Hi all, I'm just starting my self build. I've been working as a joiner building children's playgrounds for the last 5 years but don't have any house build experience (apart from building a tiny house we've been living in for the last 3 years).

 

I've just dug my strip foundations but the soil is really rocky so the trenches have ended up far too wide in places where I've pulled out rocks and boulders. Would you usually use ply shuttering in this instance to reduce the amount of concrete required when filling the strips? Dos the ply need to come back out once the concrete has begun to set?

 

Also, for measuring the depth of the concrete I was hammering in rebar pins every 1500 mm to the final depth of the foundations. I've read it that can lead to problems as the exposed end of the rebar (sitting flush with the poured concrete) can rust and damage the concrete. Is this true? Are wooden stakes better?

 

Thanks for your help

Leaving the ply in won’t do any harm if you can’t pull it out 

The rebar rusting won’t do any harm 

 

You might be better just filling the trenches up rather than trying to shutter it all up 

Rather than using rebar for depth A much easier way is to set your laser and tap 100 mil nails in the side of the banking every 450 

13 hours ago, nod said:

rebar rusting won’t do any harm

In the short term it should be ok, but over time and as rusting increase it could start cracking in the concrete. Corroded Steel takes up 6x the volume of not corroded Steel.

 

13 hours ago, nod said:

Rather than using rebar for depth A much easier way is to set your laser and tap 100 mil nails in the side of the banking every 450 

Laser is the way to go.

 

20 hours ago, Bagpipes said:

I've just dug my strip foundations but the soil is really rocky so the trenches have ended up far too wide in places where I've pulled out rocks and boulders. Would you usually use ply shuttering in this instance to reduce the amount of concrete required when filling the strips

I would say no, you are not supposed to back fill foundations. There's info in building regs on what is allowed and not allowed. As this will also be an inspection point for building control. Get it right know the facts.

On 16/06/2024 at 19:37, nod said:

Leaving the ply in won’t do any harm if you can’t pull it out 

The rebar rusting won’t do any harm 

 

You might be better just filling the trenches up rather than trying to shutter it all up 

Rather than using rebar for depth A much easier way is to set your laser and tap 100 mil nails in the side of the banking every 450 

Ok great, thanks. I'm not sure I can even get nails in! It's mostly weathered rock I'm digging out. Nightmare stuff!

On 17/06/2024 at 08:57, JohnMo said:

In the short term it should be ok, but over time and as rusting increase it could start cracking in the concrete. Corroded Steel takes up 6x the volume of not corroded Steel.

 

Laser is the way to go.

 

I would say no, you are not supposed to back fill foundations. There's info in building regs on what is allowed and not allowed. As this will also be an inspection point for building control. Get it right know the facts.

Ok, thanks. So I'll flood the trench with concrete to fill all sides rather than use shuttering. Makes it easier for me too!!

 

I've been pulling out rocks and boulders that sit proud of the base of my trench. Would you normally leave these voids and fill with concrete too rather than back filling with material that is likely to sink?

 

 

22 minutes ago, Bagpipes said:

Ok, thanks. So I'll flood the trench with concrete to fill all sides rather than use shuttering. Makes it easier for me too!!

 

I've been pulling out rocks and boulders that sit proud of the base of my trench. Would you normally leave these voids and fill with concrete too rather than back filling with material that is likely to sink?

 

 

it was impossible to dig down to 1800 on our previous build and keep a neat trench Not pretty But worked well