Expert: Bruce E. Johnson - 5/15/2009

Question
QUESTION: Dear Bruce,

I am building a 3-sided, double wythe brick wall on the perimeter of my small property. I'm building it on top of concrete blocks set on a concrete footer.

The block is 8" wide, and two bricks side-by-side are about 8" as well, including mortar.

Questions I have are as follows:

1) Do I want an empty cavity between the two wythes? I don't think there will be much room between the two wythes, since the two courses will sit on the CMU. If I fill in the cavity with mortar, do I still need weep holes at the bottom, and if so, what length of spacing between them?

2) I was planning on using rebar every 6' that will go in between the two wythes. Excessive? (I am using wire truss joint support every third course along the entire wall length).

3) Should I use buck anchors to tie the wall to where it meets the house, or should I use foam backer rod and chaulk where wall and house meet?

4) There will be an opening for a door between patio and sidewalk. Should I use rebar to support the wall at the point where the two wall segments end (and where the door will go)? I'm under the impression that this will help stabilize the wall. But is it necessary since I'm using the wire truss every third course?

Thanks a lot.

Regards,
John

ANSWER: Hi John, on a double wythe fence wall the width or thickness is normally the length of a full brick.  This allows for cross brick tie-in and fits the supporting masonry. This width also allows for a 3/8" cavity between the brick.  Weep holes are more important on residential veneer brick to keep moisture from penetrating into the living area.  On a fence the weep holes would be to keep the inside of the fence from filling up with water and then seeping back through the mortar joints or leaching through the brick itself. Weep holes are created using cotton rope (1/2" min)laid across  the wall at the point of the brick that is slightly above finished grade.  All courses below this are filled solid in the cavity.  On this finish grade starter course you lay your chord every 16".  The purpose of the chord allows for water to seep out but bugs can't get in..there are probably other methods out there but I use the chord method.  Using ladder type HGH is good, every 16" in height is probably adequate but if you want to go every 12" that's ok too.  Vertical rebar at 6' is okay, you can also run pencil bars(3/8" rebar) in the open cells (fill cells)of the brick in lieu of trying to do something in the cavity.  Vertically laid brick can act as a header with horizontal steel also.  Definately do fill cells at both ends of the wall.  On the house side you can do either one, attach to or not attach to the house..If you attach leave a caulk joint in the mortar against the house.  Strike that edge with a heavy nail and caulk with urethane after at least two weeks.  A cold joint at the house without a tie in should leave the brick 3/8-1/2" from the house pack with rod and caulk with urethane..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com

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

QUESTION: Great answers Bruce, thank you very much.

I'm writing to seek a bit more clarification and ask a few related questions.

First, I should have mentioned that the bricks are antique, are totally solid, and hence have no cells. So is it OK to still put the pencil rebar in the cavity? (I'll have to cut notches in the bricks, or shave them to get the rebar to fit) Also, the bricks are about 4" wide, so I'm planning to have really no cavity, just mortar  between the wythes. Is that fine with regards to water getting in there?

Since the bricks have no cells, do you think rebar will or won't be needed at the ends of the walls (both where they meet the house and where they meet the door)? [I'm still planning rebar every 6', but not sure if I need specific rebar support at the wall ends.]

Great idea about the cotton rope for the weep holes!! Do I lay the rope right on the course below, and then fill mortar on top of the rope? I imagine so, since you want to keep out the bugs, but just want to be certain.

I asked about tying the wall to the house because I thought tying it to the house would help prevent it from possibly bowing in the years to come or just getting out of alignment with the house. But maybe with the wire truss and rebar that won't happen, i.e. it won't move? But maybe the footer will? Your thoughts?

Last, two questions I forgot to ask previously. Do I need to build expansion joints into the brick fence every 20' or so? I don't think I've seen it in residential brick walls around here. And if so, what's the correct approach? And I was thinking of using a Type N 1:1:6 mortar? Sound fine with old bricks? (I worry that the cement component might crack the brick during expansion).

Thanks for your excellent answers. Sorry in advance for all the questions. For what it is worth, your assistance means a lot to me.

Regards,
John

Answer
Hi again John, you need some sort of vertical support on this wall if it is over 4'high..one method is to do "pilasters" every twelve to sixteen feet and at each end.  The pilaster in your instance would be two and a have brick on each side or two and a half brick on the sides perpendicular to the wall and two bricks wide on the wall face.  By building a square or rectangular column such as this you can then put rebar in the fill cell created by the column and fill it up with grout or mortar.  I say 2 1/2 bricks wide to allow for every other course to key directly into the pilaster but you can make the pilaster any size you desire.  As far as weep holes go, if your wall is solid you really don't need weep holes. But if you chose, yes lay the strips of chord on top of the brick and then just lay your mud bed normally trying not to displace the chord.  As I mentioned earlier weep holes are necessary if the wall is part of the house to keep water from getting into the living space or if the wall is hollow and can fill up with water.  Expansion joints are normally used in structural masonry walls and yes they are often spaced at 20'..In your application I don't think they are necessary.  I prefer type S mortar for it's compressive strength but N is widely used in this application and is acceptable.  It has a higher lime to cement ratio so it sticks real well but has half the compressive strength of S..
As far as tying into the house wall..it can be a two edged sword..if the wall begins to shift it could pull against the structure of the house and create potential problems.  Your best bet is to do a wide enough footing on a well compacted sub grade and not tie the wall to the house, use pilasters for vertical stability, and make your footing at least two times the width of your wall thickness or in the case of unstable soils three times the wall thickness..i.e. 24" wide for an 8" wall.. Here is a great website for brick bond types that may be helpful..http://www.slideshare.net/siddharth4mba/brick-bonds

..I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com