Browse Forums Building A New House 1 Sep 23, 2014 2:56 pm Hi everyone Just had a call from our builder noting that I need to water our site for two hours per day, seven days before commencement. This was a requirement in the engineers report: "Pre-wetting of the site prior to the commencement of siteworks is required. Watering may be carried out using garden sprinklers for approximately 2 hours daily for a period of 7 to 10 days or until all visible cracks in the soil have closed up. This watering must be carried out before the underfloor filling is placed. After watering, construction must commence within 3 days. " Has anyone else had this requirement? BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 2Sep 24, 2014 1:37 am Some engineers now require site wetting on KDRs as a result of the looming slab heave legal maelstrom. Limiting it to KDRs is a small but nevertheless positive move. To re-hydrate properly can take more than 7-10 days of 2 hour daily waterings, the subsoil moisture levels need to be monitored at different depths with a NMM to determine whether the re-hydration has achieved consistent levels within the desired moisture range. There can be no blanket watering rule as now seems to be applied, local weather conditions and soil types also need to be factored in the calculations. One would assume that a geotechnical engineer has taken a range of subsoil moisture levels at different depths and has been the one who made the recommendations. The thread that I have linked below discussed pre-watering and there have been 'mentions' in other threads. viewtopic.php?f=1&t=70614 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: Pre-watering of site 3Sep 24, 2014 9:41 am I posted this response to a fellow Adelaidian. My engineer report stated to pre-wet soil for 2 hours for 2 weeks using dripper or weeper hose which is very vague. I actually spend $600 on an independent moisture test (on my blog) and the moisture content is consistent and was advised by the geotechnician that I don't need to prewet. I contacted the builder's engineer firm and they state to follow their instruction so I spent like $100 (25m - 13mm black dripper hose was ~$9.40 each, connections etc) from bunnings and did the thing myself and (to me seems just surface wetting only). I didn't want to buy weeper hoses as I was afraid it will get stolen, the cost would have probably been the same between the dripper or weeper system. I figure I better follow the instruction otherwise it is a get out of jail card for builder. Forgot to mention you can use a timer and get someone to turn on the water for you, I have family nearby our block so they turned on the timer for me. When I am there on the weekends, I used a sprinkler system (as in my pic). http://boostaoakfordsa.wordpress.com/page/2/ You will need to measure out your area to be prewet and your placement of your sprinklers. Using the sprinkler system is so much easier. http://www.bunnings.com.au/holman-12mm- ... p_p3110661 - I used these with something like this: http://www.bunnings.com.au/multi-tap-ad ... h_p3120268 (make sure you check the fittings fit, you can buy these cheaper at the variety shop like reject shop, cheap as chips) and garden hose. http://boostaoakfordsa.wordpress.com Site works: 26/8/14 Trench: 2/9/14 Slab: 8/9/14 Frame: 18/9/14 Bricks: 24/10/14 2nd fix: 24/11/14 Handover: End Feb 2015 Re: Pre-watering of site 4Sep 24, 2014 9:59 am Thanks everyone. My first task is to work out what fitting I need in order to connect to the mains water. There is currently a male thread from the mains tap which looks like it measures (will need to confirm) 100mm. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 5Sep 24, 2014 10:11 am Shambini Thanks everyone. My first task is to work out what fitting I need in order to connect to the mains water. There is currently a male thread from the mains tap which looks like it measures (will need to confirm) 100mm. Got a picture? The demo company turned my water meter upside down and took out the old fitting so I went to the plumbing section at bunnings: Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ http://boostaoakfordsa.wordpress.com Site works: 26/8/14 Trench: 2/9/14 Slab: 8/9/14 Frame: 18/9/14 Bricks: 24/10/14 2nd fix: 24/11/14 Handover: End Feb 2015 Re: Pre-watering of site 6Sep 24, 2014 10:17 am boosta Shambini Thanks everyone. My first task is to work out what fitting I need in order to connect to the mains water. There is currently a male thread from the mains tap which looks like it measures (will need to confirm) 100mm. Got a picture? The demo company turned my water meter upside down and took out the old fitting so I went to the plumbing section at bunnings: Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Looks fairly similar to what the demolition company left me with. I am going by the site after and taking some measurments and photos then making a visit to the hardware store. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 7Sep 24, 2014 10:27 am boosta My engineer report stated to pre-wet soil for 2 hours for 2 weeks using dripper or weeper hose which is very vague. I actually spend $600 on an independent moisture test (on my blog) and the moisture content is consistent and was advised by the geotechnician that I don't need to prewet. I contacted the builder's engineer firm and they state to follow their instruction. I figure I better follow the instruction otherwise it is a get out of jail card for builder. Good post boosta. What you have posted is the very concern I have with engineering reports that all seem to give the same pre-wetting advice, at least in the case of all the one I have heard of. The only way to know whether re-hydration is needed is to do moisture level tests at different depths and then if needed, have the same geotechnical engineer formulate a management plan that is NMM monitored. The steps you took to have you own moisture tests professionally done was correct and I seriously question the original engineering report. Naturally, the builder's engineering firm was not about to admit that their direction either had no basis of fact or was wrong when you contacted them. 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: Pre-watering of site 8Sep 24, 2014 10:30 am It is a bit disheartening when you can't rely on the advice provided by the engineering company. Sound like it is a blanket recommendation for all KDRs irrespective of if it is actually necessary. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 9Sep 24, 2014 10:46 am Interesting read guys. But i dont agree with what the engineers have suggested. How on earth can you confirm that the moisture is uniform across the site. It would be impossible. Also great that there will be less of a problem with ground swell. But what happens when it dries out. The slab will fall. Re: Pre-watering of site 10Sep 24, 2014 12:22 pm B STAR Interesting read guys. But i dont agree with what the engineers have suggested. How on earth can you confirm that the moisture is uniform across the site. It would be impossible. Also great that there will be less of a problem with ground swell. But what happens when it dries out. The slab will fall. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ This is what I did - The moistures need to be taken at 1m,1.5m, 2m, 2.5m depth and make sure at least one is taken in the middle of the old houses footprint. By the term "moisture is uniform", this is what was explained to me by the geotech, each borehole and its relevant depth, the moisture content is uniform / consistent, though BH2 (the middle when new house footprint) had a range from 23.2 to 30.8. Cheers http://boostaoakfordsa.wordpress.com Site works: 26/8/14 Trench: 2/9/14 Slab: 8/9/14 Frame: 18/9/14 Bricks: 24/10/14 2nd fix: 24/11/14 Handover: End Feb 2015 Re: Pre-watering of site 11Sep 24, 2014 1:15 pm B STAR How on earth can you confirm that the moisture is uniform across the site. It would be impossible. The proper way to do it is to have a geotechnical engineer come in and drill numerous holes and take moisture readings at various depths with a Neutron Moisture Meter (NMM). The moisture levels will not be uniform. The geotech then determines how much hydration is needed and a management plan then put in place. At the end of the program, the moisture levels are taken again but while they should all be in the desired moisture % range, they won't all be the same. This is unavoidable but a natural phenomena called matric suction then acts on the soil matrix to distribute the moisture more evenly. B STAR Also great that there will be less of a problem with ground swell. But what happens when it dries out. The slab will fall. Home owners must know how to protect their slab from seasonal subsoil moisture variances. There are several threads that deal extensively with slab heave and what must be done and what not to do to protect the foundations. One of the first things that new home owners need to understand is that many new estates are now being built on land that was formerly shunned as not appropriate to build on and this includes former flood plains and areas of highly reactive soil. If persons build in such estates, they must ensure that they follow the appropriate guidelines to protect their home from both heave and subsidence. 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: Pre-watering of site 13Sep 24, 2014 2:00 pm A neutrons moisture meter is not practical very expensive and not required. moisture samples across the block is all that is required. If the moistures are relatively consistent then no further action is required . Re: Pre-watering of site 14Sep 24, 2014 8:26 pm I managed to get the right connections so the hose is ready to go. Found a 40 to 20 mm reducer at the hardware store around the corner. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 15Sep 24, 2014 9:51 pm I hadn't heard of pre-wetting before, this is an interesting topic. What I don't understand is that in a KDR scenario, generally speaking, most people would be re-building in the same or similar position as the recently demolished house. This recently demolished house would have been in that location for (in most cases) 50+ years. The soil, where the old house was, would/should be bone dry 1.5-2.5 metres below the surface, particularly towards the middle of where the house was. What is the reason for now introducing moisture to this area, for two weeks prior? I have seen the word re-hydration used, but why is it re-hydration if this area hasn't been subjected to seasonal rain influences, or hydrated, for the past 50+ years? Re: Pre-watering of site 16Sep 25, 2014 11:08 am A trusted Google search informs me that in new construction where expansive soil is a concern, the engineer may require (as is the case in our build) controlled pre-wetting of the soil prior to placement of the foundation. This will cause pre-expansion of the soil with the idea that further expansion pressure on the new foundation will be minimised. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 17Sep 25, 2014 1:25 pm Building the Dream What I don't understand is that in a KDR scenario, generally speaking, most people would be re-building in the same or similar position as the recently demolished house. This recently demolished house would have been in that location for (in most cases) 50+ years. The soil, where the old house was, would/should be bone dry 1.5-2.5 metres below the surface, particularly towards the middle of where the house was. What is the reason for now introducing moisture to this area, for two weeks prior? I have seen the word re-hydration used, but why is it re-hydration if this area hasn't been subjected to seasonal rain influences, or hydrated, for the past 50+ years? There are several reasons and insider is the forum expert on this subject but for what it's worth...one simple reason is that if you build on bone dry soil and there is ponding during or after construction or perhaps a pipe leaks under the slab, the soil will expand and if there is resultant heave, the slab will not return to its original state. On the other side of the coin, you shouldn't build on slush at the height of a wet period. Ideally, sites should only be built on when subsurface moisture levels are within a mandated range but mandates do not apply at this time. What does currently apply is for builders to have the correct site cut/slope and drainage during construction but even now, this isn't always done despite the regulations and widespread publicity surrounding the numerous cases of documented slab heave. Maybe in the future, new home buyers will have the option of installing subsurface moisture monitors under the slab and an option to trickle feed harvested rainwater to specific areas that indicate below optimum moisture levels. 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: Pre-watering of site 18Sep 25, 2014 5:36 pm What H2O says is right.But you don't even need a broken pipe to have centre heave The reason for pre watering is that the previous house, even though on the same location as the proposed new house, would have been a timber floor house.This allows the soil under the house to dry and not get re charged with water like the outside exposed ground would.So when you build your new slab over the dry ground that used to be below your timber floor it has a high suction and will drawn moisture from the wetter areas around the perimeter and hay presto center heave.The effects of this are increased if the demo house was old and had overflowing gutters which a lot of the knock downs do.Add in a few trees that have been removed to make way which again increases the potential for that previously dry so to re bound with new moisture. This is not a theory I have seen the results of centre heave and it is very hard if not impossible to fix. I don't agree with the idea of pre wetting based on guess work.I generally prefer that this situation be taken into the engineers design.As I have said to Boosta who had a similar situation,a series of moisture samples around the site and in particular in the middle of the proposed slab will tell you if it is required and will give you a idea of how much you need to wet the soil if at all.If you do have to wet the soil up when your finished you can take a second series of moisture test to see if the moisture conditions across your building envelope are relatively even. Re: Pre-watering of site 19Sep 25, 2014 9:20 pm Why don't the builders and engineers recommend moisture samples in order to determine the right level of pre watering? The professionals can't expect the layman to research the topic and realise that their recommendation is a blanket one. We pay professionals and expect that we can rely on their advice to be reasonably accurate. BLOG: http://www.ourphoenix38.blogspot.com.au H1 THREAD: viewtopic.php?f=31&t=70454 Re: Pre-watering of site 20Sep 25, 2014 10:04 pm Good question Shambini. I suspect that these things just get repeated and repeated, no one questions them and it is automatically printed out.It's a bit like the drainage design, printed off with no regard of the actual soil condition. We've had the offer of a short term tenant whilst waiting for CDC/DA home approval and demolition for our knock down rebuild. It would achieve a pretty low rent as it's… 0 13744 The fastest thing a builder will do is bank your cheque, those systems work perfectly with lightning speed, everything else is slow burn. Just the way it is. 1 8702 Just to makea point about this, an approach that some people have found sucessful in negotiating these rises down, Is to provide some workings to the builder, specifying… 4 81667 |