Give me a chance Doug - can't give you it all in one go cos I will have nothing left for tomorrow.....anyway just been making a cupp and a banana sandwich....
can we talk, calcium sulphate screeds
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Give me a chance Doug - can't give you it all in one go cos I will have nothing left for tomorrow.....anyway just been making a cupp and a banana sandwich....
Now then......... what should we look at next......specification I think..
the specification of the screed is essentially in the hands of whoever is taking design responsibility for it. Sometimes this is the architect, sometimes the screeder, sometimes the builder etc etc. I am able to help write specifications but I generally do not accept design liability as there are too many things outside of my direct control so I offer what are called Model specifications. Ideal designs if you like. The general rule of thumb is that the key to success is to play to the strengths of the material and design out the weaknesses. The one thing which crops up time after time after time is screed depth. In the uK we seem to be stuck fast into the mentality that a screed should be 65mm or 75mm deep. Take the average house ground floor where you will often see the screed and insulation zomne specified at 150mm in total i.e. 75mm insulation and 75mm screed. This zone has some merit in traditional masonry build as it fits very nicely with brick coursing i.e. 2 courses of bricks and mortar is 150mm. To acheive the necessary U value a designer will often specify a polyurethane type insulation in this scenario. Placing anhydrite screed deeper than it needs to be has a number of undesirable effects, most notably the drying time. This screed dreis naturally at a rate of 1mm per day up to 40mm depth and then add on 2 days per mm thereover so a 75mm screed will take 110days to dry. Not conducive to anyones build programme. It can be very effectively force dried but if you design it at a much thinner depth it would have a much reduced natural drying time and so you can see zoning is something which is very important. In domestic situations it can be laid to a depth of just 35mm and in commercial applications 40mm when laid over insulation. Even thinner when not on insulation but more on that in a later chapter. The more shrewd amongst you will notice that we now have 75mm of polyurethane insulation and 35mm of screed which does not fit conveniently into the brick coursing. What I tend to do here is simply increase the depth of the insulation to 110mm and the screed to 40mm. When you increase the depth of insulation to this depth it is quite possible to acheive or exceed the U value by changing the insulation type to polystyrene which is generally quite a bit cheaper. Typically an EPS or XPS 100 insulation will offer an improvement to the U Value and allow the screed depth and hence the drying time to be reduced significantly.
How am I doin so far.........
the specification of the screed is essentially in the hands of whoever is taking design responsibility for it. Sometimes this is the architect, sometimes the screeder, sometimes the builder etc etc. I am able to help write specifications but I generally do not accept design liability as there are too many things outside of my direct control so I offer what are called Model specifications. Ideal designs if you like. The general rule of thumb is that the key to success is to play to the strengths of the material and design out the weaknesses. The one thing which crops up time after time after time is screed depth. In the uK we seem to be stuck fast into the mentality that a screed should be 65mm or 75mm deep. Take the average house ground floor where you will often see the screed and insulation zomne specified at 150mm in total i.e. 75mm insulation and 75mm screed. This zone has some merit in traditional masonry build as it fits very nicely with brick coursing i.e. 2 courses of bricks and mortar is 150mm. To acheive the necessary U value a designer will often specify a polyurethane type insulation in this scenario. Placing anhydrite screed deeper than it needs to be has a number of undesirable effects, most notably the drying time. This screed dreis naturally at a rate of 1mm per day up to 40mm depth and then add on 2 days per mm thereover so a 75mm screed will take 110days to dry. Not conducive to anyones build programme. It can be very effectively force dried but if you design it at a much thinner depth it would have a much reduced natural drying time and so you can see zoning is something which is very important. In domestic situations it can be laid to a depth of just 35mm and in commercial applications 40mm when laid over insulation. Even thinner when not on insulation but more on that in a later chapter. The more shrewd amongst you will notice that we now have 75mm of polyurethane insulation and 35mm of screed which does not fit conveniently into the brick coursing. What I tend to do here is simply increase the depth of the insulation to 110mm and the screed to 40mm. When you increase the depth of insulation to this depth it is quite possible to acheive or exceed the U value by changing the insulation type to polystyrene which is generally quite a bit cheaper. Typically an EPS or XPS 100 insulation will offer an improvement to the U Value and allow the screed depth and hence the drying time to be reduced significantly.
How am I doin so far.........
D
DHTiling
LIke i said Info to follow and his name is Ajax...:lol:.. i just tile them.. he makes the stuff..
The next thing I always look for in the specification is the divorcement of the screed from any residual construction moisture from concrete sub slabs etc. A typical ground borne concrete slab will have a depth of 100mm and can take in excess of 12 months to dry. There will often be a DPM under the concrete so the only direction the residual moisture can go is upwards. If this moisture is allowed to rise through the screed it can extend the drying time of the "floor" - notice I do not say of just the screed - significantly. This can in turn have a number of undesirable effects - e.g. delaying fixing of final floor coverings to in extreme cases poly sulphide attack ( although the latter is very very rare). Concrete being cement based does not mind moisture being trapped within it, in fact it is desirable. By the simple expedient of placing a 1200 gauge polythene membrane over the top of the concrete prior to placing the insulation and screed can save loads of time in the build programme. I like double membrane systems where the DPM is under the insulation and a slip membrane is ont top altough I accept the commercial aspects associated with using the DPM as a slip membrane as well. this does not however suit heated screeds where a double membrane system should always be used IMO.
In heavier duty environment consideration has to be given to the deflection created when the insulation compresses under loadings so it is often wise to stick with the PU type insulations where heavy traffic is to be used e.g. hospital beds, school library shelves etc.
Blimey that one was dissapointingly short........now where di I hear that before....oh yes the Mrs is sitting on the sofa as well.....😳
Blimey that one was dissapointingly short........now where di I hear that before....oh yes the Mrs is sitting on the sofa as well.....😳
T
The Legend; Phil Hobson RIP
Thanks Ajax, Thats what I meant. :lol::lol::lol:
Sorry I missed an installment tonight - went off to play Snooker instead.......Lost:incazzato:.....so as it happened would have been better coming here. Will be back with the next installment tomorrow. We'll probably talk more about design and perhaps about underfloor heating next Any other special requests considered unless they invlove contortion....:yikes:
Any other special requests considered unless they invlove contortion....:yikes:
D
DHTiling
Tut tut snooker...:smilewinkgrin:
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