Mortar, Hot Melt, Hot Glue or Silicone

For over 100 years, companies did glass block the same.  Glass block was put together in one way and one way only — with mortar.  But things have changed.  Some changes are good, and some bad.

First the good:

• Pre-fabrication vs On-site building:  Glass block used to be built completely on-site.  The Mason would lay down each block and “butter” them with cement prior to laying them.  This was an effective, but time consuming, system but it resulted in some blocks being slightly cocked to one side or the other.  Homeowners had to take off extra time because it could take a week to install new glass block windows in a home.
• Today, most companies measure windows and then pre-fabricate them off-site.  This allows for quality control measures such as uniform grout lines as well as reducing the time impact on the homeowner who previously had to take more time off to accommodate the installation schedule.

The Bad

• As time went on, companies looked for ways to make their windows cheaper and while some companies still use the tried and true method of mortar, others have switched to using caulks, silicones and hot glues (re-branded by some companies as “hot melt”).
• These systems allow companies to throw together a window in as little as 5 minutes and all they have to do is cement it in on installation day.  While it may sound appealing to have a low-cost option, these “throw together” windows tend to have problems such as leaking, flaking and failure of the sealants, causing breakdown of the window and any structural integrity the customer was sold on.

The Ugly

• While marketing these cheap “throw together” windows, some companies have used deceptive marketing techniques.  Homeowners need to not only ask if the window is mortared, they need to ask if there is mortar between the blocks.  These hot glue and silicone companies sometimes tell people they use mortar and technically they are not lying.  Technically.  They can say this because they mortar their glued windows in on the sides.  So while their windows are truly mortared into the opening, they lack the structural integrity and the security that a mortared glass block window has.

Do the bottom line is, be cautious and ask a lot of questions.