Bottom line, you have a wet slab.
RH levels do actually fall rather quickly once the slab starts drying. By rather quickly I mean a 1 - 2 points a week if conditions are right.
As long as you have done the testing according to the instructions in your test kit, you can trust the readings. You should be 2.4" into the slab, brushed and vacuumed holes, drilled straight and true, you don't wet drill right?
If it makes you feel any better, I did a job last fall where they waited 16 months for suspended floors to dry and they were still at 98%. The 4" slab on grade areas were down to the mid 80's to low 90's.
6" slab, 3 months for the first 4" and 2 months more for 2" more. I have a 5" slab in Sacramento made the same way. It sat at 99% for four months then dropped to 91% then dropped to 88% the next month. Have patience. When in doubt, blame the structural engineer who build a 6" slab for a small room. They SE's are the source of >90% of my issues.
Once back in the early 80's I went to do some vinly out in the sticks. Some dude out there was building custom ranch houses. As I was driving into the development...these were like 20 acre parcels each. I drove by a newly poured slab which had sprinklers spraying water on it.
When I asked WTF with the sprinklers, he started into this thing about how it hardens the concrete and keeps it from cracking. The sprinklers had been wetting the slab for a month.
Got into the house and the concrete was black with white-ish patches all over it. What did I do next?
I just did a floor in a gym done with sprinklers. It turned out great and the RH got down into the 80's in a fair amount of time.
Wet curing is the way we recommend all concrete be cured that is going to receive moisture sensitive flooring. I recommend a 3 day wet cure.
The longer concrete is kept wet, the harder it gets.
I like to see burlap over the top myself. That guy was sprinkling the surface and it was pitted.
Burlap is put down to hold the moisture. They wet the burlap. Water can't be put on the concrete until it is hard enough to resist damage.
the independent lab of my client will be retesting the floor with their nucleo meter and the flooring contractor will be testing it with his meter this week. I predict both meters will read that the floor is ready (or near-ready since 2 weeks ago, only 1 percentage point lower was needed to start). But ofcourse that's at the surface.
My Rapid RH are reading below surface which is the right reading, BUT everyone is having trouble trusting this "new" technology, especially when the readings haven't moved.
So here is my dilemma, do i let them go ahead and do the floor or do i be an "a-hole" and tell them to its not ready? Maybe they should do it. After all they are responsible should something happen and the flooring contractor has to guarantee the floor. Right? But should the floor fail, it will be huge head-aches for me since I am the GC.
Q1: Does anyone know what the Rapid RH reading has to be at for my type of installation ("floating" type)? From my research, I've read it has to be at about 80%.
Q2: Has anyone installed wood floor at high RH (and how high) and didn't have problems?