Not sure if this is the best forum, but none of the others seem to quite fit, so:

I'm gaining in plumbing confidence, so I have embarked on my next job: replacing the Hummer-sized washbasin in our not-so-Hummer-sized bathroom.

I bought a basin at a well-known DIY chain at the weekend, having already ordered fisher wall fixings along with the other fittings I need, from a well-known online retailer.

Only thing is, the basin, instead of having the usual outsized fixing holes near the top of the basin, has these weedy little 6mm holes at the bottom edge. The pedestal is clearly designed to be entirely load-bearing, with the minimum of stability provided by some screws into rawlplugs.

One of the reasons I am replacing the Hummer is that it is not fixed to the wall - in any way. I want to do a proper job and replace it with something that our 4 year old cannot pull over.

So, in the forum's view should I:

a) drill some 14mm holes in the back of the washbasin, using the posh new diamond encrusted tile bit which I just paid £15 for, and fit the fischer anchors? Can you drill porcelain, or will I end up with £59 worth of broken crockery?

b) leave things well alone and follow the instructions?

PS the back wall is tiles over plaster over breezeblocks.

You can drill porcelain, but it's not easy and you run the risk of weakening the sink IMHO.

Is there a specific reason why you do not want a pedestal?

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DIY | Donnas dream house

14mm is the size of the wallplugs not the fixings!

We all relieve a basin fixing hole sometimes cos often they are not formed well. Usually the screws are only there to hold the basin in place until the silicone holding it to the wall has gone off!

And as Scruff seems busy tonight:

It's a basin Chez not a damned sink

I *do* want the pedestal. I just want to be assured that it's safe.

The basin in question is pictured here. The hole in question is near my index finger in the first photo, and at bottom of basin in the second. The larger hole is a casting hole and does not go through both layers of porcelain.

It's a bathroom sink up here

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DIY | Donnas dream house

I know it's not 14mm - its an M10 bolt. But I only have a 14mm tile bit, and the fixing comes with oversize (about 25mm) plastic bushings, so a 14mm hole would work really well - if I can drill it.

For the benefit of my ignorant brain, "relieving" a hole = opening it out, yes? And on the subject of silicone, is this a joke? Is it normal to glue the basin to the wall? Is this in addition to a proper fixing, or instead of it?

I doubt if you can make the existing holes any bigger, without weakening them.

The silicone is not a joke, it is superb for fixing things!

You can drill porcelain if you really want to, but it will be difficult to get it started without some kind of guide or by using a pillar drill.

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DIY | Donnas dream house

Not a joke I've seen whole kitchen and bathrooms held together with the stuff!

You will find that the basin never sits properly flat to the wall the moulds just aint that good

And don't mark a straight line on the wall for the screwholes they probably won't be in the same plane

Set the sink on the pedestal and move it around for best fit with a level across the top. When you're happy mark a line around the sides for alignment and (with a very skinny pencil, propelling one is great) mark both fixing holes, I usually mark a small line underneath them cos it can be hard to find them afterwards.

Remove all and drill the holes 7mm is more than enough! Start with drill horizontal then angle it to drill slightly upwards.

Brown plugs in holes.

Good splodge of decent silicone over back of sink with a nice 10mm or so bead about 5mm in from edge.

Number 12 screws 3 1/2" long with nylon washers

Offer it up and engage the screws slightly then gradually pull it back into place letting the excess silicone squirt out.

when it's reasonably secure (not too tight or it will crack) smooth excess silicone and leave for 24 hours.

Job done have a beer

I take your point about the existing holes - I was going to drill new ones higher up. Getting started would indeed be a pain.

The consensus seems to be that drilling is a terrible idea, and fixing with silicone seems a much more attractive proposal with less swearing and no drilling involved.

I take it we're not talking about the stuff used to seal the tops of baths, showers etc. Could you direct me to a suitable product? My wife seems to finally be accepting that I can do this kind of stuff without flooding the house or dropping a hole in the floor - I wouldn't want to screw it up now!

Dow Corning 785 most pros will not use anything else

2" x 10 screws is plenty large enough.

You can always use No more nails if you like but Silicon will never move once it's set, if you get plenty down the back.

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Great post Raxor, thanks. Sounds much easier than drilling pottery!

Thanks - time to go shopping!

Ok, I'm gonna get some 785 - assuming my local builders merchant stocks it.

A quick note to all who responded to my post - the new basin is in place, sealed with DC785 and looks a treat. The tile drilling was a breeze with an 8mm tile bit. The silicone is going off now, there's a leak in the trap to hunt down and then final tail connections.

Thanks to everyone for their help!