does not lend itself to being a good bonding substrate for thinsets, so even a more expensive thinset won't bond well and would shear off.
2) 3/4" screws won't get you any warranty on your materials. As a matter of fact, the amount of thread in the osb will be minimal as the tapered point doesn't really count. You've also probably came close to popping the screws in half trying to countersink them into the backer, so consider them to have only half the strength they started with, if not even less than that.
3-4)You should have used Ditra for this installation or Wonderboard/Durock as they have better thermal mass for holding the heat than hardi. You could also have just used the Ditra. An easy way to pull up Hardi that has been thinsetted and screwed is just to unscrew it. You'll be pleasantly surprised how easy thinset will shear from osb. The fleece on the back of Ditra will allow for the tow substrates to move independantly which is why it is ok to thinset ditra to osb. Hardi must be taped and thinsetted at the joints. It makes the surface act as one continuous sheet of underlayment and strengthens the joint between boards.
5) Versabond on backer board works fine. Unless you have a really hard to bond porcelain tile and need the extra adhesion that the Kerabond/Keralstic would provide.
You could continue as you are doing and put Ditra over top, but I would expect problems just from issues associated with improperly installed Hard under the Ditra. Crack isolation membranes won't help anything if the Hardi pops a few screws and creates a verticle movement problem. Is there any way to map out the heating tubs with a couple holes drilled up along side the tubes through the floor to use a reference points for chalk lines to know where to hit the board with the proper screws? You will be able to get some areas with the 8" oc spacing and then some others with more conservative spacing such as 4-6" for the rows and back to 8" oc within the rows.
#3
03-07-05, 03:54 PM
Thank You!
Tilebri,
Thanks for the quick and thorough reply. I truly appreciate it.
I will unscrew one of the hardibacker boards and try lifting it up. I will also see how easy it is to clean up the thinset off the Advantech. As you stated, it might be easier than it seems, especially with a floor scraper.
If it turns out to be too much of a project, I will take your second piece of advice. I will drill a couple pilot holes along each joist and snap a chalk line between them along the length of the joist. I will remove the 3/4" screws and replace them with 1-1/4" backer screws every 4 inches. This will give me the proper screws on a 4"x16" grid.
I may even drill some pilot holes down the center of the I-Joists, which would allow me to get a 4"x8" screw grid, which exceeds the hardibacker recommendations.
Assuming I screw it down properly as discussed above, will it be a lasting installation or could I still have problems? Should I still think about using Ditra over it? What will this gain me?
Thank You
Thanks for the quick and thorough reply. I truly appreciate it.
I will unscrew one of the hardibacker boards and try lifting it up. I will also see how easy it is to clean up the thinset off the Advantech. As you stated, it might be easier than it seems, especially with a floor scraper.
If it turns out to be too much of a project, I will take your second piece of advice. I will drill a couple pilot holes along each joist and snap a chalk line between them along the length of the joist. I will remove the 3/4" screws and replace them with 1-1/4" backer screws every 4 inches. This will give me the proper screws on a 4"x16" grid.
I may even drill some pilot holes down the center of the I-Joists, which would allow me to get a 4"x8" screw grid, which exceeds the hardibacker recommendations.
Assuming I screw it down properly as discussed above, will it be a lasting installation or could I still have problems? Should I still think about using Ditra over it? What will this gain me?
Thank You
#4
03-08-05, 07:36 AM
If the temperature of the floor is maintained pretty consistant and proper expansion gaps are used throughou the installation, then you may be ok. (emphasis on "may") An uncoupling system would provide better protection against issues arising from rapid temperature changes in the floor.
#5
03-08-05, 09:59 PM
Tilebri,
What do you consider proper expansion gaps?
I have an electronic injection control system that varies the water temperature in relation to the outdoor temperature. It also limits the water temperature so the floor does not get too warm.
I'm also using extruded aluminum heat transfer plates, which allow a lower temperature water to be run and dissipates the heat more evenly through the floor.
I tried removing one of the boards and it did not come up easily. The remaining thinset on the Advantech was difficult to remove and pieces of subfloor were being chipped away in the process. This was confusing because everyone I talked to said Advantech was terrible because nothing sticks to it. Well in this case, the thinset stuck to it quite well.
My Advantech floor on the first floor was exposed to the elements for quite some time and well weathered. The waxy finish was worn away and the surface was pretty dried out. I think this is why the thinset is adhering to it so well.
Besides thinset, is Ditra secured to the subfloor using staples or screws? If so, what is the grid pattern for securing it, every 8"?
Also, what is the approximate cost of Ditra per sq. ft.?
What do you consider proper expansion gaps?
I have an electronic injection control system that varies the water temperature in relation to the outdoor temperature. It also limits the water temperature so the floor does not get too warm.
I'm also using extruded aluminum heat transfer plates, which allow a lower temperature water to be run and dissipates the heat more evenly through the floor.
I tried removing one of the boards and it did not come up easily. The remaining thinset on the Advantech was difficult to remove and pieces of subfloor were being chipped away in the process. This was confusing because everyone I talked to said Advantech was terrible because nothing sticks to it. Well in this case, the thinset stuck to it quite well.
My Advantech floor on the first floor was exposed to the elements for quite some time and well weathered. The waxy finish was worn away and the surface was pretty dried out. I think this is why the thinset is adhering to it so well.
Besides thinset, is Ditra secured to the subfloor using staples or screws? If so, what is the grid pattern for securing it, every 8"?
Also, what is the approximate cost of Ditra per sq. ft.?
