Brick weeps
alan72
| Posted in General Questions on
This isn’t a ‘green’ building question. Just a building question.
Is there a product that works well in the Midwest (SE Michigan), to use as a vent in brick weeps?
new construction, brick veneer
Seems like the options range from open weeps to steel wool to metal vents to plastic vents.
Looking to keep critters out and keeping maintenance low. I imagine these can get clogged with debris and stop functioning/draining.
Thanks, Alan
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Replies
Alan,
I don't know that it would still be an option because codes may have changed, but I have encountered brickwork done in the 40's-60's that simply inserted a 4-5" piece of 1/4" cotton rope between every third brick forming the first course. I noticed little fuzzy dot's embedded in the mortar at the lowest point on the first course bricks, which peaked my curiosity. By chance, I had a remodel where I needed to break out the brickwork and confirmed what I had seen was indeed rope with the end bent upward to rest against the tar paper.
The condensation that collected behind the bricks would likely saturate the rope, which would then dry to the outside. I can't profess that it is the best option, just one I have seen. The rope had survived for some 35 years at the point I found it and the wall behind the tar paper was in good shape. However, the bricks were almost vitrified, so maybe the load behind them was primarily due to the mortar. Steel wool if stainless or bronze wool might survive as long. Not too sure that ordinary steel wool would last a year. Perhaps a modern equivalent to the cotton rope is being made.
I think one thing to be very aware of is the gap between bricks and whatever WRB you chose for the structural wall. The old brick work I have dealt with almost always had a 1" gap. This may seem extreme, but trimming the squeeze out as you set each course can be done better with this gap. The good masons would lay the brickwork almost as neatly cleaned as the face side. Sloppy masons leave the squeeze out, which can either fall out or make direct contact with the tar paper/WRB. If the globs fall down the wall gap behind the bricks they can clog the weeps and create a wet mass down low on the wall.
It may be instructive to note that many of the stone and brick veneer horror stories seem to me more often of the non-gapped adhered veneer type. I would suspect that the moisture load of all that mortar in direct contact with the supporting wall alters the behavior of the WRB. Or at least its longevity. I hope for your sake that the "masons" you will have on the job are actually that.
I appreciate your input -- my understanding of the cotton weeps was that they were to be removed at the end of the work day leaving a little tunnel for drainage - but I don't know if that is true or not.
I see there are many products to maintain the air space behind the brick veneer from mortar droppings as well as weep covers - I imagine that the more skilled the mason is, the better the execution will be with or without these products - like most things - it's difficult to gauge the quality of the work because you can't easily see if there are issues on their other work. Our GC is very confident in her mason.
Do people have an opinion on these items? (like mortarnet.com?)
Seems like the biggest impact after installation is inspecting the weeps periodically to verify that they aren't covered with landscaping material/dirt/mulch...
Thanks
Somewhere there has to be data on this question; I don't have it at my fingertips. You want more than just "weep" action (i.e. rope) at the bottom of an air-gapped masonry veneer wall. The plastic vents (so-called "cell vents") also provide airflow. Presuming there's a place at the top of the wall for air to flow out, this establishes a convective loop for air drying behind the masonry. Those 1950's-era uninsulated and tarpaper-sheathed walls may have allowed some drying towards the inside, but that's NOT where we want moisture going these days.
Cell vents look like a bundle of plastic soda straws that most insects can't traverse. Once in place you can ream them with a piece of wire.
Alan,
I would point out that contrary to Andy's desire for more than just weep action, I am not aware of any brick or stone veneer application that specifically provides for significant air exchange in anything resembling a convective loop. Indeed, the paste on faux stone/brick veneers are often lucky to have even a minimal capillary break layer figured into the design. Many full brick walls are also set well under the 1" traditional gap.
Even brick walls that are set a full inch off the structural wall would be very poor at useful air exchange due to the gap size and lack of adequate vent cross section at the bottom of the wall.
I would reference the many discussions on GBA regarding just how free air flow under roof decks with small gaps isn't free, as well as the recent references about potential fire spread behind rain screen siding designs.
The article which I believe is in a recent issue of Fine Homebuilding suggests that gaps in rain screen assemblies up to approximately 1" do NOT contribute to fire spread behind the siding. I think this strongly suggests that air flow behind a brick wall would be very limited. If a fire under the siding can't establish a convective loop, then it would seem doubtful that mere moisture variance would do so.
The alternative materials suggested, such as plastic vents, can not provide useful amounts of air venting relative to the total wall area nor would they do much to "weep" the wall moisture. Rather they would only pass bulk water which would limit their effectiveness to only the condensate falling directly onto them. I would also not wish to be faced with the lifetime of poking wire into the holes to maintain their effectiveness.
While I cannot be certain that a tar papered structure is not subject to a certain amount of
inward moisture pressure, I do suspect that much of the moisture load is handled by the foundation. The brick ledges that I remember were often several inches lower than the sill plate position. This has the immediate visual value of getting the brickwork closer to the desired grade lines. A perhaps overlooked additional value lies in having the weep line well below the sill plate. If condensate does form on the back of the brick wall (and the mortar work has not clogged everything up) the condensate will slide down to the bottom brick course and saturate the foundation and brick weeps. Safely below the sill plate.
Wind washing of brick, foundation and rope weeps would all work to redistribute the moisture load back out to the air. I believe the old method here is functionally more valid than attempting a design more like a rain screen for siding.
If you are going with a full brick on ledge design, I would suggest confirming that the ledge will be set at least two brick courses lower than the sill plate and preferably three. I will leave it to you to ponder how one does water management and weeps for the lintels over windows and doors.
Search for good masons.
Here are some useful masonry resources. The first is detailing for more commercial construction, but the principles would be useful for other construction types as well. The second compares the types of weeps. Andy is correct that there are studies that show cotton weeps to be ineffective long term compared to alternative types.
http://imiweb.org/masonry-detailing-series-3/
https://www.masonrymagazine.com/blog/2016/10/24/weeps-getting-water/