Browse Forums Owner Builder Forum 1 May 21, 2009 11:08 pm Hi O.Bs I now understand not all concrete is the same. It’s not all grey stuff that pours out the back of the truck. It has different grades. Can anyone comment on the following? Ready mix concrete Strength of 20 mpa (is that strong) Standard for a waffle pod slab? Minimum slump of 80mm & max of 100mm. (I think that may be the thickness on top of the slab) Bulk pours at 15mpa. I need a bulk pour for footings is 15mpa OK. Trench mesh to be lapped at least 500mm with 20mm cover. (whats that) Fabric to be lapped a minimum of one full row. I’m doing a waffle pod slab by the way. Is it possible for a builder to skimp on mesh and concrete quality in the slab? The mesh I believe also comes in grades or thickness. Cheers KW.......... “It's just as unpleasant to get more than you bargain for as to get less” George Bernard Shaw. Re: Concrete questions. 2May 21, 2009 11:35 pm 20mpa is not regarded as strong. 40mpa might be. 55 is strong We get conc delivered at less thasn 80 slump , 60 mostly for benchtops Typically 32 / 14 / 60 (32 mpa 14 mm agg and 60 slump) and 20 & 25mpa for house slabs and hardstands. ..there are additives such as rapid hard, air, super plas, silica fume, fibres, colours, airaters etc. ...your footings, likely should be 20mpa, don't skimp TM - Trench mesh needs to be lapped, joined with wire ties and a lap of 500mm. (lock in the TM cross wires) The plastic membrane needs to be taped to the next piece/cuts/penetrations etc. Many grades of mesh f53 f62 +++(west coast talk) also the amount of wire in a sheet of mesh. Don't skimp anywhere, but least of all in your footings Where you are coming from is where you are going to... Re: Concrete questions. 3May 21, 2009 11:41 pm onc_artisan, I'm going to temporarily steal this thread to ask some questions. You seem to know your concrete. What are your opinions regarding waterproofing admixtures? Also, I'm after low thermal resistance concrete. I understand lightweight concrete may do the job. Any suggestions? Cheers, Casa Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Concrete questions. 4May 22, 2009 12:19 am onc Thank heaps, now Im worried. There must be a Aust. standard for this stuff ? It is for a M class site, does that make a difference. And its waffle pod, I dont have an engineers slab plan yet. Would you say its below standard for this slab? The stronger the better I say, but more cost. Thanks again. KW......... “It's just as unpleasant to get more than you bargain for as to get less” George Bernard Shaw. Re: Concrete questions. 5May 22, 2009 12:54 am Kw - you need an engineers report this will give you the best oportunity to have a sound footing for you house. ...and avoid cracking/limit reduce thermal co-efficeints(SP?) issues yarda yarda... Don't skimp casa2 - yep heaaps of ads, many pre/ready-mixed places have their own brew found this on the wiki.. Resistivity is a material property and refers to that material's ability to resist the flow of heat. Resistance on the other hand is an object property and depends on both the resistivity of the material and its overall thickness within that particular object. As resistivity is the inverse of conductivity, and conductivity values are far more readily available for most building materials than resistivities, it is possible to calculate the material's resistance using conductivity I prefer to think in thermal cycles IE 12 hrs to heat up and 12 hrs to cool is ideal. A brick wall will heat up in hours and cool in a few hours. a concrete wall will take hrs to warm but will stay warm for hours too begining to rant soz... but in winter let the sun in, in summer your house is in shade and has deciduous plants to the north Light weight will also amass less stored heat...and b..... xc Where you are coming from is where you are going to... Re: Concrete questions. 6May 22, 2009 10:10 am onc_artisan Kw - you need an engineers report this will give you the best oportunity to have a sound footing for you house. ...and avoid cracking/limit reduce thermal co-efficeints(SP?) issues yarda yarda... Don't skimp At last somebody has said the magic phrase! A structural engineer is the only person who should be advising on the strenght / grade of concrete for a slab. Pat. Re: Concrete questions. 7May 22, 2009 10:25 am King willy Hi O.Bs I now understand not all concrete is the same. It’s not all grey stuff that pours out the back of the truck. It has different grades. Can anyone comment on the following? Ready mix concrete Strength of 20 mpa (is that strong) Standard for a waffle pod slab? Minimum slump of 80mm & max of 100mm. (I think that may be the thickness on top of the slab) Bulk pours at 15mpa. I need a bulk pour for footings is 15mpa OK. Trench mesh to be lapped at least 500mm with 20mm cover. (whats that) Fabric to be lapped a minimum of one full row. I’m doing a waffle pod slab by the way. Is it possible for a builder to skimp on mesh and concrete quality in the slab? The mesh I believe also comes in grades or thickness. Cheers KW.......... when you get your plans drawn up then get a slab design engineered... i think it cost me about $800, but im in the country and not alot of places to shop around! when they do it up they give you a report telling you what strength mesh, concrete etc, you dont need to guess it, itl be drawn up to aussie standards. every1 thats looked at our says its way over engineered, but atleast it should make it strong! bloody better with what i paid for my slab! Re: Concrete questions. 8May 22, 2009 10:50 am KW, Quote: Ready mix concrete Strength of 20 mpa (is that strong) Standard for a waffle pod slab? Minimum strength of concrete for slabs. I went 25 MPA Quote: Minimum slump of 80mm & max of 100mm. (I think that may be the thickness on top of the slab) Quote: Trench mesh to be lapped at least 500mm with 20mm cover. (whats that) Fabric to be lapped a minimum of one full row. All advice given by other posters is correct, slab design must be done or approved by a structural engineer. There're quite a few discussions on concrete and slabs on this forum, with plenty of advice, use the search to find them. And no, I'm no concrete expert, just an O-B badly burnt on the slab pour, who had to learn on his own errors. Chris My father rode a camel, I drive a car, my son flies in a jetliner, his son will ride a camel.Saudi saying Personally, considering your layout (study/work desks in bedrooms), I don't think you have any other option but to leave NW windows and make them as big as possible e.g.… 7 10469 We had this happen to us last year and got charged a variation. Try and give away as much as you can that is usable to charity otherwise if you are in Sydney I have a… 1 4494 |