View Full Version : glass block wall

11-16-2000, 10:36 AM

I'm building a shower in a corner, two walls tiled, and for the "third" wall I have planned to use a small pony wall on the bottom (18") with glass block on top to a heigth of about 7'. A plumber friend brought up a concern I need clarified... he wondered if the glass block wall would be "stable", ie, maybe it might move at the top ? I didn't think so, as I have seen glassblock shower kits from Pittsburgh Corning that have freestanding glassblock walls that are on the actual shower base. Input appreciated.



11-16-2000, 12:51 PM
My hat is off to your plumber!

You should be VERY concerned: even enclosed glass block panels are considered non-structural (by open, I mean one or more panel edges are not restrained by a structural member).

Unless you build in strength with proper reinforcing, the panel will fail. Don't use glass block spacers on open panels since these interrupt the continuity of the mortar. Some glass block panel reinforcing is not waterproof, making those types a poor choice for a shower area. Consider adding a brace at the top unless you are capable of engineering your reinforcing.

I use double rows of very carefully spaced and positioned 1/8-inch stainless steel rod (in both vertical and horizontal joints) for reinforcing. A past article in JLC describes the process I use (you can find back issues on the JLC CDROM).

11-16-2000, 08:11 PM

Thanks for the info.. not what I wanted to hear, but better to hear it before doing it :) What puzzles me in that Pittsburg Corning sells glass block shower kits, complete with special bases that the blocks mount on. While all have the freestanding blocks for walls, one of them has two quite elaborate freestanding walls. How do they get away with this ? Is this a "fault" in their product that they are either unaware of (unlikely) or peddle anyway ? Your thoughts on this are appreciated. For a look at what I'm talking about, go here




11-17-2000, 05:35 PM
Perhaps these installations utilize a thin metal reinforcing header hidden in the top hollow of the upper course of blocks.

I am not current with PC glass block reinforcing panels and other accessories. Most of my panels are curved which produces a rather strong wall assembly. Nevertheless, I still rely on extensive and accurately placed stainless steel rod reinforcing.

David Meiland
11-18-2000, 09:20 AM
Just my $.02...

I would not build a flat glass block wall without tying it in to framing on at least two sides. I recently installed a couple of 4' x 4' panels into framed window openings, using PC 8" block. They are VERY heavy and definitely flexible until the mortar sets and grabs on to the reinforcing rods and panel anchors. Once the mortar sets they are absolutely rigid, but it is hard to imagine how they would have strength without the panel anchors and rebar coming in everywhere.

I would engineer it with either a horizontal or vertical member carrying through, so that you have three sides anchored.

11-18-2000, 12:40 PM
Like David says, anchoring it on three sides makes the panel very stable but I have dove several installations that were anchored on one side only. As I said earlier, much of the work I do is curved. In one house, I installed four curved panels approximately 10-feet wide X 8-feet tall as privacy screens. Each panel was set on cast concrete forms. The "rebar" was actually high-strength threaded stainless steel rod. The lower ends of the vertical rods were bolted to a stainless steel base that was then cast into the concrete. The base was approximately 1-inch wide and ran the length of the concrete form. Similar bases were fabricated and fitted onto the top and sides of the panels after the blocks had been set (the base, the ends of the protruding rods, nuts and flat washers were buried and hidden beneath a final capping of white glass block mortar).

With its base anchored in concrete, sides and tops reinforced with steel plates, and each interior joint reinforced with a pair of rods, these panels are exceptionally strong. As well, each is completely surrounded by an 18-inch deep planter box that has keept the panels out of touch and safe from damage since they were first installed.

Unless special engineering supports are provided, though, I would shy away from any active installation (like a shower stall or a pony wall) where the panel was only supported along two edges. these just don't seem to last.

11-18-2000, 07:49 PM

What diameter all-thread can you fit in those joints?


David Meiland
11-19-2000, 11:33 AM
Kelly, using PC 8" block and the usual spacers, you could fit a 1/2" rod in the void but it would be kissing the block on both sides. 3/8 rod could be embedded nicely in the mortar.

MB, thanks for the great description of the freestanding walls. It's nice when a customer with taste and money comes along and orders up a job like that.

11-19-2000, 01:15 PM
300-series stainless steel is incredibly strong compared to the metal in rebar. All the glass block specialty installations I have done used precisely-placed 1/8-inch rod or 3/16-inch threaded rod.

The method I use allows for a precise alignment of the rod because THAT and surrounding the rods with high-performance mortar is the key to building strength into the installation. The method also eliminates plastic spacers. Plastic spacers are OK for some flat work, but on "working" panels--like you would find in shower stalls, curved or serpentine walls, or unsupported panel edges, spacers can weaken the overall installation because they sharply interrupt and perforate the mortar.

Basically, I create a lightweight wooden frame designed to isolate individual glass blocks in their exact position while I install the reinforcing and the mortar. After a certain amount of mortar has been installed, the framework is removed and the remaining mortar joints are filled and finished.

I go to great lengths wiring the grid of rods together into a powerful skeleton that can bear the weight of the entire installation and carry that weight away from the glass blocks. If you ever witness the destructive power of the flying glass chards created when a glass block is overcompressed, you will understand completely why most blocks are non-load bearing.

Only latex-modified mortar treated with a mildewcide should be used. Mildewcides suitable for use with portland cement materials are available in many paint stores. With the framework assuring that the size of each mortar cavity is consistent (half a mortar joint width all around a block plus the volume of the indented sides of the block), mortar is pumped in with a grout bag. As each cavity is being filled, a 1/4-inch tuck pointer is used to ensure that there are no voids in the mortar.

All the details will be in a book I am doing for Taunton Press and available in a year or two.

11-19-2000, 09:58 PM

Are you suggesting that an eight foot tall wall of un-reinforced glass block construction would not be capable of self-support because of weight alone? This is aside from the problem of horizontal stability.