Anhydrite moisture testing, putting some ideas to you Trusted People

[The D]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

Why is that Deano? Is it because you don't believe what you were told on the day and it didn't sit right with you? (as is you're well within your rights to do) or because you followed what you were taught and it still had a failure?




That's a different matter and that should be the specifier for the high jump if it has been specified in unsuitable circumstances or time frames, i'm sure it happens all the time with slick salesmen and soecifiers who don't understand it but does it happen more often than not? I get that there are extra steps needed and it's much more involved but i'm not hearing that it's an unsuitable substrate to tile to point blank.

Alan did an amassing job of making me understand what these screeds can do to cement based adhesives if the floor is not completely dry and thoroughly sanded and primed. How ever am I sanding to remove the laitance or just to prep the floor ???? I thought it was to remove the laitance but what do I know. I could get myself a fancy moisture test gadget to determine whether the floor is dry but if I do I will need to ignore the manufacturers instructions turn around three times and hop up and down on one leg and hope it gives me a correct reading as if it does not I will be in the frame as I ignored the manufacturers instructions . Then we have the debate epoxy primer or acrylic primer cement based adhesive or gypsum. I am convinced that acrylic primer and cement based adhesive does not give a strong enough bond as the tiles I have removed from the floors that I have fixed came up far to easily and my knowledge of gypsum adhesive is limited to what I have been told witch is very little. So you see I am no expert so how can I go and specify and guaranty a safe method of installation.

 

[Spud]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

when I sanded the last anhydrite floor I tiled I used a 9inch grinder with a 7inch diamond cup wheel with a dust extraction cowel 1500w dustex hoover with a preseperator, a slow speed machine might have been better but i am of the opinion the floor is not properly sanded until you can see the aggregate which why I used the grinder ,the floors take an age to dry here because our sites are far more open to the elements ,one of the last thing fitted on sites in the uk are the doors and windows until we build like the europeans we will keep getting problems with this type of screed Alan does have a good point too builders in germany have strict contracts which covers every detail so they is never a grey area on whose responsibiilty it is to do which part of the the job

 

[Ajax123]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

You don't need to sand low laitance screed till you see the aggregate. In fact this could be counterproductive as you can grind too much off and leave the screed too thin. I agree with your comment that a slower machine but with ideally a sixty grit paper. Worst case scenario is that a copper disk would be needed but this is not a common scenario. A slow 75 rpm 18" (ish) STR floor scarrifier is the right type of machine although last year I had a lot of success with enclosed shot blasting for larger floors. This works just as well. This is done tomsimply prepare the screed by removing extraneous construction debris as the screed does not for a laitance to speak of. if it does ther is something wrong and it should be batted straight back to the main contractor/builder and in turn presumably the screeder.

If it is a non low laitance screed sanding should be done before the screed is heated and this will easily remove the laitance. My opinion is that this is part of the screed installation and should be done by the screeder but as already stated this is a contractual matter and anyone can contract to do it if they want. That is not something that the screed manufacturer can control. As I say though this part should in my opinion be done by the screeder. This will expose a textured porous surface very similar in appearance to tha of a sand cement screed but generally much lighter in colour. Then just before tiling the screed will probably need a light abrasion to remove extraneous material as it will have got dirty and have a stuff dropped on it.

Sreeders generally dont like to sand off laitance and builders often don't plan their sites to allow for it in a timely manner. That is why there are so man failures on the old laitance screeds and as a result most of the anhydrite screeds that go into the market these days are the low laitance variety.

 

[Colour Republic]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

So let me understand this

if it's low laitance screed, you are only sanding to remove builders crap So say for example a screed was laid and no one went near it until it dried and there was no dust in the air, then technically you could tile straight on to it... with suitable adhesive.

If it's normal screed, then you need to sand it to remove laitance but ideally before the screed is heated, you'll then have to do another sand to remove builders crap if used before tiling?

 

[Colour Republic]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

Alan did an amassing job of making me understand what these screeds can do to cement based adhesives if the floor is not completely dry and thoroughly sanded and primed. How ever am I sanding to remove the laitance or just to prep the floor ???? I thought it was to remove the laitance but what do I know. I could get myself a fancy moisture test gadget to determine whether the floor is dry but if I do I will need to ignore the manufacturers instructions turn around three times and hop up and down on one leg and hope it gives me a correct reading as if it does not I will be in the frame as I ignored the manufacturers instructions . Then we have the debate epoxy primer or acrylic primer cement based adhesive or gypsum. I am convinced that acrylic primer and cement based adhesive does not give a strong enough bond as the tiles I have removed from the floors that I have fixed came up far to easily and my knowledge of gypsum adhesive is limited to what I have been told witch is very little. So you see I am no expert so how can I go and specify and guaranty a safe method of installation.

It seems on a busy site the hygrometer isn't a good method unless under armed guard 24/7 but there are other methods not prone to some idiot booting it across the floor.

Maybe this is one for Gary and 'co to do a test on with regards to compatable addys, or even yourself seeing as you started the whole ball rolling with these tests?

Alan does a sample section of screed have the same properties as a typical floor... i.e is there any reason why a 1mx1m sample wouldn't act like a large floor, in realtion to testing addys I mean?

 

[Ajax123]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

So let me understand this

if it's low laitance screed, you are only sanding to remove builders crap So say for example a screed was laid and no one went near it until it dried and there was no dust in the air, then technically you could tile straight on to it... with suitable adhesive.

If it's normal screed, then you need to sand it to remove laitance but ideally before the screed is heated, you'll then have to do another sand to remove builders crap if used before tiling?

Thats pretty much it although the low laitance may need a vaccuum cleaner running over it.

As a small example I Have low laitance screed in my own house and I placed smoothing compound (gypsum based) on it without testing for moisture, without sanding in any way and with only a light coat of acrylic primer diluted 3:1 ( think from memory it was BAL) that was about four years ago following a vac using the dyson. I Also stuck some ceramic tiles to it using creativeimpressions gypsum based adhesive. I left the tiles there for three weeks before tryin to take them up as I was laying laminate and not tiles. ( It was just my own test) The tiles would not come up without breaking and the adhesive wold not come away from the screed at all. I levelled over the adhesive residue after using the angle grinder to grind off as much as i cold. It is all still there and has even been wetted several times as I had a leaking roof. None of this has come apart. I know it works and is incredibly robust but professionally I am not allowed and will not condone cuttin corners.The reason get away with it is because I know how these things perform together cos that is my job.

ALL screeds should be sanded, vacuumed and moisture tested prior to fitting bonded floor coverings.

 

[bugs183]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

I'm doing my best Deano to come up with the answers we need:
As discussed Mapei have gypsum adhesives available on the continent, but not here. I phoned technical and they recommend Adesilex fixed to primed anhydrite with Eco Prim T or Primer, and have no news of importing their gypsum adhesive (very odd).
Bal give much the same spec with cement based adhesives.
From my small tests and from previous jobs i won't use cement based adhesives for direct fixing to Anhydrite.
I've tested a few Gypsum adhesives and yes they stick well to gypsum but not very well to porcelain, which is now in the majority for floor tiles.
In a few weeks i've a 60m2 floor and i've spec'd Creative Impressions GBTA adhesive. From what i've hear it's very impressive stuff so i'll test that against the others. I'm kinda feeling confidence that this will be the adhesive i've been after.
But it it fails then, we do know that gypsum adhesive sticks to gypsum, but also sticks well to Ditra, which i was surprised about. Fix this and go onto the ditra with cement based, it solves the cement to gypsum problem and the gypsum adhesive to porcelain debate, and when used with underfloor heating then this is going to be a good system as the Ditra absorbs any screed movement.
So all is not lost matey, we'll get there.

 

[Ajax123]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

It seems on a busy site the hygrometer isn't a good method unless under armed guard 24/7 but there are other methods not prone to some idiot booting it across the floor.

Maybe this is one for Gary and 'co to do a test on with regards to compatable addys, or even yourself seeing as you started the whole ball rolling with these tests?

Alan does a sample section of screed have the same properties as a typical floor... i.e is there any reason why a 1mx1m sample wouldn't act like a large floor, in realtion to testing addys I mean?

I have only ever seen two instances that I can remember where hygrometers were booted across the floor. Both were major hospital projects of several tens of thousand square meters. The simplest thing to do to prevent this is to mark it out as a test area with a bit of danger style tape and some cones or bits of wood or just put a bloody great kerb stone on topof it. stuff like this is available on most commercial sites. I often get this as a objection butin reality I do not beleive it happens often. On small sites it is not generally necessary.

there is no reason why a small sample will act differently to a large sample except obviously it is relative to the conditions it is kept in. In fact most of the adhesive company's test adhesives generally on much smaller samples I.e. 600mm x 600mm

 

[Gazzer]

Re: Anhydrite moisture testing, putting some ideas to you Trusted Peop

I would certainly be happier going the Ditra route but again more cost. I had enough trouble getting the job I am doing at the moment due to extra cost of Gypfix over a cement based adhesive.

As for the Hygrometer getting knocked about, I have had one trod on and another they swept all the other trades rubbish over it.....The Hygrometer was well protected and had a sticker on it saying do not remove, floor under test. You really cant believe the stupidity of some people.