Expanding bolts into concrete gravel board?

[Careful_Bodger]

I have access to only one side of a concrete gravel board. There is very limited access to the other side (i.e. barely finger reach).

Can expanding bolts be used without cracking the concrete? Would a toggle fixing be an option for outdoors?

If so, what fixing products might I consider for a 10-11mm diameter through hole?

Alternatively (and perhaps in addition), can the concrete be drilled for a rawlplug and/or concrete bolt approach, again without overstressing and popping the concrete?

 

[Swwils]

What are you fixing?

 

[conny]

A 5mm toggle screw needs a 14mm hole. A 6mm needs a 16mm hole.
Depending on what you intend to fit to the gravel board may depend on what fixing you are best to use.

 

[Careful_Bodger]

What are you fixing?

The installer forgot to fit a centre stump, and I am assuming I will have to do the remedial work.

A 5mm toggle screw needs a 14mm hole. A 6mm needs a 16mm hole.
Depending on what you intend to fit to the gravel board may depend on what fixing you are best to use.

Thanks - looks like toggle fixings are not appropriate then.

 

[Tigercubrider]

Could you not drill right though and use a tapped piece of metal?
You could use a bit of plastic/ strip wood to position the steel, maybe coated with epoxy on the back.
Possibly embed the steel in a dollop of cement to prevent it spinning?

gravel boards normally have rebar in them

 

[JohnD]

I think it is very likely to crack.

What benefit do you anticipate?

A reinforced concrete gravel board, on edge, does not need central support. It will not sag.

 

[Careful_Bodger]

A reinforced concrete gravel board, on edge, does not need central support. It will not sag.

I agree!
However, based on other installs I have seen, the centre stump reinforces the lower arris rail by fixing to the gravel board.
While sag is perhaps less of an issue with the boards supported as shown, there is still the chance of lateral flex.

(not my picture)

 

[Careful_Bodger]

... use a bit of plastic/ strip wood to position .... embed the steel in a dollop of cement to prevent it spinning?

Nice idea! The old nut on a stick strategy. (With one at both ends if you include the nut holding it......)

 

[Tigercubrider]

With the picture above, is there a ready made solution, or one that you could fabricate, based on a folded bit of strapping?

I am thinking a basic pre drilled galvanised/stainless strip.
Folded into a Z shape at one end.
The first fold is maybe 50-75mm at right angles. This would slip under the existing fence between the board and gravel board.
Second fold is the width of the gravel board.
Third fold returns the strap to the same plane as the first fold.

You could then either fit a piece of pre measured arris rail so that it slips in and hinges up to mate with the horizontal rail, or tweak the idea so the whole thing is metal with an angle to meet and match the horizontal.

It may not need the "hook" over the gravel board, simply resting on top may suffice?

 

[JohnD]

With the picture above, is there a ready made solution, or one that you could fabricate, based on a folded bit of strapping?

I am thinking a basic pre drilled galvanised/stainless strip.
Folded into a Z shape at one end.
The first fold is maybe 50-75mm at right angles. This would slip under the existing fence between the board and gravel board.
Second fold is the width of the gravel board.
Third fold returns the strap to the same plane as the first fold.

You could then either fit a piece of pre measured arris rail so that it slips in and hinges up to mate with the horizontal rail, or tweak the idea so the whole thing is metal with an angle to meet and match the horizontal.

It may not need the "hook" over the gravel board, simply resting on top may suffice?

Sounds very much like a joist hanger.