So my liquid anyhydrate screed was laid in December, the laitance was removed mechanically by a sanding machine with diamond cutter 5 days later. I'm on the verge of getting the floor tiled in the next week or so. I commissioned the ufh a few weeks ago. Now I'm getting cold feet thinking the laitance hasn't fully been removed. I've attached pics for all you pros to see and hopefully reassure me that everything is fine and I'm overthinking. The floor does need a good sweep and vac but my question is do I need to get the guy back to sand it again?? It cost me £200 to get it sanded in the first instance.
Thanks mate! I made the mistake of not hoovering all the removed laitance immediately and left it so I was worried the laitance had bonded back to the screed. Is that possible?
Nah. Just hoover it up. What method are you using to tile it ?
Ideally I would like to use anhyfix to fix the ditra mat but finding it hard to source the product. Ontop of the ditra itll be setaflex to fit the tile. If I cant get hold of the anhyfix what would the next best method?
You're help and advice is very appreciated.
Might be wrong but not sure anhyfix is suitable for ditra. Best check with schluter. It’s not an adhesive I’ve used.
What would be your preferred method? What adhesive would you use with Ditra matting and porcelain tiles? And what primer?
Thanks
I’ve done quite a lot of them now. I prime with acrylic primer 4 to 5 coats following directions for anhydrite screed. Fix matting with spf rapid and same for tiles. I use weber products. The screed must be dry and fully commissioned.
4 to 5 coats?? What dilution ratio do you use per coat? I'm getting alot of conflicting information in regards to the type of adhesive used with anyhydrate screed. Some say cement based adhesive is a no no as can it can have issues with bonding to the screed and anhyfix (gypsum based) is the way to go and some say there's nothing wrong with a cement based adhesive. I just dont want to make a very expensive mistake.
I use a 4:1 ratio and not had a single issue with bonding . Yes gypsum adhesive can be used to adhere the tiles but like i said , not sure schluter uk advise to use it with Ditra.
Is that 4 parts water to 1 part primer or the other way around? And do you use the same ratio for every coat? Thanks
Yes. 4 water to 1 acrylic primer or whatever the primer says. Sone have different ratio. 4:1 is one i use PR360.
Thanks mate!
Thanks mate
The only test I've done is laying a dpm on the floor with planks of wood on either side to weigh it down and checked if theres any condensation underneath 24 hrs later
Are those small patches of laitance the lighter shades of the floor?
Then you need a proper test. Are you DIY tiling or getting a contractor in
Getting a contractor in
How do I go about getting it properly tested?
I have a humidity reader which measured relative humidity at 30% when I had the ufh on. Does that say anything?
yes it does... without wishing to be in any way harsh - it tells me that you don't know what you are looking at. to be dry the screed needs to be below 0.5% moisture or 75% RH. when it was made in the factory it had perhaps 13% moisture so your 30% is clearly wrong.
The 30% was the RH in the room once the ufh was running and when ufh was turned off the RH crept upto 60% and has been consistent at that figure. When using anhyfix adhesive isnt the figure 85% RH? I maybe wrong.
Update...had someone come out to sand down the floor again. He used a diamond disc sander. I've hoovered all the muck but I'm still getting patches that are stuck to the floor (definitely not loose) of what I think is laitance on the floor?? Is there enough on there to fail the floor? Or am I overthinking?
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Thanks mate. I know you're the resident expert here when it comes to these screeds so I appreciate you're help and advice.
There are similar tiling threads here
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