Casting a bell in snadmark.

[Linda K M]

Hello
I am going to build a deck, so I need to cast some footings.
I have bought an earth auger from Jula that is 150 in diameter.
I don't need the footing to go above ground level since I will have posts up to the "beam."
The ground is sand, as I live on a sand ridge.
Is it okay to cast directly into the hole or should I use a tube, considering if the frost affects the footing?
Is a diameter of 150mm sufficient?

/Johan

 

[andersmc]

It is fine to cast directly in the hole. We must assume that the sand you're on is not so loose that the hole collapses.
150 mm is enough for a deck.

 

[Linda K M]

I have heard that you would need to cast a block in the bottom so that frost heave cannot lift the pier, is this true?
Do you need to have reinforcement bars in the pier?

/Johan

 

[anaitis]

You should place some form of plastic bag/sack in the hole before you pour concrete, otherwise the concrete will be weakened.
Maybe it will work fine without it?
But it's a cheap insurance.

 

[Linda K M]

Why is a plastic bag/weight needed in the hole, what is its purpose?

 

[anaitis]

Why is a plastic bag/sink needed in the hole, what benefit does it provide?

It keeps the concrete mixture where it should be, i.e., where a pillar is to be formed.

 

[andersmc]

It keeps the concrete mixture where it's supposed to be, i.e., where a footing is to be formed.

You mean otherwise the concrete will seep into the ground and disappear?

 

[anaitis]

Parts of it at least, mainly perhaps the concrete paste and the cement/water mixture

 

[Linda K M]

Isn't it good if a little concrete spills out to the sides so it has better grip?

 

[H_L]

The sand risks drawing out moisture from the concrete, causing the concrete to cure too quickly and thereby become weakened.

 

[Linda K M]

Is reinforcement needed in the foundation?

 

[andersmc]

It will probably be fine anyway, but reinforcing is quite a small hassle, so I think you can do it just to be on the safe side.

 

[Danneå]

Use plintrör, they don't cost that much....

I would at least throw some concrete in the bottom, then you press in the rebar and the pipe in place and fix them. When it has set, pour in the rest of the concrete to the plint.

 

[Linda K M]

It became 200 mm plinth pipes and 1.2 m down into the ground with rebar. I have drilled and dug some today, 6 holes, so now there are only 7 holes left to drill and dig, so the casting will be next weekend.