Browse Forums Building A New House 1 Aug 11, 2009 11:33 pm just wondering how long most builders leave the slab to dry before progressing with brickwork? we thought it was 4 weeks but our builder has commenced after 10 days. is this too soon? thanks about to build our first home! Re: time for cement slab to dry/cure? 3Aug 12, 2009 9:33 am Firstly it also depends on your MPa and the mix, ie whether they used any accelerator in the mix. Higher MPa means earlier work on the slab. In our case we have 25 MPa with 10% accelerator, the Builder drove a 4 tonne machine on the slab (Rubber Tracks so it spreads the weight) after 7 days. No visible cracks bar one hairline which looks like a shrinkage crack in the garage. Framing is starting after 10 days. However he has told me that he won't do brick work until around 2o+ days. That is because the frames generally are built on top of the slab and bear down on reinforced beams or pads, whereas the bricks are on the step down which has a lot of referred force and can cause a crack along the angle bend upwards or further up the step down into the beam. Not sure if i am explaining myself well. You did not say whether you are building full brick or brick veneer. In any case the outside course is in the same boat as for veneer. Dan C Re: time for cement slab to dry/cure? 4Aug 12, 2009 5:16 pm thanks for the replies. We arebuilding full brick. Not sure about mix etc, but we are having slab inspection this fri so might ask the inspector. about to build our first home! Re: time for cement slab to dry/cure? 6Aug 14, 2009 3:11 pm My slab is down, so I was curious about how long they will wait.... To cut out a part of the email response: "he has advised that the frame will be starting next week and the slab no longer has to sit for weeks to set like the slabs of long ago used to." I don't understand, are they now using some magic new formula? Re: time for cement slab to dry/cure? 7Aug 15, 2009 4:30 pm webbiegareth I don't understand, are they now using some magic new formula? Yes the magic formula is get the job done and get out of there Additives don't make concrete any stronger, and rapid 1, 2, 3 will make them more brittle. onc_artisan Where you are coming from is where you are going to... Re: time for cement slab to dry/cure? 8Aug 15, 2009 9:50 pm Just to put a more technical slant on it. Concrete will gain 70% of its compressive strength (the strength of a cylindrical sample crushed in a test specimen) within 7 days of pouring. This assumes appropriate curing and compaction (two things that I have never seen on a residential concrete slab). Other things that happen if the concrete is appropriately cured is that it shrinks and dries in this period as well. Adding brickwork or timber framing should have a very limited effect on the slab. The predominant design for a reinforced concrete slab on ground is actually the likely settlement that will occur over the life of the slab. This is caused by drying and shrinkage or wetting and expanding of the soil beneath the slab. These are often very slow processes and will not be likely to occur in the first 28 days (the time to gain 100% strength - which actually is not the case, the concrete actually continually gets stronger, however according to AS3600 the compressive strength used in design should be the 28 day strength). Some structures that I have been associated with have had load applied to them within 1 day of having poured the concrete. These are unusual cases, however I would not be concerned. View our blog at: http://room4acubby.blogspot.com/ Re: time for cement slab to dry/cure? 9Aug 15, 2009 9:58 pm Our slab cured for 14 days before frame started and they used a mix of 20mpa, so far, so good, no cracks or hairline stress cracks, so here's hoping it will be fine. We are on day 25 since our slab pour and no sign of any brickwork yet. All good thus far! Building Thread viewtopic.php?f=31&t=13002 Site start: 8th July 2009 Handover: 11/12/2009! 5 months total build time. 40 sqs of luxuary...Bliss! Re: time for cement slab to dry/cure? 10Aug 15, 2009 10:16 pm They're building a house next door with PD and the very next day after the slab was poured they were there doing the frame. The frame was finished within the week and the brickwork commenced the next week. TBH I don't see the problem, if the surface is okay to walk on then what damage is putting the frame up actually going to do? I'm sure the hurry was hardly for the customers benefit, they just fit you in as best suits their schedule and if you wait 1 day or 1 month for the slab to cure it has nothing to do with their concern for the slab. Re: time for cement slab to dry/cure? 11Aug 16, 2009 11:59 am one_artisan - what is the purpose of accelerator? Re: time for cement slab to dry/cure? 12Aug 16, 2009 12:22 pm Well, winter concrete is slower to 'setup' (to get a finish) and since the first load to the last load cure at a different rates, sometimes we will add rapid (accelerator = rapid hard). If the conc 'sets up' at different times, it makes it difficult to 'finish' evenly. Summer conc and winter conc have slightly different additives as you can now imagine. For example : In winter depending on how many loads you have, the first will come as standard, then rapid 1, and the last might have rapid 2. Hope this helps onc_artisan Where you are coming from is where you are going to... Re: time for cement slab to dry/cure? 13Aug 16, 2009 12:28 pm Oh OK. I found the last delivery note for our concrete and it had full accelerator. I would assume then that all the loads would not have full accelerator then. What is the normal load for a truck - 5m3? Re: time for cement slab to dry/cure? 14Aug 16, 2009 12:38 pm Normally yes 5CU mtrs (if we need 5.4 we can sometimes get it in 1 load) But the last load we would organise it to be at least 3.4cu mtrs. Full accelerator, Hmmm ... we do try not to use Rapid2 and so we could be a pest to a builder by choosing not to pour on a particular day ( I have mentioned before about the moon and stuff and after all these years have a good handle on what to expect ) onc_artisan Where you are coming from is where you are going to... It's possible but a soak well is usually much larger. Your 'soak well' only holds 424 litres when full. What is your soil type? Soak wells need sandy soils. 10 9017 DIY, Home Maintenance & Repair Ditto 3M Claw, expensive but best thing I've used to date. I put two of the 11kg ones in for a 12kg mirror on the wall, and its been great for 4 years now. 4 2156 Hi, Currently building, we are on a sloping block so we have from floor level to the roof in axon cladding. Below floor level to the ground I want to put brick facings /… 0 4495 |