Decking support in water

[lee171181]

Hi guys,

Need to replace some decking in my garden that runs parallel to a small shallow stream. The existing support posts have rotten due to the water so it all needs to be replaced.

My question is, what is the best way to install the new support posts as the ones at the front are in the water? I was planning on using wooden posts again but I think they need to be concreted somehow to protect the wood but I don't know how, - I have heard sonotubes mentioned before, but don't really know what these are or how to use them (or even if this is the right thing)?

 

[SittingBull]

Why not use a concrete post?

 

[lee171181]

I would still have the issue of how to secure it in the water?

 

[freddiemercurystwin]

Can't you cantilever the deck over the stream, you shouldn't be placing supports in the water at all. Anyway concrete sets in water.

 

[lee171181]

How far can it be cantilevered ie what distance?

Whether it is in the stream or not it is running next to it so pretty sure wherever I dig will hit water at some point so just need the best solution for securing the supports

 

[dhutch]

How far can it be cantilevered ie what distance?

Depends how you design it....

http://2.bp.blogspot.com/-arnduuU3QIE/TrWuZEFVkgI/AAAAAAAADw4/Tz5DgDwXY7s/s1600/05082010321.jpg



Daniel

 

[lee171181]

Impressive, but is there any set guidlines or general rule of thumb?

Ive heard somewhere it can be a 3rd of the overall length is that correct, e.g. if the deck was 2m long then it can only hang over 66cm? or could it be longer depending on joists etc?

 

[dhutch]

Just depends really.

Assuming its anchored well, you could proberbly manage about
- 1ft on 2*3
- 18inch on 2*4
- 2ft on 2*6
Beyond which your going to have to start getting a bit more clever then just a lump of wood.

The risk then is that you lift the anchor point (ie, the opersite end) out of the ground, and the failure mode may become more interesting if it isnt strong enough or does become rottern.


Daniel

 

[freddiemercurystwin]

Generally you are about right on the 1/3rd overhanging. That's won't do it for you presumably?

 

[john4703]

Build a coffer dam round where the post is to go using sandbags, bale out the water, or if you have the cash hire a pump, dig a hole in the bottom of the stream and set the concrete post in concrete, leave the sandbags in place for a few days until the concrete is hard then move them to the next post position. Concrete sets under water and as long as the stream is not deep sandbags will keep it dry enough for you to work, you will get wet.

 

[lee171181]

Generally you are about right on the 1/3rd overhanging. That's won't do it for you presumably?

not realy, thats why the support post has to go in the water! Like the idea of building a sort of dam round it tho so looks like thats my best solution.

What would be the best way to encase a wooden support post in concrete that come above the ground ie so the concrete is higher than the water level? Need like some sort of cylindrical cast to set the post and concrete in?

 

[dhutch]

Still struggling to invisage exactly what is required here.

Have you considered driving steel tubes in as a foundation to the posts, reclaimed scaffolding bar is always a common choice.



Daniel

 

[Deluks]

Set post in concrete in a bucket. Once set, place into position.
Maybe a concrete spur in the bucket, and fix to a timber post which is fixed to the structure with a heavy metal bracket, which could be repositioned were the bucket to sink due to future settlement.
Bucket of concrete is heavy so would need a mate to help position it. Bolt a temporary 'handle' onto the spur using a length of timber and grab an end each.