Bonding Construction Joints
Bonding Construction Joints
(OP)
The site I'm on is casting pad foundations and sub-columns in two stages.
So we cast the pad foundation, leave a few days to harden, chip the joint area back a bit for a nice solid interlock, put the sub-col formwork up and cast away.
For the majority of the work done so far, no bonding agent was used. I'm aware of sika grout but for bungalows it's a bit of an overkill.
The contractor has suddenly decided that adding a few mm of cement powder to the bottom of each formwork before pouring will give a stronger bond. As far as I can see, it'll only fill up the chipping and rob the new concrete of water.
The senior site engineer is happy to go with a small amount of VERY watery mix of cement powder and water. I think I can see the use, it provides extra water to saturate the old concrete, the cement powder might help gum up any cracks from chipping and the two will mix well with the poured concrete.
I'm just not convinced the benefits are worth the faff. are there any good sources for a site newbie like myself?
So we cast the pad foundation, leave a few days to harden, chip the joint area back a bit for a nice solid interlock, put the sub-col formwork up and cast away.
For the majority of the work done so far, no bonding agent was used. I'm aware of sika grout but for bungalows it's a bit of an overkill.
The contractor has suddenly decided that adding a few mm of cement powder to the bottom of each formwork before pouring will give a stronger bond. As far as I can see, it'll only fill up the chipping and rob the new concrete of water.
The senior site engineer is happy to go with a small amount of VERY watery mix of cement powder and water. I think I can see the use, it provides extra water to saturate the old concrete, the cement powder might help gum up any cracks from chipping and the two will mix well with the poured concrete.
I'm just not convinced the benefits are worth the faff. are there any good sources for a site newbie like myself?





RE: Bonding Construction Joints
RE: Bonding Construction Joints
RE: Bonding Construction Joints
RE: Bonding Construction Joints
As it is, the one set of cols they cast this way had the worst set of honeycombing so far, with two or three needing deep chipping and repairing at the join.
The contractor has quietly gone back to the old approach of chip, clean and cast.
RE: Bonding Construction Joints
RE: Bonding Construction Joints
RE: Bonding Construction Joints
Ron is on target as far as the "neat" cement. Generally though, column-to-footing joints never seem to get more involved than simply cleaning all loose material.
Regarding the honeycombing - that's a concrete placing problem that should be addressed.
Ralph
Structures Consulting
Northeast USA