Framing for Glass Block Window
Rich-in-WA
accept a glass block window? I'm also interested in flashing/trim
details etc to prevent water incursion due to weather. These windows
are located in a bathroom and are 24x36 inches in size. They're not
near a shower so water from inside (other than condensation) should
not be much of an issue. I'm designing a new house (for myself) and I
want to get this right. The house has broad (4-foot) eves above these
windows, but they'll still be subjected to wind-driven rain.
I've built one other block window in the bathroom of my previous
home. In that case, I was replacing a rotted out wood double hung
window that was actually in the bath/shower stall (go figure...). In
this case, I replaced the sill with pressure treated wood finished
with some type of tough exterior varnish and then primed and painted.
The sill was of course sloped to promote runoff, but there was no
actual flashing around the block. The mortar sat right on the
pressure treated sill. I was really careful to get the mortar joints
perfect and I sealed them with several coats of sealer to try and keep
out moisture. One hairline crack appeared in time, and I caulked this
to discourage water from getting in. I'll be first to admit I made up
this entire installation, but in close to ten years, that window
showed no signs of leaking while being exposed to 2-3 "rainstorms" a
day. TIA
Richard Johnson PE
Camano Island, WA
David Meiland
Richard,
I assume you are going to set actual glass block, not one of the
pre-fab nail fin units.
I've done three of these windows. The first two I did according to the
Pittsburgh Corning instructions, and glazed directly into the rough
openings. I wrapped the entire opening with Vycor (12" sticky
membrane, like bituthene) and then added a sloped redwood sill on top
of the Vycor over the rough sill. This was in new walls with sheathing
but no siding on, and it was easy to integrate the waterproofing of
the rough opening with the exterior felt. That method worked OK and I
was comfortable with the waterproofing but it was tricky to trim out
on the exterior.
The last one I did was more like a typical window. I made up a jamb
set with a sloped sill, all out of redwood. I set that into the
flashed rough opening and then glazed it with block. I left a space of
1.75" at the top to allow easy installation of the top course, and
when it was set I toe-screwed a piece of redwood 2x4 in to fill the
gap, allowing the specified quarter inch space at the top.
In both details the block is flush with the inside finish, whether
tile or sheetrock. There are stops on the exterior that meet the face
of the block, near the edge and at the fattest point of the 'bulb' of
the block, if that makes any sense. The edge of the stop is run with a
bead of silicone before it's set.
I think a window like this needs more maintenance attention than a
factory window because there's really no good way to stop against an
irregular surface like block. You need to check it out every year and
re-caulk and/or re-paint if it's weathering, and of course it starts
with a good job of wrapping the opening in the first place. If you
want to go all out, have a sheet metal shop make a copper pan for the
opening.
I can make a sketch and fax it to you if you want. My scanner isn't
handy at the moment...
---
David Meiland
Friday Harbor, WA
http://davidmeiland.com/
**Check the reply address before sending mail
Rico dJour
>
>Is anyone aware of the proper way to frame an exterior 2x6 wall to
>accept a glass block window? I'm also interested in flashing/trim
>details etc to prevent water incursion due to weather.
Hey Rich. David's post is right on. You might want to take a run down to Home
Depot - the other day I noticed that they had glass (and plastic) block and the
PVC extrusions.
R
Eunoia Eigensinn
What I've done in the past is move the plane of the outside surface of the block
out 1.5 inches to the plane of the O/S surface of a ventilated rainscreen
cladding by laminating 2x2 furring strips to the rough opening, and then
bending-up galvalume sheet into channels to flash the opening (with #15 AIF
underneath), with an integral drip edge bent into the sill piece.
Instead of setting the glass block in mortar, I stacked all of the block into
the opening dry, with 2 rows of 3/8" clear vinyl tubing between courses to serve
as shims/caulking stop, and then applied GE 25-yr silicone caulking between the
joints.
15 years later, there's no sign of any problems.
I have used mortar in other glass block panels but I've found that heat-driven
moisture tries to bleed through the joints in winter, where upon freezing at the
outside plane, results in spalling of the mortar.
and then
On Fri, 16 Jan 2004 23:18:36 GMT, remove...@meiland.com (David Meiland)
wrote: