Installing an Island Over a Radiant Slab

Cab installers ponder how to attach an island cabinet over a heated concrete floor, without puncturing any tubes. January 11, 2008

Does anyone have experience with installing cabinets over concrete with in floor heat? This is an island, so I believe using mechanical fasteners to be a problem. Would Liquid Nails be adequate?

Forum Responses
(Cabinet and Millwork Installation Forum)
From contributor S:
Do you think that it really needs anchoring? Would a little ballast in the bottom work? Put it on casters and charge extra for rolling furniture. I would not punch a hole in a radiant heat floor unless an engineer did the layout and took the heat (so to speak). If it was a retrofit floor where the tubes were nailed up from below the floor, maybe. I have done some installs where we anchored a template to the floor around electric boxes and data feeds and then attached the fixture/millwork to the template.

From the original questioner:
Thanks for the reply. Unfortunately I am not confident there was a set of engineered plans for this remodel. At least when it comes to the concrete part. I may be wrong and I shall check into it.

Casters would be great, except there is to be a dishwasher and sink in the island. My main concern is that it will have a stone slab with an overhang of about 12-16" on the back side toward the living room. So if someone were to push down on that part of the counter, it has potential to pick the island up. Maybe I am overthinking this. The island is 24" x 101" total and will have three corbels to support the slab.

From contributor G:
We built and installed an island in the same situation about a year ago. Stenciled concrete with in floor heat. We used Titebond construction adhesive (e-61000 I think) to glue blocks to the floor to screw the cabinet to. I put more blocks in than were needed to be able to really put the screws to one. I used an impact driver to put the screws in and could not pop the glue. The glue had set up for 18-20 hours.

From contributor S:
Perhaps it is best to express your concerns to the homeowner. I do think like you and would want a positive mechanical connection to prevent a 10' chunk of concrete from tipping over like a giant rat trap.

Talk to the floor/HVAC man about what it will take to locate the tubes and what it will take to repair one should you hit one. The saving grace is that the damage will be under the cabinet if it did need to be chipped up for repair. It has been my experience that nothing sticks to concrete when you want it to and everything sticks to it when you don't.

Again, if you were just going to glue it, a full sized template with the anchoring blocks attached to it would increase the surface area for the glue. My test for stability on the tip over of the unanchored cabinet would be to see how easy it was to push up off of the floor. If I could rock it with one hand, I would be sweating bullets. If I had to put all of my weight into a lean to get it to budge, then glue would be fine. Somewhere there is a number for the lateral pressure that a handrail must be able to withstand (I am thinking 250lbs). There may be a similar computation for fixtures.

You sound like you are concerned and I am glad that you have enough forethought to consider something like this.

From the original questioner:
I will certainly count on going over the install with the homeowner and the GC before I start. In fact I may give the GC a call today and see if indeed there is a layout for the tubing. However, I really do like the idea of gluing the blocks to the concrete and fastening the cabinets to the blocks. My thought process before was that of the countertop industry, in which they normally just glue the stone to the cabinets via the 3/4" walls. Your ideas sound much better.

Had I thought about it some more I should have realized this is the reason I glue and stapled 3.5" stretchers all along the top edge of the base cabinets. So the countertops would have more gluing surface. Never have liked the factory made cabinets. Thanks again for the great input!

From contributor W:
I remember an HVAC guy telling me once that you can sometimes get the tubing to "ghost" through the concrete by wiping the area down with a mixture of water and alcohol (forget what type of alcohol he said), and that the mixture would evaporate more quickly directly under the tubing. Might be worth a try (and I'd be interested to hear if it worked). Would imagine you'd want the heat turned on, and running as high a temperature as allowable.

From contributor J:
Another option for a positive no-tip install would be structural/attractive columns attached directly to the ceiling. This addition could also house pots/pans etc.

From contributor S:
I would bet that they could be located with some clever trick like mentioned above. We have to have post and pre-tensioned slabs x-rayed all of the time for proposed penetrations (x-ray would be overkill for this situation). There is also a scanner that just shows waves on a laptop that I see being used a lot.

I would say that you should be able to lay out on the floor exactly where your island is going to sit and the GC should locate the tubes in that area for you.

If you knew for sure that denatured alcohol would not eat the finish, it would be interesting to see if there was a different rate of evaporation over the tubes. Sounds solid to me.

From contributor O:
This may be crazy, but would a good stud finder work? All they do is detect changes in density. Guess it would depend on how thick the slab is and how deep the tubes are...

From the original questioner:
Not sure about a stud finder. Don't they usually detect metal? Maybe there are different types. It probably is about time I bought one. For years my middle finger knuckle has done the work. Not very accurately...

If the GC isn't any help, I may try the alcohol tip. And if that doesn't work, then at least I will have cleaned the floor to make for good adhesion of some polyurethane glue. Thanks to all for the insight!

From contributor M:
Do you know how deep below the surface the pipes are? I would find out and maybe you will be lucky enough that you can use plywood (pt), lots of Liquid Nails and a nail gun (like the Hilti), and shoot some nails into it. Make sure you use a round disk with the nails so that the nails don't go through the plywood. You can use 11/2"-13/4"nails. Only if the pipes are deep enough! Then you can attach 2x or 1x to the plywood. Would this help?

From contributor O:
Is this a new house? If so, I'd be surprised if they are running pipes under the island. Seems weird to heat your cabinets...

From the original questioner:
Sort of new. The house was gutted down to the studs. The kitchen portion which is going to be tiled is a new slab that was poured. I'm sure they weren't even thinking of the cabinets to be a concern. It seems lately I have dealt with several builders that have been in business for years that don't seem to look far enough down the road for what is coming up.

Me, I probably agonize over it too much. But I am constantly thinking of what needs to be done next and if this is done, then how is it going to affect the next step. Part of the biz I suppose. Oh well...

From contributor Y:
Just glue it with construction adhesive. It works really well and is really easy.