Length of screws to fix through double thickness plasterboard?

[angularbanjo]

Hi

I'm trying to put a shelf up in my daughter's house. It's a semi detached and the wall I'm trying to put the shelf onto is the dividing wall between her house and the neighbour's (living room to living room). It's apparently double thickness plasterboard with a space in between for fire regs (1990's house). I was going to use gripits but looks like the plasterboard is too thick and I've never used one of those undercutting tools before and don't want to 'practice' on my daughters house!

I was then just going to sink screws through the holes in the L brackets, through the plasterboard and into the studs. I tried this with 70mm screws but they didn't find the studs. Does anyone have any idea what length of screw is likely to be needed for this job?

As always thanks in advance

 

[DAZB]

There must be some form of blockwork between the houses i would have thought but even so if you haven't hit a stud with a 70mm screw then you must be in the wrong place. A stud detector will help or try the old fashioned method of knocking along the wall until you hear the difference.

 

[opps]

I own a number of Gripits, I even have the undercut attachment. Nevertheless, I now use the Zip Fix toggle fittings.

Zip-Fix Cavity Wall Fixings - Zinc

TIMCO is a supplier of essential products that trade professionals rely on every day. Over 7,000 quality products across all essential categories: Screws, Fasteners & Fixings, Nails, Adhesives & Building Chemicals, Powertool Accessories & Hand Tools, Building Hardware & Site Protection, Security...

timco.co.uk

They can deal with numerous thicknesses of plaster. The above brand is supplied with two differing lengths of machine screw.

The smaller Gripits have the advantage of letting you use regular wood screws but, from memory, the undercut drill attachment is to big for the smaller fittings.

The main problem with the larger gripits is that the required hole can be massive.

 

[angularbanjo]

There must be some form of blockwork between the houses i would have thought but even so if you haven't hit a stud with a 70mm screw then you must be in the wrong place. A stud detector will help or try the old fashioned method of knocking along the wall until you hear the difference.

Starting to think you might be right. The problem is that with the plasterboard being so thick you can't hear much difference with the knocking method. Think I'll opt for plan C and just use the self drill heavy duty metal fixings instead.

 

[opps]

Starting to think you might be right. The problem is that with the plasterboard being so thick you can't hear much difference with the knocking method. Think I'll opt for plan C and just use the self drill heavy duty metal fixings instead.

Seriously... the load bearing of the ones that I recommended are much higher than the self drill ones.

 

[foxhole]

Probably double boarded with 15mm plasterboard. Depending on shelving style you may be able to use these.

Easyfix Hollow Wall Anchors 16-32mm M5 x 72mm 10 Pack - Screwfix

Order online at Screwfix.com. Provides permanent threaded anchor in cavity walls. For use with setting tool. FREE next day delivery available, free collection in 1 minute.

www.screwfix.com

 

[freddiemercurystwin]

You really need to understand the wall construction, is it timber frame or masonry?

 

[StephenStephen]

You might want to use a magnet to find the studs...