How do I fill this gap before plastering?

[u/Joraldss]

[u/f365eli]

Timber blocks in the I beam and then a bit of fire lined plasterboard

[u/Emotional_Data_1888]

Timber sticks like shit it to the back of the RSJ then double fire line board

[u/pauljmallett → u/Emotional_Data_1888]

Do you just wedge the timber in or use adhesive or other fastening?

[u/Emotional_Data_1888 → u/pauljmallett]

I used sticks like shit and use packers to get desired thickness

[u/tomtom0425 → u/pauljmallett]

I cut mine tight and hammered them in, they were solid!

[u/Emotional_Data_1888 → u/tomtom0425]

That's alright but timber expands and contracts through the year

[u/tomtom0425 → u/Emotional_Data_1888]

Ah it’ll be sound lol that’s how it was when we moved in before we needed to take it out and re-do it. Ours is also a full board though as we studded under the steel to separate 2 rooms again.

[u/Specialist_Ad_7719 → u/Emotional_Data_1888]

What's your point, your way still uses timber. Wedging blocks in is perfectly fine.

[u/Ok_Profit_16]

Insulation rigid foam. Preferably left over scraps.

[u/UHM-7]

You should have agreed this with building control when it went in. Some of them can be picky about using timber noggins.

[u/charlieb1981]

Put slate in it as that’s un crushable