Electric Underfloor Screed & Tile Expansion Joints?

[Rob Z]

Hi Dingers and Ajax,

The figures quoted by our TCNA (Tile Council of North America) are a bit more conservative than what have been posted here, and as far as I know they don't make any distinction about the type of substrate and the required joint spacing. They also want to see those joints go all the way down through the layer on top, whether it be a mud bed, gypsum screed, etc. Schluter Dilex is a good product to use for this although after the fact it isn't an option.

I think one of the best rules of thumb to follow are the guidelines given by Schluter: place soft joints in all doorways (ie: divide up all rooms as separate fields of tile), have a clean perimeter joint all around the room (filled either with sealant or nothing at all-no grout or setting material, and cover with base trim), and ensure that all fields of tile are in either squares (not always possible) or rectangles that have a ratio of the sides not to exceed 1:1.5.

Dingers, did they install foam around the perimeters of all the walls so the pour will be separated from the house?

 

[dingers]

Hi,

They installed what I would call a relatively thin (4mm) blue soft like sponge material, which I assumed is an insulatation barrier or spacer albeit small.

dingers

 

[Ajax123]

Hi Dingers and Ajax,

The figures quoted by our TCNA (Tile Council of North America) are a bit more conservative than what have been posted here, and as far as I know they don't make any distinction about the type of substrate and the required joint spacing. They also want to see those joints go all the way down through the layer on top, whether it be a mud bed, gypsum screed, etc. Schluter Dilex is a good product to use for this although after the fact it isn't an option.

I think the advice of the TCNA will reflect that of the UKTA which says that the screed should be split into bays of 40m2 using a full thickness isolation joint. It also caveats this advice by suggesting that advice should also be sought from the screed manufacturer. I agree that the use of full depth joints at door thresholds, separate hating zone interfaces and at areas where high levels of thermal gain are best practice. However as you rightly say that advice is no use now cos the screed is in place. Whilst very good products Schluter is by no means the only way.
The idea is to give the screed some movement accomodation and short of taking it all out and starting again the best way to do this in this instance is to saw cut the joints in post installation.
Fortunately calcium sulphate screeds are very forgiving in terms of dimensional stability so the effect of leaving the joints out is not a complete disaster. However where there are restraint points e.g. through doorways there is some risk of the screed cracking.

I think one of the best rules of thumb to follow are the guidelines given by Schluter: place soft joints in all doorways (ie: divide up all rooms as separate fields of tile), have a clean perimeter joint all around the room (filled either with sealant or nothing at all-no grout or setting material, and cover with base trim), and ensure that all fields of tile are in either squares (not always possible) or rectangles that have a ratio of the sides not to exceed 1:1.5.

Query - Does the material manufacturers advice not count for anything then? rrr:

Dingers, did they install foam around the perimeters of all the walls so the pour will be separated from the house?

Do the TCNA have any published documentation about substrate design. I guess there is a standard governing the design and installation - in the uk BS 8204 part 7

 

[Rob Z]

Ajax,

The TCNA handbook is copyrighted, and I think I probably can't post details on here from the disc that I have (of the current handbook). Yes, they always take the "CYA" approach and say, regardless of their recommendations, to follow whatever the manufacturer has to say in their literature. If I have a product to install that has less-stringent installation standards than the genaric guidelines in the TCNA handbook, I follow the more-stringent standards of the TCNA.

For exterior installations, for installations in direct sunlight, and for heated installations, the TCNA handbook recommends soft joints as close as 8' to 12' on center.

The Schluter "1:1.5" ratio is a good one, I think, and isn't unique to that company. I see evidence of that principle on a lot of new jobs going in around here, for concrete and brickwork especially.

Yes, the TCNA has info about substrate design. I could count all the details in the current handbook, but my guess is that there are ~100 separate details covering every conceivable generic installation and type of tile setting product.

 

[Rob Z]

Hi,

They installed what I would call a relatively thin (4mm) blue soft like sponge material, which I assumed is an insulatation barrier or spacer albeit small.

dingers

Dingers, this sounds like the same thing we use...I think it is about 3/16" thick....which might be about 4mm?

 

[Ajax123]

Ajax,

The TCNA handbook is copyrighted, and I think I probably can't post details on here from the disc that I have (of the current handbook). Yes, they always take the "CYA" approach and say, regardless of their recommendations, to follow whatever the manufacturer has to say in their literature. If I have a product to install that has less-stringent installation standards than the genaric guidelines in the TCNA handbook, I follow the more-stringent standards of the TCNA.

For exterior installations, for installations in direct sunlight, and for heated installations, the TCNA handbook recommends soft joints as close as 8' to 12' on center.

The Schluter "1:1.5" ratio is a good one, I think, and isn't unique to that company. I see evidence of that principle on a lot of new jobs going in around here, for concrete and brickwork especially.

Yes, the TCNA has info about substrate design. I could count all the details in the current handbook, but my guess is that there are ~100 separate details covering every conceivable generic installation and type of tile setting product.

normal maximum bay size for cementitious is 6mx6m and the aspect ratio we work on generally is 2:1 rather than 1.5:1 but the same principal applies. This changes with heated screeds but the relevent standards don't seem to take account of this. There are significant differences when using Calcium Sulphate when the aspect ratio changes to maximum linear bay length of 40m with an aspect ratio of between 5 and 8 to 1 unheated or 300m2 for heated screeds.
Do you come across Calcium Sulphate much in the US. I know we as manufacturers have just launched in Canada and parts of the States but I don't come across much info outside of Europe generally. It is interesting to note that the TCNA handbook has specific details outlined. I don't think that the UKTA has that - I do have a copy of their document tiling to calcium sulphate screeds which is quite comprehensive although now a bit out of date on some aspects. (it was done in 2001).
Biggest issue I have in the UK is disseminating information to those who need it. Usually they make contact with people like myself when it is too late instead of seeking technical guidance before building. There are so many "experts" in the industry giving out information and some of this is very poor advice. Still I will keep trying hence my involvement with the forums.

 

[Ajax123]

Dingers - I am curious to know why you selected a French based system instead of a UK based one - or is the project in France?

 

[Rob Z]

Hi Ajax, the Current TCNA handbook is only $12...a real bargain as far as I am concerned. Even at that, some guys still complain...


TCNA - TCA Publications

I'll be back to talk to you some more...but in general gypsum screeds here in the US have a bad reputation...I know of a lot of failures here in my area (I'm sure most if not all are because of installation errors). In other markets of the US I am told that the material is used quite often.

 

[dingers]

Hi,
Yes the house is in France and it as the Electricians choice.

I have just come back from the build, nothing happening today forgot its Bastille Day. The material on perimeters of each area is marked with the name "EFIRIVE", which I haven't Googled yet.

dingers

 

[Ajax123]

Hi,
Yes the house is in France and it as the Electricians choice.

I have just come back from the build, nothing happening today forgot its Bastille Day. The material on perimeters of each area is marked with the name "EFIRIVE", which I haven't Googled yet.

dingers

That explains the French system then. It was not Lafarge Beton so I am guessing it was a Hemi Hydrate screed. That would be usual with the type of mixer use although interestingly the UK equivalents all use anhydrite.

The practical difference from your point of view is negligible.

I am not entirely surprised that the electrician used this type of screed. Possibly of interest to Rob Z something like 75 to 80% of the French screed market is Calcium Sulphate and around 80 to 85% of this is tiled. The French too have had their share of issues with these types of screeds in the past but for the last 4 or 5 years Lafarge at least have receomnded the use of Calcium Sulphate tile adhesives rather than the more traditional cement based and there have been very few reported problems since. The product is still growing in both France and the UK so not everything can be wrong.
I mirror France's view and recomend the use of Calcium sulphate Tile Addy. It should be much more readily available there than it is here and probably cheaper as well. Its use removes any risk whatever of ettringite reaction. It also exhibits similar expansion and contraction characteristics to the screed thus reducing any risk of delamination due to substrate movement. The ones I know of can be laid when the screed is still at 85% RH (Although I don't generally recomend it). Make sure the heating is commissioned and run prior to tiling as well.
The equivalent "blue stuff" in the UK is called Gefficel, and comes in 5, 8 and 10mm thicknesses, although there are a variety of others in pink, yellow, black, grey, white and probably other colours I have not yet seen.