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masonry, how to handle CMU T-intersections kevinfishburne 09-03-2006
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Posted by on September 3, 2006, 1:54 am
I've laid out the base course of a structure using 8x8x16 CMU (on the
PC, not real world). The course includes rooms, hallways, openings for
doors, and several T intersections. I have the option of having the
intersecting CMU rest against the other wall or to be placed inside it
so that it will interlock as courses are added. However either method
leaves me needing 8x8x8 CMU to fill the gaps left in every other course
around the intersection. Openings for doorways would also require these
smaller blocks. I'm a novice at best but this seems like it would be a
common problem.

My questions are:

1) Should the intersecting wall interlock with its "host" wall, or be
built up beside it and attached to it with other methods?

2) Would the use of 8x8x8 CMU at wall intersections every other course
reduce the structural integrity of load-bearing walls? The walls will
ultimately be around 36' high.

3) Assuming my questions are founded in perverse misunderstanding and
ignorance, what would your run-of-the-mill mason do in this situation?

Thanks in advance.


Posted by Italian Mason on September 3, 2006, 2:26 am
I really dont see the need to change how we have refered to BLOCK for
the last.....forever but somebody did and it really irratates
me.....having said that...

> 1) Should the intersecting wall interlock with its "host" wall, or be
> built up beside it and attached to it with other methods?
interlock for strength and sheer.

> 2) Would the use of 8x8x8 CMU at wall intersections every other course
> reduce the structural integrity of load-bearing walls?
these are called "halves" as in a half of a full block. Since block
are modular in measurment and structurally laid at half bond it would
be impossiable to build a wall or any sturucture without the use of
halves.

> 3) Assuming my questions are founded in perverse misunderstanding and
> ignorance, what would your run-of-the-mill mason do in this situation?




kevinfishburne@gmail.com wrote:
> I've laid out the base course of a structure using 8x8x16 CMU (on the
> PC, not real world). The course includes rooms, hallways, openings for
> doors, and several T intersections. I have the option of having the
> intersecting CMU rest against the other wall or to be placed inside it
> so that it will interlock as courses are added. However either method
> leaves me needing 8x8x8 CMU to fill the gaps left in every other course
> around the intersection. Openings for doorways would also require these
> smaller blocks. I'm a novice at best but this seems like it would be a
> common problem.
>
> My questions are:
>
> 1) Should the intersecting wall interlock with its "host" wall, or be
> built up beside it and attached to it with other methods?
>
> 2) Would the use of 8x8x8 CMU at wall intersections every other course
> reduce the structural integrity of load-bearing walls? The walls will
> ultimately be around 36' high.
>
> 3) Assuming my questions are founded in perverse misunderstanding and
> ignorance, what would your run-of-the-mill mason do in this situation?
>
> Thanks in advance.


Posted by dave on September 3, 2006, 10:30 am
block ties and go,go,go I need 650 blocks a day or I'll get your money

Posted by DanG on September 3, 2006, 10:36 am
It would be quite unusual to interlace partition walls, I don't
know that I have ever seen it. It would be normal to tie the
reinforcing of each wall together. This would not do away with
the need for 8's, in fact it would probably increase the count.
If you were to interlace, it would restrict intersecting walls to
modular locations.

36' walls will need pilasters, sheer walls, or some form of
stabilization. If the walls are load bearing, these issues become
even more important. The walls will need vertical control joints
to prevent cracking. Block walls require reinforcing both
horizontally and vertically at roughly 4' on center and each side
of all openings. How do you intend to handle headers at openings?
Do you intend to insulate? Will the block be exposed both faces?
What are you designing? Electric and plumbing in the block or
surface mounted? Foundation and soil bearing requirements for
that tall of walls will be substantial.



______________________________
Keep the whole world singing . . . .
DanG (remove the sevens)
dgriff237@7cox.net



> I've laid out the base course of a structure using 8x8x16 CMU
> (on the
> PC, not real world). The course includes rooms, hallways,
> openings for
> doors, and several T intersections. I have the option of having
> the
> intersecting CMU rest against the other wall or to be placed
> inside it
> so that it will interlock as courses are added. However either
> method
> leaves me needing 8x8x8 CMU to fill the gaps left in every other
> course
> around the intersection. Openings for doorways would also
> require these
> smaller blocks. I'm a novice at best but this seems like it
> would be a
> common problem.
>
> My questions are:
>
> 1) Should the intersecting wall interlock with its "host" wall,
> or be
> built up beside it and attached to it with other methods?
>
> 2) Would the use of 8x8x8 CMU at wall intersections every other
> course
> reduce the structural integrity of load-bearing walls? The walls
> will
> ultimately be around 36' high.
>
> 3) Assuming my questions are founded in perverse
> misunderstanding and
> ignorance, what would your run-of-the-mill mason do in this
> situation?
>
> Thanks in advance.
>



Posted by on September 4, 2006, 2:51 pm
DanG wrote:
> If you were to interlace, it would restrict intersecting walls to
> modular locations.

I think I'll go with interlacing, as all the walls are snapped to an
8x8" grid and I don't want to have to worry about ties if I don't have
to.

> 36' walls will need pilasters, sheer walls, or some form of
> stabilization. If the walls are load bearing, these issues become
> even more important. The walls will need vertical control joints
> to prevent cracking. Block walls require reinforcing both
> horizontally and vertically at roughly 4' on center and each side
> of all openings. How do you intend to handle headers at openings?

The overall structure is 64x64' and square. I misspoke earlier when I
said the walls would be 36'. The building will be 24' (two floors)
except for the center, which will be 36'. The center is a large room
that is 24' high without an intermediate floor. Its walls continue up
to 36' to form a smaller third floor.

Three pilasters/buttresses are distributed evenly across each of the
four exterior walls, formed by interlocking CMU. I plan on reinforcing
them with rebar and filling them with concrete. Are you saying that
something like rebar will need to run vertically every 4' and that
horizontal reinforcement will need to be between every 6th course (4')?

> of all openings. How do you intend to handle headers at openings?

I plan on having round arches at each door opening and lancet arches
for windows. I'll measure and cut these myself from solid concrete
blocks, or possibly use natural stone.

> Do you intend to insulate? Will the block be exposed both faces?
> What are you designing? Electric and plumbing in the block or
> surface mounted? Foundation and soil bearing requirements for
> that tall of walls will be substantial.

All CMU is splitface. Where windows must occur the CMU will be back to
back with no space between, which should provide sufficient insulation
with water repellant/sealant applied to both sides. The four exterior
walls consist of back to back CMU with no space. The interior walls are
arranged similarly but with 2' of space between the back sides of the
CMU. The 2' of separation provides a continous unfinished "utility
corridor" running around all rooms and halls and will house electrical,
ventilation, and plumbing for easy access/maintenance.

As far as the walls being load-bearing I'm still not certain. I was
thinking about using large timber frame construction for the center
room and reinforced concrete columns supporting precast reinforced
concrete groin vaults for the rooms. If I can help it I do not want the
walls to be load-bearing since it will make things more difficult.

The structure will be built in the suburbs of Atlanta, GA (USA), and
will be my primary residence. I do plan on having an architect give
unofficial approval of the final design before construction begins, and
hiring contract labor when absolutely necessary. I'm a big DIY kinda
guy so I'm trying to learn everything I can. You've all been helpful
and I thank you.


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