Control Joints

[bobloes]

My understanding for putting control joints in a concrete 'pad' ie one which is on the surface, is because it will be exposed to temperature variations and the joint allows for expansion and contraction. Therefore concrete footings for a wall do not need control joints because they are (of the order of) a metre below the surface and the temperature is assumed to be constant hence minimal expansion or contraction. Hopefully you all say AYE. If so that answers my first question.

As I am a slow worker I anticipate that I will not be able to lay the complete footing in one day. Do I put in a (control) joint when I lay the second part or just go right up to the (probably) already cured concrete? The footing is 11.5 metres long and then has a right angle for another 4.5 metres. Depth of footing 225mm, width 300mm.

Why are control joints put in retaining or free standing walls? Is it for the same reason as the concrete pads? If so why do house walls not have control joints?

All answers gratefully received I am pouring tomorrow!!

Cheers

 

[jeds]

Joints in foundation concrete should really be properly designed. At the least this would mean including some reinforcement across the joint. 800mm T10/12 rebars or therabouts. Also concrete thickness would be increased 600mm either side of the joint. Depends what you are building, the loads involved and ground conditions though.

I assume by go slow you mean you are mixing by hand. Have you really thought that through? readymix is very quick and easy and I don't think the saving gets even close to outweighing the work involved.

 

[ColJack]

control joints in foundations are probabluy a bad idea.. the idea is to make a solid structure that doesn't move, or if it does, it moves as one..
think about it.. if one section sinks a little then the walls will crack ..

retaining walls and free standing walls tend to be linear and don't have any right angle connections to it to provide stability.. whereas houses do.

 

[Static]

Construction joints are normally avoided but do occur on larger foundations. You would be better off getting someone to help you mix or use ready mix option.. but..

There are a couple ways to form them in shallow strip footings, either a piece of expanded metal lath to form the joint between the older and new concrete or a couple of reinforcement bars as Jeds suggests.. the later always being the method i would recommend.

Course would depend on what you are building a little.. ie. if its just a shed or car port.. also where you plan to put the joint should be a consideration.. ie.. not on a corner or under a heavy loaded post..


Movement joints in retaining walls are for water shrinkage / expansion or thermal movement due to the sun heating up the wall. Movement joints and construction joints are two different things.

(dang its been a while since i last posted)

 

[bobloes]

Thanks for the advice and info. Got my butt into gear and laid the lot in one go today. I used a mixer and once the rhythmn was established it went well. Recovering tomorrow. Will consider the ready mixed version next time. Cheers