Browse Forums Paving & Concreting 1 Sep 06, 2011 9:33 am Hi all, I want to know if I can put a new slab over and existing slab to raise the floor height. The existing slab is only a few months old, but the builder has poured it at a level that means we will require a step to get in to our living room. The current difference in level is 255mm (plan says 100mm) So I am wanting to pour a new slab over the existing one to raise it up to the specified 100mm difference. That means our rear yard concreting will be at a better level and we wont have to dig out the drains to reset them at a lower level. http://i104.photobucket.com/albums/m184/cgem21/garagefloorlevels.jpg Also, Do I need to lay anything between the slabs or can I just have an extra 150mm thick slab poured? I was thinking that perhaps I'd need a few holes cut in the existing slab to have footings or piers dug to make sure the weight doesn't sink the level too much in the future? Anyone have any ideas about how to raise this floor? FWIW I thought it would be wasting money to rip up the existing slab, thats why I want to put the new one straight on top. Thanks in advance Re: Slab over existing slab? 2Sep 06, 2011 1:26 pm Just pour over the top, Throw down some filll dust to save on concrete, scrape a few thickened beams in and cover with plastic. If the existing slab is already piered properly i wouldnt bother with new ones.... Re: Slab over existing slab? 3Sep 06, 2011 3:01 pm Wouldnt a step be cheaper ? Why would you raise the level of the whole garage floor when you only need steps? Also, the bearing capacity of the garage slab edge beams may not take into account the added weight.... be very carefull here. Sometimes it is necessary to bite the bullet now and pay the extra bucks to rip out the old slab and re-pour , OR, add steps (much simpler). Suburbia is where the developer bulldozes out the trees, then names the streets after them. Re: Slab over existing slab? 4Sep 06, 2011 3:24 pm Chris, I'm waiting on quotes to do similar to the exterior slab areas....alfresco, front porch and laundry porch as the builder did something similar to yours. I've emailed Onc and got recommendations from him so I know if the concretors are BSing when they come to quote, maybe he could help you too? The builder is not admitting to the mistake although he did come back and build a step from house to garage, which to my way of thinking is admitting there 'is' a mistake...how can the step be too high at one door and not at the others? This garage step is ?acceptable and only affects foot traffic, although as far as I know they only placed bricks on the garage floor and tiled over them!!! I suppose time will tell? Topping a slab can sometimes cause a drumming effect and that's what I was trying to avoid. Once the slabs are topped then tiles can be laid and I won't have to look at yucky, stained, gouged concrete any longer...not holding my breath just yet though!! Re: Slab over existing slab? 5Sep 06, 2011 3:38 pm First thing that came to mind while reading your issue is also the bearing capacity of any of the components of the existing slab, as well as the soil. Concrete is very heavy. Although, if you drill the exisitng slab to pour the new piers, maybe that's not an issue. This obviously calls for a structural eng (a good one). In fact, talk to a few of them, at least over the phone. BTW, by "foam" on the sketch, do you mean expansion joint material (like the now somewhat famous Abelflex )? You also say that the builder poured it at 225, but the plan said 100 - so isn't he supposed to fix this? And how big is the garage (/ new) slab? My signature is distracting people from my wise posts ... Re: Slab over existing slab? 7Sep 07, 2011 10:00 am You have the right idea from your sketch. I would be asking questions of the builder and coming to a compromise. Assuming the garage slab was done right and has mesh then weight should not be a problem. 1m2 of concrete 100mm is around 250kg. A car could weigh 500kg on each wheel much smaller surface area than 1m2. I often see garage floors lower than house slabs not sure why. However structural engineer is cheap insurance if doing it yourself. Good luck Pulpo Re: Slab over existing slab? 8Sep 07, 2011 10:30 am The garage slab was poured separately from the rest of the house ( around 5-6 months later). I have no idea if it has edge beams or not. I know there is mesh on it but I have no clue about anything else. On the left side (looking in ) is the house and the right side is garage wall that is retaining wall to 1200mm high double brick with steel starter bars and concrete fill cavity. xanthrope, I don't want the step, that is the point. The original design does not have a step, just a level of 100mm lower than the house. A 100mm step up is acceptable to me, a 255mm that requires an extra step is not. The original design was to allow drive through access to the rear yard. The need for a step hinders that IMO. This will be the most used entrance to our house and I want it as I agreed it should be in the plans. Lex, yes expansion joint material (abelflex or similar ) Re: Slab over existing slab? 10Sep 15, 2011 4:25 pm I had a similar experience about 3 years ago. Slab for house and garage were poured (although both were done at the same time). Design was for garage floor level to be 100mm lower than house. The drop of only 100mm from house to garage was so that we could have wheelchair access into the house, from house to garage, garage to backyard etc. The concretor put the garage slab lower than it was supposed to be - don't remember the exact level, but think it was about 300mm below the house. (It was definitely at least 100mm lower than it was supposed to be.) It took quite a lot of persistence to get it to happen, but the builder eventually rectified the problem. Basically, they put more concrete over the top to bring it up to the required level. The second pour was done after framing was in place so the additional layer of concrete has a smaller top area than the first garage slab. (Formwork was put on the inner side of the framing for the garage walls.) REALLY frustrating when you specify levels and things don't get done according to the design!! I couldn't believe how difficult it was for people to get their heads around the idea that the drop of 100mm between house and garage was the _maximum_ acceptable difference in level...because wheelchairs aren't designed for steps!!! (And it's not possible to lift a powered wheelchair up a step unless you have a hydraulic lift. Strange, I know, but we really didn't want a lift at our front door...) One corner of my shed slab will be directly over a 1400mm diameter concrete soakwell. Is it feasible to fill the soakwell with concrete then lay the shed slab over the… 0 666 4 11221 1 19742 |