How to extend concrete landing step by 100mm?

Question

Hi,

I have to extend my landing step by 100 mm to an existing concrete landing step. Just wondering if i need to insert rebar for just 100mm to existing concrete or not really. Tbh, anybody can help me with the whole process of how to diy it would be grand. Thanks. Size is around width 100mm x length1800mm x depth x 200mm.

Noyade · Answer

It's an odd profile @thomasbhattarai96 - looks like the bevel was created with a demolition saw? Is it your intention to bring this profile forward?

JacobZ · Answer

Hi @thomasbhattarai96,

I agree with the advice and couple of points @R4addZ has made here. There are a few inaccuracies in the render above relating to where the formwork is placed, but they are easy to deal with by simply moving the formwork on the right in line with the edge of the concrete and removing the piece on the left altogether and ensuring there is a stake to support the formwork right up against the existing concrete.

Start by adding 75-100mm of compacted road base to give the new concrete a solid pad to sit on.

To tie the concrete masses together, I'd suggest using these

https://www.bunnings.com.au/jack-450-x-12mm-hdg-dowel-bar-5-pack_p0579929

, which are hot dip galvanised (HDG), and setting them into the existing concrete using

https://www.bunnings.com.au/ramset-300ml-chemset-ultrafix-plus_p2264757

.

After the dowel bars are in place, run a length of

https://www.bunnings.com.au/australian-handyman-supplies-12mm-x-2m-reinforcing-round-bar_p0918839

along the width of the new concrete, and tie it to the dowels using tie wire.

This reinforcing will do a whole lot in terms of increasing the strength of the extension and I would say it is the most important aspect to the job. Without it, a small length of concrete will not last long term.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

R4addZ · Answer

Hi @thomasbhattarai96

So the issue is less about structural strength and more about tieing things together but I can see where EricL is coming from. firstly, if you go with EricL"s suggestion, you don't need the piece of formwork on the left as it would be neater to join up with the existing concrete there and not have a gap. Secondly there is the issue that unless you tie the new concrete to the old, then it can just move independantly and end up at angles with the existing.

I suggest drilling about three holes (more if you can) into the side of the existing concrete (two in the long axis and one in the short) and you need to do this very carefully, I would turn off the hammer feature and use a sharp bit on drill only (it will take time) Then get some stainless bar and fix it into the holes using a chemical anchoring system and if possible tie that to the rheo bar you are using (if not put some twists into the bar if you can). This will halp keep things lavel and put the least stress on the existing installation!

Edited to add that the formwork depicted on the right should be further out to give an edge that aligns with the existing concrete! You just can't trust AIs these days  😊😊