Discuss Anhydrite not dry in the Australia area at TilersForums. The USA and UK Tiling Forum (Also now Aus, Canada, ROI, and more)
Good Evening All.
Had been making plans to hopefully start the tiling of a anhydrite floor at the end of the week but the first readings from the digital hygrometer is it floating between 87-90 rh.
The screed went down in December and has different depths the deepest I believe is 90mm so quite thick.
I have commissioned the system and ran it 10 days on maximum and turned it off a week ago.It has been on and off before I appeared.
Not been the greatest weather for opening all windows for ventilation and also windows shut at night for security so some of the moisture may have sucked back into the screed.
It has been sanded and I will be using gypfix and ditra.
Question is the what is the best and quickest way to reduce the rh?,bring the floor up to max again for 3 days and allow to cool or maybe even hire some humidifiers if this works or any other ideas.
Also what is the true technical reasons that floors fail when the moisture content is to high?
Other trades on site proving a pain as they see if it must be fine as one can walk on it!
Cheers all.
Kevin
Ajax would be your man to answer the technical spec but I wouldn't touch that floor till that reading was at 75% rh max.
I would stick the heating back on & get dehumidifiers in to get rid of the moisture & try & get some ventilation through the building.
My experience is that this stuff seems to have a mind if it's own regards drying out. I've had my schedule messed up twice last year with estimated dates for commencing put back over a month to 6 weeks. But I suppose it's better to follow the guidelines. Better safe than sorry
I'm no expert on anhydrite but my understanding is that if there's too much moisture trapped under a layer of tiles then it builds up underneath on the top layer of the screed thus weakening it. This results in failure as the weakened top layer no longer holds the tiles securely to the substrate., Some primers can be wreaked or emulsified by excess moisture resulting in bond failure too . Hope this helps
Cheers Guys.
I am hoping Ajax is around to give his input.
From what I gather if it is a cement addy the RH max is 75 but if it is a gypsum addy like gypfix which I intend to use this then pushes up the RH up to 85.Also with ditra been used and moisture can disperse through its gridded system the RH can be even slightly higher though probably best for Ajax to confirm if this is true.
To true ama about schedule disruption and affects of how moisture in the screed sounds familiar, just need to confirm things as will be meeting up with an upset customer tomorrow and what my options are.
I've been lucky where I was busy on both occasions with plenty other work to go to. Won't always bob the case though. The ditra may help but technically speaking if its adhered correctly then there won't be any voids underneath to let mousture disperse . I've heard of it if finding the joints in ditra and darkening natural stone. Never used any gypsum based adhesives yet but interested to see how they compare .
Cheers Guys.
I am hoping Ajax is around to give his input.
From what I gather if it is a cement addy the RH max is 75 but if it is a gypsum addy like gypfix which I intend to use this then pushes up the RH up to 85.Also with ditra been used and moisture can disperse through its gridded system the RH can be even slightly higher though probably best for Ajax to confirm if this is true.
To true ama about schedule disruption and affects of how moisture in the screed sounds familiar, just need to confirm things as will be meeting up with an upset customer tomorrow and what my options are.
I'm sure there's something else to be wary about with using Ditra with a reading of + 75% rh, I'm certain Schluter advise about it.
You can use a gypsum addy at 85%rh but there was also something about this with certain tiles...
check Ajax's previous posts. his phone number is in his signature. giv him a call.
Don't worry about an upset customer either. Print off the technical data/recommendations and show them . Tiling it once is enough but if they have the money tell them you can re- do it a few months down then line when the tiles DO FAIL. Take heed, Make your position clear and even draw up a disclaimer or contract to keep yourself right in the event of a failure due to their persistence or negligence . I'm sure it won't come to that though
The mystery deepens with anhydrites.
I have done quite a few know with gypfix and ditra and fingers crossed no issues.
Hopefully ajax appears shortly and can advice but anybody else please give there thoughts.
I think I am accepting it is probably not yet ready as I said today to another trade it is not the length of time but more the circumstances regarding the drying.
I do have Alans number but just got his answer phone today.
Good to hear of others experiences as well and to bring it to the forum.
schluter says 85 rh is fine to crack on with ditra. well thats what i was told.
Sorry guys. Been pretty busy today with meetings and whatnots. Anyway here I am.
Right in answer to the first question as you already realise the screed ain't dry and there is almost no chance that you will be tiling at the end of the week. At 90mm you would be looking at a natural drying time with a non LL screed of around 140days in good drying conditions. The issue with the drying conditions at the moment of course we are in the worst part of the year and it's flipping wet so that will go up. Additionally there is some evidence to suggest that the addition of the LL additives used in some screeds impedes the drying rates so will slow it down further.
You have 2basic options. Dry it out further ideally using the heating or put the whole thing at risk.... The latter is a bit tongue in cheek as I know you ain't gonna do that.
Running up the heating again may work but at that sort of moisture level you are likely to need a full commissioning cycle again so you are looking at least three weeks and at that depth and with that moisture level possibly a little longer.
90mm is just too deep in my opinion and the use of non LL would have been far better IMO as removing the Laitance to provide a nice open surface texture has been shown to aid drying but there you go.
I think,I am right in saying gypfix can not be used at levels above 75% these days although it used to be 85%.
According to suchluter, ditra can be stuck down to anhydrite at 2% moisture but the million dollar question is "what with"?? As I am unaware of any adhesives that will work at that higher level.
The danger of entrapment of the moisture is more to do with damaging and weakening the interface between primers and screed or adhesive and screed rather than weakening the screed itself. There are combinations of things than can club together to cause the failure if moisture is present but the most common is emulsification of the primer. Another potential issue tp you have with the LL screeds is the difficulty it creates in getting the primer into the surface of the screed. I tend to suggest primerless or at least heavily diluted primers for these types of screed.
The other thing to double check is that there is actually an operative DPM between the screed and the substrate. This would be a 1200g polythene membrane underneath any insulation but on top of any concrete or beam and block.
A lot of builders don't use a polythene membrane. Especially when using polypipe ( egg box plates) I hate them.
If ths is done on block and beam, ie block- kingspan- egg box- pipe then screed. You can have the scenario where you have the moisture from the blocks and anything that is under them to concede with!
Many thanks and a wonderful response.
I will need to look into the RH maximum tomorrow as the screed company and the screed layer both mentioned 85 rh max also I myself thought it was that but the Gypfix technician mentioned 75 and 80 absolute max.
The screed companies logo is on the gypfix bag so both companies do work together but are giving out different figures.
I do wonder if it is know 75 RH what has happened for it to have been reduced.
Have digested your info on drying on LL screeds and it is by far the thickest screed I have worked on so understandable how long this is going to take to dry.
Interesting point about checking there is a DPM as well.
I think a full commissioning with better ventilation over a 3-4 week period is the only option I can offer.
The customer has told all trades he would like to be in for April so tomorrow could be interesting!
Many thanks and a wonderful response.
I will need to look into the RH maximum tomorrow as the screed company and the screed layer both mentioned 85 rh max also I myself thought it was that but the Gypfix technician mentioned 75 and 80 absolute max.
The screed companies logo is on the gypfix bag so both companies do work together but are giving out different figures.
I do wonder if it is know 75 RH what has happened for it to have been reduced.
Have digested your info on drying on LL screeds and it is by far the thickest screed I have worked on so understandable how long this is going to take to dry.
Interesting point about checking there is a DPM as well.
I think a full commissioning with better ventilation over a 3-4 week period is the only option I can offer.
The customer has told all trades he would like to be in for April so tomorrow could be interesting!
that was a marketing thing I set up when I was at gyvlon...
the reason it was reduced from 85 to 75 was simply to reduce risks of moisture entrapment under large format tiles and to take account of the possible difference between a builders 85% and a real 85% rh.
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