Expert: Bruce E. Johnson - 10/29/2008

Question
QUESTION: Hi again david, There is a difference between the shoring and the Furring for
the door installation.  Now you probably could use the 2x8 header for the
shoring and leave it in place after the masonry is complete, that is up to you.

Glad you mentioned this, Bruce as I have run into a problem with the door
rough opening-being new to this, I was not consistent enough with my 3/8
mortar beds for my first 6 courses and will need to increase to 9/16 for each
of the remaining 4 courses that will frame the door rough opening, and I will
NOT be able to leave that PT header in place.

First question, will a 9/16 mortar bed be too thick and compromise the
strength of the wall, and if so would adding 1/2 rebar in each of the beds
solve that problem-my thought is that besides adding strength, this would
guarantee that the thickness of the mortar beds is uniform and the
necessary 9/16,  but doesn't leave much room for mortar-maybe it would be
better to go with 3/8 rebar??

Second question is about that bond beam header-is this just part of the last
two courses of bond beam blocks that I think you mentioned I should have
before adding the concrete roof?

Thanks so much, your help has been outstanding and invaluable!!

ANSWER: Hi again david, you shouldn't need to worry about a 9/16 mud joint.  Do what you have to do.  That vertical cell on each side of the door should be filled with grout anyway so it is solid concrete when you're done.  

Generally the last two courses of a bond beam are U-block with a bar of rebar in each course.  In your case, the top course ties into a slab.  You will need to add hook bars to your fill cells so that when you pour your slab the hooks will secure the slab steel and the slab to the top of the wall.  If you want to avoid a lot of formwork around the edge of the building you can do a header block at the top of the wall and contain the slab inside the masonry.  A header block is like a U block with the inside face cut out so it is kind of L shaped.  Using a header block in an 8' wall will only give you 7'8 of head room because the slab is recessed.  So sometimes when a header block is used for the slab edge another course of masonry is used to compensate for the loss of the slab thickness to the interior height of the room.  This added course only needs to be a half high block.    I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

---------- FOLLOW-UP ----------

QUESTION: Wow-so much to know, so little time!! Thanks so much Bruce! Just want to
make sure on that 9/16's joint-you didn't mention whether or not I should
reinforce it by embedding 1/2" or 3/8" rebar in the mud. I will include a
picture of the mock up I did with full blocks along the door bucks so you
could see what I am dealing with. I really like the idea of the Header block
and since head room is NOT an issue it sounds like what you are saying is all I
need above the door is the bond beam course and then the header block
course. Are those hook bars you spoke of still used in that header block? If so   
what size are those and how exactly do you tie those in with the slab steel.

Thanks for your patience with so many basic questions-I've searched the
internet trying to find simple pictures or instructions but only end up finding
very technical stuff.

Answer
Hi again david, I see your dilemma, for some reason when you said 9/16 mud joints I pictured the butt joints and not the bed joints, sorry about that.  If you go with a 9/16 bed joint that is a bit too much.  What we normally do in masonry walls is to build your wall up with normal bed joints up to 8'-0".  This should leave you about 2" short of the top of your door height.  Your door header needs to be set at 8'-2" or whatever the actual height is.  On each side of the door you cut a piece of half block to make up that 2" and then trim your header block 2" to even it out with your next full course of masonry.  Again as I mentioned before that fill cell on each side of the door is filled solid anyhow and there should be a bar of vertical steel in it.  If you are using a precast lintel then you either buy a 6" high one or trim the 2" off of the last course of masonry over the door.   As far as your hooks for the slab go: each fill cell you have at the corners and beside each opening should have a vertical piece of steel in it tied to the foundation.  Say the top of that steel bar is exactly the height of your finished wall..your hook would drop down into the wall 40 bar diameters or approximately 24" and then angle out into the slab 12" minimum.  A 24" x 24" corner bar works good for this.  That gives you 24" down and 24" out. I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com