Sealing an Undermount Sink

[Spinny]

Both our kitchen and utility sinks are stainless steel and will be undermounted to quartz worktop. We have asked for the worktop cut outs to be sized to match the sink bowl without an overhang. Partly preference, partly because we will have hook over sink accessories, partly to preserve the bowl size for ease of use.

 

So I am wondering how we can ensure that the worktop fitters seal the join between the sink and the worktop in a clean and tidy manner ?

 

We have been thinking use a clear silicon sealant, but should we be masking up the edge of the sink bowl with masking tape before they come to fit ? Should we get the silicon ourselves ? I have seen references to sinks being sealed to the worktop with the worktop placed upside down - however I severely doubt that the fitters are remotely likely to do such a thing ? The island has a sink and is 3m by 1m and 30mm quartz - they were indicating it would take 5 people to carry it in. The sinks are currently on supporting framework in the units so I imagine they will just want to silicon the sink and drop the worktop onto the top ?

 

How can we ensure we end with a nice tidy seal between sink and worktop ?

Edited yesterday at 12:07 by Spinny

[Mr Punter]

The masking tape sounds sensible.  Run round the join with a fugi to remove any excess, then remove tape before it cures.

[Nickfromwales]

Use clear CT1 not fix the sink onto the quartz, not silicone. Silicone is crap.

There are two jobs that need doing here, possibly, 1) to bond the sink 2) to cosmetically seal the finished article, after the installation of the sink and quartz is complete and the CT1 cured. 

 

Clean excess CT1 off with baby wet wipes, lots of them, and you’ll never know it’s been on there. If this is suffice, do nothing more. 
 

If there is a valley that needs filling afterwards, then use silicone but expect to redo it every few years as it won’t stand up to the amount of wiping etc that it will experience.

 

My 2 cents is to do the CT1 and wipe it back, and then leave it at that. You can clean any valley / small gap with a cloth and rinse back to new each time.

 

I have said they should be grinding tabs into the quartz to be able to install stainless steel tabs into 2-part epoxy resin, to do the mechanical holding ling term.
 

Is this not being done, or have you just not asked? 

[Spinny]

8 hours ago, Nickfromwales said:

I have said they should be grinding tabs into the quartz to be able to install stainless steel tabs into 2-part epoxy resin, to do the mechanical holding ling term.
 

Is this not being done, or have you just not asked? 

I have not asked about this. I think they just said the sink would be fixed using a sealant/adhesive.

I am confused as given the weight of the quartz and the use of silicon or CT1, and the timber edge supports shown underneath shown in the photos, will that not be sufficient ?

 

These people will be fitting 100's of worktops every year, is it too much to just expect they know what they are doing ? Especially given I am spending a large sum on the job. I can imagine only 1 in 100 customers would actually ask, specify (or perhaps pay extra for) grinding, tabs, and epoxy ?

 

I am scratching my head a little about how to double check their laser device measurements. If a corner between the front edge of the worktop and the side wall is not a perfect right angle would you expect them to be cutting this slightly out of square to fit ? This is unclear from their drawings, where all the cuts look visually as though they are 90deg and have no specified angle shown. I can appreciate an angle greater than 90deg would not be possible because of the need to be able to slide the worktop in, but presumably an angle less than 90 would be easily done ?

[Gone West]

2 hours ago, Spinny said:

I think they just said the sink would be fixed using a sealant/adhesive.

When I fitted our undermounted sinks, I used G clips to fix them.

 

http://www.gclip.co.uk/Home.html

 

2 hours ago, Spinny said:

If a corner between the front edge of the worktop and the side wall is not a perfect right angle would you expect them to be cutting this slightly out of square to fit

All that should have been taken care of when it was templated. If there is to be an upstand then minor gaps are covered.

Edited 8 hours ago by Gone West

[Big Jimbo]

Those cut outs are going to have to be spot on. A bit of top sink ledge showing here, and a tiny bit of overhang there, will drive you nuts. There will be a radius on the top edge of the sink, so that will need filling with something. @Nickfromwales makes a good point that Silicon will last a good few years, but CT1 around the edge joint between the flat bottom of stone, and filling that small curve at the top of the sink would do a good job. I expect that the worktop fitting company will just use clear Silicon.

My tip would be to ensure that that small radius is not filled after, but that whatever sealant is used it is put around the top, flat ledge of each sink before the tops are fitted. That way it splurges out into the sink area, and is cleaned off by the installation team.

[saveasteading]

2 hours ago, Spinny said:

expect they know what they are doing ?

Expect yes. Have certainty, no.

 

It's easy though to show interest and ask how they deal with your concerns.

 

You can't expect perfection just because it is expensive.

The big house developers (some) sell poor quality.  There are lots of rubbish builders.

 

Nobody starts a business on rhe basis of   ' I think I will set up a stone worktop business.  It's expensive,   skilled  and high risk.

They will have been making gravestones and tiles first , as an example. Then the fashion for worktops comes along and they segue into that, take on staff and expand.

 

If they are passionate they won't mind the questions.

 

 

[ProDave]

With ours, the stone provider did all this.

 

When they came to template the worktops, as well as making their plywood templates, they took the sink with them, so ensure the hole they cut in the worktop fitted the sink correctly.

 

They also fitted their preferred type of fixings to the worktop to secure the sink (not the ones supplied with it) and on fitting the worktop they secured and sealed the sink to the underside of the worktop.

 

In our case, the hole in the worktop is a few mm smaller than the size of the sink, so there is a very small lip around the sink.  I don't find this a problem, and it has the advantage that you don't see any of the sealant used unless you put your head down into the sink.

 

I was very glad it was a supply and fit contract.  When two strong men walked in carrying a long heavy granite worktop with a sink hole in the middle and the two halves joined by just the strips front and back of the sink hole, it looked very vunerable to damage at that stage, and I was glad it was them fitting it not me.

 

 

[saveasteading]

In a nearby worktop company's yard I saw a rack of large offcuts, broken slabs and some with holes for sinks. 

A high risk business. Although maybe that was years' worth.

[Spinny]

5 hours ago, Gone West said:

All that should have been taken care of when it was templated. If there is to be an upstand then minor gaps are covered.

There is no upstand. There are 3 worktops:

1/ the hob run backs against the rear wall which will have a glass splashback templated and fitted after - the ends finish against tall cabinet panels and they said they would be polishing the cut ends to help the worktop slide in without damaging the cabinet panels if it is a tight fit.

 

2/ the island which is nice and square from the fitter and has the sink cut out (2 taps) and a waterfall end

 

3/ the utility which has a sink cut out (1 tap) and runs in against the window frame to seamlessly form the window cill. Although no upstand, we will be tiling the walls at one end, in the window reveal, and along the back wall.

 

I have been sent the template drawings (created by a laser scanner device, not by any physical template being made) but trying to check them is tricky. I will post them so you can comment. My own measurements of the utility piece give me some concerns. It is basically L shaped to run into the window reveal with the long edge into the reveal marked as 868.51 mm. However the short edge is marked as 640.33mm and the other dog leg marked 232.95mm. Now that adds up to 873.28 which is almost 5mm longer than the other end. And if I measure the actual dog leg it is 227mm or almost 6mm less than they have. And my measurements show the worktop space will be 870mm from overhang into the window frame and exactly parallel to the window frame. So by logic that implies a potential 7.5mm gap at the back of the worktop away from the window. Yes I am going to tile it but doesn't seem a reason to leave the worktop 7.5mm short ?!? There is also no measurement given for the distance between the edge of the sink and the edge of the worktop.

 

I am really loath to sign off templating done invisibly when there is a large sum of money and an irreplaceable (out of production) quartz involved and obvious queries ?

 

What do others do, just sign the template off blind ?

 

Edited 2 hours ago by Spinny

[saveasteading]

I'd be nervous too, and measuring has  been my life.

The two decimal places is false and unnecessary precision. 

 

7mm difference is perfectly normal.

 

But what if the shape isn't quite square?  Actually it can't be with that 7mm.

A proper template would tell if all the corners were 90 degrees.

OR they would show diagonal distances as checks 

I think I'd be telling them it's their job to measure and get it right... which clearly they aren't comfortable with. ... which puts their measuring skill in doubt. 

 

And point out the missing dimension.

[Gone West]

1 hour ago, Spinny said:

What do others do, just sign the template off blind

I've only ever seen physical templates which were easy to check. I wouldn't want to rely on a drawing.

[Spinny]

I don't understand why they have not provided diagrams that clearly show the measured position of the walls/perimeters with the planned dimensions and positioning of the worktop super imposed onto it. That is the obvious way to allow a customer to buy off a drawing.

 

When they were here they commented that there would be a 10mm gap at the sides of the window frame so it was just as well we were tiling the sides. That is why I have focussed on checking the utility piece in particular. I have used a machine cut piece of board and the edge of a spirit level to to form the planned position of the straight front edge of the worktop. This shows me (using spacers to measure) that the 5mm overhang will be 5mm at one end increasing to 7mm and then falling again to 4.5mm at the far end because there is a small misalignment - but visually unnoticeable - of the front face of cupboards/appliance bays.

The right angle on the cut board, checked with a set square, shows me the long edge, if cut to 90deg will taper somewhat away from the wall and I will end up with an 8mm gap on that side near the window where the reveal isn't straight. Tiles will just about cover.

[Spinny]

By the way the sink corners have radii of curvature given by the manufacturer which I looked up when they came to template. For the utility it is 35mm radius, and for the kitchen 25mm radius. For the bowl width and length they have gone with 1mm less than the manufacturers specified dimensions - so in theory should be 0.5mm beyond the edge of the bowl all around.

 

They did tell me the cutting would be done on a CNC machine, so should be a very close reproduction of the dimensions fed into the machine.