How to bond old concrete to new concrete?
Summary
When bonding old concrete to new concrete, there are several approaches you can consider. Some forum users have different opinions on the best method, but they all share helpful tips. From using bonding agents to mechanical methods, here's a summary of what our forum users are saying to help minimize cracking and ensure a strong bond between the old and new concrete. Ultimately, the best approach depends on the specific circumstances of your project.
What our forum users are saying:
- Some suggest using a bonding agent like Weldcrete to help with moisture loss and improve bonding. However, it's important to remember that a bonding agent is not a replacement for rebar. One user says:
- "Weldcrete does work for its intended purpose, read the instructions." -- G&Co., Contractortalk.com
- For minimizing cracks, one user explains:
- "What I am trying to do is minimize the chance of cracking where the two slabs meet by way of not letting the moisture from the new concrete to wick into the old concrete...It seems everywhere I look, the reason I get is that it is due to moisture being sucked out of the new concrete, which doesn't let it cure properly." -- jerryham2, Contractortalk.com
- Another user suggests a mechanical approach:
- "Drill for 1/2" rebar, install shingle layer between new, & exist conc. Keep shingle below top enough to do a proper finish edger. After cure, use Sonolastic, or similar, across joint. Rebar keeps new/exist same ht. Isolation stops cracking, & moisture loss while curing. Csulk stops freeze damage." -- Railman, Contractortalk.com
- If there's no room for rebar, one user suggests:
- "If you don’t have room for pins (why not?) you can saw/grind grooves/keyways in the old slab and just dump the new concrete in the hole. Broom it right up flush with the old work. Tell them it’s a repair and it will walk talk and act like a repair but it’ll be less expensive than redoing the whole thing." -- reggi, Contractortalk.com
- Another user recommends:
- "Probably just the carpenter in me but I would use ice and water on the old slab held down about an inch. Drill some rebar and cut the joint between new and old once cured. I mean it's only 2'x'2 so I wouldn't think too far into it." -- JoeStanton, Contractortalk.com
Post Mentions
- If you don’t have room for pins (why not?) you can saw/grind grooves/keyways in the old slab and just dump the new concrete in the hole. Broom it right up flush with the old work. Tell them it’s a repair and it will walk talk and act like a repair but it’ll be less expensive than redoing the...
- Drill for 1/2" rebar, install shingle layer between new, & exist conc. Keep shingle below top enough to do a proper finish edger. After cure, use Sonolastic, or similar, across joint. Rebar keeps new/exist same ht. Isolation stops cracking, & moisture loss while curing. Csulk stops freeze damage.
- Probably just the carpenter in me but I would use ice and water on the old slab held down about an inch. Drill some rebar and cut the joint between new and old once cured. I mean it's only 2'x'2 so I wouldn't think too far into it.
- good Morning: I'm pouring a 2'x2' concrete slab and joining it to an existing patio slab. I cut out the old section and have no room to install rerods at this point. A product called Weldcrete has been recommended by one of my vendors. It is a bonding agent that brushes onto the existing...
- Not at all clear what you're trying to do, but a concrete bonding agent is in no way a replacement for rebar. Weldcrete does work for its intended purpose, read the instructions.
- Concrete does not glue to concrete. Think of it as two boulders. Two boulders (without knowing their pronouns) will never mate permanently. The same is with Concrete. .
- is the purpose of the sonolastic to help keep water from getting between the old and new concrete . also since i already asked one question - what 'shingle layer' refer to .
- What I am trying to do is minimize the chance of cracking where the two slabs meet by way of not letting the moisture from the new concrete to wick into the old concrete. I'm not even sure that I need anything applied to the old concrete. I went to the website and it wasn't clear if that was...
- All good solutions. Thanks for the help. I can always count on Contractor Talk to get solutions. Reggie, Your finished repair looks pretty good!
- Pretty good pays the bills! 🤣
Related Threads
- good Morning: I'm pouring a 2'x2' concrete slab and joining it to an existing patio slab. I cut out the old section and have no room to install rerods at this point. A product called Weldcrete has been recommended by one of my vendors. It is a bonding agent that brushes onto the existing...