Reinforcing silestone countertop

[jeffmacswan]

Hi. Our kitchen remodel design involves a silestone countertop which hangs over the pony wall on an oval, with the longest point (middle) being 15 inches out. The person who took the measurements said that the countetop could sag and break in time if we do not add special reinforcement. Any ideas on how to do this? The installers will put down a piece of 5/8" plywood under the countertop, but that's it. Any ideas about how to support the weight where the counterop will hang over? Maybe still reinforcement or angle iron? Thanks.

Jeff

 

[Bassman]

I'm going to have to solve the same problem soon with a 10 inch overhang. If you aren't going to use corbels to reinforce, the way I've seen it done is to have flat or tubular steel pieces laid into the plywood for support.

 

[Sponsor]

 

[hj]

silstone

Corbels or cantilevered arms are about the only way to protect it.

 

[Spaceman Spiff]

You can notch the top of the cabinets to accept some 1x1x1/8" square tube steel that span from the front, to the back and then out to the edges of the counter. These tube steel pieces should be about every 12" on center. Then the 5/8" ply sits on top of that (3/4" would be better) then the Silstone on top of that. Construction adhesive between the steel and the ply and self drilling screws attach the ply to the steel and adhesive between the silstone and the ply will greatly increase the shear strength of the assy. Have your installers put adhesive on all the ply/silstone seam if at all possible instead of just here and there. Hope this helps!!!

 

[Geniescience]

flat steel, not angle iron. At least 1" height, at least 1/8" thick (across). More is Better. Paint it to prevent rusting.

If you can get a tube of 1/2" by 1" (with tube walls only 1/16th" thick), that is good too, and it looks good because of the rounded corners on a factory made smooth tube. Any other way to round out the corners is made by a handheld grinder, or with a belt sander, or some other tool, and may give fairly good results. A tube also have the advantage that it is easy to get a screw through it and into the plywood.

The steel has to go underneath the 15" piece sticking out for at least 12", and then back inside underneath the counter for at least 18". More is Better. Screws into the ply all the way through and then barely into the silestone.

How many plies (layers) does the plywood have? More is Better.

This is just my assessment, based on my experience with steel. An angle iron is not stronger than a flat bar in this case. A U channel is better, and the best is a tube or a solid 1/4" or 1/2" thick. The height is the most important dimension, not the thickness. That is why I said "flat" -- Now, you are probably wondering how to screw a flat bar... and for that, you would have to weld a few pieces of a 1/2" flat bar, or an entire flat bar onto one side. In other words, the only advantage to an angle iron is its screwability.


david

 

[Bob NH]

Steel will work. But so will wood.

Doubling the thickness of plywood, properly assembled, will reduce the deflection by a factor of 8. Low deflection is the important factor when supporting stone and tile products.

You can use a single thickness for the last 3" at the edge so it doesn't interfere with normal trim.

The first (lower) layer of 3/4" should extend to within 3" of the edge for the area where there is going to be large overhang. The grain of the outer ply should be in the direction from the support toward the overhanging edge.

Then add a second layer of 3/4 plywood that must be GLUED AND SCREWED to the bottom layer. The glue provides the strength to make the two into one, and the screws clamp it so there will be a thin bond line. Use "drywall" screws that will give at least 1/2" engagement into the lower layer.

The joints in the top and bottom layers should be across (not along) the counter, and the joints between layers should be offset by at least one foot.

 

[jeffmacswan]

My plan ...

I talked to a welder who makes subtops out of square iron tubes for a large kitchen designer. They use only the iron, with no wood, and press the countertop to the iron subtop with caulk and that's it. This is perhaps a bit unothodox but seems like a good design. What do others think?

Our installation is a re-do (incorrectly cut sink hole). When the top was removed it was apparent that it was bending a bit at the overhang. We can't really build up the 5/8" subtop (previously plywood) so it wi

ll be replaced with 5/8 square tubing which will be welded into a grid undergirding the entire stone top, including the overhang.

Comments welcome.

 

[Geniescience]

1/4" solid metal will work, too, if you need to keep the whole thing THIN and unobtrusive. Think of those steel plates you may seen in HD that they sell to go on top of basement sump pump well boxes. E.g. 12"x12" or 20"x20". Since it's a such a small overhang, you could do the whole thing with solid metal without breaking the piggy bank.

Remember you only need to support 80% of the part sticking out, not to cut a perfect replica. The welder may need to be reminded of that; he could be a perfectionist; I have seen that several times where they overdo it; at other times they do the opposite and insist "t'll be plenty strong enough". That's jsut my experience getting tons of little things custom welded. Final answer, after a bit of time off to think about it.


David

 

[Bosun]

Find a new installer?

This is what you are paying them for, right? I went through this on my old kitchen--ended up finding some people who actually new what they were doing. I spent many nights fretting over how to support the span. Not worth saving a few $$$.