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Browse Forums General Discussion Re: Slab Heave Cause? 42Aug 02, 2018 6:49 pm 3in1 Supadiverta. Rainwater Harvesting Best Practice using syphonic drainage. Cleaner Neater Smarter Cheaper Supa Gutter Pumper. A low cost syphonic eaves gutter overflow solution. Re: Slab Heave Cause? 45Aug 03, 2018 10:14 am 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: Slab Heave Cause? 53Aug 06, 2018 4:45 pm MyFirst Quote: Piers will protect you from soil subsidence/settlement I would have thought where clay soil shrinks due to lower than normal moisture or sinks due to excessive pressure from the house. It just doesn't protect you from soil heave where higher than normal moisture is encountered and clay soil expands under the house. So in this case when building waffle slab it should be build on rainy season? Where the soil has been heave with all the extra moisture? For example if you built during the start of the very wet period of 2010-2011 then you still could have encountered significant heave.This is because the soil moisture was incredibly dry from the drought.So it is more about the starting moisture of the soil during construction rather than the climatic conditions.They are related but there can be a lag between wet periods and wet soil moisture conditions. Really soil testing companies should be taking soil moisture tests in summer and extended dry periods this wasn't done by all companies 1997-2009, 2015-2016. Re: Slab Heave Cause? 54Aug 06, 2018 4:48 pm insider MyFirst Quote: Piers will protect you from soil subsidence/settlement I would have thought where clay soil shrinks due to lower than normal moisture or sinks due to excessive pressure from the house. It just doesn't protect you from soil heave where higher than normal moisture is encountered and clay soil expands under the house. So in this case when building waffle slab it should be build on rainy season? Where the soil has been heave with all the extra moisture? For example if you built during the start of the very wet period of 2010-2011 then you still could have encountered significant heave.This is because the soil moisture was incredibly dry from the drought.So it is more about the starting moisture of the soil during construction rather than the climatic conditions.They are related but there can be a lag between wet periods and wet soil moisture conditions. Really soil testing companies should be taking soil moisture tests in summer and extended dry periods this wasn't done by all companies 1997-2009, 2015-2016. Just out of interest. If during 2010/2011, if those houses were constructed using raft slab would it have solved a lot of heartache from slab heave. Re: Slab Heave Cause? 55Aug 06, 2018 4:53 pm MyFirst Just out of interest. If during 2010/2011, if those houses were constructed using raft slab would it have solved a lot of heartache from slab heave. Nobody knows for sure but it certainly would have been fewer and less severe defects as when AS2870-1996 came out, in ground raft was the mainstream option. Waffle pod was still in its very early days and not a lot of data was available. However, AS2870-1996 did say the standard applies to "waffle rafts" but I guess they stuffed up. One of the major changes in 2870-2011 was splitting class H into H1 and H2. In the Metricon slab heave case, the estimated Ys was 72mm. AS2870-1996 requires rounding to the nearest 5, so it was rounded down to 70mm and classified as class H. Now think about that for a minute, nature works on a continuum, not some arbitrary cut off set by a bunch of homo-sapiens. The couple got a slab designed for 40mm - 70mm. That's a WIDE range for basically a one size fits all design. I still blame the fact that 2870-1996 had a lot of data for in ground raft but very little data for waffle pod, especially in extreme weather conditions so that wasn't taken into consideration which meant a lot of people are suffering right now. Re: Slab Heave Cause? 56Aug 06, 2018 4:57 pm No I have seen raft slabs heave from that period.There may be slightly less damage but it is hard to compare directly to waffle slabs because each situation can be different as far as cause and degree of wetting etc. The reason you don't see as many raft slabs heave as waffles in that period is simply there were much more waffles built than rafts. I still prefer a raft for several reasons one being that the perimeter beam is dug into the ground providing a minor barrier to water getting under the slab. Re: Slab Heave Cause? 57Aug 06, 2018 4:58 pm insider No I have seen raft slabs heave from that period.There may be slightly less damage but it is hard to compare directly to waffle slabs because each situation can be different as far as cause and degree of wetting etc. The reason you don't see as many raft slabs heave as waffles in that period is simply there were much more waffles built than rafts. I still prefer a raft for several reasons one being that the perimeter beam is dug into the ground providing a minor barrier to water getting under the slab. Question for you insider, I see some of our SA friends still use in ground raft slabs even for budget builds, why is that? Re: Slab Heave Cause? 59Aug 06, 2018 5:11 pm Yes its ironic isn't it.They invented the waffle and now they don't use them.The reason is that they actually call site class"E" in SA so for waffles the step up is too much.With the raft "E" it can be dug in and the step up isn't a problem.Here in Vic everyone is too scared to call a site "E" as they are afraid they will lose their client to someone who calls it a "H2" and the builder can still use waffle slabs. During the drought the ground movement calculations were done as if it were normal conditions but in reality they should have been increased significantly.Therefore a lot of site should have been classified as "E" but weren't basically because builders wanted to use waffles and would take their business to someone who classified "H2 so they could keep using waffles. Re: Slab Heave Cause? 60Aug 06, 2018 5:14 pm insider Yes its ironic isn't it.They invented the waffle and now they don't use them.The reason is that they actually call site class"E" in SA so for waffles the step up is too much.With the raft "E" it can be dug in and the step up isn't a problem.Here in Vic everyone is too scared to call a site "E" as they are afraid they will lose their client to someone who calls it a "H2" and the builder can still use waffle slabs. During the drought the ground movement calculations were done as if it were normal conditions but in reality they should have been increased significantly.Therefore a lot of site should have been classified as "E" but weren't basically because builders wanted to use waffles and would take their business to someone who classified "H2 so they could keep using waffles. That's terrible. So only people in SA have brains and the rest of the states are filled with consumers with too high expectations and builders too willing to please whatever the cost? Is it the water that's special in SA or something? Firstly the ableflex that has been installed needs (manufactures specification) a sealant cap over the top, preventing water draining down between the slab and the… 3 8023 1 6825 |