Proposition: Cavity drainage material (“mortar net”) is a quality control device. If you were certain that the mason wouldn’t get (or leave) mortar in the cavity, you could eliminate the cavity drainage material.
Do you agree or disagree with this proposition? Are there other valid reasons to use “mortar net” products besides keeping the cavity clear of mortar?
(Yes, we are being asked to eliminate it as a v/e measure)
Tell them that at the completion of the wall, you will perform a quality control measure by dumping several buckets of water into the cavity. Any weep holes not functioning properly will need to be adequately cleaned out (even if it requires removal of the wall). State that the test will be repeated until all weep holes function as intended.
Maybe that will get their attention.
I disagree. It is not practicable to construct a cavity wall without some mortar dropping into the cavity. I’ve discussed this with skilled masons on the job and watched them build. If it could be done, productivity would fall so low that the wall would become uneconomical. I believe the quality of the joints would suffer as well, because there would be a tendency to hold back the mortar in the bed joint from the back side of the veneer, making it less than full. Snot boards aren’t workable when you have ties every 16 inches vertically, with anchors already in the backup wall–how do you get them past? I never saw anyone actually use “cleanout” units at the base of the wall, but I’d think it would be hard to install units in the hole that so they weren’t visibly “patched.” Before cavity drainage materials, we used pea stone, which worked okay, but not great. I think cavity drainage materials are a definite improvement to any of these, and are a necessity.
I agree that it is not practical to expect NO mortar to fall into the cavity. Cavity drainage materials are high enough to keep mortar dropings high and dry from the weep holes. I specify laying the outer wythe bricks on a beveled bed joint to allow a minimum of mortar to be squeezed out of the joint to fall into the cavity.
I also include “Use wood strips temporarily placed in air space to collect mortar droppings. As work progresses, remove strips, clean off mortar droppings, and replace in air space.” I do not know if this actually is done and may be problematic as John noted above.
One document (dated June 1984 and pre-mortar net) that I have carried with me in my personal library recommends the following spec requirement. “Approximately every third or forth brick in the first course over foundations walls and lintels be left out until the entire wall panel supported by that course of bricks is constructed, and the cavity is cleaned and inspected, after which such bricks can be permanently set in the finished wall.” This also appears impractical and I have never seen it done.
I would be suprised if BIA does not have a positon paper or technical note on the use and abuse of mortar net type products.
You simply CANNOT eliminate this. Every detail I have seen (some going back quite a ways) has something in that location helping drainage. It is accepted standard practice and the cost of mortar net is so small that if they have to balance the budget on the back of cavity drainage you have bigger problems than mortar net!
DO NOT give in to this absolutely lame suggestion!
Think of the lawyer asking you on the witness stand at the envelope failure lawsuit.
Did you know that this was standard practice? Yes
Did you know that this was included in every detail of these areas on the BIA and other web sites? Yes
And yet you deleted this material because it saved the project X,000 dollars? Yes
I rest my case your honor.
Thank you, Marc.
I have had masonry subject matter experts tell me that the “snot” board is undesireable because the act of picking it up and moving it dislodges bricks after the initial mortar set, causing another set of problems.
I have seen the bottom of wall brick cleanout used on high quality institutional construction. A good mason can fill in the missing brick in a way that is not later noticeable. Note that the same would be required over shelf anges and lintels. Having said that, I specify cavity drainage material.
Anyone want to talk about peel and stick temporary flashing? It’s another favorite CC item. (CC = cost cutting. VE = value engineering. Let’s stop letting people confuse the two.)
Or a discussion about whether or not the bed joints in brick masonry should be furrowed or not.
That’s a “goodie” [have a good written piece on this, with examples, if interested]
Thanks for all the comments in support of our position. (No surprise). I wanted to follow up with the resolution of this issue:
The cavity drainage material is still in the project. The suggestion to eliminate was floated by the CM, and immediately rejected by the mason with the statement: “Why would we ever want to take it out? It’s cheap insurance for us.” Our project architect went into the meeting armed with all of your excellent observations, but didn’t have to say a word once the mason spoke.
Did it ever occur to the Owner to delete the CM as a cost saving measure?
The CM actually suggested this without consulting his mason??? Talk about a waste of time and money. I agree with anon above.
What does this thread have to do with construction contract administration?
It addresses a technical issue that occurs during construction but is that the same as administering the construction contract?
John - I posted it in this area because it was a suggestion that came up during construction. I agree it could legitimately be a Product thread, but since it was a CM effort to save pennies to meet a low-balled GMP, it seemed more appropriate here. The idea behind the original suggestion was that mortar net, if it were exclusively a quality control issue, could be eliminated if the CM could find other methods and means for assuring the cavity would stay clear of mortar. The implication is that then the GMP stays the same. If it becomes a product elimination, then a credit accrues to the Owner by change order. At least I think that was the logic behind it. And in either event, it requires administration of the contract either by ASI or by Change Order. [Incidentally, I feel more confident with this discussion being in CA area than the other one you commented on Concrete Cure ].
Anon Indeed, no one was more surprised than we were that the CM hadnt run this past the mason first, except maybe for the mason himself.
I know the issue has been resolved, but I had to throw my comments in. In our Technical Notes 7, page 5 (2005 edition) we state the following: “While it is not mandatory to include drainage materials, they may help to keep the air space open for drainage. However, the use of drainage materials should not preclude good workmanship and an effort to keep the air space
clean.”
The pull board, although we show it in other Technical Notes, can’t be used without a lot of hassle. It would be nice to have perfect construction, but nothing is perfect. As a colleague once told me, “Clean, but not pristine” for a cavity. Don’t expect it to be totally clean, but clean enough to allow drainage. The mortar drainage products allow that to occur.
Brian Trimble
Brick Industry Associaton