Countertop basin - waste fitting & seal?

[Rory_Fire]

I've been commanded to fit one of those bowl type countertop basins on to what is basically a piece of 30mm thick kitchen worktop.

What I'm somewhat baffled about it how to seal the waste? I imagined that the waste flange would be recessed up into the basin but it isn't

- it's flush with the base. Trying to ensure a seal between the flange and the worktop (to catch water that comes out of the slot in the waste) would seem an extremely uncertain task.

Obviously I could just chop a big hole in the worktop but then there's no way to secure the basin, other then by glueing it.

Is there a recognised way of doing this?

[Lobster]

Don't understand the question. What sort of waste fitting are you attaching? The process is essentially the same regardless of whether the basin is a free-standing sink, recessed-into-the worktop kitchen sink, bathtub, whatever - which makes me think there's more to your query than I'm getting. Do you have a picture?

David

[Rory_Fire]

The basin sits completely on top of the worktop and I understood that the normal way to secure them is to cut a hole the same size as the waste and then put the waste's washer and nut under the worktop so that it pulls the basin and worktop together and this would also stop the basin moving. The waste is a slotted pop-up waste (not one of those operated by a lever).

The problem, as mentioned earlier, is that the basins waste flange is flush with the worktop and I'm baffled as to how to seal that "interface" especially as slotted basin wastes can leak at the best of times.

[Rory_Fire]

Do you have a picture?

It's very similar to this one. Note that the waste isn't (as I expected) recessed underneath - it's just flush with the base.

I can just cut a large hole in the worktop, but that leaves the problem of securing the basin. Clearly I can just glue it but that doesn't seem ideal.

[Lobster]

Ah, now I've got you. You're on about one of these sorts of things aren't you:

As to how you fix the waste: sorry, haven't a clue never fitted one of these. But I can't imagine for a moment that the waste thing is to be sealed against the underside of the worktop: surely it will seal against the sink itself. Otherwise water will get into the cut edge of the worktop...

David

[Rory_Fire]

Exactly. :) So the only way to do it would be to cut bigger hole. As the underside of my basin is pretty flat I do have space to do that, but you imagine that on some bowl sahped basins there wouldn't be much underside to play with and securing them would be difficult.

[PeterK]

Don't know if this is any help but I had a quick look at villeroy & boch site and they appear to use a hook shaped bolt(s) . The hook going into a hole in the basin and then through a hole in the counter top For the basin at

shows the bolt assembly shows the hole positions

Peterk

[Rory_Fire]

Thanks for that, but there's certainly on physical way of bolting down the one I've got.

I suppose that they might often be placed on slate and so the same issues as I've got with a worktop getting wet don't arise. However you'd still probably want to seal between the basin flange and the slotted waste otherwise you could end up with water leaking from under the basin and spreading across the slate.

I'm thinking I could put the waste in place in the basin (it's a pretty close fit in the hole) and then glue it in place with Sticks Like Sh*t - my concern there is that if it doesn't work then I'll be a bit stuffed!

[Rory_Fire]

Thanks for that, but there's certainly no physical way of bolting down the one I've got.

I suppose that these sort of basins might often be placed on slate and so the same issues as I've got with a worktop getting wet don't arise. However you'd still probably want to seal between the basin flange and the slotted waste otherwise you could end up with water leaking from under the basin and spreading across the slate.

I'm thinking I could put the waste in place in the basin (it's a pretty close fit in the hole) and then glue it in place with Sticks Like Sh*t - my concern there is that if it doesn't work then I'll be a bit stuffed!

[A.Lee]

Just use silicone. It'll be fine. Cut the hole in the worktop for the waste. I reckon at least 10mm clearance all round. Seal the hole with silicone or paint.Fit the waste to the bowl, then silicone the whole lot down to the worktop.

If in future it needs to come up, then a bit of levering will get it up.

Alan.

[Rory_Fire]

Thanks - I think that probably is the only way to do it, relying on a bead of silicon around the base of the bowl to hold it firmly in place. I suppose I could always make up a piece of sheet steel or something and use that, with a second waste nut, to clamp the whole assembly together.

I will seal the edges of the hole in the worktop too.

[Dave Plowman (News)]

You'd normally bed it on silicone - you wouldn't want water getting between the worktop and basin bottom.

[Dave Plowman (News)]

There'll be no need - silicone will hold it firmly enough, After all it's unlikely to have much sideways force applied to it. I have an inset one - and the only thing that stops it moving is the silicone seal - and you've got a much larger area to play with.

[Rory_Fire]

I hope that's true, but I have to allow for a couple of teenagers (and their friends) who can sometimes be astonishingly heavy handed.

[Rory]

Done this job now - I did simply cut a much larger hole and I used cone shaped bung from B&Q to seal the slotted trap directly to the basin. This worked well, first time, and without any additional sealant - for general interest details of the seal here:

. It's made by Robimatic but the packaging has changed as noted in the thread - if only I'd read that first I might have found it quicker in the shop!

I then stuck the basin in place with silicone sealant - the basin had two "rings" of points of contact with the surface and it appears to have stuck fine.

[Carlo]

Hi, using the waste nut to secure the basin would be a very bad Idea. I've seen plumbers recommend that and they obviously don't understand their trade.

1. The waste has a rubber washer under the sink, upon which the backnut pinches ahainst the basin. This seal MUST be watertight. Why would anyone wish to introduce counter-top material into the middle of a watertight seal?

[Fredxx]

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