granite reinforcement over washer/drier
In the past I mentioned the use of steel plates to reinforce granite tops but didn’t have any deflection numbers, so measured things on my latest granite top over a 4′ opening.
A 3″x3/4″x 49-1/2″ mild steel strap deflects slightly less than 1/8″ when I stand in the middle (about 200lbs) with the ends supported. My current client admits to liking to stand on the counter top when cleaning so I used two of the 3″ straps side by side along the front edge of the cabinets for less than 1/16″ deflection with my weight and about 1/32″ with the client’s weight. I still can’t get myself to think of granite as being self supporting with all the crazy things teens and preteens do when parents aren’t around.
The steel straps could simply be laid on the cabs with a little construction adhesive and wouldn’t go anywhere if the metal is installed when the tops are, but I installed them a week before the granite with countersunk holes for screws so the client could see how it all goes together without risking them falling on someone’s toes.
Cost for the two hot rolled straps was about $120, but in the past I’ve purchased used steel in near new condition for less than half of new.
Good building!
Beer was created so carpenters wouldn’t rule the world.
Replies
I've used steel form stakes in various lengths epoxied into the plywood underlayment before the granite is installed. In one case I had an island countertop that had a 21" cantilever on two sides with virtually no deflection. In fact the biggest problem was securing the island cabinet to the floor so that it would not tip over.
Bing
That amount of deflection seems like to much. Can a granite slab actually flex that much without cracking? I'd think angle would be stiffer than flat stock.
I never would have guessed two pieces of mild steel would cost that much. Cheap compared to the cost of granite though.
The span is at normal counter top height over a washer/drier side by side. Raising the counter to allow for angle is not desireable.
As for the stiffness, most of the counter top installs in these situations is done with no additional reinforcement!
1/32" over 4' isn't all that bad.
Beer was created so carpenters wouldn't rule the world.
Granite is surprisingly flexible. The least flexible, most brittle color is probably the black granites (absolute black, black galaxy, etc).Colors like Giallo Veneziano (gold) are extremely flexible.I bend pieces of backsplash all the time to conform to bowed walls. I just need to brace it in place while the adhesive sets up and it holds the curve fine when I remove the bracing a day or two later.I try to avoid bending it whenever possible but it always surprises me how much bending I can get away with.Karl