Browse Forums General Discussion Re: Warning about suggested repairs of slab heave 3Jun 07, 2012 12:05 pm Some people apparently have nothing better to do than comment on other people's sigs. Re: Warning about suggested repairs of slab heave 4Jun 07, 2012 12:38 pm Building a Delta 21 at Craigieburn - http://homeofzero.blogspot.com.au/ Deposit: 26/02. Contract: 22/05. Settlement: 29/05. Site start: 18/10. Re: Warning about suggested repairs of slab heave 5Jun 07, 2012 12:58 pm Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Warning about suggested repairs of slab heave 11Jun 08, 2012 10:18 pm Building a Delta 21 at Craigieburn - http://homeofzero.blogspot.com.au/ Deposit: 26/02. Contract: 22/05. Settlement: 29/05. Site start: 18/10. Re: Warning about suggested repairs of slab heave 13Jun 20, 2012 11:59 am Quote: As for your curing issue, well concrete achieves 80% of it's maximum strength after 24 hours so it is possible to start after only a day of curing time, cmhamilton this is absolute rubbish and you really shouldn't be spreading such crap on a topic that involves slab movement. It takes a lot longer to reach 80% strength and your lucky for it to even reach 80% if it's only air cured. Its probably under 10% strength at 24 hours. 7 days and its still under 50% strength. Have a look at the diagram below and take note of the x axis I doubt any of the major builders water cure their slabs, so they never actually reach their designed strength which is a worry. Re: Warning about suggested repairs of slab heave 15Jun 20, 2012 5:43 pm Hi JimmyL Would you please specify design strength of the sample tested, to me it appears to be 35 MPa and perhaps not relevant to residential slabs which are usually 20 MPa Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Warning about suggested repairs of slab heave 16Jun 20, 2012 8:05 pm JimmyL cmhamilton this is absolute rubbish and you really shouldn't be spreading such crap on a topic that involves slab movement. It takes a lot longer to reach 80% strength and your lucky for it to even reach 80% if it's only air cured. Its probably under 10% strength at 24 hours. 7 days and its still under 50% strength. Have a look at the diagram below and take note of the x axis Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ I doubt any of the major builders water cure their slabs, so they never actually reach their designed strength which is a worry. You're absolutely right, I had a total brain fade there (mixed up "safe to walk on" with compressive strength) - not sure what I was thinking (obviously not much at that point in time). As for your percentages, well that depends on the concrete mix and whether any chemical treatments are applied to the slab to prevent excess drying out of the slab surface. You also need to factor in that the slab itself isn't going to be under any real sort of excessive load for at least 3-4 weeks after the pour (when the tiles and then bricks are laid), by which time the slab will have had time to cure further. Still I apologise for the misinformation - just a bit of a facepalm moment... Some people apparently have nothing better to do than comment on other people's sigs. Re: Warning about suggested repairs of slab heave 17Jun 22, 2012 12:22 pm Sorry i cannot find the link but you can just google 'concrete cure' and have a look at various articles. Air drying is not really a good way of curing the slab (especially in warmer weather and direct sunlight) and some of the smaller builders will water cure but building a small dam on the slab and flooding with water. I'm not saying this is the reason for houses moving but on highly reactive P class soils where an engineer has designed a slab specifically for the site his calculations would be based on a certain % of the strength being reached. Re: Warning about suggested repairs of slab heave 18Jun 22, 2012 9:46 pm You are right JimmyL concrete strength has nothing to do with slab movement. For the record in over 40 years of building I have not come across concrete strength failure. It's always either defective design or poor workmanship or both. The only reason slabs move is because of foundation instability caused by changing moisture content of reactive soil from poor drainage, flooding from leaking pipes or interference from tree roots. Slabs on sand, rock or stable soil will not move. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Re: Warning about suggested repairs of slab heave 19Jun 22, 2012 9:59 pm Quote: You are right JimmyL concrete strength has nothing to do with slab movement. For the record in over 40 years of building I have not come across concrete strength failure. It's always either defective design or poor workmanship or both. How do you differentiate between them? So if a slab was designed to be half as strong as it should you would not expect it to affect the movement? Slabs are not 100% rigid and bend and warp just like anything else. Surely you would want a slab to reach its designed strength and be as rigid as possible unlike my house where one side has lifted a great deal compare with the other. I'm not arguing but you have just stated that the strength of the slab has no impact on movement. Re: Warning about suggested repairs of slab heave 20Jun 23, 2012 8:10 am Yes, if the concrete is under strength slab stiffness will be reduced but in foundation heave it will make no real difference. I have seen slabs with heaved corner or a side and slabs with tilt across the whole house. It does not matter how strong the concrete is or how reactive the soil is because if there is no change in moisture content there will be no movement. This is why I believe that on reactive soils (among other precautions) a concrete apron around home is a must as a part of the design and cannot be an optional extra, or be left out for the owner to do. Foremost Building Expert in Australia,assisting with building problems/disputes, building stage inspections,pre-contract review advice for peace of mind 200 blogs http://www.buildingexpert.net.au/blog Does anyone have a suggestion for a good hydronic in slab heating speacialist who may be able to help me with an existing system and wether or not it may need a seperator… 0 5558 Hi all, I have a lovely two story mid century house built 1962 with flat roof, box gutters and wide eaves. Unfortunately a tree came down on one corner and damaged a 4m x… 0 1472 The concreter will take and reuse. In my case I bought structural LVLs and scraped them back and used them as joists. 1 5885 |