Frequently Asked Questions

Learn what glass blocks can do for your home or business projects.


Can you make a window that fits my opening?

Yes!  We can pre-assemble glass block windows to fit virtually any opening.  The blocks are multiples and/or combinations of 5.75 and 7.75 inches.  Generally, the overall dimensions of our windows will start at about 11.5 inches and each larger size is approximately 2 inches larger.  (11.5”, 13.5”, 15.5”, 17.25”, 19.25”, etc…)

Are your windows “mortar” or “silicone”?

We’re making windows, so we use materials consistent with the manufacturer of windows.  We use a silicone adhesive/sealant that is manufactured for use in the window industry for window manufacturing.

Do you install with “mortar” or “silicone”?

While all our windows are assembled with silicone, we do still use Type S Masonry Mortar when we install them.

I’ve heard a “mortar” window is stronger than a “silicone” window.  Is that accurate?

Silicone is both an adhesive and a sealant whereas mortar is neither.  In a silicone window, each block is essentially bonded to one another creating a single unit that is both waterproof and flexible enough to absorb minor deflection from expansion and contraction.

Are your glass block windows fire rated.

There are very specific rules that pertain to fire rating.  The blocks themselves carry ratings of 45 minute up to 120 minutes, but that is dependent on the application. Unfortunately; no pre-assembled glass block windows meet those specifications.   For fire rated openings, see this:  (link to high-performance glass block fire rated brochure).

I’ve heard anyone can “cut” a block out of a silicone window to gain access, is this true?

Because of our tight manufacturing tolerances, once our window is installed, someone would need access to both sides and both a prying tool and a very thin (thinner than a utility knife) blade to cut a block free from a panel once installed.  Even our installers when servicing our windows cannot get a block out without destroying it or the window in its entirety, or both.

How heavy are your windows?

That depends entirely on how many individual blocks are in the window.  Each block weighs about 5.5 pounds which makes most basement sized windows 50-90 pounds.

What is the “R Value” or “U Value” of your windows.

Typical 3” thick Thinline Series block have an “R Value” of 1.85 to 1.89, and a “U Value” of .53 to .54.  Window assemblies themselves are not tested for these values.  More technical data can be found with specific block collections on this site.

Can I build a free standing bar out of glass block?

Glass blocks are non-load bearing so without some other structure to carry the weight of the bar top, the answer is “no”.  However, there are several ways to build a bar with glass block and hide the structural components so that it appears to be free-standing.

Do you install windows in the winter?

Yes!  We install year-round.  We have chemicals additives we can use in our mortar which keeps it from freezing but rarely need to use them.  In most cases we will have multiple installers on your project to make sure it gets done quickly and limit the amount of time the windows are open.

I’m outside of Greater Cincinnati, can you ship windows to me?

Yes!  We can ship any of our products to virtually anywhere in North America.  We also have distribution and installation partners in many metro areas across the country.

My window wells fill with water and flood my basement, will glass block windows stop this?

While our windows are significantly more weather and waterproof than operable windows, we do not guarantee them to hold back standing water in a window well.  In virtually every instance our windows slow down the water intrusion, but we make no guarantee to that effect.  If your windows hold water, they aren’t draining properly and that should be addressed to resolve the problem.

Where do I find a copy of your warrantee?

You can find our installed window warrantee here: LINK and the glass block manufacturer’s warrantee here:  LINK

Why would I want fresh air ventilators in my new windows?

Our windows are completely air-tight when installed.  Without a vent you have no option for opening a window to let air in or out.  We receive many requests each year to install vents in existing non-vented windows.  It is considerably less expensive to include them with your original order than it is to add them after the installation.

I have seen claims that windows with mortar between the blocks are more efficient than silicone windows, is there any truth to that?

There are 3 ways energy is transferred- Radiation, Convection, and Conduction.  A solid conducts more energy (heat or cold) than air itself.  That’s why you can hold your hand over your coffee, but get burned if you put your finger in it.  That’s conduction energy.  The blocks in our windows are bonded to one another just beyond the interior and exterior surface of the blocks.  This creates a space where ambient air is present which greatly reduces the energy transferred through the window.  It’s science!


Notes of interest about our windows as compared to mortar assembled windows:

  • Silicone is an adhesive, mortar is not.
  • Silicone is waterproof, mortar is not.
  • Silicone is flexible, mortar is not.
  • Silicone is translucent, mortar is not.
  • Air is an insulator, mortar is not.
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There is no better name in Glass Block. Cincinnati Glass Block provides block, installation, & consulting/design. For contractors we offer training classes. Contact us now and see how Glass Block can improve your home or business.

Call Us Anytime: (513) 744-1946