Removing laitance from the top of footing for CMU retaining wall
Removing laitance from the top of footing for CMU retaining wall
(OP)
I'm brand new to this site and kind of new to special inspection. I have a lot of questions!
I was called out to do a special inspection for a CMU retaining wall. The project plans gave the contractor the option to wet set the first course of block into fresh concrete after the footing had been poured,OR they would have to construct a keyway. I was called onsite by the owner to begin inspection after the footing had been poured but before they started to lay up the wall. I immediately noticed that they had not wet set the first course AND there was no keyway. In addition, masonry code and ACI specify that laitance be removed and the footing be cleaned before putting down the first mortar bed. I notified the contractor of this and he seemed perplexed. He didn't know what "laitance" was. The owner called the guy who designed the wall and was told that the contractor needed to grind out a keyway and remove the laitance. After chatting with the contractor as the job progressed I learned that he hadn't done much masonry work in the past (just concrete work) and that this project was a costly learning experience.
On another project I had the same experience with bewildering the contractor when pointing out laitance removal. Is this something that is looked over by other inspectors? Am I being too strict in this regard? Any tips are appreciated. Thanks!
I was called out to do a special inspection for a CMU retaining wall. The project plans gave the contractor the option to wet set the first course of block into fresh concrete after the footing had been poured,OR they would have to construct a keyway. I was called onsite by the owner to begin inspection after the footing had been poured but before they started to lay up the wall. I immediately noticed that they had not wet set the first course AND there was no keyway. In addition, masonry code and ACI specify that laitance be removed and the footing be cleaned before putting down the first mortar bed. I notified the contractor of this and he seemed perplexed. He didn't know what "laitance" was. The owner called the guy who designed the wall and was told that the contractor needed to grind out a keyway and remove the laitance. After chatting with the contractor as the job progressed I learned that he hadn't done much masonry work in the past (just concrete work) and that this project was a costly learning experience.
On another project I had the same experience with bewildering the contractor when pointing out laitance removal. Is this something that is looked over by other inspectors? Am I being too strict in this regard? Any tips are appreciated. Thanks!






RE: Removing laitance from the top of footing for CMU retaining wall
RE: Removing laitance from the top of footing for CMU retaining wall
RE: Removing laitance from the top of footing for CMU retaining wall
Removing laitance is not difficult. It can be done mechanically or chemically. I prefer mechanically. Use a bush hammer or even a weld de-slagging tool (air powered). Comes right off and then you can bond to it.
As for a keyway and wet setting the first course of block.....I think neither is a good idea. Use rebar. Craftsmanship in construction has declined to the point the finess construction is no longer viable!
Yes....it is deplorable how little knowledge there is in the construction industry.
RE: Removing laitance from the top of footing for CMU retaining wall
RE: Removing laitance from the top of footing for CMU retaining wall
RE: Removing laitance from the top of footing for CMU retaining wall
Another term is green cutting, which is sandblasting or otherwise removing laitance while the concrete is still green or not fully cured.
RE: Removing laitance from the top of footing for CMU retaining wall
6.4.2 "Immediately before new concrete is placed, all concretion joints shall be wetted standing water removed"
11.6.9 "... If µ is assumed equal to 1.0 lambda, interface shall be roughened to a full amplitude of approximately 1/4""
ACI 530 Specification 3.2 page S-52 "Prior to placing masonry, remove laitance, lose aggregate, and anything else that would prevent mortar from bonding to the foundation"
Keys are required at grout pour joints ACI 530 3.5 S-68, the codes intent was not to include the foundation as needing a key.
Wet setting anything is bad practice, a key in the base of the wall is unnecessary for typical applications but are "easy" to form and place correctly.
RE: Removing laitance from the top of footing for CMU retaining wall
RE: Removing laitance from the top of footing for CMU retaining wall
The contractors that worked for the utility, SDG&E, knew the utility's "system" and were very cooperative with field staff since they always wanted that next job.
Other contractors can be crooks. I've been threatened with chainsaws and airless paint sprayers.