What is interesting - well it is to me anyway - is that the thread, although entitled anhydrite is actually about a hemi hydrate screed. Mark S and myself work for Manufacturers of Anhydrite, Mark for Gyvlon and I for Francis Flower. Our materials are ostensibly the same, and in fact until recently Francis Flower made Gyvlon binder for them and even more incestuously Mark took over my role at Gyvlon after I moved to Francis Flower a few months ago. Our respective materials perform ostensibly identically in all aspects, drying, thermal properties, optimum depths, formation of laitance etc etc. All of us in the construction industry are after an edge I guess and one of the perceived problems with anhydrirte screeds is the need to sand them to remove laitance or skin. Actually sanding the screed at an early sage is beneficial in a number of ways. The formation of laitance is common to ALL screeds as I have said on numerous occasions. Hemi Hydrates, which incidentally are also supplied by Larsen work slightly differently in that the chemical reaction tends to tie up the laitance in the surface of the screed whereas with anhydrites it sits on top. The Hemi boys seem to think that this means that the screeds dont need to be sanded. Lafarge readymix (as opposed to Gyvlon - different companies) some years ago now began to use admixtures in order to prevent the formation of this skin thus mimicing the hemi hydrates. This was done primarily to redcue the need for sanding because no one wants to sand the screed as this is an extra operation and extra cost and the are practical difficulties on some sites. The draw back of these closed surface systems is that they are much more dense and much less easy to get primers and the like to soak into and adhesives to key to.
What I find interesting is that the anhydrite boys (Mark S and mself) say sanding yet it appears that the hemi boys do not. If you think about the characteristics of the screed and then think about the nature of a general building site which gets dirty you will understand the need for sanding. Whose responsibility is it depends on how the contract is set up. My own advice reflects Marks... if in doubt - sand it. There is a distinction to be drawn here as well MArk and I work for the binder manufacturers. Neither of us make or sel screeds. That is down to our customers the likes of Bardon, Cemex, Tarmac etc etc. We would always hope that our own guidelines are best practice and are mirrored by our customers and in turn their customers. This does not always happen of course as we deal with human beings with alll their frailties. However you can rest assured that a simple call to me or any of my colleagues on the binder side will help you to get it right.
The argument is never as simple as "there is a lack of information given to clients" or "the screeders dont do their bit" or even " the manufacturers dont pass on the information". All of the information about these screeds is in the public domain and available free of charge in official data sheets should it be requested from us as manufacturers.
Harping back to many threads to which I have contributed prep is really straight forward, sand it vac it, prime it (if your adhesive needs a primer) then tile it.
These screeds are here to stay and as I have said many times before you will come across them more and more. There are two options as I see it. Learn about them, learn how to deal with them and get the job done or walk away. It is not for me to decide which is right and which is wrong. That is a business decision for you guys to make. Some have gone one way and some the other.
I dont think the failure in this instance really has anything to do with lack of sanding though.
Anyway that is me done for now as I am off out soon and need my tea
What I find interesting is that the anhydrite boys (Mark S and mself) say sanding yet it appears that the hemi boys do not. If you think about the characteristics of the screed and then think about the nature of a general building site which gets dirty you will understand the need for sanding. Whose responsibility is it depends on how the contract is set up. My own advice reflects Marks... if in doubt - sand it. There is a distinction to be drawn here as well MArk and I work for the binder manufacturers. Neither of us make or sel screeds. That is down to our customers the likes of Bardon, Cemex, Tarmac etc etc. We would always hope that our own guidelines are best practice and are mirrored by our customers and in turn their customers. This does not always happen of course as we deal with human beings with alll their frailties. However you can rest assured that a simple call to me or any of my colleagues on the binder side will help you to get it right.
The argument is never as simple as "there is a lack of information given to clients" or "the screeders dont do their bit" or even " the manufacturers dont pass on the information". All of the information about these screeds is in the public domain and available free of charge in official data sheets should it be requested from us as manufacturers.
Harping back to many threads to which I have contributed prep is really straight forward, sand it vac it, prime it (if your adhesive needs a primer) then tile it.
These screeds are here to stay and as I have said many times before you will come across them more and more. There are two options as I see it. Learn about them, learn how to deal with them and get the job done or walk away. It is not for me to decide which is right and which is wrong. That is a business decision for you guys to make. Some have gone one way and some the other.
I dont think the failure in this instance really has anything to do with lack of sanding though.
Anyway that is me done for now as I am off out soon and need my tea
