Embedding glass induction hob in granite worktop

[Andy Bernard]

As part of the long overdue kitchen revamp, we are looking at an induction hob mounted on a granite worktop. It is a De Dietrich hob, glass with no frame round it, and we would like to embed this into the granite so that the glass hob surface is at the same level as the granite.

I have been told that we would have to leave about a 5 - 10 mm gap around the glass to allow for expansion; I do not believe this to be true as glass does not expand very much and it is an induction hob with small, localised hot spots. I would have thought a 1 - 2 mm gap around the hob, probably filled with a black silicone compound would have sufficed.

Does any one have any experience of this, or comments?

Thanks

Andy Bernard

[Grunff]

I don't have experience of fitting to granite, but I do have a DeDietrich induction hob (it's like magic!), and it definitely doesn't expand 10-20mm when in use (5mm gap all the way round = 10mm linear expansion. I'd be amazed if it expans as much as 1mm. I'd say a gap of

2mm would be more than sufficient.

[Michael Chare]

It might be worth asking De Dietrich.

As you say, only the area under a pan gets hot. The edge of hot plate does not get hot, otherwise you would not be able to operate the touch controls. When you think about it, there must be a temperature gradient across the ceramic surface leading to internal expansion problems. Much worse on halogen hobs as they get hotter.

I am also an induction hob fan. Excellent temperature control, but not as indistructable as a stainless steal solid plate hob!

Michael Chare

[Pete C]

If the granite isn't cut perfectly straight it will be a lot more noticable with a 1mm seam than with a 5mm seam.

Also if the hob expands 1mm into a 2mm seam it will be more likely to squash the sealant out than with a 5mm seam, plus the hob itself will get much more compression stress.

Finally if you ever need to get the hob out you'll have a devil of a job with a 1 or 2mm seam compared to a 5mm seam.

cheers, Pete.

[Tom]

According to my bible!! the coefficients of expansion (alpha) for the following substances are: Granite = 8.3 Soft Glass (soda?) = 8.5 Borosilicate glass (pyrex) = 3 Fused Silica = 0.5 All these figures are multiplied by 10 to the power of -6.

It is likely that the so called ceramic surface probably has a coefficient somewhere between 3 and 0.5 The equation to apply is probably?? Orig length * (1+alpha * T) = Final length. I would imagine that the ceramic surface would only gain heat from the container being heated, one of the party tricks I believe, is to place a piece of paper between the saucepan and the hob and to marvel at it's unspoiled condition after extended boiling. The induction coil itself generates some heat hence the need to allow adequate air flow under the hob. It's difficult to apply the info above as the change in temperatures is known only to the manufacturers. Hope this helps Good luck Tom (BTW, I'm hoping to install one in my kitchen when it's refurbished next year)

[Andy Bernard]

Hi

Many thanks for your postings - they confirm my initial thinkiang and the question is now with De Dietrich to ensure that no warranties are invalidated as a result.

Andy Bernrd

[Tom]

Andy Insert lara to contact. I would very much like to read the results of your investigations and enquiries with De Dietrich ( French Manufacturer??). I would be grateful if you can post again. Regards Tom (rheidol@c-*?-.co.uk)