Browse Forums Building A New House 1 Dec 25, 2009 12:54 pm “It's just as unpleasant to get more than you bargain for as to get less” George Bernard Shaw. Re: Expossed slab reinforcement 2Dec 25, 2009 1:55 pm Where you are coming from is where you are going to... Re: Expossed slab reinforcement 4Dec 25, 2009 4:11 pm Hi jw What did your builder do when this was spotted? Is it an easy fix? Re: Expossed slab reinforcement 5Dec 25, 2009 4:39 pm If there is one exposed then I susspect there are a few more very close to the surface... Minimum cover is 50mm. Where you are coming from is where you are going to... Re: Expossed slab reinforcement 6Dec 25, 2009 4:52 pm My engineering specifies, for reinforced steel cover: Piers: 40 mm Slab on ground: 30 mm Suspended slab: 20 mm I've had the slab on ground and suspended slab poured and so far there is only one very very small crack on an internal corner of the suspended slab (that the engineer told me would occur). Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Expossed slab reinforcement 7Dec 25, 2009 6:46 pm Casa Out of interest what was the concrete strength associated with various elements. I'm tipping the suspended slab was a reasonably high strength mix to allow you such a small cover. The reason for clarifying is that by only stating cover it may be misleading to others - 20 mm would be unacceptable cover for domestic slab mixes. Sorry for the pedantry... mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Expossed slab reinforcement 8Dec 25, 2009 6:50 pm TDL - that is the reason for the variation. I was going to add... unless otherwise specified. ( mybad) Where you are coming from is where you are going to... Re: Expossed slab reinforcement 9Dec 25, 2009 7:32 pm If the reinforcement is visible/just under the surface in a setdown area (wet area) how should it be rectified? Will it be more likely then for the metal to start corroding or for the concrete to crack ![]() Re: Expossed slab reinforcement 10Dec 25, 2009 7:38 pm Yes, unless as I said, it was specified that way. Where you are coming from is where you are going to... Re: Expossed slab reinforcement 11Dec 25, 2009 8:05 pm ![]() If the reinforcement is visible/just under the surface in a setdown area (wet area) how should it be rectified? Will it be more likely then for the metal to start corroding or for the concrete to crack ![]() Good point Blue. Im seeing this a lot on slabs with insitu, step down, showers. With visable rust. Step down is around 35mm. So how is 35mm of over all cover for reo going to cover it in the shower step down. Have a look at a slab thats just had heavy rain, you see the shower step down full of water with maybe 5 mm of concrette cover. If it sits like this for say 1 month will it affect the reo eg start to rust. What is the bare minimum of concrete cover for the top of a slab as per building codes, forget the plans. Ive seen some slab plans say 20mm for on top. They tell me steel needs oxygen & water to rust or to continue to rust. So once the shower insitue is covered with water proofing then grout & tiles will it be OK? ONC hope you can shed a bit of light on the topic if you get time. Have a good night all. Cheers and best wishes KW.............. “It's just as unpleasant to get more than you bargain for as to get less” George Bernard Shaw. Re: Expossed slab reinforcement 12Dec 25, 2009 8:06 pm ![]() Casa Out of interest what was the concrete strength associated with various elements. I'm tipping the suspended slab was a reasonably high strength mix to allow you such a small cover. The reason for clarifying is that by only stating cover it may be misleading to others - 20 mm would be unacceptable cover for domestic slab mixes. Sorry for the pedantry... Concrete strengths Piers/footings: 20 MPa Slab on ground: 32 MPa Suspended slab: 32 MPa I suspect the suspended slab does not need as much cover since it (should) never wet. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Expossed slab reinforcement 13Dec 25, 2009 8:07 pm ![]() If the reinforcement is visible/just under the surface in a setdown area (wet area) how should it be rectified? Will it be more likely then for the metal to start corroding or for the concrete to crack ![]() Wet areas get waterproofed, so they may be OK with minimal (or no) cover. Demolition August 2009, Construction Started September 2009, Completed December 2010 Re: Expossed slab reinforcement 14Dec 25, 2009 8:20 pm Setdowns are to allow a topping to create falls to waste. The slab spec will include the setdown and the detail will require the mesh to contour the minimum cover. Phew... intoxicants and all ![]() ![]() But did it make sense ![]() Not OK with no cover... why would there be reo in concrete... Plenty corrode and blow the tiles off. Waterproof membranes prevent ingress from the top. 200um builders plastic from the bottom is to stop ingress from underneath. All this conjecture is for what? To fatten the allowable stuff ups? Why not just have a rule that says if it is not to spec take it out ![]() That might change the slack ar*e mentality. Where you are coming from is where you are going to... Re: Expossed slab reinforcement 15Dec 25, 2009 8:28 pm ![]() If the reinforcement is visible/just under the surface in a setdown area (wet area) how should it be rectified? Will it be more likely then for the metal to start corroding or for the concrete to crack ![]() You mean how would it be resolved? Cut, remove and re-instate is the only way. Where you are coming from is where you are going to... Re: Expossed slab reinforcement 16Dec 25, 2009 8:55 pm ![]() ![]() If the reinforcement is visible/just under the surface in a setdown area (wet area) how should it be rectified? Will it be more likely then for the metal to start corroding or for the concrete to crack ![]() Wet areas get waterproofed, so they may be OK with minimal (or no) cover. The reinforcement is protected from corrosion by the alkalinity of the concrete. A passive oxide layer is formed around the reinforcement in reaction to the concrete. This alkalinity of the concrete gradually neutralises and therefore no longer protects the reinforcement (carbonation of the concrete) - this takes decades though. So the right concrete mix provides the perfect protection against steel corrosion and all you have to get right is the cover - easy peasy. Waterproofing agents are not a replacement for good concrete placement. mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Expossed slab reinforcement 17Dec 25, 2009 9:06 pm ![]() ![]() ![]() Carbonation is aided by cracks, moisture ingress, atmospheres heavy in carbon (cities) Acid ground water and rising saltwater tables are a big issue and will be bigger in the future. just have a look at the preventitive measures that are taken in commercial properties. Onc Where you are coming from is where you are going to... Re: Expossed slab reinforcement 18Dec 25, 2009 9:13 pm ![]() Just have a look at the preventitive measures that are taken in commercial properties. Yep...like hanging an engineer out in a bosun's chair to take core samples from a water reservoir outlet tower... ![]() ![]() mmm....donuts Homer Simpson 1956- Links: Site Costs Ready Reckoner | H1 Addiction Medical Advice | Château TDL: The Backyard Re: Expossed slab reinforcement 19Dec 25, 2009 9:16 pm ![]() Why not just have a rule that says if it is not to spec take it out ![]() That might change the slack ar*e mentality. ![]() ![]() ![]() Re: Expossed slab reinforcement 20Dec 25, 2009 9:17 pm The concrete would have achieved 50mpa and likely had been treated with anti-carbonation solutions after cure. ... as well as used additives to prevent ingress during placement ![]() Where you are coming from is where you are going to... Thank you!! I thought it was a bit odd to have the cages at that depth, I'll check with the engineer. Thanks again 2 4241 Hey There. No problems re jumping in. 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