Rusting Joint Reinforcing

Archive of Older Topics Archive - Product Discussions #5
1

When I was first starting in architecture back in the late 1960s and early 1970s Dur-O-Wal Tri-Rod joint reinforcing, or a similar product by other manufacturers, was often used. It had a rod in each face shell of the block, and a third rod in the brick, all tied together with a truss. The theory was that it would tie the block & brick veneer together so the wall thickness for evaluating h/t could be taken from the outside face of the brick to the inside face of the block, rather than just the thickness of the block.

Forty some years later I’m inspecting several community college buildings built during this era to determine maintenance needs and seeing horizontal joint cracking every 6th brick course. In a couple cases the mortar has popped out and I can see that the rod inside the brick has rusted.

Has anybody been involved in repairing something like this? I’m guessing that a veneer transplant, along with cutting off the rusted part of the joint reinforcement and installing new brick ties, will be required at some point in the near future, but is there a system that will tie the brick & block together? A lot of these walls are bearing walls, and the block is too thin for the height of the wall.

2

Do you mean something like this?
http://www.helifix.com/

3

I have also speced the Helifix system on several projects with very good sucess. The long term performance of this remains to be seen of course but I have some projects well over a decade old with no additional movement or issues.

I have also used the helifix bars to do “crack-stiching” at problem areas with very good success. the website should have a good example of how the “crack-stiching” works

4

First you need to understand the source of the moisture that caused the rusting. Any solution needs to address this problem.

My guess is that most of the retrofit products are more appropriate for attaching veneers than for situations where you need to make the multiple layers of masonry work together. If the original product was intended to reduce the H/t ratio you have this problem.

You need to understand if the rusted reinforcing means that you do not have the amount of steel needed for structural reinforcing.

You need to have a structural engineer look at the problem.

5

If I understand your comment, Mark, you are referring to composite construction where the brick facing and the backup are acting together structurally. I agree that it must be understood whether this was the case with the original design. Otherwise, the trusses described are only acting as veneer anchors, and retrofit products may be a solution.

I also agree about understanding the source of the moisture, but in veneer systems it is expected that there will be moisture in the cavity, so the presence of moisture does not necessarily indicate a problem. If the system is indeed decades old, then rusting at this point would be expected. Another factor to consider is that the applied knowledge of building envelopes to control heat, air and moisture has advanced a lot since this building was built. It may be beneficial to replace the veneer if there are other conditions indicating that improved wall performance is recommended. This could be poor insulation; excessive air leakage; or moisture getting introduced to the interior, or to the structure. These conditions can be corrected at the time the veneer is replaced.

6

If the joint reinforcement has not all been rusted then over time the rusting process will continue and the crack sizes will continue to grow.

The cracks suggest that at these locations there is no bond and hence no ability to transfer horizontal loads between the layers of brick. This lack of bond might influence where the supplemental ties get installed.

7

Thanks for the comments and advice. I’m going to have to look at the original drawings to see whether the block is thick enough to consider the brick as a non-structural veneer, or if the brick is needed to get the required h/t.

I’ve always thought of masonry walls as being good for a century or more, but I also recall hearing that galvanizing would protect the steel for about 50 years, so the ties in these buildings appear to be rusting right on schedule.

Rusting of the joint reinforcing in the brick doesn’t surprise me, because cavity walls assume that water may get into the brick from cracks, bad workmanship, etc., but it will be drained out before it gets into the block.

In any case, whether the reinforcing is structural or just ties the brick to the block, we will probably have to plan on doing a lot of veneer transplants in the near future to get rid of the rusting joint reinforcement and resultant cracking.

8

Paul, if you do not need the brick to serve as a structural component and are able to remove and reinstall, a couple of possible headaches and solutions to consider:

  1. If you can remove the brick, apply an air/water barrier to the face of the block, and then re-anchor the brick using a veneer anchor, you may be in luck. Just remember to consider whether you need that barrier to be vapor permeable or not.
  2. This may be an opportunity for the building owner to add insulation outboard of that barrier mentioned in 1. Of course now you’re talking about adding short-term cost, and of course longer anchors. I’m working on the assumption that property lines and setbacks aren’t an issue.
  3. Possibly the biggest issue, no matter what you do, is to remember that you’re going to significantly change the equilibrium of the building. There is possibility that after all this work is done, the building may experience peeling paint, problems with windows, difficulty balancing HVAC systems, and other wonderful experiences.

Isn’t it nice to have something to look forward to?

9

Ken, you’re so encouraging.

By now I’m (too) familiar with the 2 laws that govern all construction - Murphy’s Law and the Law of Unintended Consequences. I have also come to the realization that Murphy was an optimist!

10

Paul: Assuming that an institution like a Community College will be around for a long time a major repair does seem warranted. However it is of course possible that the economics of the institution may not be in a position to address the problem at this time.

One alternative may be to simply tuck point the walls while making the Owner very aware that you are applying a band aid to attempt to slow the problem down while they work to budget for the major repairs/“fix” in the future. I would also think it may make sense to impliment a “fix” of one building or area to allow this new system to act as a living Mock-up before the “fix” is used through-out the college.

You will have to document that the tuck pointing is only a band aid to protect yourself but it is not inconceivable that this could buy the college a decade or even two before this situation becomes an immediate issue.

Of course this is all based upon the assumption that the brick is only a veneer and not a crucial part of the design. It also assumes that the reinforcing is not to close to the surface since this could destroy the band aid in short order. (I have seen some jobs where the outside wire is 1/4" to 3/8" from the exterior and this makes it very difficult to keep motar in place.)

11

I worked on several masonry restoration jobs at the University of Washington where the reinforcing bars had rusted to about the thickness of a pencil lead, and the projects were about 20 years old by that time. The original construction was concrete backup with brick veneer, (full thickness bricks, not “thin brick”) but the brick was doing things that brick doesn’t do well: soffits, sloped faces, and trying to meet up with concrete frames that expanded a little too much. The UW hired a masonry consultant, and here is the basic list of what was done:
removed all brick veneer, plus roofing, soffits, and parapets
cut back and sealed any reinforcing still anchored in the walls.
reinstalled brick veneer with strict attention paid to “panel sizes” – setting off expanses of brick with sealant joints from all doors, windows, penetrations; and also putting in protective sealant joints every 20 feet on center in the face of the wall.
replacing all reinforcing with stainless steel; replacing all flashings with stainless steel; making sure that proper drains and weeps are part of the wall construction; redesigning top of wall to keep the water out. And then finally, a somewhat breathable protective coating on the brick that would keep out bulk water and yet allow vapor to transpire.
The re-skinning of the buildings ended up costing nearly as much as the original construction cost. location: Seattle, so there were seismic concerns that had not been adequately addressed the first time around. (original construction was early 1970’s).

12

Is it possible that brick masonry is not as durable as in the past? Esthetically, it’s still a wonderful material. But there are so many pieces, with an increasing number of details and precautions, and a decreasing number of capable masons. Toss in the ever-present need for design innovation, and the imperative to compete economically with other materials. I remember masonry industry ads that they “build for the ages” but it seems that it may no longer be a material that we can reliably recommend to an institutional client.

13

Tony:You raise an interesting discussion and I will assume you made it as a point of debate and as such here is my counterpoint for your consideration. (I may not even completely agree with everyting I state. simply taking a different side of the same discussion)
1)is there a NEED for design innovation or does pushing the reasonal boundries of designing with masonry lead to prolems (ie: Anne’s example) “Innovation” that abandons traditionally sound practice may not be innovative at all. (I will admit that my detailing of masonry walls runs on the more traditional side)
2)Do we design fewer masonry building because of a deceasing number of masons or are there a decreasing number of masons because we are to quick to abandon the design of masony buildings. (chicken/egg, egg/chicken?)
3)economics; that is a tough one if you are talking about a strip mall or a budget hotel but for an institution the life cycle analysis can be justified for a much longer period. (a school will be a school for decades. same is true for a fire or police station, hospital, museum, etc.) As the life cycle is extended the cost effectiveness of a well designed masonry building can be very favorable economically.
4)Due to the life cycle considerations the institutional client may be the last bastion of the well designed and detailed masonry building
Just a different point of view to an interesting topic.

14

Here in Houston, HISD is demolishing a number of school buildings that were built in the 1950s and early 1960s (as well as some structures from the 1920s and 1930s although there are very few of these left). While it is easy to poke fun at Houston because we tend to be quick with the demolition ball, the truth is that these buildings no longer served the required demographics or were no longer technologically current with regard to energy efficiency and wind storm resistance. Throughout this area many schools built during this time were designed with single loaded exterior corridors with a lot of windows for cross ventilation. This was the acme of energy efficiency back in the day: lots of daylight and adequate cross ventilation reduced energy consumption. As soon as air conditioning schools became the norm, these buildings turned into energy hogs. The expanse of glazing also presents a danger during periods of high winds.

Many of these buildings (especially at the elementary level) are on smaller sites and serve 250 to 350 students with no room for expansion. Newer campus for elementary schools consolodate 2 or more campuses into facilities that serve 600 to 800 students.

The HVAC systems, many of which were originally installed in the 1960s and early 1970s have been replaced, but are, in most cases older, less efficient systems which are conditioning air for spaces withing building envelopes that are obsolete.

Let’s not get started on how much asbestos was incorporated into these facilities.

Although these buildings were “built-to-last” with masonry, glazed structural masonry, and CMU; they no longer economically serve the purpose for which they were intended. Their life span was, in most cases, 50 to 60 years. Where sites are too small, facilities are being demolished and the land sold to fund future growth.

I would suggest that at the high school and university levels, there is land available for flexible modernization and expansion. Most elementary schools and many middle schools, especially those built at the height of the baby boom, are maxed out. Interestingly enough, the much older facilities, the ones with double-loaded interior corridors and punched windows (instead of window wall) may be more likely candidates for economical renovation to current sustainable and structural standards.

Masonry is a great material, but, like all materials, it does take care to detail, construct, and maintain. Visit any cathedral in Britain and see how much time and money the parish spends to keep the “fabrik” in service.

15

Since most of my career I was involved with institutional clients (health care, and higher ed, typically) masonry was the common exterior expression for the building. However, even in my working life, the typical wall construction has changed to something much thinner and lighter weight (ie, less structure) than what we did when I was starting out. Typical masonry wall construction when I started was either poured in place concrete structural wall with a masonry veneer (with a 1" standoff); or a CMU structural wall with masonry veneer (again with the standoff). In the past decade or more, the typical masonry building I’ve worked on is brick veneer over steel studs and some cementitious or fiberglass backer board.
When you have a wall that is 12 or 15 inches thick, you don’t need to be especially proficient to keep water out and keep the building reasonably climate protected. In fact, such mass masonry walls are coming back into fashion for residential work – typically “green” construction. (and the same goes for roofing materials – put enough mass up there, and eventually it won’t leak). However, with masonry veneer walls and thinner wall sections overall, you have to do the construction properly for it to work, becuase there is no excess material there to provide backup. I think bricks are fine, and the mortars we have now are in some ways better than before. the reinforcing is better engineered. I still miss lead flashing for masonry buildings (no one wll use lead on the west coast). Our increasing demand for energy efficiency can exacerabate bad detailing and construction, which means that all the more care needs to be given to the construction of the wall – and that’s the hard part.

16

I am concerned by the tendency to move away from masonry back-up on institutional buildings. Steel stud back-up makes for an initially lower investment but will that still hold true when viewed across a century of use. (of course a steel stud wall, if it is designed and detailed properly, could surely last that long but the cost savings relized by using a steel stud frame would also be diminished considerably).

I realize the architect is not always in a position to control the budget or the direction a public body takes. Still my firm works very hard to design every institutional building with the intent that it will still be in use long after I am dead. When working with the public’s money I believe you are burdened with the responsibility to think this way.

Many times in this country that type of thinking is viewed as to expensive and idealistic but I wonder is you had the same conversation in Europe would you recieve a different tone. It pains me to see architecture becoming more and more a part of a disposible society.

17

One problem with the masonry backup walls is that they add considerable mass to the building which causes problems in earthquakes. This is made even worse by the all to common situation where these walls do not have enough reinforcing or they are not anchored top and bottom.

These rigid walls ake it much harder to accomodate the differential drift between floors without causing major damage.

18

Back to the original question, more investigation is needed to determine an optimum patch, repair, or replacement. How much rusting is on the rods? How deep are they? Does this rusting extend to the transverse rods? Is the brick, indeed, contributing to the design strength of this wall? Is there separation in the collar joint between brick and block? Is there rusting and cracking in the block work? Id recommend digging deeper to determine the full condition.

It is probable that carbonation of the mortar has reduced the alkalinity of the mortar sufficiently to permit rusting. If so, this carbonation may not have penetrated very far and the rusting (a progressive disease of steel) may be limited to the outer rod. If that is the case, repointing (often called tuckpointing) could be the solution, lasting 20 years more. As a preparation for such repointing, Id use a needle blaster to remove the accessible rust after old mortar is removed. Then, Id prep the metal surface with a rust-inhibitive paint or a neat portland-cement slurry or portland-cement/very-fine-sand slurry, applied with a narrow brush. The slurry offers a high-pH condition at the steel surface, which will inhibit rusting. Repointing the entire wall will have a better/more uniform look than repointing only the cracked joints.

You can approach brick replacement and tying it back or structurally bonding it with the block once you know answers to the other questions above.

19

Boy, you don’t log in for a few days and your entire industry has been called into question!

First, I’ll deal with the original question. Joint reinforcement and wall ties have evolved over time just like many other products. Prior to about 1970 it was common to use wire reinforcing that had no corrosion protection on it. Beginning in the 1970’s and 1980’s it became apparent that wall ties and joint reinforcement needed some type of corrosion protection to keep from rusting and that is when hot dipped galvanizing became more widely specified and used. It is interesting to note that famed masonry consultant Clayford “Tom” Grimm wrote a paper, “Corrosion of Steel in Brick Masonry” in 1985 where he stated that hot dipped galvanized ties could have a life expectancy of 15 to 60 years. Hmmm, that’s about now on some projects. I believe that installing new ties is appropriate for this project. If that means tearing off the veneer and reinstalling it to repair and/or upgrade the wall, then that is what must be done. Helifix, Hohmann + Barnard, and other tie manufacturers all have solutions for retrofit wall ties. I would suggest you consider using stainless steel wall ties if you want the steel to last as long as the brick and block.

There is some great discussion about the longevity of masonry walls in this thread. As some of you have mentioned the move towards thinner walls and ones with more moisture sensitive materials in the envelope ends up shortening the lifetime of the masonry envelope. If we were able to build multiwythe brick walls with lime mortars using headers to tie the wythes together, we would likely get a wall that lasts over 100, nay 200, years. However, as we rely on masonry accesories in our wall to perform - flashings, wall ties, reinforcing - that don’t last as long you will get a wall system that doesn’t last as long. We are applying all of the great building science research to make our walls more efficient, but the fact remains that the wall is only as good as the weakest link, and in some cases that happens to be the wall ties/joint reinforcement. If money were no object, I would promote stainless steel wall ties all the time, but the reality is that owners are not really willing to pay for a structure to last that long.

To address Tony’s point, I think brick masonry is as durable as it was 100 years ago, even more so today with brick making technology, but we are putting brick into different conditions than we did in the past and the brick is just one part of an entire system. We must continue to learn from our mistakes, continue training the next generation of installers and try not to expect too much out of our buildings if we (rather, owners) aren’t willing to pay for quality.

IMHO

Brian Trimble
Brick Industry Association

20

Part of the problem is that truss-type horizontal joint reinforcing for composite brick/CMU walls does too good a job. CMU shrink after installation, but brick go through an irreversible expansion. The brick may also have more thermal movement than the CMU backup wythe. The stress of these opposite forces may be cracking the mortar, thus allowing moisture to get to the reinforcement.

If you remove the veneer, the horizontal joint reinforcement for the brick wythe could be cut off flush and waterproofed, and then individual ties used for rebuilding the veneer that would allow some minor horizontal movement differential.