It seems strange that you would need to support stone slabs with thin sheets of wood, but in many cases, it is true! While it takes a lot of force to make granite bend, it only needs to bend a little bit to start forming cracks. But can you install granite countertops without plywood?
You can install granite countertops without plywood only if the granite is 3cm thick or more. 2cm thick granite will require a ¾” plywood subtop for support. 3cm will require a plywood subtop in certain places, like the gap for the dishwasher. With 3cm, overhangs of 3.8cm or less do not need support.
Now that we have a basic idea of when plywood is or is not needed to support granite countertops, it is time to get into the specifics. In this article, we’ll be looking at when plywood is needed, how to measure and install it, and when you need to support granite overhangs.
Table of Contents
Why Use Wood to Support Stone?
It seems very counterintuitive (pardon the pun) to think that a thin sheet of wood could make any difference to the strength of a slab of stone. However, plywood is a surprisingly durable material, and granite is actually fragile if the slab is thin enough. Another reason to use plywood is that it is quite inexpensive, especially when compared to solid hardwoods. Using wood to support stone, then, is not so crazy after all.
If you are using 3cm (1.18in) slabs, you will need to use multiple stones and join them together, which can leave unsightly seams if done incorrectly. 2cm (0.79in) slabs, however, can be much bigger without needing multiple stones since they are much easier to transport and install due to the weight.
That means that while you will have to install plywood subtops for 2cm (0.79in) granite, you will also have a smooth and seamless countertop.
Does 1cm Really Make All the Difference?
Yes, it really does. It may not seem like much, but 1cm more of granite will do a lot for the structural integrity of the slab. Neither a 2cm (0.79in) or 3cm (1.18in) slab is likely to break, but an unsupported 2cm (0.79in) slab might break if it takes too much weight at once. Given the price of granite, it is better to err on the side of caution and make sure the granite will last as long as you need it.
Overhangs and Gaps
This is where things get a little complicated. Many countertops have a gap where the dishwasher goes or a space that can be used as a desk with a gap for your legs. If you are using 2cm (0.79in) granite, you will certainly need a plywood subtop over the gaps or risk breaking your countertop.
If you are using 3cm (1.18in) granite, then you can probably get away with a wire mesh to support the slab, but plywood is still the safer option.
Many countertops have an overhang, which means that they come out further than the edge of the cabinets underneath. As mentioned above, if you are using 3cm (1.18in) slabs, then you will not need to support an overhang of 3.8cm (1.50in) or less. If you want a bigger overhang, for example, for a bar top, then you will need to factor extra supports into the design of your countertop.
Here are a few common types of support used in granite countertops:
A corbel is a support in which the back attaches vertically to a wall or cabinet, and the top acts as support, which you can rest other objects on. They are similar to L-shaped brackets but are made as solid 3D objects which are designed to be seen. Unlike brackets, they are designed to be aesthetically appealing as well as functional.
Corbels are a great way to support a bar top overhang since you can leave a space for your legs between the corbels.
Pretty self-explanatory. Poles come straight up from the floor and provide support to the underside of the countertop. These are a good idea if you plan on doing a large overhang, but it should be mentioned that some kind of subtop is also recommended for the overhang, be it wire mesh or plywood. Again, it is better to be cautious and have a ¾” (1.91cm) sheet of plywood between the poles and the granite.
Brackets come in many shapes and sizes, but they are essentially like corbels, which are usually designed not to be seen. An example of a hidden countertop bracket is the L-shaped bracket. These work exactly like corbels, being mounted vertically to the cabinets, with a space on top to support the counter. The difference is that there is nothing between the top and the back of the L-shaped bracket, making it almost invisible.
Another example is the knee wall (or pony wall) bracket. These are straight brackets which are mounted horizontally into a knee wall, which is a wall that does not extend all the way from the floor to the ceiling.
In other words, you cut holes into the wood underneath where you plan on installing your countertops, then install straight sheets of metal into the wood, which will jut out and support the weight of your countertop overhang.
Plywood Subtop Measurements
It is very important to get all your measurements right before ordering your granite countertop. Not only is granite very expensive, but it is also very difficult to shape. If you order granite of the wrong dimensions, then it will be a nightmare to sort out.
One good way to make sure your measurements are right is to measure and install the plywood before ordering the granite. It is much easier to fix plywood of the wrong size than granite.
For measuring, you will need a pen, paper, measuring tape, and a calculator. Here are some tips for measuring the plywood:
- Always measure twice to ensure accuracy. As we have just discussed, being a few centimeters off can end up being a disaster.
- Draw a scale diagram of the counter space. This will allow you to better visualize the space and figure out how you need to cut the plywood to fill that space. Include gaps like the one for the dishwasher in your scale drawing.
- When measuring the length of the space, make sure to measure from wall to wall rather than from the ends of your current countertops.
- In order to get the square footage, multiply the length of the space by the depth (both in inches), then divide by 144 to get the area in square feet. That will be the figure that really tells you how much granite you need to buy.
Laminate Edge Profiles
One more thing to consider when installing a granite countertop is the ‘edge profile,’ which simply refers to how the edge of the stone is shaped. This is relevant to what we are talking about in this article since what you do to the edges of your countertop will depend, to an extent, on whether or not you have a plywood subtop.
This will not affect your options for different shapes around the edges, but it might affect whether or not you want lamination.
In the context of countertops, lamination refers to the process of gluing another piece of stone to the bottom of the countertop at the edges. This makes the countertop look thicker, which in turn makes it look more impressive. What it can also do, however, is hide the unsightly plywood subtop.
If you decide to go with the 2cm (0.79in) granite, it is a good idea to install plywood underneath, then hide it with some clever lamination.
The final thing to look at is the relative cost of getting 2cm (0.79in) granite with a subtop on one hand and 3cm (1.18in) granite without on the other. As a general rule, 3cm (1.18in) of granite will be about 25% more expensive than 2cm (0.79in) of granite. However, that does not tell the whole story. When you add the cost of installing the plywood and the cost of lamination, the cost comes much closer together.
In any case, the thicker granite will almost always work out more expensively.
It is up to you whether you want 2cm (0.79in) granite or 3cm (1.18in) granite for your countertop. However, if you go with the 2cm (0.79in), it is a very good idea to install a plywood subtop for support. The last thing you want is to spend lots of time and money on a countertop that is going to start cracking in a short time. If it is worth doing, it is worth doing well.
Depending on how much of an overhang you want, you may also have to invest in supports to make sure your bar top doesn’t collapse. That is true whether you are working with 2cm (0.79in) or 3cm (1.18in) granite. Good luck with installing your countertop!