Dry stack vs Mortar stack

[PlanoPhil]

What's the recomended method for placing the cinder blocks? I've noticed that some folks mortar the blocks in place and some dry stack.
Also, how important are the vertical rebar placement that are embeded in the foundation and pass up through the cores of the blocks? Again it seems that some do and some do not include them.

Phil

[Les]

Re: Dry stack vs Mortar stack

I dry stacked my block - it goes a lot faster. I put steel in the corners of the foundations of the island and a couple in the middle of the run. It may not be needed with all the weight but it will do no harm.

Les...

[dusty]

Re: Dry stack vs Mortar stack

I did exactly the same. I then filled every-other-one with concrete. I filled the rest with brick cutoffs and left over motar and stuff to keep the garbage can from weighing a ton.

dusty

[Les]

Re: Dry stack vs Mortar stack

I then filled every-other-one with concrete. I filled the rest with brick cutoffs and left over motar and stuff to keep the garbage can from weighing a ton.

dusty

That's funny - thats where I put all the left over gravel/sand I was going to have.

Les...

[kebwi]

Re: Dry stack vs Mortar stack

I dry-stacked, but I don't have any rebar connecting the foundation to the walls (I didn't set any rebar sticking out of the foundation awaiting the wall placement), so the walls are effectively resting on the foundation, except for any "glue" effect between the concrete poured into the cores and the foundation.

I think that if you don't mortar the walls -- if you dry stack and fill the cores -- it is pretty important to put some rebar in the cores when you fill them...I guess, I dunno. I suppose it seems like filled cores are in a way stronger than mortared bricks since a filled core is basically a column of solid concrete.

Whatever, you'll be fine. Round up on the rebar. I sure as heck did.

[Tscarborough]

Re: Dry stack vs Mortar stack

Going by what I have seen here, 98% of the ovens are built atop bomb shelters. That is not a bad thing, but it can sure burn up excess time and money. Using calculated loads (leaving out seismic and frost issues), a pile of dirt is good enough for most ovens.

[kebwi]

Re: Dry stack vs Mortar stack

Agreed. When I first started my build, I ran some numbers and concluded that I could push against the foundation with my thumb harder than the pressure that would eventually result from the oven and stand. Run the numbers yourself and see what you get. It's a simple calculation. Weight of the stand and oven divided by the footprint of the stand (foot print of the concrete blocks plus the foot print of the filled cores). You will be surprised how low the load really is.

[Les]

Re: Dry stack vs Mortar stack

I ran some numbers and concluded that I could push against the foundation with my thumb harder than the pressure that would eventually result from the oven and stand.

I totally understand. I live in a state that is 3rd or 4th in seismic activity. I went with the fact that if everything would bounce and shift together, I had a better chance of survival. Rebar is really, really cheap, compared to the rest of the build.

[Tscarborough]

Re: Dry stack vs Mortar stack

Seismic and frost are totally different issues. For seismic, each unit needs to be tied together, and the important strengths are not compressive but bond and shear. For those situations, you need a bombshelter, because you have a heavy load subject to lateral movement.

For frost, you have to create a foundation that is able to withstand heave, i.e. extend below the frostline and be able to counter lateral stresses in the foundation. Above that, however, the stresses are normal.

[fxpose]

Re: Dry stack vs Mortar stack

During the '94 earthquake we had here, a row of queen palms in large 30" terracotta planters on our driveway bounced and shifted a couple of inches. It's easy to tie the stand to the foundation but what about the oven to the hearth when the next big one hits?

[Dino_Pizza]

Re: Dry stack vs Mortar stack

Oooh, fun subject. During the '94 quake my entire 3 sides of yards perimeter block wall cracked at the base and fell over in whole chunks or crumbled. So, I (over) built and put rebar sticking out of my ovens base into the blocks and did a bond beam at the top.

If I didn't live in earthquake country, I'd still put steel in the 4 corners, maybe 1-2 more. You'll know exactly where your cmu's will be when you place your perimeter forms.

Another good reason to dry-stack is you only have to truly level your base slab. Then just stack the block. AND if you are a fraction off by the time you're at your top final row, you still have the oven base to pour that's your last chance for a really flat oven base. It was surprisingly easy for this novice, me.

[david s]

Re: Dry stack vs Mortar stack

For those who are scared about laying blocks, you can use adhesive, like liquid nails, for masonary. Filling the block cavities creates the required strength.

[Wiley]

Re: Dry stack vs Mortar stack

I dry stacked my cement blocks and glued together with subfloor adhesive. Of course the is always the problem with the design of the blocks, they are designed to have a mortar line and so two of the width of 8x16 blocks is less than the length of one block. This makes for a gap when dry stacked. The advantage to me of using subfloor adhesive was that if I accidentially bumped the structure which pouring the infill it wouldn't move out of position.

As a bizarre aside: About 20 years ago I was offered a cement block maker from the fellow from whom I purchased my cement mixer. As it was free and looked cool I took it. In case one has never seen such a contraption it is a manually operated machine for making cement blocks one at a time. It has a mold for the block which one fills from the top and when filled and suitably compacted one pulls a lever and the plugs for the holes are pulled downward and out of the block. Then releasing a bail and the sides fold down. Pulling another lever and the block is rotated toward the operator to rest on its side. The block is then removed from the machine to set aside to cure. Another piece of wood (which forms one side of the block mold) is inserted and the whole process repeated. Very third world but I found it cool in a Rube Goldberg sort of way.

The mold is adjustable in many different ways and has inserts to make both stretcher and ender blocks or a combination, one end stretcher and one ender. One could also adjust the length of the blocks such that when dry stacked there would be no gap. I always had the idea that it would be great to make wedges for the ends so that one could produce a trapazoidal block. With such a block one could theoretically make a serpentine structure having two rooms and only one wall. One could even build a small diameter tower. And as one side of the block form was a board one could cast a curve in the outside of the block making for a smooth cylinder tower or base for a pizza oven. I have been told that at one time it was possible to purchase molded boards for the side which then gave the blocks the look of cut stone. A creative person could make walls with images or patterns cast in relief.

But alas, I have never found the time to experiment with the machine. However, I just checked the machine and it still works and with a few hours work it could easily be cleaned up to start producing blocks. New boards are needed. So an offer to anyone within reasonable driving distance of where I live in Western Washigton: if you would like to borrow this machine and make your own blocks send me a PM and we can talk. It produces what is commonly called Eastern Blocks, they have three holes. And yes, I have a formula/recipe for the mix and the machine has a divider so it can make two half blocks. It's about the size of a small cement mixer and is a two man carry.

Bests,
Wiley