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Old 07-14-2011, 06:53 PM  
nicky
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Default concrete over concrete

Hi all, first time here.

I have a back entrance porch which I am going to seal off, raise the floor level level with the two rooms which come off it and re-line etc. to make more kitchen space.
The concrete floor slopes down from the sides like coving everywhere but under the outside door, where it is just flat and as there is no doorstep has always let wind and water in.
I want to concrete up this bit to make the outside concrete foundation continuous.
Will new concrete "stick" to the old? Or will water get in at the joins?
My nephew is going to build up the floor with timber and wooden overlay, but I want the outside concrete bit watertight.
I would welcome advice.



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Old 07-22-2011, 02:49 PM  
RD55
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new concrete should stick to the old. good luck!



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Old 07-22-2011, 08:05 PM  
inspectorD
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Default Sorry Rd

Concrete does not stick to old. It is called a cold joint and will leak if any water flows in between, It can also freeze in the cold climates and break it all apart, Sorry.
The new concrete will need a bonding agent , and will have to be cleaned really well with an acid wash first.
Sometimes it's just better to let the pro's do it, and not have an issue in the end. Do not go to a big box store for your supplies, go to the concrete supply store in your area and ask questions about what you are trying to do , if you insist on DIY.

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Old 07-24-2011, 12:51 AM  
RocLok
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Nicky,

Unfortunately InspectorD is correct, it will be a cold joint, his preparation steps are advisable. It sounds like you are going to extend the living space over this new area, meaning it will be load bearing and you will want both sections to be seamless and even. So is this just a concrete slab on grade, or is it a step? Is it tied to the foundation or was it poured after, it would be normal for it to be poured after the foundation. This means you already have a cold joint between the foundation and the porch.

If this is the case I would jackhammer out the porch concrete , dig down for a proper foundation, form the foundation to be flush with the old one, make sure it meets current code (the thickness may have changed since your house was built). Then you will need to remove the old door, siding and get back to the old framing, build your new floor like the old one. The load will transfer when you modify the structure (unless you explicitly load it a special way, so you need to have a solid foundation to start from.

In Portland here we have had many homes that enclosed spaces like you are talking about, some were done without making sure the new foundation was solid and the section slopes after 20 years.

Good Luck,

-Ryan

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Old 07-24-2011, 06:01 PM  
nicky
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Thanks for your replies. The job was done last Monday. I bought a bonding agent and even some reinforcing fibres but was unable to persuade my nephew the builder that any of it was necessary.
He has however done a most excellent job of cutting 'wavy' cladding to match the house's old fibre cement cladding!
And the job is done, while I have spent the last 15 years pondering what I could do with that useless and draughty space.
I have been under the house several times, Ryan, and the slab is a step but inside the foundation, there are no joints that I can see. The door bit was apparently added later.
Thanks again for the sound advice.
Nicky

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Old 07-25-2011, 12:37 AM  
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Perfect,

That is great to hear that you are done, so did he not use the fibers and bonding agent? Hopefully he did, it always helps.

If your fiber cement siding is anything like what we have here, it has a lot of Asbestos in it, so you want to be very careful when you remove it, sand it or cut it. Asbestos is an issue if it is airborne so wetting it down can help, take a look online for more resources. I have no idea if the same stuff was sold in New Zealand as in the US...

Congrats on getting past the thought process and getting it done. It is amazing how easy and fast it can get done, isn't it?

-Ryan



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