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Replacing cracked or broken glass bricks

From: Russell Perry
Category: Repair Question
Remote Name:
Date: 18 Aug 2007
Time: 20:53:39 -0400


What to do if your glass brick window is cracked or broken... I often get calls from people who have older glass brick windows in their homes that have blocks starting to crack, chip and even explode and want me to replace them. Unfortunately to fix the problem, it often isn't as simple as breaking out the damaged glass bricks and installing new ones.
This tends to happen because the glass block window is under extreme pressure (either that or local tear away kids are launching projectiles through them!) The reason for the intense pressure is generally that there is no expansion joint in the panel (if the glass bricks or the surrounding structure can't expand then the glass bricks tend to break because they are generally weaker than the surrounding brick, steel or concrete structures).
What causes this need for expansion is temperature change (getting warmer), causing the glass bricks to grow and or the surrounding structure expanding in on the glass bricks and crushing them.
There is another cause for expansion that is far less obvious and really tragic because it could have been avoided altogether.
That is when the steel rods used to reinforce the mortar joints weren't galvanized or have been constantly wet causing the steel rods to rust and subsequently expand and expand unchecked (also known as "concrete cancer" - see photos on Blog News Glass Bricks Blocks.htm). This causes massive pressure and is generally the prime cause of breaking glass blocks. Photos showing rusty steel rods in the mortar joints and how the rods need to be cut out thus weakening the structure if done frequently.
The problem with replacing a brick here or there is that you haven't stopped the problem of the steel rods continuing to rust away causing more pressure.
The other concern is that if you replace a brick here or there, eventually you will weaken the wall structure (especially if you have to cut the steel rods out of the way and therefore lose the continuous reinforcement through the panel). My advice for a quick fix: replace the damaged bricks (if you can get a matching glass brick colour as the sand colour can change with each glass brick manufacturing batch) and then waterproof the entire panel of glass blocks to prevent further water penetration because this is the real enemy. I recommend two products for this: 1: Thomsons Water Seal  - a clear penetrating liquid that you paint on to the mortar joints (at least 3 coats to have a chance of fixing the problem) 2: Sure Seal. - an aerosol can that sprays on and dries absolutely invisible (again apply 3 coats to be sure) Now if you don't have large cracks lifting the glass bricks off the mortar joints you may be able to waterproof the panel. If the cracks are too large then you really should consider replacing the entire glass block panel.
My advice for a long term fix: My stronger advice is to bite the bullet, curse whoever provided you with this nightmare and fork out for a new, improved glass brick panel.
The installers of glass bricks today have a much greater awareness of the waterproofing issues than those of fifteen to twenty years ago when glass bricks were very new to Australia so you can rest assured that if you replace it AND waterproof it using the products above then you will not have a repeat performance (and the glass bricks will probably be laid even neater than your old panel that may well have been done by a first timer (my first effort laying glass bricks twenty years ago was woeful as is the case for many in this industry). link to web page with pics Blog News Glass Bricks Blocks.htm)

Last changed: 10/20/07