Supporting Marble Slab Countertop
by Kyle Laughlin
(Los Angeles, CA)
I recently had a 3/4" carrara marble slab with an 1 1/8" mitered edge installed over my washer and dryer. Beforehand, I had a 5/8" sheet of plywood installed, supported on three sides.
The marble counter top fabricator/installer did not glue the marble down to the plywood and put a tile backsplash around the marble. The plywood seems to be sagging in the middle, not fully supporting the weight of the marble slab.
Today I noticed slight, light colored (almost white) cracks in the middle of the mitered edge. I have not put very much weight on the counter.
Am I going to have an issue with this marble slab cracking? If so, what should I do to prevent a bigger issue? I have about an 1" gap between my washer and dryer. The width of the slab is 57" and 39" deep. Please advise. -Kyle
Kyle, you should install some sideways 2x4 or metal cross bracing under the plywood that extends from wall to wall at or near the front and again half way back of the countertop.
You need a completely solid and stable base for the marble slab. That plywood will fatigue and continue to sag putting stress on the center of the counter top. Eventually that little crack you have will break through the whole slab.
If you can fit it, I'd also place a pole or support in between your washer and dryer from the floor to the plywood base or to one of the cross pieces.
Also, you can consider installing a corbel or two near the center. Not the standard type of corbel shaped like a triangle, but one made of a thick metal strip that attaches to the back wall and is bent at a 90 degree angle to then attach to the bottom of the plywood support sheet.
This should work given the limited clearance to the washer and dryer.
Supporting Marble Tile Countertop Sink Area
Do I need to reinforce the plywood under where the sink that will sit on top of a marble tile countertop?
Marble tile isn't nearly as heavy as a marble slab, so support isn't quite as crucial. But certainly you need adequate support for the sink and all the activity that occurs around a sink.
Typically the cabinet walls will provide sufficient support if close enough to the sink. If not and especially if the sink is a heavy porcelain or ceramic, then a little extra support under the plywood wouldn't hurt.
As an aside: if this is a kitchen countertop I'd advise that you go with a granite and not marble tile.
You'll find plenty of info from other similar questions found at the bottom of this marble countertop page
, but the short of it is that marble tile will require far more maintenance (etching and scratching in particular) compared to granite. Many regret installing marble slab or marble tile as a kitchen countertop.