8 or 10 inches ?

[Sp@ce_d]

Thinking of using one of these for concrete pier for the EQ6.

POSTAL TUBES - DEFENDA SUPER STRONG 10" Wider Diameter - FREE DELIVERY

A. Is 8 inches enough, I'm tempted to go for 10

B. Has anyone else used one?

C. Anyone see a problem/disadvantage with this idea?

[pete_l]

If it was me, I'd buy the 8 inch. Then the supplier would have to ship it to you - hopefully packaged in a 10-inch .

Seriously, we recently had some new carpets and the cardboard cores in the centre looked massive. When I whipped out my ruler I discovered that they were only a 4 inch inside diameter. Now, that is too small for a concrete pier, but on that basis I'd go for an 8 inch I.D. That seems wide enough that the threaded rods you'll use won't be too near the edge. Also, a 10 inch tube will need 50% more concrete.

Q: The sides don't look very thick - 3mm. Will they support the weight of concrete once they get soggy?

[ Update: 8 inch diameter, 2m long is about 1/16 m³. (63 litres). Reckon on concrete weighing about 1.75 tonne/m³ is just over 100kg of goop. All that weight is bearing on the bottom of the tube. ]

[Sp@ce_d]

Q: The sides don't look very thick - 3mm. Will they support the weight of concrete once they get soggy?

[ Update: 8 inch diameter, 2m long is about 1/16 m³. (63 litres). Reckon on concrete weighing about 1.75 tonne/m³ is just over 100kg of goop. All that weight is bearing on the bottom of the tube. ]

That is one thing I'm not sure about.. I was planning on painting it with a waterproof paint/sealant/glue or/and using some of the heavy blue plastic damp proof I have.

[Tinker1947]

It will rot away being cardboard this won't take to long, there by leaving a 3mm gap all round the concrete pier and i would think allow movement...??

[yesyes]

I was under the impression that the OP wanted to remove the cardboard after the concrete had set...

[Sp@ce_d]

Yes I was thinking more of a concrete former.. plus even with a plastic pipe you wouldn't want to have too much below the surface so you get a good bond between the concrete in the "Plug" and the tube.

The worry is though that it may not support the weight in the tube long enough to set. Maybe the plastic tube is the way to go after all.. just haven't found an 8" length shorter than 6mtrs and less than £110. let alone going to 10"!

[Gina]

I used a 7.5" postal tube but it was over a quarter of an inch thick. It came as packaging for plumbing supplies and was over 2m long - very stout. That stood up very well to the wet concrete. I pulled it off after a week or so when the concrete had well hardened off.

[Chris]

Might be worth checking out your local civil engineering merchant, this is where I got a 2.1m plastic drainage tube from with a diameter of 170mm for 10 quid, this was an off cut but the whole 6m pipe was still only 30 pounds.

[Seme]

For my pier iv'e gone for 250mm 1.5m Spiral Ducting with a 250mm - 200mm Reducer a bit over the top.

But i have got a 50mm Drain Pipe going up the middle to pier top for the cable run.

That goes upto 2 x 12mm steel cnc cut plates.

Ducting i got from Ebay £23 free delivery.

[Sp@ce_d]

Might be worth checking out your local civil engineering merchant, this is where I got a 2.1m plastic drainage tube from with a diameter of 170mm for 10 quid, this was an off cut but the whole 6m pipe was still only 30 pounds.

Good price.. I found a 3m piece of 8" at the local Jewsons in the end. Let me have it for £30 as the end had a bit of damage.. so it's now sitting in a metre cube of concrete

For my pier iv'e gone for 250mm 1.5m Spiral Ducting with a 250mm - 200mm Reducer a bit over the top.

But i have got a 50mm Drain Pipe going up the middle to pier top for the cable run.

That goes upto 2 x 12mm steel cnc cut plates.

Ducting i got from Ebay £23 free delivery.

.. and I thought my £30 was a good deal... had fun drilling my 10mm steel plates last weekend too.. was a good excuse to get a bench drill

[Astrokev]

I'd second the idea of trying to source spiral air-con ducting. I was lucky and managed to pick up some FOC from my last company, currently taking up space in my shed waiting for the day I decide to start on my observatory. May be worth trying ebay or local scrap yards?

[Gina]

I tried really hard to source some of that when I was about to build my pier it would have been absolutely ideal IMO. Still, my pier turned out alright in the end

[laser_jock99]

I went for 9" dia steel tube if that helps - cost about £100 from local steel stockist. Rock solid.