Concrete Block on Floating Slab

[Jason Raabis]

I have poured a 28x40 concrete floating slab destined to be a general garage and shop. I did not go with a grade beam (frost wall) due to cost. Up here in Canada, one has to go fairly deep. However, I am now wishing I did; I'm not keen on the timber sitting right on grade.

I have searched this forum the best I can, but I need to pick your brain for some more info. Can someone walk me through the process for adding a course (or two) of concrete block ON TOP of the slab so I can add a stick built timber frame on top of that? I already have anchor bolts protruding from the slab.

I would be quite greatful!

 

[bmwpower]

How thick is the slab?

 

[Stuart in MN]

My garage is a floating slab, and I have one row of blocks around the perimeter with the walls on top of that, for the very reason you're considering it. The garage was built over ten years ago and it's still looking good. I'm in Minnesota so we have harsh weather as well. The slab is 12 inches thick around the perimeter if I remember correctly.

As I recall they just mortared the blocks in place over the anchor bolts sticking up from the slab, then filled the webs of the blocks with concrete and stuck anchor bolts in them for the wall plates.

I still used treated lumber for the plates, with regular 2x4s for the wall studs.

This is the only digital picture I have available and it doesn't show a lot of detail, but on the far end you can see the one layer of block underneath the walls.

 

[Jason Raabis]

Thanks Stuart. There's hope then! My slab is 5 or so inches thick thickening to about 12 inches at edges, with plenty o' rebar. I guess I'll just have to find a "how-to" book on mortering and stuff. Any wise words about the process?

 

[Stuart in MN]

Thanks Stuart. There's hope then! My slab is 5 or so inches thick thickening to about 12 inches at edges, with plenty o' rebar. I guess I'll just have to find a "how-to" book on mortering and stuff. Any wise words about the process?

Sorry, no wise words...I don't know enough about masonry to give any advice, that part of the work was done by the contractor. It may be worth checking around to find a contractor, or maybe a handyman that can do concrete work - just putting in a single row of blocks is probably a small enough job that a regular concrete guy wouldn't be interested, but there are handyman types out there that specialize in smaller projects.

 

[64dragnwagon]

I poured a floating slab with 12" deep around the perimiter. We just mortored the block to the slab. I have 3 courses of block. I then poured concrete into some of the blocks and set the anchor bolts. Then I used a treated sill plate and framed it out. You DEFINATLY want to run at least one course of block. Do not set the wall directly on the slab. Also a few courses of block is a cheap way to gain ceiling height.

 

[MAINIAC]

I have a 28 x 36 garage on a floating slab and didn't want to have to hand lay and morter each course so I used a fiberglass reinforced sparge mix. That is I mortered the first course to the existing slab(compensating for the floor pitch) and then dry set the next two courses and "coated" the inside and outside with appx 1/4" of the special mix. The building inspector loved the outcome and actually researched it to be sure it comformed to "BOCA" rules and it has very high ratings. Your local concrete supply house should know of the product. You will have to mix it and apply, but alot faster and stronger than morter. Hope it works for others as well as it has for me.

 

[wrench409]

Hi, new here and reading like mad regarding concrete block construction.

Has anyone built using concrete block as the WHOLE perimeter - IOW all the way up with a timber cap truss roof?

We have terrible termite problems here in TX and I just tore down a shed that was termite ridden.

Thanks,
lefty

 

[chaingang]

I am about to get started building my shop I have contemplated that very thing since termites in GA can be bad also. Labor for block is about $1.25/block laid plus the cost of block and mortar. It gets more expensive if you go high enough that they have to set up scaffolds. Framing is much cheaper and is easily insulated. I now plan to pour a concrete slab with footers and run three course of blocks then pressure treated sills and frame up after that. The block does have advantages like being able to wash down the walls if I want to paint a car but costs are of a primary concern now.