Best hollow-wall fixings through tiles?

Those Gee-Fix fittings looks very good but I think you're right: they wouldn't be ideal for a ring of closely-spaced screws such as I have on the mounting plates of the grab rails. I haven't watched to the end yet.

The English chap gets extra points, too, for not yelling at me.

Quite - if pretty tottery, a walk in bath would make more sense. Although a seat in the shower might help too.

My enclosure is quite wide, so a grab rail on the back wall under the shower head the best compromise.

Unless you have already used them to stand up and then slip sideways on a slippery shower or bath floor whilst still holding on to the rail. Grab rails are not only installed to help with removing yourself from, say, a bath but also to provide a means of support whilst stepping out of a shower tray. In a friends rented house a previous occupant had installed grab rails to help them get off the toilet - Installed on a wall facing the toilet seat. In this case all the force would have been in the horizontal direction.

But not full body weight.

I don't see anything about the spacing of the bar from the wall in your calculation. Any weight on the bar exerts a torque to bend its way off the wall.

yes, but that force will be exerted on the top screws and will be the same whether its mounted on brick or tiles. If the brick case works - i.e. the plug doesn't pull out - then so too will the tiles.

I've juat had another idea, although a bit ugly.

Basically it increases the size of the rail mountings to spread the loads. Use sheet metal screws to attach each flange to the underside of a metal dinner plate. Fix each plate to the wall using three screws into wallplugs in the plasterboard, two at the top and one at the bottom.

If the rail is grabbed in a fall, the sudden inertial force could well make the total force even greater than the person's weight. The total force will exert a torque tending to pull the top screws out and press the plate in at the bottom. But because the plates are so much larger than the original flanges the in-out forces will be proportionally less. Also each screw has its own area of wall to stress, unlike the original clustered arrangement.

The plates could either be the same colour as the rail or painted to match the tiles.

Yes - those spade tile drills have a very sharp point and don't wander anything like a more conventional drill.

I find just giving the back of the drill a thump (with it stationary) enough to give it a pilot. If you have a fairly steady hand.

I can see the sense in that, so thanks. But in my case - as advised here - I need the wall plug to be a close fit to the hole in the tile to ensure a good grip when it expands.

Since the surface of the tile immediately around the fixing holes will be covered by the base of the mounting brackets for the grab rail, I have wondered about trying to scratch off the glaze where the holes have to go in order to provide better grip for the drill bit. Something to try on my test tile.

Interesting thought, thanks.

Yes, just a bit. It could look good given suitable surrounding decor but not, alas, in my case. Nice thought though.

IME there is absolutely NO grip to the plasterboard at all. SH's method is intelligent for e.g tiled MDF, but in terms of tiled plasterboard you are attaching to a tile that spreads the load to the plasterboard and other tiles.

the core drill will wander all over the place and do that...;-)

I think the ONLY thing that worked for me was a bit of MDF with a 6mm hole in it.

How did you hold it in place?

I've been experimenting on a spare tile and using the start-at-an-angle technique I've successfully drilled a 6mm and an 8mm hole with very little chipping around the perimeter. But drilling two holes in a tile clamped horizontally in a Workmate in a room with with lots of space to move around is presumably rather different to drilling ten holes in a vertical tiled wall while standing in a shower enclosure.

One thing that I do now know: when the core drills broke completely through the tile, the drill slammed forward and the face of the chuck met the tile with some force. There was nothing behind it, where in the actual job there will be plasterboard (which should make a slight difference, maybe), and no damage to the tile resulted, but it's still something to be wary of.

Tomorrow I tackle the actual work...

wiv me ovver hand...

I rather suspected that might be the case. I would have thought that the MDF would be prone to slipping about on the tiles, but clearly you managed to stop it doing so. I might try another test tomorrow.

Thanks.

Be careful that the scratch doesn't extend beyond the diameter of the hole or it could be the starting point for stress crack in future.

I've successfully drilled tiles for plugs by just using the tip of a tungsten tile cutter to scratch a small hole in the glaze and then drilling with a standard masonry bit.

John M