Anhydrite Screed - after Laitance removal, rough or smooth?

We had a 50mm anhydrite screed down over a DPM around 100 days ago. For the first 50 days the conditions were far from ideal for drying @1mm/day (early Feb, definitely no where near 20 degrees air temp, fresh plaster throughout, room open to elements). After around 50 days we comissioned the UFH as recommended, and this has been running along with a dehumidifier for a few weeks now.

The floor wasn't sanded after 7 days, but was sanded with an STR around 70 days in.

We've done a RH floor box test and also a multiple tramex tests. Unfortunately the readings still appear to be too high. The driest part of the floor is where the floor prep machine has taken the scree down to white colour with a rough "sandpaper" like feel. This currently reads 1.0 on the tramex and 58% RH. The rest of the floor is pink/brown in colour with a very smooth-to-touch feel. Readings on this part of the floor are consistantly around 3.0 on the tramex everywhere (87%RH on the one section I measured).

So... In summary, the UFH has been on for around 3-4 weeks during good weather, with 1.5 weeks in combination with a dehumidifier.

When you remove the laitance, what sort of texture should you be left with? I'm wondering if the laitance has been baked on by the UFH, and we've only actually properly removed it in one place (where it's more white and rough to the touch).

Any advice would be gratefully received! We're getting desperate now!

 

Something seriously wrong there. 50mm with ufh should be dry, even with laitance. Have they flooded the place? Could try going over it with a copper disk, see if that opens in up?


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It's not been flooded, no. Here's 2 photos. First is how the majority of the floor looks. Second is the rougher, whiter patch I talked about that demonstrates better MC. Most if the floor is very smooth. Does the whiter section look more like it should do to you?

 

It looks like it's had a lot of water on it. Looks like mould growing on the surface!


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No, UFH turned off 72 hours before any tests done. Here's a pic. The circle is the surface under the pink/brown surface. Is the pink/brown surface the baked on crust? Should it all look like a grey concrete like texture inside the circle?

 

It's been a working site for the whole time, so brown stuff is probably just foot traffic dirt.

 

It looks right inside. Looking at the state of the top you may have to remove it all.


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Thanks merit - appreciated. Does anyone else have any thoughts too? Surely how a finished anhydrite screed is meant to look is quite a well known thing?

 

Bth I've never had to grind that much off the top of anhydrate. Normally get rid of the weak stuff, prime the hell out of it.


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What's the right gear in your opinion Spacey?

 

As others have said, it looks like the top layer has 'cooked' and it will be hard to remove, but an Str should do it. You can get diamonds for them, which will do the job. You dont want anything too heavy on there, as once the top is off, it can be soft.
Once the surface is open, it should dry pretty quickly.
Did you see them lay the floor ? I have watched it being laid, and depending on who does the job, they sometimes thin it right out with water.
I have seen guys with a hose running constantly, making it a wetter mix. Thats fine for them, but can take forever to dry out, and often leaves a thick crust on the top.
Whereabouts are you ?

 

Thanks Neilydun, I'm in Sheffield. So you're in agreement that it should be taken down to the whiter grittier surface seen in the middle of the hole?

 

Yes, get that crustyness off.

Whats going over the top ?

 

Tile in one room, engineered wood in another