Browse Forums General Discussion 1 Jan 05, 2010 1:57 pm We have purchased a newly built home, approx. eight months old. It is a slab construction, with a one-metre cut retaining wall at the rear of the home, and a 1.8 metre high retaining wall holding fill at the front. Both of these walls are of sleeper construction, and supposedly engineered.
In the past month, we have "holes" appearing going under the slab at the front of the property, about about eight in total, along the front of the slab. They are about 8cm in height and appear to be about 30cm in depth under the slab. We are also noticing cracks in the lawn, and every corner of the interior of the house has hairline cracks. In four places, these cracks are between 2-3 mm wide. The driveway, which sits on fill, is also showing a number of large cracks. As we are on clay soil, we realise there is soil movement, but for a house only eight months old, should we be worried about these things? Does anyone know if this is classed as normal? I do have pictures, but am having trouble uploading them; need to ask hubby to try when he gets home from work I would not like to ask advice from the builder until I talk to others, as the builder was deceitful with us during settlement about the legality of the walls, and produced misleading documents, so to ask his advice and believe it would be hard for me!! Re: Advice on holes under slab, cracks etc. Please! 3Jan 05, 2010 2:09 pm Presumably the area where a you are has dried out considerably. Just re-read your post... Hmmm doesn't sound too good. If it is as bad as you say, then I'd be asking for an inspection to be done. The person to do the inspection MUST be qualified and be prepared to 'sign off' on his/her assessment. ... and can substantiate their claims. IE: No point in having a box ticker whom cannot elaborate coulpa bobs worth Where you are coming from is where you are going to... Re: Advice on holes under slab, cracks etc. Please! 4Jan 05, 2010 4:47 pm onc_artisan Presumably the area where a you are has dried out considerably. Just re-read your post... Hmmm doesn't sound too good. If it is as bad as you say, then I'd be asking for an inspection to be done. The person to do the inspection MUST be qualified and be prepared to 'sign off' on his/her assessment. ... and can substantiate their claims. IE: No point in having a box ticker whom cannot elaborate coulpa bobs worth Oh, just found your other post ... "my" guy *cough* can actually be found in a few cases (only a few) in the AUS legal database ... in all of his cases, his client won !!! and his reports were apparently valued by the judge. That's one of the reasons why I haven't switched to someone else (yet ) ... Goes without saying, but I think we all try to check and double check, and since we don't have any "real" references, we google and then pick whatever seems a good option ... so we don't have the benefit of knowing until we've gone and used them!! and we may find out only too late if XYZ is just a box ticker (and how can we aks them !!! oh no, I actually did ask mine something similar, like any problems with inspecting this builder's work, any conflict of interes, any friends there ... all nays ) My signature is distracting people from my wise posts ... Re: Advice on holes under slab, cracks etc. Please! 5Jan 05, 2010 6:17 pm Photo's would be extremely useful...but it sounds like the fill has dried out and the slab has lost a bit of corner support. mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Advice on holes under slab, cracks etc. Please! 7Jan 06, 2010 10:36 am http://yfrog.com/9g1001656xj http://yfrog.com/jl1001662j http://yfrog.com/e51001634mj http://yfrog.com/5j1001628p Hopefully these work Have taken many tries!!!! Re: Advice on holes under slab, cracks etc. Please! 8Jan 06, 2010 11:27 am Does much water flow in that area? Where you are coming from is where you are going to... Re: Advice on holes under slab, cracks etc. Please! 9Jan 06, 2010 12:00 pm Hmm, I am definitely no expert at all. I am (very slowly) learning some things about building as we go. Once it's built, and a problems appears, I wouldn't really know where to start. Anyway, I'll scramble my thoughts anyway ... they might provoke some actual meaningful help from those who do know something ... OK, since this is quite a new building, did you receive all the plans for the house? I think you should have. It would have a sheet for Slab Plan. Is this a waffle pod slab? If yes, I don't understand how could there be some holes forming underneath the concrete ?!?! It doesn't look just superficial on the pics. Maybe this piece of slab is an add-on concrete? Can you poke it with something horizontally to see how far the hole spreads horizontally under the slab? The cracking of the plaster/cornice might be due to settlement (I think within first 12-24 months this can be expected??). I don't know, but maybe it's not related to the holes under the slab (although it's hard to ignore them!!)!? And after you gather your thoughts (from all the comments you will get here), I think you should get an inspector to have a look. Are you in Sydney? And since you're not building, if you're not happy with him, you can even get another one. If you go ahead with that, just make sure you prepare lots of questions for them and show them all areas that you've noticed (in case they miss some). Sorry I can't be of any real help, I hope you at lest find out what are you dealing with and I hope it's nothing major. My signature is distracting people from my wise posts ... Re: Advice on holes under slab, cracks etc. Please! 11Jan 06, 2010 12:09 pm Me again ... this is so bizzare (even with heavy clay) ... the slab should be in ground and vertical, not like that (unless this is the very bottom of the slab rebate, ie. where the slab sits on the plastic (or whatever else) ... Did you have a pre-purchase building inspection? My signature is distracting people from my wise posts ... Re: Advice on holes under slab, cracks etc. Please! 12Jan 06, 2010 4:28 pm Thank you for your posts, your help is much appreciated. To onc_artisan: we live in South-East Qld, so not too wet and not too dry - and even though we are on the side of a hill, we have an easement beside our land for water-flow, while the house sits higher and doesn't receive much water. Both my hubby and I have discussed whether water could be the problem, even a problem water pipe under the slab, but have decided it wouldn't be the problem. (The ground looks wet in the photos, but that's because we have had beautiful rain every day since Christmas!!) To Lex: We did do a building inspection when we purchased, but of course the house was brand new, and there wasn't much wrong. These problems have all occured in the last month or two. They are still building around us, which could cause soil movement, but I wouldn't expect this much As this part of the house sits on fill, I do wonder whether it was compacted properly before the slab was put down This part of the slab is on fill, and the ground falls away from the slab. While we know the slab is a waffle pod slab, we are double checking on this part of the slab. Even though it is like an "outdoor room", the slab is 450mm high, so I would be inclined to think that it would be also a waffle pod slab, otherwise it would be a lot of concrete ?? On a further check around the side and back of the house, the soil in places seems to be sinking down the perimeter of the slab, although not to the extent of seeing the bottom of the slab like the front. Re: Advice on holes under slab, cracks etc. Please! 13Jan 06, 2010 4:50 pm SE qld is wetter than us southerners know. Couple of metres a year?? And does the roof have gutters? Is the guttering plumbed to Storm water drainage? If not I suspect you have a large amount of water removing soil ( atleast compacting it.) Where you are coming from is where you are going to... Re: Advice on holes under slab, cracks etc. Please! 14Jan 06, 2010 8:56 pm my opinion is the holes under the slab shouldnt be a problem as long as it is the case where the soil has just been erroded and the slab has been built correctly. THis is because waffle slabs are rigid and should be able to handle some soil displacement. ALthough this may indicate the quality of the builder. THe photos of the cracked skirting and plaster buggs me. Yes the skirting can crack very easily on a join like that. However the plaster should never crack like that because there should be "exy"- not sure of the spelling which will prevent it cracking like that. Is this a sign that the builder has skimpt out on items to save a few dollars. Plaster should never crack like that on an external corner. Re: Advice on holes under slab, cracks etc. Please! 15Jan 06, 2010 9:19 pm Quite right borg internal and external corner molding Where you are coming from is where you are going to... Re: Advice on holes under slab, cracks etc. Please! 16Jan 06, 2010 10:32 pm Hmm, a little hard to tell the extent of the damage from the photos, are there any signs on the brickwork cracking as well? Any movement in the gyprock or cornice should only be hair line crack and certainly not run down the corner of the walls.... have a good look around the rest of the house as you may find another corner where the house has lifted, check all door for operation and see any jamb, this can also give some clues as to what is going on. even a waffle pod slab can only take so much and a major issues is ensure water is always moved away from the slab that is why it is recommended to have you soil/lawn slope away from you house to the boundary.. if this spot is flat or worse sloped towards your house i'd say you are having subsidence issues. There are only a few builders that actually scarify the soil under a slab and design the slab to suit. so I doubt yours has been designed this way. I would contact the BSA and find a suitable building inspector to have a look. Re: Advice on holes under slab, cracks etc. Please! 17Jan 06, 2010 10:45 pm borg my opinion is the holes under the slab shouldnt be a problem as long as it is the case where the soil has just been erroded and the slab has been built correctly. THis is because waffle slabs are rigid and should be able to handle some soil displacement. ALthough this may indicate the quality of the builder. Correct...to a certain extent. Although we don't know the classification of the soil and whether the slab was built to spec. It would appear to me from the photos that the foundation soil below the slab is directly exposed to the outside environment and therefore water ingress and then subsequent drying. The cycle of wetting and drying may lead to future foundation problems. Most slabs have deep edges beams around them which is not apparent in the photos - for strength - but it also means the foundation soil maintains a relatively even moisture content and therefore reduces the shrinkage/swell cycle. A tape measure or some other scale (e.g. pen) would help to provide an indication of size of problem. In any case given the history with the builder and the extent of damage I'd be seeking professional assistance - they'll be able to look at the cracks, slab exposure, piece together the cause of the cracking and prepare a cogent document for you to give to the builder. mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Advice on holes under slab, cracks etc. Please! 18Jan 07, 2010 8:04 am Thank you for your posts The storm water and gutters are all connected properly, and the ground does fall away from the slab; until last week it was really dry in this area, so soil settlement through dryness is always an option. The site is "M" class, and the area where the holes are forming is under a waffle pod slab. Have been able to confirm through the slab plans that the engineer-drawn footings have not been followed properly. We have posts on the corners to hold up the roof which should have a 900mm footing, but as these holes have formed, I can't see any footing whatsoever. The plan says "Typical P1 Pad Footing" - does that mean it is mandatory, or just a drawing they suggest should be followed?? While we have hairline fractures in every corner of the house, the crack I have taken a photo of is similar to one I have in the kitchen, which runs along the bottom of the cornice, and appears to be lifting the cornice, and also along the door in the laundry. We have one medium sized crack in the brickwork, but as it is horizontal and through the grout, I wasn't too worried, as I thought that you only become concerned if the cracks go through the bricks. Will take it further, as I just wasn't sure if all this was normal, but had an inkling that it was a bit odd for such a newly built home. My guess is that they haven't compacted the soil properly, or filled it with unclean fill. Thank you for all your help Re: Advice on holes under slab, cracks etc. Please! 19Jan 07, 2010 9:20 am melly ... The site is "M" class, and the area where the holes are forming is under a waffle pod slab. Have been able to confirm through the slab plans that the engineer-drawn footings have not been followed properly. We have posts on the corners to hold up the roof which should have a 900mm footing, but as these holes have formed, I can't see any footing whatsoever. The plan says "Typical P1 Pad Footing" - does that mean it is mandatory, or just a drawing they suggest should be followed?? ... Hmmm, just thinking maybe it would have helped to build a concrete pathway all around the house immediately after the house was finished (of course, you couldn't have influenced that). Say 70 cm wide at least. I think that kind of thing helps prevent surface shrinkage in the immediate vicinity of the slab edges ... helps prevent soil cracking due to differences in wet and dry wheather because it protects the soil closest to the foundations from wetting. I am also wondering how did you discover that engineer-drawn footings have not been followed properly? I thought that you can only see it for yourself when they are drilling the pier holes. Also, our slab plan doesn't specify the depth of the holes at all! The drilling guy "determined" them himself on the spot, primarily based on soil colour ... He told me that he drilled the holes in our fill section until he reached the same colour as in the cut section ... all approximation, really ... quite scary. Also scary that you are thinking you should be able to see the piers!! Never crossed my mind, but it makes sense (scary because I would hope that piers should be "hidden forever") ... Any comment from those in the know??? My signature is distracting people from my wise posts ... Re: Advice on holes under slab, cracks etc. Please! 20Jan 07, 2010 9:56 am Melly - If the plan says typical then that is what you should have. Typical being the design used in a set of conditions. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Where you are coming from is where you are going to... The CSIRO BTF18 explains differnt types of cracks and what "normal" is Google this and the top result is actually the latest version. You normally have to buy this from… 9 9320 it depends on the natural ground level, if they excavated their boundary wall needed to be built as a retaining wall. If you filled, which sounds like the case then you… 1 7085 I know foam has been around since the 90's and CSR started manufacturing Hebel in 1989, so it's definitely possible 5 5451 |