Bell shaped holes?

[Bleedin Thumb]

Mate those calcs are fine except you have failed to take off the volume of the post in the hole ...... you may just end up with a few bags of conc left over.

You will be ok setting it up first and leaving but honestly you have done all the hard work - use rapid set concrete mix (forget mixing your own) and you can set it then and there on day one.

all you have to do is plumb the posts, thats the easy part.

[demuire]

Thanks heaps everyone If I use rapid set concrete mix (this is the all-in-one premix stuff like from Bunnings?) wouldn't I need like a lot of bags? The shed builder I called yesterday recons I'd need like 6 bags (20kg each) per hole, which is like 24 bags! At like $25 per bag that could get expensive really quickly... Or maybe his estimations were all wrong... It does sound like a hell of a lot of concrete...

I try and stick to about 0.7:1 i.e. if you put in 10lt bucket of cement you put in about 7 litres of water. The more water the weaker the mix. Being post holes you could probably get away with a dryer mix (less water).

Do you mean cement or concrete? I'm getting a little confused

[demuire]

Found on another thread (https://www.woodworkforums.com/showthread.php?t=25229) that each bag of all-in-one premix makes like 0.01m3 of concrete, so I'd need like 20 bags.

I can't remember how much the bags are (for some reason I thought they were $25ea) but on that thread it indicates that perhaps it's closer to $6ea. That's still $120 worth of premix...

*edit* found a site that sells stuff (http://www.centenarylandscaping.com/...GravelSand.htm), and for "concrete mix" they have 10mm and 20mm size, which should I be using?

[ian]

That volume (0.2m3) sounds about right.

From memory you need about 16 bags of concrete (20kg) per m3, so you will need 4 bags. Also when using all in mix (sand and gravel already mixed) you should use 5:1 or even better 4:1.

I too get about 0.2m³ of concrete
But I make it more like 112 (20kg) bags of premix to the m³ (=2400kg of finished concrete) — but read the bag to be sure — so you'll need about 20 bags of the premix — you don't need extra cement. Buy at least 30 bags (to allow for over break in the hole) and return what you don't use.

If you can't get a small mini-mix load, buy the bags and hire a mixer to mix it in. If I'm doing my sums right, you want to add just over a litre of water per bag of premix — this should give a water:cement ratio of about 0.6


ian

[scooter]

On the 20kg bags at work I'm pretty sure it says one bag will do 0.2sq m of concrete at 50mm thick.

That equals 100 bags to the cubic metre.

[Bleedin Thumb]

Demuire - have you taken the displacement volume of the post off the calculated concrete volume.

I look at that photo and KNOW that you wont use 20 bags. I would say 8 bags - 12 bags MAX.


BTW you dont use a mixer with Rapid Set - read the instructions on the bag.

[Vernonv]

Do you mean cement or concrete? I'm getting a little confused

I mean cement. i.e. the ratio of cement to water should be 1:0.7 i.e. 1 cement to 0.7 water.
So you're mixing (assuming your NOT going down the rapid set or premixed bag route) is 4 all-in (sand and agg), to 1 cement, to 0.7 water.

Quote:
<TABLE cellSpacing=0 cellPadding=6 width="100%" border=0><TBODY><TR><TD class=alt2 style="BORDER-RIGHT: 1px inset; BORDER- 1px inset; BORDER- 1px inset; BORDER-BOTTOM: 1px inset">Originally Posted by Vernonv
That volume (0.2m3) sounds about right.

From memory you need about 16 bags of concrete (20kg) per m3, so you will need 4 bags. Also when using all in mix (sand and gravel already mixed) you should use 5:1 or even better 4:1.
</TD></TR></TBODY></TABLE>
But I make it more like 112 (20kg) bags of premix to the m³

Sorry, I should have written 16 bags of CEMENT per m3 not concrete.

[demuire]

Demuire - have you taken the displacement volume of the post off the calculated concrete volume.

I look at that photo and KNOW that you wont use 20 bags. I would say 8 bags - 12 bags MAX.


BTW you dont use a mixer with Rapid Set - read the instructions on the bag.

No, have not taken that into mind - but am keeping in mind that I'll need extra for the "bell" (more like ball, haha), and for the top (the cement needs to be shaped into a cone shape at the top so the water will run away from the posts right?). I'm also unsure as to how far the posts stick into the holes...

BUT, assuming the posts sit 500mm deep, from memory they are 75x75, I think that means they'll take up 0.003m3 each, which equates to 0.012m3 all up.

0.2 - 0.012 = 0.18m3, which isn't much less at all...

BTW, on this website: http://www.landscapesonline.com.au/c...eid=1123478519
It lists the post mix concrete as "for simple non-structural concreting". Does that mean it's not as strong? Is a carport footing considered "structural"? I think I'd prefer to use normal concrete as it's cheaper and I have no idea how slow I'll be in putting the concrete in, and setting time isn't much of an issue for me I don't think - as long as it's strong...

[Vernonv]

BTW, on this website: http://www.landscapesonline.com.au/c...eid=1123478519
It lists the post mix concrete as "for simple non-structural concreting". Does that mean it's not as strong? Is a carport footing considered "structural"? I think I'd prefer to use normal concrete as it's cheaper and I have no idea how slow I'll be in putting the concrete in, and setting time isn't much of an issue for me I don't think - as long as it's strong...

Post mix is normally a weaker mix. Are carport footings structural? I don't know for sure, but is the relatively small increase in cost to use normal concrete, worth the risk of problems later on?

I personally would just get the 4 bags of cement and the appropriate amount of all-in (i think it's 1.2 or 1.3 x the volume) and mix it on site.

[Bleedin Thumb]

Mate your going to pour a reinforced slab over the top anyway. you just want the post footings to hold it in place until your pour. If youre short - make it up when you pour your slab.

AFA putting a cone on the top - just think about how usless that would be under a slab.

[Barry_White]

T?

Also, would it be safe to put up the frame of the carport by itself (not concreted in) and have it left for a week or so before pouring the footings in? It's just that I doubt we'd have time to square and level it all up properly this weekend after we put it up... I'm thinking that it's sort of like a big table (without the top so the wind shouldn't blow it away), and as long as the bolts are done up it should just stand there by itself and not fall over...?

It would be OK to put just the frame up just don't put the roofing on until the footing concrete has gone off. This certainly is the best way to get every thing plumb and square.

[demuire]

Mate your going to pour a reinforced slab over the top anyway. you just want the post footings to hold it in place until your pour. If youre short - make it up when you pour your slab.

AFA putting a cone on the top - just think about how usless that would be under a slab.

Apparently I need to get council to come and approve it before I can pour the slab on top (I think). So I think I'll need at least a small cone...

[Barry_White]

Apparently I need to get council to come and approve it before I can pour the slab on top (I think). So I think I'll need at least a small cone...

I think you would find that if it was poured in combination with your footings they would require an engineers certificate for the slab, but a separately poured slab shouldn't matter as your footings are designed to hold your carport down/up so the slab shouldn't come into the equation.

[joe greiner]

I still have some distaste for this detail. I can't see it clearly enough in the pic, but there may be something shown between the top of the footing and the bottom of the slab. Without cushioning, the slab is subject to cracking in the vicinity of the post under vertical loads inboard on the slab. About 12-25mm of something very soft, like styrofoam with a crushing strength on the order of 1 psi (7kPa, I think) should help.

Joe

[demuire]

... and I have a storm water connection