Tiling over radiant heated concrete
BoJangles
| Posted in Construction Techniques on
I am interested in experiences (good or bad) that any of you have had with laying ceramic tile directly over 4″ radiant heated concrete slabs.
I am not concerned with anything except the possibility of tile cracking because of minor movement in the slab due to the radiant heating.
We have done this several time before, but people lately seem more concerned about this potential problem and lots of people around here seem to be using Ditra or some type of isolation membrane. I don’t know if this is overkill or if there is a real need for it.
I personally, have never had a problem just tiling right over the slab, but if anybody has or has some advice to throw my way, I’d like to hear it.
Replies
Since ditra physics has changed and tile will just fly off a heated slab. Luckily you've heard the good word and will cease your standard practices before flying tile hits someone in the eye!
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I'm with you on this one. I have yet to see or hear of modified thinset with a little flex let loose from a heated slab or cause a tile to break.
I do see an advantage with ditra for protection as far as potential slab cracks go. Lately I've been following a half dozen high quality slabs locally that were perfectly ok after the first month but have developed significant cracks unfriendly to tile by the 6 month mark.
Beer was created so carpenters wouldn't rule the world.
Do you think these slabs cracked because of the heating....or some other issue??
Some slabs are plumbed with pex, but none have been fired up yet.
The cause seams to be a combination of settling, shape, and lack of contraction joints at some points. It's been quite strange because all the slabs have been very well preped with coarse sand compacted well and a great installer who pays close attention to the mix and environmental conditions while finishing.
It seems too few contraction joints caused small cracks right away. These then were the weak point as slight settling occured around the perimeter and the cracks widened. The temperatures were pretty moderate and slump as low as would pump so curling didn't seem a major concern.
On one hand the cracks are not continuing to move so anything applied now would most likely last indefinitely, but there may well have been some problems had tile been installed a month after the pour.
Since most of these aren't on our jobs it's impossible to say if the excavator overdug and simply used the bucket to "compact" those over dug areas, which never works well although it's done all the time.
To us the cracks aren't bad, definitely allowable by NAHB specs, but it is disconcerting to the homeowners who don't understand the difference between a small non-moving crack and the end of the world.
The clients are also well aware of the tradeoff between the cost of adding metal and reduced width of cracks. They choose not to add metal, but still want to complain about the width of the cracks.
In these situations I can appreciate both sides. Top dollar paid for good mud placement, extra time spent on prep and compaction and still having noticable cracks is a bummer. However, the guy doing the slabs is upfront with everyone about every slab having some cracking and the cracks that are there appear stable.
The homeowners will probably continue to be unhappy. The flatwork sub will continue his frustration with the clients. We're just a little surprised at the magnitude and consistancy of the cracks, not necessarily that they're there.
Beer was created so carpenters wouldn't rule the world.
I did about 1500 square feet of a basement at a buddies house two years ago. He has in floor radiant heating with 2 inches styro underneath. We get about 4-5 months of winter in this area. Tiled right onto the concrete. Not a crack yet.
I think the ditra would somewhat defeat the radiant effect of the heat and would have been a waste of money at this house.
Have a goo day
Cliffy
skip the ditra and spend the money on adequate expansion and control joints both on the slab AND around the perimeter the perimeter seems to be a neglected area and the expansion mateial is cheap
sink wire mesh into the slab, use the heavier gauge "highway" wire ifn budget allows mesh helps slab retain is shape, but is usually placed only in the garage slab, not the right way to save compact the base well before slab's poured; a whacker on stone fill or sand, placed in proper depth lifts
check for out of level on the slab w stringline and then a 6' level and adjust fill the dips w a portland base leveler like from Ardex
if it's over old work, look into the membranes to run over cracks to isolate them from your tile
use thinset w latex milk additive, laticrete makes a good onefor over concrete
Good advice. That's basically exactly what we do now.
If you read and use the TCNA Manual (2006) you will note that it requires a crack isolation membrane for tile over hydronic radiant slabs.
Jeff
Laying tile over anything is a rarity for us, so I don't get involved much with any reading material. ( I will now ) Therefore...I haven't the slightest idea what the TCNA manual is or where to find it.
BTW, if you are a tile layer, what do you think about the Mapei Keralastic/Kerabond thinset system. It sounds to me like this is a very good solution to the problem without going to the expense and trouble of using something like Ditra??
Here's the link for the handbook. TCNA is: Tile Council of North America.
They act as the secretariat for ANSI and the international version of ANSI.
http://www.tileusa.com/publication_main.htm
Membranes have been a requirement for quite awhile now. Just so you understand where I'm coming from, I am a Ceramic tile and stone contractor and have been in the industry for 37 years. (yea, I'm old!) I also do job inspections and consulting. I can tell you without a doubt, that floor will crack. We just don't know when. Uncoupling membranes have been on the market for better than 10 yrs.in this country, while Europe has a much longer track record. Then again radiant heat is common over there.
My suggestion is to call the manufacturer of a uncoupling membrane directly and talk with their tech. dept. All major manufacturers have 800#'s and technical dept.
Thanks Jim !
Just a crazed architect sir!
Jeff
Well at least you're man enough to admit it!