Adding new concrete block foundation to existing.


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Old 08-23-12, 08:34 PM
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Adding new concrete block foundation to existing.

Hello!

We are moving the door a few feet into the garage, so we need to build two walls off the cement garage floor, and then move the door to the new wall. (In the picture, the new walls are to be where the ruler on the floor is.)

Here's my quick plan, piecing together stuff I have read. I would appreciate any recommendations/help to make this better:

1. Spread and furrow mortar bed with Pr Finish Quikrete Blended Mason Mix. Apply 3/4" high. (No pre-wetting of floor or blocks required.)
2. Position and align corner block. Press down to 3/8" high from foundation.
3. Position remainining blocks, 3/8" between (up to 3/4" if needed for block spacing)
4. Rebar in every other cell (length = footing to flush with top of block wall) using Quikrete 5000.
5. Horizontal joint reinforcement in ladder pattern.
6. 1/2" Anchor bolts, 6 ft max on center and within 1 ft of each end of sill plate, and not where the floor joists will be.
7. Sill plate sealing foam gasket
8. Pressure treated sill plate (2x8?)
9. Flatwasher and nuts to anchor bolts.
10. Header joists and floor joists.
11. Subfloor
12. Walls, including frame for door.
13. Electrical
14. Underlayment and floor
15. Drywall, trim, and paint.
16. Stairs.

Questions:

1) How do you attach the gasket material? Is it adhesive, stapled, or just let the sill plate hold it down?
2) I have seen both 2x6 and 2x8 called out for the sill plate...?
3) Is horizontal joint reinforcement required? (We are in Georgia near Chattanooga.)
4) Mortar outside the blocks (connecting them), and concrete inside the blocks (for the rebar/anchor bolts), right?
5) How do I tie in to the existing block foundation? Or do I just build up next to them?
6) Does anything go between the two layers of block? Steel mesh and/or just mortar?
7) Do I need to drill holes and sink the rebar into the floor, or just drop the rebar to the floor?

That's all so far. I appreciate your help!

Regards,

Leaning
 
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Old 08-24-12, 05:08 PM
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I'm surprised chandler hasn't chimed in here to help a fellow Georgian.

Your questions indicate you're trying to complicate a relatively simple project. Sill plate width depends on the wall thickness you're building on top of it--just match the two. Gasket doesn't need adhesive, but if it makes you sleep better at night, go for it. I'd at least dowel into the floor, with rebar anchored in drilled holes. The biggest problem I see in the photo is lack of a proper landing in front of the door--most codes require a minimum flat space of 36" or so, before stepping down. You might want to make sure there's a substantial-enough footing underneath to support the new construction--drilling the rebar holes should tell you that. I wouldn't rely on a just a 3" or 4" slab for proper support. I also wouldn't anchor into the existing wall, although doing so wouldn't hurt anything unless you damage it during the anchoring process.
 
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Old 08-24-12, 08:42 PM
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Bridgeman,

Thanks for the info. We bought the 12-year old house a year ago, and that's the way the steps were. Our home inspector noted the lack of rails, so the homeowner put that in for us, but nothing was ever said about the lack of landing. Grrrr!

AFA complicating everything...guilty as charged. But I try to get as much (too much?) information on everything I do so that things like the lack of landing won't pop up. <shrug>.

I was going to break off the top steps since they will be in the way of the new flooring, and just leave the rest of the stairs there in the "crawlspace". The concrete blocks for the door wall will go up against the bottom step.

(When you go through that door, you are in a hallway area to the kitchen with a pantry under the stairs going up to the finished half of the attic. I want to move the washer/dryer out of the garage, and into this inside area of the house, but without making more room (moving the door), the door will hit the washer/dryer.)

Regards,

Leaning
 
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Old 08-24-12, 10:34 PM
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Bridgeman,

If the garage concrete depth is 6" (hopefully, not 4". I'll check first), how deep would you recommend sinking the rebar? 3" or so?.

And then the top of the rebar would be a little less than the top of the two courses of block? (So, something less than 19")?
?

Thanks!

Leaning
 
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Old 08-25-12, 11:15 AM
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The 3" depth into the floor sounds about right. Blow or vacuum the drilling dust out of the holes, then use either a low-modulus epoxy gel or anchoring grout (or even neat Portland cement slurry) to glue the bars in. I'd use No. 4 bars, making the length at least an inch shy of the total block height. Drill the holes with a 5/8" masonry bit, but it's often easier to start with smaller-diameter bits first, then enlarge with the larger size. And using a hammer-drill works best.
 
 

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