Masonry Control Joint 1

[SperlingPE]

During a site visit, it was discovered that cmu wall control joint was not installed. The block wall was stopped and started and some "filler" material was put in the gap to make it look like a joint was there. Long story short, what can I do now that won't look like cobbled up mess? The wall is a wall of a grade school gymnasium.

 

[DaveAtkins]

What you describe DOES sound like a control joint. What am I missing?

DaveAtkins

 

[SperlingPE]

There is nothing (T-bar) in the joint holding the wall in alignment.

 

[AggieYank]

In control joints, there is a small gap of air or filler grout (expandable/shrinkable) running from the foundation up to the top brace (beam) in the wall. We don't use bars between the two walls to keep them together. They are braced at the bottom and top by foundation and beam, or rarely, they are cantilevered up. But in either case, you don't need anything attaching the two walls on either side of the vertical control joint.

 

[SperlingPE]

The detail that is used in our office calls for a + shaped bar in the joint to hold the walls in alignment. The joint is then sealed (rod, caulk, sealant) or some other means. So there is no use for the + shaped bar except maybe as convenience for the mason?

 

[phuduhudu]

There are two types of joint. A control joint and a movement joint. A CJ allows only for shrinkage and is basically a preconstructed crack. An MJ allows for both shrinkage and expansion and therefore needs to have a compressible filler. Where we have MJs in brick walls and we want one side of the wall to provide lateral stability to the other side we often use bent up ties in the joint which are just like a small flat metal concertina that can stretch to allow the walls to move apart but does not allow the walls to move laterally relative to each other. So if you don't need that then you don't need any connection between your walls.

Carl Bauer

http://www.bauerconsultbotswana.com

 

[SperlingPE]

Not talking about brick. This is a joint for a cmu wall.

 

[DaveAtkins]

When we do need to transfer shear across a CJ (for example, where the CMU above a large door opening resists wind load by spanning horizontally and there is a CJ at one side of the door), then we have a detail that shows building paper on one side of the keyed joint with grout poured into the keyed joint. This only works with the kind of CMU units that have the face shells "sticking out" at each end.

DaveAtkins

 

[samdamon]

How long has the building been up? Whats the distance between the vertical joints? If the block has had time to dry out you have probably experienced most of the irreversible moisture-related shrinkage that control joints are intended to relieve. From now on its seasonal thermal forces you have to worry about, and from what you describe the as-built joint might work for those. You can check if the as-built clear joint width is sufficient based on the expected seasonal temperature variations at the building site, and the coeff of thermal expansion for cmu. I use delta = 115 deg F for my practice here on the east coast. I assume the wall is designed to span vertically.

If the joint width is found sufficient, one way to finish it is to rake it clear of all mortar, installing a backing rod and tooled sealant on ea face. Choose a sealant that has the ability to accomodate the expected movement.

If the joint is not wide enough or otherwise is not clearly working as a mechanical break between the two walls, suggest sawcutting it, or possibly sawcutting a new joint nearby.

 

[SperlingPE]

Masonry experts.

Since the "+ shaped" pre-formed piece was left out of the joint, is there any possibility of the wall getting out of alignment (transverse to the length of the wall) due to thermal movement or wind forces? Backer rod and sealant can be installed to do the as built joint.

 

[haynewp]

If it hasn't been sealed very well you may get air and water penetration through the joint you wouldn't get with a rubber + shape. And you can get different displacement perpendicular to the wall at each side of the joint from lateral if a shear key is not used. The wall is also laterally unsupported along the joint if no shear tranfer is capable. So I think it is a good idea to use one of those rubber + shapes. But with all that, our standard detail doesn't use a + shape either.

I am sure there are a lot of buildings out there that have been erercted the same way you describe which have not had any problems. But to CYA, I would make the contractor send me an email taking responsibility for whatever maintenance problems may occur from neglecting the detail if he doesn't want to fix it.

 

[SperlingPE]

Now back to my original question.
Contractor is on the hook for fixing this. That has been agreed to.
How to fix this problem?
Does it need fixing?

 

[AggieYank]

The wall shouldn't be out of alingment at all, assuming it was designed to span vertically. The only time I could see it getting out of alignment with the wall on the other side of the control joint is if one of the walls is braced by another CMU wall, right at the control joint, and even then, I don't see why this would be a problem. The braced wall wouldn't deflect at all due to wind, while the unbraced wall would deflect less than L/600 at midspan (halfway up) the wall. Thermal movement in the direction transverse to the wall will be very very minimal, as there is only ~8 inches of block that will expand in that direction. Wind movement will be higher, but should be the same on either side of the control joint, and won't be a problem.

 

[haynewp]

If it is a structural problem by not having shear transfer across the joint, then yes of course it needs fixing. But only you can determine that. Otherwise, I see it as a potential aesthetic and maintenance issue.

It seems ridiculous to tear down part of a wall to insert a little rubber strip. I would find out what kind of "filler" he used to seal the wall, and talk to the manufacturer about movement perpendicular to the joint and distress to the sealant and breaking down the joint over time.

The edges of tilt panels don't usually have a shear key and the joints seam to hold up fine. Contact Dow Corning, they may have a product that will work or tell you if what he put in is going to hold up or not.

http://www.dowcorning.com