Sheffield bike stands in postcrete

[PeteMars]

I've used postcrete to embed the bottom 20-30cm of my Sheffield bike stand. It hardened up nicely. A week later though and, the stand had a wobble and a hard tug willslide the post up a little from its base. Incidentally the posts have no flange at the bottom and so I thing I could prob slide them out now.

Did I do installation wrong or should I just have used concrete?

Thanks

 

[Munroast]

could of just drilled a hole through the bottom and shoved something like an M10 bolt through, then it would never move - even if you had just flattened the end a bit with a sledge hammer - it doesn't take much to stop them moving

not sure what you can do now - take it they are galvinised so they won't rust into place

 

[Harry Bloomfield]

A week later though and, the stand had a wobble and a hard tug willslide the post up a little from its base.

Is that a crack, running front to rear, through the rack? If so, that suggests your postcrete was far too shallow in depth, and had no strength to resist movement of the rack.

 

[PeteMars]

The surround ground was clay earth so bolting on wasn't an option... its not a crack , just a gap in stone covering an old membrane. The postcrete is set in soil and those 'kerbs' are just set there to retain stones a bit.

Sounds like you both expected postcrete to be absolt solid and using concrete wouldn't have made a difference? Because I can dig it out and redo...

 

[freddiemercurystwin]

Concrete is stronger than postcrete, they are not the same, the ingredients are different and designed to cure fast, you would (or should) only really use postcrete when you have to or to save mixing it properly before curing, if you have the space to mix concrete that would be better. But there's no easy fix, it's not going to get any better. If you did a fence post the post would (or should be) about 600mm bellow ground which is a fair bit of concrete, sounds like you have less than half that and the tubes are smooth and barely expand unlike timber posts. Postcrete should be saved for fence posts even then I'd be uneasy following the postcrete instructions to the T it doesn't rub well for me, I've only ever mixed it first before hoofing it into the hole.

As mentioned one or two bolts fixed through the ends of the tubes underground to give it some better grip would help and the concrete should be at least 100mm deeper than the tube ends so your holes should be about 400mm deep assuming 300mm of the tube is supposed to be below ground.