floor screeding info

[TF Ed]

heres a little info on the different types of screeding systems that you will come across.
traditional and pumped.. nothing fancy just the basic fundamentals ...

Screeding Information

ed

[hillhead]

Good stuff Edward.

[terrygrant]

Handy info and easy to digest...thanks

Terry

[Ajax123]

That website should be BANNED for it's flagrant abuse of fact most especially in relation to its flowing screed section. Some of the ridiculous comments made are quite preposterous and some of the claims have remained unsubstantiated despite several requests for case details. I know of at least 2 major screed suppliers who supply both flowing and dry screeds have asked the owner to modify some of his comments and to remove others altogether. Screeding information my eye more like screeding propoganda...........

[Sir Ramic]

That website should be BANNED for it's flagrant abuse of fact most especially in relation to its flowing screed section. Some of the ridiculous comments made are quite preposterous and some of the claims have remained unsubstantiated despite several requests for case details. I know of at least 2 major screed suppliers who supply both flowing and dry screeds have asked the owner to modify some of his comments and to remove others altogether. Screeding information my eye more like screeding propoganda...........

Oooops

[Scott]

Dont you like that Ajax.....?

[Rich]

That website should be BANNED for it's flagrant abuse of fact most especially in relation to its flowing screed section. Some of the ridiculous comments made are quite preposterous and some of the claims have remained unsubstantiated despite several requests for case details. I know of at least 2 major screed suppliers who supply both flowing and dry screeds have asked the owner to modify some of his comments and to remove others altogether. Screeding information my eye more like screeding propoganda...........

I have put up a few info posts that have touched on screeds and it seems to be a bit of a spikey subject, the info seems to be hard to get hold of and when you do a lot of it seems to be wrong.

Can you recommend the best place to get the right info Alan? It is very important stuff and something that very few of us know as well as we should (inside and out).

[Dave]

I have just reading the flowing screed section and see where Alan is coming from..

[Rich]

Still, thanks for putting it up Ed

[garythetiler]

flow screeds can be problematic for tilers and do need to be handled with greater care when installing tiles on to them that said they are extremely popular in Europe on residential jobs,I did find that the bathrooms were often screeded in sand and cement even if the rest of the floors were anhydrite due to the fact gypsum screeds dont take water well

[Scott]

Does anyone want to elaborate on whats not right?

[Glasnevintiling]

cool

[Ajax123]

flow screeds can be problematic for tilers and do need to be handled with greater care when installing tiles on to them that said they are extremely popular in Europe on residential jobs,I did find that the bathrooms were often screeded in sand and cement even if the rest of the floors were anhydrite due to the fact gypsum screeds dont take water well

Not sure where in Europe you were working but in France is is actually building code which drives cement screeds into bathrooms. i can never understand the phrase "gypsum screeds don't take water well". they take water just the same way as other screeds don't they.

[garythetiler]

Not sure where in Europe you were working but in France is is actually building code which drives cement screeds into bathrooms. i can never understand the phrase "gypsum screeds don't take water well". they take water just the same way as other screeds don't they.

I guess that Statement is slightly vague Alan, to clear it up I was always told that tile installations on gypsums screeds are prone to failing if they come into contact with excessive amount of water ,this was back in Germany in the 90's perhaps its why the french have made it a bulding reg for cement based screeds in bathrooms,perhaps I was misinformed but I thought gypsum/alabaster is water soluble

[Dave]

My understanding is that Gypsum screeds are not suitable for wet areas like bathrooms etc Al..?

[Ajax123]

Gypsum is chemically classed as slightly soluble in water. However it's robustness can be improved in a number of ways. These have to do partly with changing the chrystal morphology and partly to do with removal of excessive void spacings between the chrystals using additives. There are other ways to improve it but these are trade secrets.

Where the chrystal formation makes large loosely packed chrystals e.g. plasterboard then the material remains relatively soft and prone to cleaving when large quantities of water are present. However gypsum floor screeds are engineered to use tiny tighly packed chrystals which are bedded around a matrix of fine aggregate e.g. sand or ground glass. This imparts very significantly greater strength and less propensity towards cleaving due to the addition of water. If a gypsum screed is left saturated for a very lengthy period i.e. quite a number of years then some small amount of swelling may be observed at the molecular level but for all practical purposes the only thing that happens to a gypsum screed when it gets wet is that it gets wet. As long as it is re dried this does not cause an issue. It is very difficult to get a floor covering to stick to a wet screed. Again there are things which can be done to improve the robustness of the bond between the adhesive and the screed e.g. use a gypsum based adhesive. These screeds began life in a big way in the late 80's early 90's but this was before the advent of gyspum based adhesives so there were the obvious issues. To put this into context for you I have been on and off involved with a recurring issue at a major hospital complex in Norflok where Gyvlon screed was placed over 17 years ago. The area was smoothed using a gypsum based smoothing compound and then a vynil floor on top. They have intermittent problems with the floor flooding and have had at least 4 occasions where large scale immersion has occurred. On each occasion they have lost the floor coverings due to the emulsification of the flooring adhesive. However on each occasion the smoothing compound has remained firmly adhered to the screed and the screed has remained unaffected apart from being wet.

[Dave]

So.. why were we advised to waterproof bathroom floors with gyvlon then..?.. or that is the way i read all the info i was given..

[garythetiler]

Gypsum is chemically classed as slightly soluble in water. However it's robustness can be improved in a number of ways. These have to do partly with changing the chrystal morphology and partly to do with removal of excessive void spacings between the chrystals using additives. There are other ways to improve it but these are trade secrets.

Where the chrystal formation makes large loosely packed chrystals e.g. plasterboard then the material remains relatively soft and prone to cleaving when large quantities of water are present. However gypsum floor screeds are engineered to use tiny tighly packed chrystals which are bedded around a matrix of fine aggregate e.g. sand or ground glass. This imparts very significantly greater strength and less propensity towards cleaving due to the addition of water. If a gypsum screed is left saturated for a very lengthy period i.e. quite a number of years then some small amount of swelling may be observed at the molecular level but for all practical purposes the only thing that happens to a gypsum screed when it gets wet is that it gets wet. As long as it is re dried this does not cause an issue. It is very difficult to get a floor covering to stick to a wet screed. Again there are things which can be done to improve the robustness of the bond between the adhesive and the screed e.g. use a gypsum based adhesive. These screeds began life in a big way in the late 80's early 90's but this was before the advent of gyspum based adhesives so there were the obvious issues. To put this into context for you I have been on and off involved with a recurring issue at a major hospital complex in Norflok where Gyvlon screed was placed over 17 years ago. The area was smoothed using a gypsum based smoothing compound and then a vynil floor on top. They have intermittent problems with the floor flooding and have had at least 4 occasions where large scale immersion has occurred. On each occasion they have lost the floor coverings due to the emulsification of the flooring adhesive. However on each occasion the smoothing compound has remained firmly adhered to the screed and the screed has remained unaffected apart from being wet.

Are you saying Alan that you recommend gypsum screeds for wet areas? and can you forsee there use in shower areas and swimming pools surrounds

[garythetiler]

From a tilers perspective poured gypsum screed is only recommended for residential or light commercial traffic in interior dry applications and in limited water exposure areas with use with waterproof membrane, it is not suitable for areas subject to continuous water immersion, source T.C.N.A handbook for ceramic tile installation which is the most repescted tile installation specification book in th U.S

[Ajax123]

No you should not use Gypsum screeds in areas where the screed will become wet. It is perfectly suitable and has been used in tens of thousands of kitchens and bathrooms and even in a few swimming pool surrounds provided a suitable floor covering is used in order to keep the water out in order that it does not interfere with the floor covering itself.

The point I am trying to make is that there is a myth that something happens to the screed itself when it gets wet. some of the examples I have been told about range from it turning back to its constituent materials, dissolving, swelling up and cracking, trning soft, floating etc etc.........None of these things happen in a practical sense. If the screed gets wet you simply get a wet screed.

Bear in mind that continuous or permanent immersion in water is different than temporary wetting. A three month flood would be considered temporar wetting presuming the screed is dried folowing the flooding.

Gypsum screed is generally recomended for use in what I term People buildings i.e. those areas where there is n heavy mechanical or dynamic loadings from industrial traffic. I have seen it used successfuly in showers, garages, swimming pools, light industrial workshops, car showrooms and Cold Store sub floors none of which would be traditionally accepted applications. Provided the right advice and the riht post installation regime is adopted when using the materials in non traditional applications then it is fine. It is when people mis treat or abuse the capability of the materail when things go wrong.

No I would not "recomend" it's use in areas where it will get wet but that is primarily because i I do I end up receiving a world of pain when it is not dealt with correctly post installation.

[jay]

so what does happen to it if its used in say a wetroom with no w/p or is this based on extreme situations

[Ajax123]

so what does happen to it if its used in say a wetroom with no w/p or is this based on extreme situations

If the flooring is defficient and not suitably sealed and a cement based adhesive and an acrylic primer is used then the tiles are likely to delaminate. This delamination occurs not because the screed softens or turns powdery or gets up and crawls out from under the tiles. It is because threr is the adverse chemical reaction which leads to ettringite and thaumesite formation. The crux of this is not should you or should you not use it in an area that is likely to have water in it but how that water can get into the screed. Clearly there is some risk attached to using it in bathrooms but provided the right precautions are taken to protect the screed from ingress of significant amounts of water (we are not talking the drips from your body when you get out the bath but more like a sustained wetting or bath overflow or something of that nature) then nothing bad will happen. Managing the risk is I guess the key and I suppose perhaps that is something we don't do very well in the UK construction industry. The only areas I am nervous of are swimming pools, communal showers where no tanking is used under the tiled floor and the great outdoors. Having said that there are a number of small Gyvlon slabs laying in plant yards following demo days and they are rained on and snowed on and frozen and cooked in the summer and they are perfectly ok. They just have no tiles on......

[garythetiler]

I dont think any one on the forum is knocking gylon screeds Alan and if you read my posts I am talking about the limitations of tile installations on to gypsum screeds which I think what I have said is fair and follows best practice advice from a tilers perspective and when you consider the cost of gylon and the added cost of the uncoupling matting ,tanking etc it is reasonable to argue that its cheaper and better to use a conventional screed in wet areas

[TF Ed]

anyway
whatever the opinions/science/info/facts on gypsum screeds, we are all a bit wiser for the info provided in this thread and thats what matters most imo...

[Ajax123]

Gary - I never thought you were knocking the screeds. I am not ina any way offended by this thread. The web site that actually started this thread has some serious factual issues about the screeds - e.g the bit about Sheffield - no cases seem to exist. The drying times are wrong, the web owner lumps Gyvlon and Supaflo in the same bag - Supaflo is sometimes hemi and sometime anhydrite and the 2 are completely different animals, the strengths are incorrectly detailed , there is no such thing recognised in British Standards as Partially Bonded Screed, "PVA Glue is a good screeding adhesive" Arrgh! - The comments about surface regularity - if done properly its as flat as wotsit, the use of 20mm Kingspan edging to prevent Shrinkage Cracking is wrong.....Who is expecting Gypsum based screeds to be pushed out as the credit crunch bites ..... No idea but in actual fact the opposite has proven true and we as a manufacturer have actually very significantly increased our market share in the recession and have actually entered the "low cost, cheap housing market". Calcium Sulphate Screed has a much higher crushing resistance than hand compacted screed - Gyvlon for example can be designed to C35 which is as strong as powerfloat concrete used for floors in Tesco and Ikea for example.

The overall cost of the screed package is often actually cheaper with Flowing screed and the long term benefits with UFH are beyond question. I would not discourage anyone from using sand and cement in a wet room but at the same time I know that Gyvlon can be equally suitable provided the right precautions are taken. There are advantages to its use as well as disadvantages to both systems. I guess one major advantage in wet rooms is that sand cement can be easily laid to falls.

Rant finished - sorry been a long day

[jay]

thanks Alan dont see any screeds of that type down here but they do look good