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Existing Masonry Wall Construction

Existing Masonry Wall Construction

(OP)
My first post...looking forward to hear your opinion and experience with any similar masonry walls.

I have a client who is looking to add 1-storey to a 2-storey masonry walls and wood floor office building. The first floor exterior masonry bearing walls are not exposed for us to view at the moment. The second floor exterior masonry walls were exposed and the attached are the pictures.

I've never come across a masonry load bearing wall with horizontal wood shims at every other joint. The shims extend approx. half way through the thickness of the wall. This looks scary to me and I'm tempted to recommend pulling out the wood shims and re-pointing the joints. The client really wants to leave as is.

Anybody come across this condition before?

Thanks for your help!

RE: Existing Masonry Wall Construction

For the additional load, I would agree with you.

I also noticed the lack of air space at the joist to brick/CMU contact locations. Bad too...

Mike McCann, PE, SE (WA)


RE: Existing Masonry Wall Construction

Interesting... I've not encountered that before, and I've been involved with numerous 'historic' masonry structures.

Off the top, I'd remove them and re-point as suggested. They do little to improve the strength of the wall and are likely a detriment, and I'm not sure what the purpose is... maybe some kind of 'nailer'.

If doing any renovations, it's best to remove them.

Dik

RE: Existing Masonry Wall Construction

Strange indeed. Two courses of concrete block, then a course of concrete brick. The wood was possibly just to give the mason something to lay the brick on. No idea why.

RE: Existing Masonry Wall Construction

I surmise the wood shims were for attachment of furring strips to the wall prior to the invention of Ramset.

Just a guess though.

Mike McCann, PE, SE (WA)


RE: Existing Masonry Wall Construction

But, if for a furring (nailing) strip, it doesn't look like the wood strips were nailed into in the previous configuration. They'd be termite bait, termite paths from the ground up to the house lumber, dry rot, mold and mildue traps.

RE: Existing Masonry Wall Construction

Very unusual. I don't think the wood strips are thick enough to be used as nailers. In my house, the nailers are full dimension 2x wood strips laid horizontally into the stone walls, however, the wood strips take up only a small portion of the wall thickness which approaches 2'-6" most locations. I have no idea why the brick courses are there, however (an I am going way out on a limb here ...), perhaps the horizontal wood was required to ensure a platform to support the mortar that the brick was laid on. Otherwise, much of the mortar would fall into the voids and the width of the brick does not span the width of the block.

I think a portion of the mystery be might solved by looking at the exterior of the walls to determine what is directly opposite the brick bands. Perhaps the wood strip is only an anchor for the small wood blocks at the window/door opening on the left of the photo.

RE: Existing Masonry Wall Construction

Maybe an attempt to create a horizontal control joint? Any vertical cracks would probably terminate at the wood strips.

RE: Existing Masonry Wall Construction

(OP)
Thanks for your input!

The wood shims are loose and can be pulled out by hand so any bearing load has to be transferred through the outside face of the block. Also, for wind loading on the wall there is no mortar bond between the block courses on the interior face. The wood shims are creating a horizontal joint in the wall.

Not sure how to analyze this to get it to work structurally???

Any thoughts???

RE: Existing Masonry Wall Construction

Just repoint it using a low strength mortar (for plastic deformation).

Dik

RE: Existing Masonry Wall Construction

When I see walls constructed in this manner the building typically has a brick veneer. The brick courses are where tie bricks are located. But,I don't see anyou tie bricks. I have never seen the wood spacers. It could make sense if there were tied bricks and the courses did not line up. But, using wood is notherwise correct.

RE: Existing Masonry Wall Construction

If the wood can be removed (stripped out), pull it out and repoint with real mortar.

Don't analyze it at anything more than 0.0 tension, and 50% compression strength (compression strength is the wood, after a crush distance of 1/32 or so (which will vary) due to the existing gaps between between the higher row of block and the board and the lower row of blocks.)

RE: Existing Masonry Wall Construction

I'll add to the chorus of "pull them out and repoint." You might also tell the client that if he wants to "leave as is" then that means not adding another story/storey.

I'd guess that it was intended as a nailer, but poorly executed. My 100 yr old masonry house has bits of wood wedged into the brick to which the vertical furring is nailed.

RE: Existing Masonry Wall Construction

That method was falling out of favour by the time concrete blocks were being used (very common with brick buildings) but that is simply the nailing strips for the interior finish. Wood lath & plaster were commonly used although I don't see stains on the block from the plaster so more likely wood or some type of panel goods in this case. The joists laid into the wall are a very common detail as well; not necessarily good but they do survive when there is adequate drying of the wicked moisture. I have a medical arts centre being constructed in a building in Niagara Falls Ontario right now that has exactly the same detail in the block walls. We're in a negligible seismic zone and the building is in good shape for its 75 year age so I decided to let the owner leave them because he really balked at the cost of repointing.

RE: Existing Masonry Wall Construction

If the strips were horizontal, wouldn't the lath run vertically? I've seen lath split from a wide board, like expanded metal lath and about 24 to 30 inches wide. It is possible this type of construction had happened.

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