Addition - Connect slabs

[teachable]

I am adding on to an existing home. I will be contracting out most of the work but wanted to understand a few basics to assure the work is being done correctly. The addition will require butting a new slab to an existing slab. Part of the existing slab is in a kitchen area that has a bay window. I will be extending this room by about 15 feet. The existing flooring is tile and I will want the tile to continue onto the new slab. My goal is to minimize disruption of the existing dwelling while the work is being done. With that said. How will the concrete folks assure that the two slabs are flush (almost exactly) so the tile will be able to extend - and hopefully not be "crack prone".

[jadnashua]

If the intent is to tile over that joint, it is possible, but you'll need what is called a soft joint - you can do this with either a caulk joint or a tiled in expansion joint. Also, unless you use a decoupling membrane like Ditra (www.schluter.com (http://www.schluter.com) they also make expansion joints), industry standard says not to tile over new concrete for 30-days after it is poured. For tiling info, check out www.johnbridge.com (http://www.johnbridge.com).

[AZ Contractor]

I don't think you answered his question.

I usually take off an inch or so of the stucco outside to expose the bottom plate and existing slab of the house.

Set your forms even with the bottom of the bottom plate and off you go.

[Lakee911]

I believe there is something you can apply to the existing slab to help the new concrete adhere. If you break up the existing edge a little (roughin it up) and then drill holes in it and epoxy some some rebar then you can tie them together.

Jason

[teachable]

Should the two slabs be attached in some way. I.e. drilling into the existing slab about 6-8" and inserting rebar -- leaving about 8" or so haning out into where the new slab will be? If so, how far apart should these -- connectors be apart from one another? Thanks,

[jadnashua]

Rebar will help keep the tops aligned, but the joint is still likely to crack. This is a question for a structural engineer. There are a couple that frequent the site I suggested.

[AZ Contractor]

Drill 1" holes 2' apart into the existing footing (stem).

Get a bottle brush and scrub out the holes and use a shop-vac to clean out the holes. Use them in sequence several times per hole.

Use a 2 part epoxy compound and extension tip and squeeze the epoxy in the holes. Insert 2' #5 rebar into each hole and allow to cure.

After this is cured pour your new slab.

[hj]

There is no way to ensure that the two slabs will meet properly, unless the existing one is exposed so the new one can mate to it perfectly. Otherwise, there is the possibility that the old slab is not perfect and although the two are aligned at one point, there will be a disparity at other areas. There was one job I worked on where they matched the two slabs in a doorway, but when the wall was removed the old slab was an inch out of level so it was that far above the new slab and required major breaking and grinding to level out.

[fidodie]

Your question is/was split in three-

1 - forms must be connected to the house outside the joint area.
2 - there must be support to maintain alignment (vertical)
3 - what about the tile over it (soft joint)

all were answered, but here is a couple tips for #2..

For the epoxy, head over to the local home depot, or lowes, and in the deck fastener department, you will find the epoxy with extension ready to be loaded into a caulk gun - follow the instructions, the first bit that comes out is not usable. I think strongtie sells it as part of their line. You don't have your part of the country listed, but since you are opening your house in the winter, i'll assume it is warm - the set up time for this epoxy varies with tempurature - and it can be very quick if it is hot out -

use a hammer drill. really, don't even think about a regular drill - if you haven't used one before, it is better than a side grinder, but not as much fun as powder actuated nailer. sawz-all being the a 5 on my cool-tool scale, i'd rate the h-drill an 8.

gl
pat