Concrete block stem wall tips please

[FunfDreisig]

Sunday I'll begin laying the concrete block "stem wall" for my 3 bay garage.

This will be the first time I've laid concrete blocks. So I'd appreciate any tips or cautions

BTW the rebar sticking out of the wall in the model indicates where I currently have 6" #4 rebar stubs sticking out of the slab. My plan is to wire on 4' lengths of #4 rebar (which will reach to just below the cap) and fill these cores with mortar as I go.

Funf Dreisig

 

[JCByrd24]

I found the following very useful on my first (and only) time laying block, credit goes to my father in law.

1) You can't work with mortar that is too thin, it won't support the weight of just 1 block, so thicker is better than thinner. About like toothpaste...it should stick to a board held vertical for a couple seconds.

2) Get at least an 8-10" trowel for laying the block and don't trowel mortar right out of the mixer, pan, wheelborrow, etc...Instead, get a chunk of 2x8 that is 8-10" long or a 8x8 chunk of plywood so it isn't so heavy, and fashion some sort of handle on it (2x2 attached perpendicular right through the middle). Load that board up with mortar and use your trowel to smooth it over so you basically get a 1 to 1.5" thick covering on your block, slice the edges right off with the trowel. Next cut your 8x8x1.5" slab of mortar into 5 or 6 rectangular mortar turds. Finally, lay down an squared 8 shape (like an 8 on a digital clock or the shape of the block) using these turds. Set your block, wiggle to get the right depth, grab the excess and through it back in the mixer or pan. Leave all joints filled flush for 20-30 minutes, then go back with your pointing tool and give it the concave look.

 

[akdiesel]

Just from doing a little brick work myself on a small piller it was not easy to get them lined up straight and even. A wall that size on that long of run can be difficult for someone who has not done it before.
Are you doing by yourself?
Plus I would look at using 3000psi concrete instead of mortor for the filling.

 

[JCByrd24]

Agreed, concrete instead of mortar for filling will be much cheaper..also, make sure to do the corners first (a few courses at a time) using a level a lot. Then you can use a string from corner to corner to get the walls straight.

 

[FunfDreisig]

Thanks for the quick replies with great tips!

I'll have some help with the heavy lifting, mortar mixing, etc.. But essentially I'll be the "responsible party" for getting right -- I'll be the guy with the levels, lasers and strings

JCByrd24: I'll build a mortar board and follow your great suggestions.

akdiesel: I just finshed reading a great article in Fine Home Building that corrected my assumptions that I could just use the spare mortar to fill the rebarred cores as I went. So I'll now be filling the cores after the wall is built with 3000 PSI concrete like you suggest.

Thanks again - Funf Dreisig

 

[akdiesel]

If you need any info on concrete/cement go to www.concretenetwork.com.
Loads of info in that department.

 

[JaysinSpaceman]

I haven't posted on this board much but since I just did my first block wall work a few months ago I thought that I would give you some of my first timer tips. I can't say that they are the pro way of doing things but they worked well for me.

1. Mix your mortar in a wheel barrow by hand, it is slightly more work but unless you have a big crew working with you, you can't use it fast enough and it will start setting up in the mixer.

2. Lightly wet (mist) your blocks with the hose. If they are dry when you set them the blocks will **** the water right out of the mortar and you will not be able to position them fast enough.

3. When you put down a bed of mortar to set a block make it 1.5-2 times more then think you will need. It is much easier to scrape the excess off the side of the block then to add more (you must remove the block to add more).

4. Home Depot (and probably other places) sell little blocks of wood or plastic that hook onto your two end blocks that you can stretch a string line between. The string will be held perfectly straight, about a 1/8" off the wall an allow you to build a straight wall with no problem (as long as your two end blocks are in the right place).

5. Wear rubber or those rubber dipped gloves. Working with cement of any kind is not good for your skin, but more over the blocks will wear the prints right off of your fingers after about two hours.


Well if I think of any others I will post them up but for now that is all I can remember.

GOOD LUCK!!
Jaysin

 

[jamm]

How high will your stem walls be? 4" rebar prortrussion from the footing doesn't create much of an overlap. If I remember correctly typical is 20 times the rebar diameter, which would be 10" minimum.

I would suggest that you use grout to fill the necessary cores rather than concrete. It's cheaper and flows a lot better because it doesn't contain aggregate. It will reach 3000 psi as well.

I don't remember the number of courses that can be laid up in a day but you should check on it so the grout doesn't sqeeze out due to the block weight.

On a seperate note tape down a narrow drop cloth on the interior side of the stem wall. This will catch any mortar the gets struck off the blocks. Or once the first course is laid spread out a thin layer of play sand. This will save you a lot of scraping in the future.

Good luck

 

[FunfDreisig]

I haven't posted on this board much but since I just did my first block wall work a few months ago I thought that I would give you some of my first timer tips.....

Welcome and those are really great tips Jaysin! Quite a first post

BTW I bought a set of the string line blocks and still don't know exactly how to use them. Did you put them directly on the end blocks of the wall (i.e. the corners) then fill in the course between the corners or did you put them on "story boards" attached to the corners?

Thanks in advance - Funf Dreisig

 

[FunfDreisig]

How high will your stem walls be? 4" rebar prortrussion from the footing doesn't create much of an overlap....

Thanks for the tips jamm.

The stem wall is only 4 ft high and the rebar in the slab is 2ft long. I pushed it into the slab 18", leaving 6" sticking up. The stubs are 16 OC so each block will have one core of rebar at it's overlap with the course above and below it. The plan is to wire tie the 4 foot sticks of rebar onto the 6" stub.

FWIW This wall will have very little pressure against it. I will be installing a french drain behind the wall which will have 4" perf pipe at the bottom and then gravel roughly half way up the wall after I water proof it.

Funf Dreisig

 

[JaysinSpaceman]

The little string blocks are meant to hook on the corner of the end block, so that it holds the string a very small amount off of the block. But if you have story boards then you can use string line from them to do the same thing, I just found the little blocks easier once the end/corner blocks were in place.

 

[FunfDreisig]

I'll be setting the last few concrete blocks tomorrow AM I really want to thank everyone who contributed to this tread. You were a big help. I can't believe I had never heard of those little line blocks. They not only work great on concrete block walls, they were a big help aligning the decking on the cabin

276 concrete blocks later (but whose counting) I'm pretty pleased with the quality of the stem wall. And seriously disappointed at my blocks/day rate. This is hard work and BORING. Knowing what I know now, I will pay someone to do it next time

After filing the rebar cores with concrete, I'll be adding 8x16x2" solid cap. The problem is that half of each cap will be over a hollow core and half over a filled core.

Is there a trick to spreading the mortar so that the filled core can be mortared solid for the sill plate expansion bolts and still get the cap to set level?

Thanks again - Funf Dreisig