Question for those in the concrete / building game

[Spada]

I'm weighing up my options for the shed at the moment. My current shed is 9m x 7m, with a 3.5m pad along the outside length of one wall. The external concrete pad is 50mm lower then the shed slab.

Option 1 - build a carport type roof over the outside slab. This is certainly the cheapest and easiest option, but does not really give me a secure area and anything parked there is still out in the elements to some degree.

Option 2 - extend the shed wall out to fully enclose the external pad. Obviously a lot more work and cost, but would increase my shed size 9m x 10.5m. The biggest problem with this option is the 50mm height difference in floor finish.

My question is about the practicality of a 50mm screed over such a large area (3.5m x 9m), what would the mix be?, would it need to be bonded to the existing slab somehow?, would it survive for long?, are there products suitable for this?

So far, I keep leaning towards option 1, but just want to fully consider option 2.

Any tips or ideas from those in the know?

[GBC]

You are extending the short dimension. Is it a portal frame shed? Do you have the structural ability to go that way without reengineering the existing structure?
7 x 3.5 x 50mm is a difficult thing to top with a slab which is both functional and cost effective. In my world the structural engineer would probably have us do a shrinkage compensated bonded screed which is going to work but isn’t going to be making friends with the wallet. I’d seek professional advice from a company such as Parchem who have reps and they are free.
50mm unbonded concrete is a bit of a biscuit and can crack up under point loads and differential heating. In a domestic situation you may get away with it if it is designed well and installed well. 50mm is the grey area between bonded and unbonded slabs unfortunately.

[Rhojef]

Have you thought about a 40mm paver on a 10mm bed. Wouldn't be oil friendly but would be fine for parking or storage.

[Spada]

You are extending the short dimension. Is it a portal frame shed?

Yep, it's a portal frame shed, but It is the long (9m) side I was considering extending, so basically creating a workshop off the side of the shed. The shed roof is 2.7 at the gutter, so I could fall the extension from the existing roof line out and still have 2.4 at the new wall. Just means that 2 of the posts for the existing frame will now centre of the room on that side of the shed. I've got my head around most of what is required for both options structurally, it's the slab height difference that appears to be the most challenging issue ? Perhaps an option might be to ramp the height change, but I'm not that keen on the idea of an uneven floor.

[Spada]

Have you thought about a 40mm paver on a 10mm bed. Wouldn't be oil friendly but would be fine for parking or storage.

Hadn't considered that, but the idea has some merit.

[Fizzie]

Or same idea but a timber deck directly off the existing slab

[Spada]

Or same idea but a timber deck directly off the existing slab

Timber is my thing (my chippie father taught me a lot), but i'm not sure I could make that work very well. Maybe some 30mm steel box section fixed down as batons with yellow tongue screwed down? Not sure it would stand the test of time in my shed environment though.

[tryagain]

Pavers would be a cheap option, especially as if it's just for a shed then you can often get used ones cheap/free on gumtree.

[trinityalyce]

Option 1 - build a carport type roof over the outside slab. This is certainly the cheapest and easiest option, but does not really give me a secure area and anything parked there is still out in the elements to some degree.

I have no idea about anything, but could propose an Option #3...

Take Option #1, but instead of leaving it an open carport, screen it in. Our garage space front and back is essentially like that and it works surprisingly well.

Just food for thought, and might be a compromise between wanting something somewhat enclosed without having to fix the floor height issues or extend the exisiting shed.

[Rumpig]

It’s not a lot of concrete required to top it so cost would be minimal really, if it were my place i’d take a punt it should be ok at 50mm, just get a smaller rock sized mix over normal slab concrete and see how it lasts...assuming weight going on it is just foot traffic mostly. Maybe they do a fibre mix that is better suited to the job?...probably best ask your local concrete supply mob what they recommend for doing the job.

[Spada]

Take Option #1, but instead of leaving it an open carport, screen it in.

That would be my plan if I go the carport option, screen the long side and put a gate on the front.

It’s not a lot of concrete required to top it so cost would be minimal really, if it were my place i’d take a punt it should be ok at 50mm, just get a smaller rock sized mix over normal slab concrete and see how it lasts...assuming weight going on it is just foot traffic mostly. Maybe they do a fibre mix that is better suited to the job?

Thats what I was thinking, use maybe 5 or 10mm agg with a fibre blend ? just thought I would throw it out there and see what people think.

[Rumpig]

That would be my plan if I go the carport option, screen the long side and put a gate on the front.

Thats what I was thinking, use maybe 5 or 10mm agg with a fibre blend ? just thought I would throw it out there and see what people think.

recently saw an extension on a house that had part of the old patio slab (abit smaller area then you are doing) being topped aswell as the new addition being poured at same time....pretty sure the topping part was lucky to be 50mm thick at best (closer to 35mm in places I  reckon)....seems to have held up so far (several months down the track). Not sure if they used anything special when it got poured, just looked like a normal slab mix to me.

[rockrat]

Hadn't considered that, but the idea has some merit.

You can some pretty large concrete paving slabs, up to 750x750mm or 900x600mm that you could lay over the existing slab.  Check out austwide2000.com.au for some ideas.

[dno]

Cut a strip Eg: 600mm wide out between the two slabs then pin and pour new conc
ramping it up the meet the higher level. Not perfect, but possibly cheap and cost effective.

"Goodbye"

[Nomad]

I remember looking at a house where the bloke that owned it poured individual concrete pavers (for want of a better term) that were about 1m x 1m over the slab and then had some type of grout between each paver.

No idea if its cost effective or not but it did look pretty good
 

[Beachman]

We had a new Driveway put in 6 years ago and the concreter gave me 2 options

•   Spend an additional $2K for ripping up and dumping the existing concrete tracks which were a minimum 100mm thick
Or
•   Drill some holes into the existing concrete tracks and hammer small pieces of Rio into the holes for the new concrete to bond with and pour over it.

Went the 2nd option and no problems to date

[Nifty1]

I won’t buy in to the floor discussion, but after costing a similar project I found that the bulk of the cost is in the slab and roof. Walls are real cheap in comparison.

[Jeepers Creepers]

Are there any concreters on here around the Ipswich area? (Hope you don't me hijacking Spada.)

I've got a fair sized area to do in a few months.

Area 1. 8 x 5 metres @ 125 thick.
Area 2. 12 x 6 metres @ 100 think and adjoins area 1.

[KeithB]

Spada,
After selecting the best concrete brew plus considering the dowels that Beachman has suggested I'd be inclined to use a bonding agent like Epirez or Bondcrete between the new and the old work. Both are used to make new concrete to stick to old.

[duggie]

Talk to your concrete supplier and ask about a shot-crete/fibre mix . Last for years without cracks and works at 50mm thickness.

[achjimmy]

It’s not a lot of concrete required to top it so cost would be minimal really, if it were my place i’d take a punt it should be ok at 50mm, just get a smaller rock sized mix over normal slab concrete and see how it lasts...assuming weight going on it is just foot traffic mostly. Maybe they do a fibre mix that is better suited to the job?...probably best ask your local concrete supply mob what they recommend for doing the job.

Yeah that mix that uses fiber strands as opposed reo

[V8ute]

Are there any concreters on here around the Ipswich area? (Hope you don't me hijacking Spada.)

I've got a fair sized area to do in a few months.

Area 1. 8 x 5 metres @ 125 thick.
Area 2. 12 x 6 metres @ 100 think and adjoins area 1.

Heaps mate, Im not far from your joint, let me know when you ready.
 :cheers:V8ute

[BaseCamp]

Are there any concreters on here around the Ipswich area? (Hope you don't me hijacking Spada.)

I've got a fair sized area to do in a few months.

Area 1. 8 x 5 metres @ 125 thick.
Area 2. 12 x 6 metres @ 100 think and adjoins area 1.

I can personally recommend Scotty Macs Concentrating, (based in Ipswich)..

Pumped in 120mtrsq of the good stuff, (32mpa), for a structural slab at my site, inner BNE last Dec...

Scott McConochie
0417 637 845



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[Fizzie]

Pumped in 120mtrsq of the good stuff, (32mpa), for a structural slab at my site, inner BNE last Dec...

Ouch!!!

Having just had 2.4m of 25mpa poured for a van slab, I shudder to even think of the $$$$$$$

[BaseCamp]

nah...   from memory it's not a whole lot more per cubic metre..  and well worth that imho..

I recall circa $400-$600 more cost? - for 3.2 cement truck loads worth of the higher mpa stuff...

But strictly speaking, if its concrete for a garage? .. then I guess 75mmD, and 22mpa will suffice..  (I just hate seeing cracks in a slab)...   

Hopefully I won't see any?   My job included massive toe and heel footings to support 2.6mtrH 300 series core filled block retaining walls....   The footings were doweled into the slab....   Loads of mesh etc..   All engineered with Form 16 Cert.

(And that was just for a 6 car carpark...  BUT future proofed,, to build on some time in the future?..).

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