Cutting joist holes into concrete blocks

[SuperPav]

I need to cut about 8 holes for 8x2 timber joists into 100mm medium density concrete blocks. These may be subject to uplift sometimes so I can't/don't want to use masonry hangers.

 

After marking out, just wondering what the best way of doing it is or how hard it's going to be? Theyr'e about 3.5m off the ground without scaffolding so if the answer is use a Stihl saw then I'll need to put up the mobile tower.

 

a) Drill 8mm holes at 50mm spacing, then knock it all out with a bolster/hammer

b) Drill 8mm holes at corners and along bottom and top edge and Stihl saw the sides

c) Any other ideas?

[joe90]

9” angle grinder (with soft start) might be more manageable than a stihl saw.

[SuperPav]

10 minutes ago, joe90 said:

9” angle grinder (with soft start) might be more manageable than a stihl saw.

 

An excuse for a new tool you say....

[Mr Punter]

It may be simpler to fix a pole plate to the face of the wall with resin studs, then use hangers for the joists.  At that height you could maybe get some trestles and scaffold planks to get to them.

[joe90]

2 hours ago, SuperPav said:

These may be subject to uplift sometimes so I can't/don't want to use masonry hangers.

Then why not use straps and hangers https://www.toolstation.com/light-duty-strap-bend/p82881 (mind you know you NEED an angle grinder, oh and a diamond disc 🤣).

Edited June 14, 2022 by joe90

[SteamyTea]

15 hours ago, joe90 said:

mind you know you NEED an angle grinder, o

After a drill, that looks like a gun, an angle grinder is the best thing you can get. Get a really large one, then pretend it is a chainsaw.

 

Can't you drill big holes to take the joists, holes are better that rectangles.

[joe90]

38 minutes ago, SteamyTea said:

holes are better that rectangles.

Not when the joists are rectangles! Plus you would need an even bigger “tool” to core drill that size 🤷‍♂️

[SteamyTea]

1 hour ago, joe90 said:

Not when the joists are rectangles! Plus you would need an even bigger “tool” to core drill that size 🤷‍♂️

Yes, why I said 'big holes'.

There is a reason portholes are round and not rectangular.

It is the same reasons we model atoms as circles (in the most basic models), all the energy levels are at their lowest.

Edited June 15, 2022 by SteamyTea

[Temp]

How about one of these oscillating multi tool gizmo.. 

 

[SteamyTea]

6 minutes ago, Temp said:

How about one of these oscillating multi tool gizmo.. 

AKA Rampant Rabbit.

Got a used one for sale, anyone interested.

[SuperPav]

18 hours ago, joe90 said:

Then why not use straps and hangers https://www.toolstation.com/light-duty-strap-bend/p82881 (mind you know you NEED an angle grinder, oh and a diamond disc 🤣).

Due to the orientation those straps won't work, I need some which bend 90 deg the other way (these joists fix to the face of a wall). 

 

I have however now found some Cullen masonry hangers which are rated to 2kN short term uplift if all nail holes are filled into the joist, so that could work.

 

The dilemma now is it's an extra £50 for the joist hangers, £50 which could go towards the angle grinder.... I'm leaning towards the latter

 

Thanks all! 

[SteamyTea]

26 minutes ago, SuperPav said:

£50 which could go towards the angle grinder

If your car is getting on a bit, and you have those stupid plastic headlight covers, large angle grinder with a polishing bonnet on it saves you getting an MOT failure.

[joe90]

2 hours ago, SteamyTea said:

Yes, why I said 'big holes'.

There is a reason portholes are round and not rectangular.

It is the same reasons we model atoms as circles (in the most basic models), all the energy levels are at their lowest.

Square pegs, Round holes 🤷‍♂️