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Problems in the UK, HELP!!!!

Hi chaps.
I'm from the UK and i'd like to pick your brains if i can.
I'm a floor and wall tiler and in our country we have happily laid millions of m2 of flooring on concrete screeds until..
The introduction of Calcium Sulphate, or Anhydrite screeds.
These self levelling Gysum based floors have suddenly appeared on site and are causing lots of problems.
Cement based adhesives react with the gypsum and the floor fails.
No body seems responcible for removing laitance from the screed after a week which slows down the drying tim and gives a weak bond to fix too, and above all, this is my main beef, moisture testing.
It appears we have introduced a product into our country without any real research by our British Standards body, we have standards for everything regarding concrete but very little for these screeds.
So do you guys use these kinds of screeds in the U.S?
If so how do you find them, and as regards to moisture testing, no one can decide which is the best method. BS advise a hood test, for concrete, but after looking at Wagners videos i can understand why this is not the best test. We use a lot of under floor heating systems with these screeds so i was thinking of getting the customer to turn off the heating for at least 48 hours before i test, get to site, turn on the heating briefly, find a clear spot with a thermal imaging gun and drill a probe into the floor.
How does that sound to you?
I am not a surveyer, do you in the States have slab only based qualifications?? This is something i'm interested in getting into as no one is doing this kind of work here.
I look forward to any replies.
CHeers, JB.

I have learned to simply walk away from anything adheared to gypcrete. But do follow the testing guidelines for it we have here. \

The sealers are just as bad if not worse as the ones for concrete because gypcrete can adsorb it more into the top.
Stephen Perrera dba
Top Floor Installation Co.

How thick are these screeds?
Are the surfaces usually sound and hard?
JD Grafton
Concrete Answers for Flooring Problems

Hiya CC.
The screeds start at 40mm (1 37/64') and up to 65mm (2 9/16'), they change all the time. But i'd guess 50mm (1 31/32') is the average.
The finish depends on the mix and then manufacturer, but usually they are a low laitence mix. Which gets left for the builder or tiler to remove, and not the screeder, so this messes with the drying times!
There are totally conflicting ideas about how to treat these floors, it's crazy!

Hi Bugs

This probably won't help you much- I think the hood test in the UK is to a different standard to the USA's F2420 (and now also in Oz)- but F2420 is totally useless where there are any surface coverings, curing compounds or densifiers etc. F2420 calls for those to be removed prior to testing. IMO any screed which is dense enough to slow down the drying time would, under the spirit of the standard, equate to those types of coverings. So, to answer your question, yeah, if you're sure you can find a "clear spot" then drill, baby, drill! A surface test would tell you nothing.

The next problem is, if you find high RH at depth, with those screeds on, its going to take a while before its dry.

We allow the hood test in Oz where there are in-slab heating pipes or similar, but would much rather do in-situ probes. How good are your thermal imaging guns and what kind are they Smile ?
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


Hi Rubens, nice answer, it helps alot to be honest, it confirms to me that the hood test isn't any good!!!

I'm not a surveyer, but a very concerned tiler with a bee in his bonnet about these screeds, so i have NO survey gear at all to speak of. I used to borrow a hygrometer with a foam hood, but now realise by the very nature of what the U.S seems to say, is that this test is useless on these screeds because of the varying densities, and seeing the Rapid system here, that made total sense to me.
So i thought mmm how do i test these floors by deep probes and thought of using thermal imaging. I saw one used on a faulty electric underfloor heating project, very impressive piece of kit, detecting the heating cables only after a few seconds of being switched on.
So i'll bounce the question back to you, what thermal equipment do you use,i'm guessing we're talking big $'s!!
One last question, to find the the pipes the heating needs to be on. Do you thermal image the floor whilst its running, mark a suitable spot, leave a few days to cool, and then drill where the mark is? My basic knowledge tells me drilling there and then with the heating on will give false readings.
Any help would be great as i'm really getting my teeth into this matter.

Heh, I know nothing about thermal imaging stuff, that's why I asked...Smile

I think this was discussed on another thread somewhere, I'll try and find it. Needless to say, equipment to detect pipes or rebar etc under concrete surface 'aint gonna be cheap...
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


You can buy an infared laser thermometer pretty cheap these days. I have used them to find tubes in the floor. Just make sure the floor is cold, then turn it on and you can easily detect where the tubes are located.

This is even reading through a floating vinyl plank I installed.

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Stephen Perrera dba
Top Floor Installation Co.

Standard procedure in the USA is to never lay over an active radiant heat system. You run it, turn it off, lay the floor, wait, turn it back on.

Also if you ask Wagner nice enough they may share with you some new 'kit' for such gypcrete.

Another thing, here in the USA gypcrete is a brand name, like xerox, you want to be careful about how you use the word. It is 'gypsum based' products. The aforementioned brand, in our experience, always has its own adhesives and most importantly primers to work with their systems. Using those have always been good but all USA flooring people always have instructions to never lay over gypsum based compounds.

Another device to think about when trying to identify tubing, rebar etc. is the Bosch D-tect 150. As long as the slab is no more than 6" thick, it will find almost anything you need in a slab.


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