Laying concrete block with zero clearance.

[madstat]

Hi guys,

My walls are standard 8X8X16" concrete block and I have a hole where a window used to be that is 32"wX24"h. I would like to fill-in the hole with new concrete block (three courses). Before just winging it, I'm a little concerned that there is no clearance (vertically) to lay in the top course because the hole goes right up to the top plate of the wall. I measured and the vertical space and it is exactly 24" so I would have to slide the top course in horizontally.

I'm sure masons do this kind of thing all the time. Is there a good method? I was thinking I could lay the mortar a bit skinny and fill in the top gap with a little non-shrinking grout.

Cheers

 

[JimVonBaden]

Your block is too big. You will need to trim about 3/4-1" off the top one to get it in with mortor.

Jim

 

[Torque1st]

I just nailed a piece of flashing against the top plate with caulk under it. Then I formed up the window and filled it with concrete. I troweled the last few inches with stiff mud. The job wasn't perfect but it looked good after a little grinding and caulk.

 

[PittsS1]

Use shims the same thickness of your bed joint or something to slide the top course in on that doesn't ruin the bed joint. Then tuckpoint it with mortar all around as you will knock a lot of it off, remove shims when all sets up and tuckpoint those holes. Worked for me when I filled in a window in the same fashion...

I see you said it's 24" exactly- you could make your joints closer to 1/4" inch and all blocks should fit... or just do as jim says and trim the top blocks to maintain a nominal 3/8" joint...

 

[BWS]

Use bricks?Yeah,make it easy....trim some off block.

 

[Steevo]

Concrete block is easy to saw. Best to cut one course to arrive at a combined three-course plus four mortar joints total of 24"

 

[Dan in Pasadena]

Concrete block is easy to saw. Best to cut one course to arrive at a combined three-course plus four mortar joints total of 24"

Yup, this is the fix. You need to have 1/2 mortar joints if at all possible. Horizontal AND header joints.

 

[brownbagg]

concrete blocks are not 8 inches tall. that eight inches with the 3/8 mortar joint, so you got plenty of room.concrete block are 7 5/8 tall, they are also lacking 3/8 in width too

 

[madstat]

concrete blocks are not 8 inches tall. that eight inches with the 3/8 mortar joint, so you got plenty of room.concrete block are 7 5/8 tall, they are also lacking 3/8 in width too

Yes, I thought this was common knowledge. The current hole is exactly the height of 3 courses ( three 7-5/8" Blocks plus three 3/8" mortar joints makes exactly 24". This means that if I wanted to keep the new courses level with existing I would also use 3/8" mortar joint and three full blocks. The trouble being that it would be difficult to slide in the top course with no clearance above.

Using shims seems like the right thing to do. I'll try that first and if I can't get the top course in without a scraping off all the bed joint I'll trim some blocks with the good 'ol skillsaw 77 and diamond blade. I've cut CMU's with that setup before and it pretty much goes like butter. If there is any gap at the top plate I'll fill it in with shims and non shrinkable grout.

I'll post an update on how the job went.

Best

 

[brownbagg]

slide in with no mortar then wet your mortar a little and pack into gap.

 

[joes169]

I'm a mason by trade, and I've done lots of projects similar to what you're encountering, including entire house underpins. Simply "squeeze" the first two courses down a tad tighter and spread the mortar bed thin for the top course as if it's too thick, you'll just knock the entire bed off. It's best if you have and extra set of hands, holding a trowel upside down, to help you fit the last two block into position. It is indeed tricky and you may still need to shim the block up a bit to get them snug. Old hard mortar or a small stone makes a good shim, as it can stay in forever and there's no need to tuckpoint at a later point. Also, NS grout is overkill for just about any wood/masonry application, especially considering it's always been a window opening.

 

[joes169]

One other thing, most block today are modular in height, or 7 5/8" high, but you can still find "full 8's" in many parts of the US. As a matter of fact, most every new block house foundation is built with them, albeit there aren't many these days, as you can pick up an additional 5" of height in a 13 cse. basement for the same price........

 

[madstat]

I'm a mason by trade, and I've done lots of projects similar to what you're encountering, including entire house underpins. Simply "squeeze" the first two courses down a tad tighter and spread the mortar bed thin for the top course as if it's too thick, you'll just knock the entire bed off. It's best if you have and extra set of hands, holding a trowel upside down, to help you fit the last two block into position. It is indeed tricky and you may still need to shim the block up a bit to get them snug. Old hard mortar or a small stone makes a good shim, as it can stay in forever and there's no need to tuckpoint at a later point. Also, NS grout is overkill for just about any wood/masonry application, especially considering it's always been a window opening.

this was great advice, I knew a mason had to do these things before! Also thanks for the tip on the NS.

 

[PittsS1]

I'm a mason by trade, and I've done lots of projects similar to what you're encountering, including entire house underpins.

joes169- a bit off topic but have you seen full 12x8x18, 3 core blocks before? My foundation was done in them and damn they're heavy. I raised the house to add two more courses, but used 16s on the new part as I couldn't find any of the old style...

 

[Bib Overalls]

If you are not in a big hurry, set two courses and let them set up. Then come back later and set the final course. With this technique you will not disturb the lower courses when you finesse the final blocks in to position.

 

[joes169]

this was great advice, I knew a mason had to do these things before! Also thanks for the tip on the NS.

I missed one important note in my suggestion: Have the helper outside with the trowel to help you lift the last 2 blocks into place......

joes169- a bit off topic but have you seen full 12x8x18, 3 core blocks before? My foundation was done in them and damn they're heavy. I raised the house to add two more courses, but used 16s on the new part as I couldn't find any of the old style...

I've certainly seen 18" long block in the past, although they were certainly old & rare. Oftentimes in the early 1900's, if the house used alot of decorative block for the veneer, the block were cast on site, and were often very unique shapes. If it was a commercially produced block and popular in your area, you "may" be able to find a brick yard or restoration contractor that has reclaimed some of them from homes being torn down for future repair, although they usually charge an "arm & a leg" for them........

 

[madstat]

I said I would post an update of the project. Not the prettiest but this was my first time laying concrete block and I simply didn't want to pay a mason for such a small job.

The first two courses went good. For the last course I had a helper stand outside and wedge the blocks up with a trowel while I shoved mortar in the bed joint.

 

[Falcon67]

Looks good - nice job!

As for cutting block - when I laid some, I was told to score the block heavily where I needed a break then tap with a cold chisel to snap off the waste. I cut half way though the blocks I needed to trim, then tapped with a chisel. They snapped all right - into several pieces of scrap block.

 

[Torque1st]

Looks great! Excellent job. It looks better than my cast in place window fill.

 

[NUTTSGT]

I'd say you did fine for the first time, well done.

 

[burleymike]

I have a couple pallets of 8x8x24 blocks that are not very old. My dad has a friend that offered them to me for near nothing. I never knew they made blocks 24" long.