It depends on the depth the screed is laid at. If its a uniform 15mm all over (not an average of 15mm - it doesnt work like that) then the drying time in the relevent drying conditions it will dry at a rate of more than 1mm per day so 10 days is entirey feasible. BUT, bear in mind that a TS15 screed can be laid to a minimum depth of 15mm unbonded. Whilst this is unrivalled in the screeds world it does not mean that it will be 15mm. TS15 and other gypsol screeds are used to level off exsiting floors. sometimes they are laid considerably thicker than 15mm. In this particular project it will run from 15mm up to 55mm. The deeper it is the longer it takes to dry with the deepest parts usually taking the longest. Force drying with underfloor heating helps enormously and can more than half the drying time. We tested 50mm depth and it dried in 13 days when properly force dried with underfloor heating. It does not have to be dry to sand it. It does not need "grinding". It needs any loose and friable material removing mechanically, ideallly using a sanding machine with something like a 60 grit or maybe a 30 grite paper. Grinding is much more aggressive and really should be reserved for polishing jobs. sanding can be carried out as early as 3 or 4 days but the reality is in most sites that wont be ready to sand at this stage as there will be pallets of plasterboard and blocks and stuff in the way. the reality is also that if you sand it early it has a longer time to become cotaminated with other construction debris which may well need to be resanded just before coverings go down. In terms of sanding vs grinding, how open textured the screed needs to be largely depends on the primers used. Obvioulsy the primer needs a key to the screed and with acrylics this relies on absorption into the screed. I use the water drop test a lot to help determine this. One thing I do encounter a lot is the thinking that if the surface is very rough it helps smothing compounds stick better. Its usually, understandably, borne out of bad experiences in the past or stories handed dow through the industry (bear in mind these screeds have been around a very long time) .. and of course a lack of industry expertise doesnt help. The roughness or otherwise of the screed is not really the issue in most cases its chemistry. If you use a cement based smoothing compound your are reliant on the primer blocking the passage of moisture borne sulphates as these sulphates can cause a chemical reactio to occur at the interfce between the elements and basically break the bond betwee the two materials. Acrylic primers particularly are not good at blocking moisture borne sulphates. Wet screed will be the source of moisture borne sulphates which means its more important for the screed to be properly dry. Additionally if the screed is wet and an acrylic primr is used then you see softening and in extreme cases complete emulsification of the primer. The smoothing compound is stuck tote primer and not the scred so if the primer softens and looses grip the whole lot comes off. I think it is failures due to this aspect that have driven people to try and make the screed rougher and rougher to give a better mechanical key. However, no amount of mechanical key is going to prevent the chemical reaction that occurs and the subequent delamination that is experienced. (bear in mind most primers and smoothing compounds are also water based/mixed so you need to enure they are fully dry as well before covering) Far better in my opinion to work less hard and use a chemcically compatible Gypsum based smoothing compounds and tile adhesives which will not delaminate due to adverse chemcial interaction. I see very few failures where gypsum compounds are used. They are much more robust to the types of things that hapen in the real world on building sites.
Problem with all these gypsum products is they don’t like water. Any leaks or moisture getting in and they start to break down. Floors fail on them rapidly. Also the companies that install these screeds have a lot to answer for. Most of them advertise they will include grinding/sanding of the surface but they don’t come back and do it unless they get asked/forced by the customer. It’s rare to find a company that offers the full service as it should Sent from my iPhone using Tapatalk
BREEM rating evaluate how friendly a building is. Thats made up in part in what recycled materials have been used. Flow screeds are very friendly. Load rating, exactly as it sounds. Lightweight screeds mean the bearing structure only has to support light weight materials.
Ah you mean BREEAM. Yes gypsum based screeds are hugely environmentally friendly. In fact it entirely feasible that you can eliminate the Carbon Footprint associated with your heating system by using Gypsol. It's not just the recycled content its the way they work. In terms of structural support you are again correct. However the mass orca 40mm gypsum screed will be equivalent to that of 65mm of sand cement but the gypsum will be considerably stronger and will perform better in terms of acoustics. Thinner screed also means thicker insulation which can lead to serious cost savings.
Oh dear. More myths I'm afraid. If the screed gets wet you get a wet screed. If its allowed to redry it's fine. It doesng vreak down. Primers and adhesives soften and do indeed break down due to the sensitivity if the polymers they contain. If it has a floor covering on it cant dry and if course the covering will fail. That's no different to a cement based screed. Actually very few screeders offer to sand the screed. Some offer it as an extra and some do include it in their package. Sanding is part of the standard requirement for floor covering preparation so is best done by the flooring contractor as he will gave the necessary expertise go know the level if prep required for zny given floor covering. A screeder does not have that expertise. Why would he? If you were a carpenter you would not expect to sand the woodwork before for the decorator to then paint it. Sanding is not considered "part of the service". It's a specific operation and should be costed as such. I could argue just as petulantly that lots of floor layers dont prep the floors properly. It's a spurious and pointless argument. When you take on a contract to do a job you should do the job. If sanding or floor prep is part of that contract you should do it. If its not why should you be obliged to?
Thats a fair argument. The problem we as flooring contractors face, and regularly, is we turn up and are told by the MC that the floor is ready to lay on, as is, no prep required. At least thats what the screeding contractor told them. Ive had it over and over again. So, then the MC is facing an unexpected cost for grinding and a more expensive bill for prep. I had it the other day with a small contractor telling me he has installed 1000`s of sq m of Amtico over these floors with no prep at all, and that its not required. In the end I gave up and just told him to find another contractor.
Now that I wont argue with and my opinion has always been the same. You are the coverings expert. You have the expertise to know if the floor is prepped to your satisfaction so you are the best person to do it. And anyone who says they have laid 1000s of m2 of any covering with no prep and never had an issue is an out and out liar. We all often come across these sort of pseudo experts and theres not much to be done other than walk away. And any MC who falls for the old line "it doesnt need prep" or "it doesnt need sanding" is a fool. Sadly one manufacturer of flow screeds says exactly that... my question would always be well if it goes wrong and ends up in court will you Mr screed manufacturer pick up the tab? Just as I dont expect flooring contractors to be experts in screeding, screeders and most screed manufacturers are not experts in floor coverings so should not be commenting on the requirements for prep unless they can support what they say. At the same time, there is a heck of a lot of misunderstanding and a general lack of common sense applied to anhydrite screeds that often gets in the way. I'm working with Uzin to deliver training workshops on the subject, the first is next week so hopefully that sort if activity will help.
Would t mind some YouTube videos Alan when you do the uzin demos. I could put you in touch with flooring tv owner if it helps.
Your reply is the exact problem I’m talking about. Let someone else deal with it Sent from my iPhone using Tapatalk
Most of the floor prep we have to do is because the builders work or subfloor is not good enough for the floor covering. Otherwise we would just leave it to dry and install. It’s all extra work for us but the customer is the one that has to pay for it all. It’s a sore point on most sites. I personally think if a screed company makes a product that will produce a weak surface they should include the removal of it. Otherwise it’s often a unforeseen cost. Sent from my iPhone using Tapatalk
And my point is why is the cost unforseen. How can it possibly be. If flow screeds were new in the market I might agree but they've been around for decades. The information in the requirements for prep us free, easy to access, widespread and to say the costs are unforseen is just an excuse.
In my experience working for domestic customers it’s defo a unforeseen cost. For me those drying times are miles off. Every time I’ve tested a anhydrite subfloor it’s taken ages to dry. But maybe I’m not doing correctly as We are also told by our subfloor manufacturers they can’t be tested with a hygrometer. Only carbide bomb test. Not cheap either. Again the screed manufacturer is the one making the drying time claims. I think they should come out and give a certificate when it’s dry. Sent from my iPhone using Tapatalk
I personally don’t mind anhydrite screeds. I’ve always used gypsum based levelling compounds over them for LvT or double primed and bonded engineered wood to them. Always after leaving them to dry for a loooong time and I’ve never had a problem with them. Only ever sanded with a buffer and course paper or copper disk. Only problem I ever had was trying to get dry readings Sent from my iPhone using Tapatalk
Sub floor manufacturers saying no hygrometer are wrong. It's one of 3 approved British standard tests. The test method is very often not done correctly which leads to unnecessary delays due to inaccurate high readings but when it is done properly they give accurate readings. I'm in the process if putting a procedure document. I'll post a link when I've done it.
That would be very helpful. As you can see we as the flooring contractor receive contradicting advise from the screed company and the preparation company. We also had a lot of that regarding the use of DPMs on anhydrite Sent from my iPhone using Tapatalk
