Casting foundation for flagpole

[Sanderson_2]

Hello!

I've never cast or worked with cement/concrete before. Now I have bought a 12-meter fiberglass flagpole that needs to be set in a concrete foundation.
We have dug a hole 120 centimeters deep, and the diameter of the foundation should be 35 centimeters.
I didn't find a casting tube in the right dimension at a reasonable price, so I'm going to build a casting mold out of wood.
Is there anything I should consider in the design of the wooden mold?

Next step, when I mix cement and pour, I've been advised to buy cement bags and then mix cement + water + gravel/gravel-sand. What are your thoughts on this? What mixture is optimal?
Is a loose mixture or a firm mixture better?
There is access to a cement mixer, which I believe will make things easier.

Then I suppose I can pour the cement mixture into the mold. Then insert straight rebar into the mix and then place the flagpole mount at the top. I also assume that I need to attach that mount to a board so it can be adjusted in height to ensure it is level.

Is there anything I've completely misunderstood? Feel free to share your thoughts.

Kind regards

 

[Nissens]

Hello!

I have never cast or worked with cement/concrete before. Now I have bought a 12-meter fiberglass flagpole that needs to be mounted in a concrete foundation.
We have dug a hole 120 centimeters deep and the diameter of the foundation should be 35 centimeters.
I couldn't find a casting tube in the right dimension at a reasonable price, so I'll build a casting mold out of wood.
Is there anything I should consider in designing the wooden mold?

The next step, when I am going to mix cement and cast, I have been advised to buy cement bags and then mix cement + water + gravel/sand-gravel. What are your thoughts on this? What mixture is optimal?
Is it better with a loose mixture or a firm mixture?
There is access to a cement mixer, which I think will help.

Then I assume I can pour the cement mixture down into the mold. Then insert straight reinforcement bars into the mixture and then put the flagpole mount at the top. I also assume that I need to attach the mount to a board so that it can be adjusted in height to make it level.

Is there anything that I have completely misunderstood? Please share your thoughts.

Regards

https://bolist.se/guide/flaggstang/

 

[vectrex]

Of course, you can buy cement bags as well as sand and gravel separately, and it is especially worthwhile if you are mixing a lot of concrete.

In your case, it is about 115 liters of concrete, which would be about 9 bags of coarse concrete. You get a significantly better mix if you buy pre-mixed coarse concrete in bags. That's what I would do if I were you. Mix according to the recipe on the bag or add water until you get a fairly thick porridge-like consistency. The concrete becomes stronger with less water (but it must also be able to fill properly, so not too thick either).

 

[Sanderson_2]

Of course, you can buy cement bags, sand, and gravel separately, and it's especially worth it if you're mixing a lot of concrete.

In your case, it involves about 115 liters of concrete, which is about 9 bags of coarse concrete. You'll get a significantly better mix if you buy pre-mixed coarse concrete in bags. That's how I would do it if I were you. Mix according to the recipe on the bag or add water until you get a fairly thick porridge-like consistency. The concrete becomes stronger with less water (though it must also fill out well, so not too thick either).

Thanks for the explanations!
Is there a difference in quality when it comes to concrete? Are all these 3 types sufficient?
https://www.jemfix.se/grovbetong-c-3240-20kg/4172/9016315/
https://www.byggmax.se/ekonomibetong-p0106
https://www.byggmax.se/grovbetong-k40-p0103

One more question. When I place the casting mold in the ground, should I fill with backfill around the mold first before casting, so that it stands securely?

 

[Sanderson_2]

[link]

Thanks for the link!

 

[Ville_Vessla]

I just poured the concrete into the hole for our 12m 13 years ago and it's still straight. No forms or anything.

 

[Sanderson_2]

I just poured the concrete into the hole for our 12m 13 years ago and it's still straight. No molds or anything.

Due to a very rocky plot, we had to abandon the shovel and call in an excavator. Which led to a rather large hole that would swallow a lot of concrete

 

[Ville_Vessla]

I managed with a narrow spade, then I had the luck of hitting rock after about a meter and drilled down some rebar with chemical anchors into the rock. I think I used around 12 bags. Don't forget the important step of inscribing the date of the casting before you shovel over the concrete. I actually bought a larger two-speed hammer drill for this project and mixed in one of those tubs that horses usually get water in, around 60 liters, well, it's called a mortar tub but is mostly used for watering horses around here.

 

[vectrex]

Thanks for the explanations!
Is there a difference in quality when it comes to concrete? Are all these 3 types sufficient?
[link]
[link]
[link]

One more question. When I place the casting mold in the ground. Should I fill up with backfill around the mold first before I cast, so that it stands firm?

Yes, all of those types are more than sufficient. The first (jemofix) and last have a slightly higher WCR value and therefore a somewhat better strength than the one Byggmax calls economic concrete. All are fully adequate for what you intend to do.

Keep in mind that concrete is heavy and there will be significant pressure on the mold when you fill it with concrete, so build your mold very stable if you're building it yourself. Alternatively, you can backfill around the mold but then it will be quite difficult to remove.

 

[-RB-]

Yes, all those types are more than sufficient. The first (jemofix) and last have a slightly higher VCT-number and therefore a somewhat better strength than the one that byggmax calls economic concrete. However, all are perfectly suitable for what you're going to do.

Keep in mind that concrete is heavy and there will be considerable pressure on the mold when you fill it with concrete, so build your mold very sturdily if you're building it yourself. Alternatively, you can backfill around the mold, but then it will be quite difficult to remove.

Well, a lower VCT generally gives higher strength and not the other way around.
https://sv.wikipedia.org/wiki/Vattencementtalet

 

[Workingclasshero]

The bottom of the hole that you cast against must be completely flat.
What can happen if you just dig a hole is that it becomes round at the bottom, then it becomes like a uniball/hip joint, i.e., a very high risk of mobility, and you want to avoid that.

 

[useless]

Is it better with a loose mixture or a solid mixture?

A firmer mixture provides stronger concrete. Keep in mind that the concrete needs to be worked down into the form so that all air disappears. Preferably with a concrete vibrator, but it also works to add a few decimeters at a time and work it down with a broom handle and tap with a hammer on the outside of the form.

then insert the flagpole bracket at the top.

Make sure to create a suspension for the bracket before you start pouring the concrete so you don't have to try and level it at the end.

One more question. When I set the casting form in the ground, should I fill up with filling material around the form first before casting, so that it stands steadily?

It will be difficult to remove the form and to tap on it during casting. Be sure to make the form stable so it doesn't crack when you fill it with a few hundred kilos of concrete.

 

[Sanderson_2]

A firmer mixture provides stronger concrete. Remember that the concrete must be worked into the mold so that all the air disappears. Ideally with a concrete vibrator, but it also works to add about a decimeter at a time and work it down with a broom handle and tap the outside of the mold with a hammer.

Make sure to create a suspension for the attachment before you start filling the concrete so you don't have to try to adjust it at the end.

It will be difficult to remove the mold and to tap it during casting. Be sure to make the mold stable so it doesn't crack when you fill it with several hundred kilos of concrete.

Thanks for the great tips!
I hope my future mold creation will be sturdy enough.

Is it preferable if I line the inside of the mold with something before I pour in the cement? So that it will be easier to remove the mold afterward.

 

[C.Lundin]

Thanks for the great tips!
I hope my future mold creation will be sturdy enough.

Is it preferable if I line the inside of the mold with something before pouring in the cement? So it will be easier to remove the mold afterward.

Upload a picture here first, and you'll get help. It's quite easy to see whether it will hold or not. (Which it almost always does, molds are usually over-dimensioned. Which is admittedly better than the opposite).
If it's timber you don't plan to reuse, you can coat it with something like cooking oil. Otherwise, it's not particularly difficult to tear down if you own a crowbar.

 

[Bengt65]

The bottom of the pit you're casting against must be completely flat.
What can happen if you just dig a pit is that it becomes round at the bottom, which then becomes like a uniball/hip joint, i.e., a very high risk of mobility, and that's what you want to avoid.

Great tip there!!