# Ceramic tile over radiant in slab heat problems



## ericjeeper (Mar 2, 2008)

Well today My daughter noticed a couple of the tiles in the hallway sounding hollow. later this evening I was out in the sugarbush and she yelled for me to come into the house.. I asked why she said"The tiles in the hallway are bubbling up".. I thought hum possibly a leak in a line.. But not a drop or rise in the radiant system. I checked as I ran into the house.. Sure enough two rows of tile going across the 36 inch wide hallway were raring up like 6 mountain goats going at it head to head. And the hallway sounded like it was about to explode grout was popping everywhere. I was shoeless as I pulled my muddy boots off in the garage.. I told my son to stomp em and break a few to get the pressure off.Once we got a row out the pressure subsided. 
   I shot the floor with the lazer temp gun and it was between 75-80 throughout the hallway. which is not out of the ordinary. House was built in 04 and has always been radiantly heated. What all the sudden caused the different expansion rates?

 I will post more later tonight. I am off to menards to get a diamond wheel for my 4.5 inch grinder so I can salvage as many tiles as possible as I only have 54 spares kept back from the build. I also need to pick up some thinset and some new darker colored grout this go around.. Almond colored grout sucks..LOL


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## SciGuy (Mar 2, 2008)

Eric,

Would you describe the makeup of the floor system? Are the tile in thinset mortar on some type of cement board screwed to 3/4 plywood or are they directly thin setted to plywood? Is the raised area along a joint? Is the system 1/2 pex in aluminum heat distribution plates?

More info will help.

Hugh with warm floors too


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## ericjeeper (Mar 2, 2008)

The system is barrier pex in a slab. 4 inches of concrete. Swell was not near any control joint in the slab.


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## BrownianHeatingTech (Mar 2, 2008)

ericjeeper said:
			
		

> The system is barrier pex in a slab. 4 inches of concrete.



Concrete or gypsum?

Joe


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## ericjeeper (Mar 2, 2008)

Concrete. Poured  cement mixed with sand and aggregate. On top of  crushed limestone for a heat bank with an 8 foot perimeter of 2 inch pink board laid flat the entire way around the house under the slab.
 I do not have any plywood or floor joist. Slab is on grade.
     I am absolutely bumfuzzled as to how the ceramic tile after 4 years decides it wants to grow all at once down the hallway.


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## Eric Johnson (Mar 2, 2008)

My only guess is that the foundation is settling, but I really don't know anything about construction.


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## Nofossil (Mar 3, 2008)

What constrains the tiles on either side of the hallway? Could that be expanding and squeezing the tiles? I'm grasping here, but if you had a wooden sole plate that was firmly attached to the slab and it got wet and expanded, that might create the effect that you saw.


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## ericjeeper (Mar 3, 2008)

The tile is cut short of the wall plates on all sides. No sign of leaks ontop of or below the slab. We used a Bullard thermal imaging camera looking for a cold water leak under the slab. But nothing shows cold under there. Tomorrow I am going to relay the tile and put a caulk joint at each end of the repaired secdtion instead of Grout. Just in case the Ghost decides to haunt me again.


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## EForest (Mar 5, 2008)

Ok Eric here's the deal.
According to my brother John the tile man (25+ yrs exp) the radiant heat was possibly turned on too soon after tile installation.
Any time he installs over a radiant floor the homeowner is told to keep that zone off for a minimun of 21 days to allow slow cure of tile cement.
He also went on to explain that the grout is strong enough to hold the tile in place for many years before the problem is realized.
All it takes is one tile to work loose two to five years later and the entire area will "pop" in a matter of hours. Sounds wild but he swears it happens every time.
Hope this helps solve the mystery.


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## ericjeeper (Mar 5, 2008)

Tell your brother his theory is wrong this time. laid the tile in June, did not turn heat on until October. of 04
 I will let you know if it pops again as I laid it right on the warm heating floor. Had no choice as wife would evict my happy ass if I turned the heat off.


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## SeanD (Mar 5, 2008)

I put an electric radiant heat element in the thinset beneath the tile when tiled our bathroom 2 years ago.  The shop where I got the tile specialized in tile - not a big box store.  They recommended that I put a poured flexible membrane between the heating element (which was covered with thinset) and the tile to compensate for differing expansion rates.   I used "Ardox 8+9".  Smelled awful when I mixed it up and spread it out, but it has worked great.
My situation is different from yours, however.  My heat is on a timer.  Goes up to 82 in the morning for a couple hours and then drops down to 70 for the rest of the day.  I would think your floor would go to 80 degrees in the fall and stay there for several months.  If the tile doesn't pop when you first turn on the heat, I would think it should be fine.


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## solarguy (Mar 5, 2008)

My first impression is the water temperature in your embedded slab installation is to hot.

I went back thru 4 years of records & any slab installation we've designed had a surface floor temperature of 65 to 68 degrees. If you have floor surface temperatures of 80 degrees, you're running the system to close to the safe operating temperature of an embedded installation. 

Although each installation is rather unique, I'd suggest you check your supply system water temperature for that portion of the installation, if it's at or close to 140 degrees you're toast.


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## ericjeeper (Mar 5, 2008)

For the most part my supply temps are 100-115 degrees. On that particular day I know for fact my storage tank had not been much over 145. So that would make my temps going to my floor about 110 tops.


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## solarguy (Mar 5, 2008)

It doesn't matter what temperature the system operates at. 145 degree water in the storage tank would not matter unless there is no tempering or mixing valve on the radiant portion of the system to maintain a constant temperature for the loop that serves your slab area. 

Most radiant systems are designed on a 10 degree drop. When I look at surface temperature & compare it to supply temperature of a slab installation, 99% of the time it is within 10 to 12 degrees. If your running 110 to 115 degree water thru that portion of the slab you could be heating the slab up to 100 degrees which is too hot. 

I hope this helps you figure out your problem but I think your water temperature is too hot for the application.


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## slowzuki (Mar 6, 2008)

The too hot is due to peoples feet.  You can run 200 F water in concrete if people were not on it.  It is a strange problem to occur.  I'm wondering if the slabs contraction during curing finally reached a point where something shifted? Concrete continues to cure for years after pouring although most shrinkage is done in the first year.

Maybe the temp was low in the slab combined with shrinkage?  It has some thermal expansion and may have cooled and shrunk a bit.  This usually opens a crack somewhere outside the shrinkage area unless you have massive amounts of steel or a post tensioned slab.

Do you have a post tensioned slab by chance?


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## solarguy (Mar 6, 2008)

Ya know I read some of this stuff, sit here shaking my head saying WTF
Run 200 degree water if it didn't  burn people's feet. 
What ailes you?


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## BrownianHeatingTech (Mar 6, 2008)

solarguy said:
			
		

> Ya know I read some of this stuff, sit here shaking my head saying WTF
> Run 200 degree water if it didn't  burn people's feet.
> What ailes you?



To be fair, it has been done.  I know of a building in southern Maine that has copper pipes embedded in the slab, running water straight off a cast iron oil boiler at 180 degrees.  And they have one of those heat-recovery things in the flue pipe (completely improper for oil), which is single-wall pipe that runs over 20 feet vertically without any support before passing through the roof.  The system has been in place for decades, and heats the building (garage, warehouse, offices) amazingly well on very little, and doesn't even burn people's feet.

Not that I would recommend doing anything like that, but sometimes crazy things do work fine.  And other times setting the flow 5% lower than it was designed to be set makes a house miserable to be in.  It's best to follow the rules, but that doesn't mean that the world will necessarily end if we don't.

The purpose of a radiant in-slab system is to heat the building.  I really don't see that the slab temperature matters, except that it needs to be no higher than is safe on the surface.  If the design calls for 80-degree surface temperatures and it will take 100-degree water to do that, due the construction of the slab, then that's what it needs to be, and the concrete contractor and flooring contractors need to use products appropriate to those parameters, or they need to tell the heating designer that it's not possible to meet his needs (or maybe not without going over budget), and the design needs to be modified to balance the heating needs of the building and the construction materials/methods to result in a total system (building and heat) that meets the customer's needs.

As far as the tiles, it does sound like they popped off due to heat.  Is it possible that the mixing system failed and delivered too-hot water to the slab, damaging the mortar and releasing the tiles?

Joe


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## solarguy (Mar 6, 2008)

Joe,

As you know from also being in the heating business, a lot of stuff is done that should have never been & just because it seems to work for the time being, doesn't make it right....

I do not know of any radiant heat program out there from a reliable & trusted manufacturer that won't sound alarms, bells or whistles whenever you exceed 87 degree surface temperature on a slab installation or 140 degree supply water temp. 

As Eric is finding out, his tiles are poping up. There's no doubt in my mind that this is directly related to high water temperature. If a professional heating company did this to Eric's house, they should be hung. If Eric installed his own system based upon information he gathered on the internet, then he's just gotten his education.

An education is something that costs you money & those of us in the heating business have had our education many many times. Too many dam times come to think of it.

Respectfully Submitted
Bob Jennings


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## SciGuy (Mar 6, 2008)

solarguy said:
			
		

> Joe,
> 
> As you know from also being in the heating business, a lot of stuff is done that should have never been & just because it seems to work for the time being, doesn't make it right....
> 
> ...



Bob,

Why would you think that 90 or 95 degree surface temperatures would "pop" the tiles? 
The thinset mortar certainly will not be the least bit affected by these temperatures when cured. 

Just wondering because I've seen tiles run at these temperatures for over 20 years with absolutely no problems.

Hugh


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## solarguy (Mar 6, 2008)

If I had to make an educated guess as to why the tiles are poping, I would learn towards expansion & contraction within the floor system. 

I'm not the one directly saying anything over 87 degrees is detramental? to a slab installation, the manufacturers of the radiant tubing are. I'm only relaying the information but it has been my experience that they are doing so because they've had their education. 

It's no different when we look at a staple up, suspended system when hardwood floors are involved. If your water temperatures are too high, the radiant loops will bleach the floor leaving streaks in it where the tubing is fastended to the sub floor. 

I'm not trying to offend anybody here. Being in the business for as many years as we've had we just adhere to good engineering practice cause if you don't it has a funny way of biting you in the ass.

So, that's my story & I'm sticking to it


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## ericjeeper (Mar 7, 2008)

In my own defense here. I have spoken to several tile guys. Professionals..
   The slab temp is no higher than what you could see on a south facing storefront floor behind glass.

   We know it is temperature related. That is not the issue.. The issue is why it happened.  Ceramic and concrete expansion rates are surely pretty close to  equal yes?
 I installed the heating system using guidelines from one of the top Radiant guys in the industry. It is designed for 92 degree delivery temps.. But I am unable to achieve such low temps.. So it sees 110-115 degrees. 
 it is in the center area of the house no insulation under the area. It is sitting on 6 inches of manufactured limestone sand .(Lime dust)
  Anyhow the tiles are back in place if the pop up again in four years I guess I will do something different. I used a modified thinset this time.So it can flex a little. Plus I caulked in some expansion grout lines to protect the great room if it ever decides to go crazy again.
Thanks all to who replied.


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## atlarge54 (Mar 7, 2008)

About 20 years ago I did my first and last tile job. I was too cheap to buy the bags of base which were to be mixed with some kind of solvent, over $300 worth. On the advice of a mason I used a portland cement mix. It was horrible to work with and timing was critical. By the time I had my kitchen done I'd had enough and still had a bathroom to do. I bought a couple boxes of the cheapest acrylic latex caulk I could find. I put a GENEROUS application on each tile and set in place. Not only did a horrible task become almost a pleasant job but the results were far superior. Both floors are still in good shape, if I ever do it again it'll be with the caulk gun.


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## BrownianHeatingTech (Mar 7, 2008)

solarguy said:
			
		

> As you know from also being in the heating business, a lot of stuff is done that should have never been & just because it seems to work for the time being, doesn't make it right....
> 
> I do not know of any radiant heat program out there from a reliable & trusted manufacturer that won't sound alarms, bells or whistles whenever you exceed 87 degree surface temperature on a slab installation or 140 degree supply water temp.



Agreed, but the reason is safety and comfort for the occupants, not protection of the floor covering.  Floor coverings can be set up to withstand much higher temperatures than the occupants will comfortably be able to walk on.

Things can be done very wrong, and still work, on occasion, because the right combination happened to occur.  I'm sure there is a "combination" that includes tiles which will withstand the temperatures he's using.



			
				ericjeeper said:
			
		

> It is designed for 92 degree delivery temps.. But I am unable to achieve such low temps.. So it sees 110-115 degrees.



I think you should look into modifying the system to allow it to achieve the temperatures that it was designed for.  Mixing valves or injection pumps can keep the water temperature under control.

Joe


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## slowzuki (Mar 7, 2008)

I think this was answered in the other posts but the concrete physically could care less what temp it runs at.  Something is causing the concrete below the tiles to be smaller than the tiles above that have been fine for a long time.  There are four things that move:

-The concrete shrinks as it cures
-The concrete expands when heated
-The tiles expand when heated
-A strained crack in a concrete slab could move on the limestone bed to relieve strain.

Re the water temps, these are guidelines only.  If I have close tube spacing and a high heatloss slab, I may well need to have short loops and 140 F plus to maintain the surface temp.  This isn't likely in a house but below walk in freezers it can happen.   Also, if I have a 10" industrial slab, I can use wide tube spacing and high temps burried deep in the slab to get my even and acceptable floor temps.

The surface temp limits of 80-90 f are based on peoples feet comfort only.  Try to remember radiant heat is used other places besides houses.



			
				solarguy said:
			
		

> Ya know I read some of this stuff, sit here shaking my head saying WTF
> Run 200 degree water if it didn't  burn people's feet.
> What ailes you?


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## Jersey Bill (Mar 8, 2008)

a few comments, 
the American Concrete Institute recomends the maximum temperature for any concrete application is 150 deg.

The radiant panel institute recomends an "anti fracture membrane" between any slab and ceramic tile application. I have used a product called "Ditra", but there are other options including mop on rubber and asphault  coatings, and rubber membranes. These products allow the ceramic tile and the concrete slab to move independantly because they have different thermal coefficient of expansions. there is plenty of information on the RPA website on this topic.

120 degree water in a slab sounds high to me for an in-slab application. what were (are) the water supply and return temperatures?

The RPA also recomends constant circulation with reset water temperatures. You mentioned that there is no insulation under this area (really bad).
One possibility is that the slab loop turned on when the floor was cold and 120 deg water went through the tubes. the large delta t caused rapid expansion of the concrete in contact with the tubes, but the tile was still cool and did not expand with the floor it was bonded to, so it had to either crack or pop up.
Another possibility is that the water in the slab tubing went really hot or really cold because of some kind of failure and that is what caused the great differential expansion between the tile and slab.


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## slowzuki (Mar 10, 2008)

If the concrete expanded the tiles would not pop up, the grout would break between them.



			
				Jersey Bill said:
			
		

> a few comments,
> the American Concrete Institute recomends the maximum temperature for any concrete application is 150 deg.
> 
> The radiant panel institute recomends an "anti fracture membrane" between any slab and ceramic tile application. I have used a product called "Ditra", but there are other options including mop on rubber and asphault  coatings, and rubber membranes. These products allow the ceramic tile and the concrete slab to move independantly because they have different thermal coefficient of expansions. there is plenty of information on the RPA website on this topic.
> ...


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## BrownianHeatingTech (Mar 10, 2008)

slowzuki said:
			
		

> If the concrete expanded the tiles would not pop up, the grout would break between them.



Yup, but you might not notice that.  Then when the concrete shrank, the fractured grout would take up more space, and the tiles would pop.

It's all theoretical, and nearly impossible to diagnose (especially remotely) due to the number of possible causes.  The only remedy (short of re-doing the floor) is to do what has already been done.

The only additional thing to do is to re-work the system as necessary, in order to supply the correct water temperature reliably.

Joe


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