#11  
Old 07-24-2007, 08:52 PM
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Default Re: Oven support wall cracking

Get comfy this is a long one...OK something is not right 5' square does not work out for standard block. With the slab on grade at 5' sq in order for full block to work out (for the sides) they would be 47 3/4" thats 4 full 16" block with head joints.
That means with the 2 side walls on the very edge of the slab the front and back walls would need to be the same dimensions 47 3/4 to fit inside of the 2 side walls without any cuts. So I don't know if you just gave me an approx measurement or what.

But here is the bottom line what ever the dimensions are. Having the blocks stacked in line with each other is like creating a series of individual walls the width and length of the blocks. So on the sides you have 4 or 5 16"X (6" or 8") walls butted up against each other, each independent of the other.

The fact that he put 3/8 rebar in the corners and the middle means that these "mini walls" have a piece of rebar in them nothing more, in this case of blocks being stacked the rebar may as well not be in there at all. 3/8 rebar is a small step above wire mesh and in my opinion if you gonna use it you might as well use the wire and save the money on materials, we never use less than 1/2" even for patios.
These walls are not tied into each other except where the slab is on top, this is like taking a playing card placing it face down and putting 4 other cards around it with their sides touching 2 on the long side 2 on the short side if you put tape where he put rebar and fold the cards under to make a base for the top card...its still very flimsy. Now take those cards that formed the base and cut them into 4 sections...not good.. this is what you have for a base. (based on your description)

If you were to bump this structure on the hearth slab say with a forklift (or an earthquake) the entire base would collapse like a deck of cards. So essentially what you have is a heath and oven structure resting a series of individual walls all the way around.

Note: If the blocks were bond beam and stacked this would be a different story because the concrete could flow through the entire wall.

If you were to stack them as mentioned it could still be made sound by putting vertical rebar (1/2") that was bent into the footing 18" and up through the block on either side of the butt joint so where each block meets you would have a piece of rebar on either side of the joint. Then if the top row of block was bond beam with horizontal steel all the way around the perimeter and all of this was grouted you could get away with it...but its much more work.

So here is my summary:
You have a 4" slab on grade that is minimal at best, with a perimeter footing, more than likely OK and should be just fine. without
You have a 3" hearth slab with 3/8 rebar which again might as well be wire making a 4' span with close to a ton of oven resting smack in the middle (coincidentally right where the crack is)
You have an EXTREMELY UNSTABLE base which has NO sheer strength.
My advice as a professional--keep pets and loved ones away form this oven in the event of an earthquake. In the mean time paint the cracks as I instructed above and keep an eye on them especially before and after each use. Id crawl under the oven asap and look at the under side of the support hearth to see if that hairline crack goes down the middle. I know this sounds alarming but this was build using minimal to inadequate materials and methods. My comments on this subject are based on years of masonry and concrete experience. But James graciously provides plans for free on this site that I believe are very good general recommendations for building the oven and base and just about everything you mention is contradictory to them.
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  #12  
Old 07-24-2007, 09:16 PM
Il Pizzaiolo
 
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Default Re: Oven support wall cracking

Uno, I'm curious....if all of the above turns out to be true; what can be done (if anything) to stabilize this oven? Or is the poor guy looking at a compete knockdown/rebuild?
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  #13  
Old 07-24-2007, 09:33 PM
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Default Re: Oven support wall cracking

Thanks for the infomation. Is there anyway to make this structure more secure? I trusted the person who did the work because Fornobravo has him listed as a recommended installer. Can you tear down the structure and salvage the oven? How about building an inner wall? I left the 2x4 wood that was used to hold the backer board under the support floor. The cracks are no longer visible since the oven has cooled unless you knew where to look and got up real close.

Mario
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  #14  
Old 07-24-2007, 11:29 PM
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Default Re: Oven support wall cracking

There is a number of things you could do all of which aren't all that bad.

1. To beef up the slab perimeter (if you don't have the footing I mentioned) you can dig around the perimeter about 6" down. Clear out about 4-6" under the slab, put in some rebar, 2 sticks of 1/2" and pour a footing you can do this in stages or all at once, the oven isn't going to move even if you excavate all the way around at one time.

2. The walls can be deterred from kicking out by pouring a curb all the way around the base. Id go 4" high by 4" wide on the outside perimeter. If you have room on the existing slab for the 4" drill holes in the slab 2" out form the block in line with the middle of each block down about 2" insert a short length of 1/2" rebar so it comes to the middle of the 4" curb so 2" up from the slab. Then with a 10' length of rebar start at the front side of the base and bend it to go around the corner if the slab is close to 5' sq like you said you will need to over lap the 2 ends by at least 24", the entire length if you have it left over. This horizontal steel should be tied to the vertical stubs. If you do not have room on the slab you need to make it part of the new footing and it should be 6" wide by 4" high. If you have the footing and do not have the space on the slab you can do this on the inside of the walls with some modifications.

3. To add sheer strength to the base you could drill into the middle of each block on the left and right (inside) walls in the back about 2" from the back wall. Do this about half way up and along the floor like above the same distance. the bar should go about half way though the wall and only 2" into the floor (slab is only 4" thick right?) Get some bond beam blocks 6" is fine and dry stack them (stager the joints) on the floor up against the back wall in line with the steel each piece of steel should enter a row of block. Then grout (fill this with concrete) before grouting you should dampen the block and add a little extra cement to the mixture to make up for having to mix it soupy to pour in the block...its gonna be tight in there. An alternative which would be quicker but probably more expensive would be to buy 2 lengths of angle iron at least 4" wide the entire height of the inside wall (you could probably find these in the scrap section of your local iron yard) have them drill holes that would correspond to the centers of the block drill matching holes in the block epoxy in some 1/2 "- 5/8" all thread and this would join the 2 separate walls.>>>>strike that I forgot the back wall was stacked the angle iron will do no good....sorry

4. Adding support in the center of the oven is the easiest of them all. Measure the height get the bond beam blocks dry stack one course fill it repeat till you get to the last course since you cannot fill the last block it will have to be set in dry or (you can use liquid nails) then you will need to cut some wooden wedges and drive them in from both sides. Or you can make shoring out of wood. Id say a 2x6" ought to do it. Cut it to double it up against the hearth slab. Cut another piece for the floor, cut the remaining the distance from the top pieces down (actually an 1/8" longer) pound them into place. One on each side and evenly space across.

Now with the exception of the underbracing these suggestions are based on the assumption that the walls for the base are as I described before. If the blocks around the corners are all tied in there is no need for the sheer bracing of the back wall. and the side curb would not need to run all the way around the back just the sides.
Check this out and get back I'm getting tired its been pretty hot the last few days and it really takes a lot out of me working in it. When its not hot heck I can go all day..well almost but when its like this I'm outta there at 2:00 and wasted the rest of the night...

Last edited by Unofornaio; 07-24-2007 at 11:39 PM. Reason: sleepy..
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Old 07-25-2007, 02:38 PM
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Default Re: Oven support wall cracking

Thanks for the information. I was wondering if you could use steel corner brackets and long steel plates to support the wall and use liquid nails to hold it on? Go ahead and laugh. Ok are you ready for some good news? The foundation has no cracks. The bad news is that half the oven foundation was placed over an existing patio and was tied in with rebar. So I can only put footings along the parts that are not on the existing patio. I already have a 4x4 across the center of the support floor and was wondering if that wood exspanded and is what cracked the mortar line? The cracks both start at the same spots the wood is at. The support floor is pretty warm the next day. Anyway thanks again for your help and let me know what you thing of the Steel to help with the wall.

Mario
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  #16  
Old 07-25-2007, 08:39 PM
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Smile Re: Oven support wall cracking

I'm not really a wood guy so I think of solutions in terms of masonry first but now that you mentioned it I don't see any reason why you could not cut sheets of OSB the dimensions of the side support walls and glue them to the block inside. This would be very easy and a relatively inexpensive way to solidify these walls. Doing this would eliminate the need for the curbing.

I suppose you could do a version of this on the outside of the back wall. Cutting a piece large enough to cover the entire back of the base. This would join the 3 walls (2 side walls (6 or 8") and center wall in-between them) You couldn't do it inside because what we are trying to do here is tie the sides and the back walls together to create a solid U shape.
Now this is assuming the back wall fits "in-between" the 2 side walls like the attachment below. If the back wall is on the "outside" of the sidewalls this will not do any good.
If this back wall is tied into the side walls either with rebar or alternating block you do NOT need to worry about the back.

Your bad news is actually good news this tells me in this (half area) where there are 2 slabs you have greater than 4", combined probably closer to 7" or so which is a good thing.. This also tells me the "new" section of the slab (slab on dirt side) is more than likely the same thickness, it would have to be to make up for the other half (slab on slab side). So it sound like the footing is more than sufficient if this is the case.

As to the 4 x 4, again I'm not a wood guy but I don't think this would be the cause. Even if your getting the heath slab hot to the touch (above say 120 deg) its going to expand in all direction and if anything place a downward load on the 4 x 4. I cannot speak as to the expansion properties of wood itself.

I think what you have is the slab expanded during use (normal) Since these center "wall sections" are tied into the slab via the rebar, also normal,(to be tied in not the sections) when it expanded it pulled a bit on these joints, it doesn't take much to create a crack along a continuous vertical joint. If it has separated thats a different story. Then again if the "new half" of the slab on grade was not compacted properly the back section could be moving slightly. Does the old and new meet below this crack? you say the slab has no cracks did you look at it under the oven where the old and new meet? Or it just could be a crack because of the blocks being stacked like they are. My gut is telling me its from the slab after all the wall has not cracked along the other vertical joints and the rebar is in the block that have the crack.

So at this point it looks like your concerns are sheering up the back wall if it looks like the attachment and keeping an eye on that crack in the hearth slab. There is no point doing anything about the hearth slab right now. Wait and see if it gets worse after a few more firings.

Please keep in mind my concerns with stabilizing the base are strictly for insurance in the event of an earthquake. The oven will probably never move, surely not on its own but if it were to move in an earthquake even a decent tremor it has no side to side strength. Based on what you described retro fitting the base would mean a difference (in a quake) between serious damage/ possible collapse and some minor repair.
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  #17  
Old 07-26-2007, 03:06 PM
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Default Re: Oven support wall cracking

The cracks along the mortar joint is about 1'' from the old slab. The cracks do show on both the inside and outside of the walls, but like I said you have to look very closely to be able to see them once the oven cools down. I Looked at the foundation under the oven and I can't see any cracks. Instead of covering the back from the outside I was thinking about using corner braces to tie the back wall to the side wall from the inside. What do you think? I think I'm still going to put some footings on the part of the slab thats on the dirt I think he only went 4" total on that part and about 2'' on the existing patio. This guy cut corners every chance he got. The oven does appear to hold the heat well and is cooking evenly. It was 400f the next day after I fired it up and 200f on the second day after fireing. This is air temperature not the oven surface. I'm no expert but that sounds pretty good to me. If you ever come to the Sacramento area I'll make you some pizza for all your help.

Mario
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  #18  
Old 07-26-2007, 04:01 PM
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Default Re: Oven support wall cracking

You are clearly frustrated with this thing but hang in there.

1" from the old slab?? that means it starts in the new slab and goes up?

The problem I see with the brackets is if the blocks are stacked like you said you really will only be tying in the 2 corner rows of block ya know what I mean? It certainly would not hurt to just do this and would help some. If you are going this route be sure to do as I mentioned with the all-thread and epoxy both available at H.D. Using the liquid nail will not work sorry If you do not have a drill the rental of one and a masonry bit slightly larger than the all-thread is very cheap. You could do the OSB thing on the inside of the back wall and the brackets it wouldn't be quite as strong as the outside but would probably be sufficient.
The epoxy you need to use is made by Simpson, you can get it at Lowe's or HD. You will also need a double barrel caulking gun but you can rent it.

I go up to the Bay Area about twice a month to work next time I might just take a slight detour on the way home and check it out, thanks for the offer.
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Old 07-26-2007, 06:30 PM
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Default Re: Oven support wall cracking

Utterly incompetent question alert:

I'm just curious. You mentioned that the proportions were wrong for standard block, but from what I've been able to learn (remember that incompetent part - 'cause I am) mortarless block at least sometimes comes in exact sizes and not the standard, adjusted for the mortar, size (i.e. 16 in. block are really 16 in). I'm just wondering if maybe he used that kind instead? (Why the mortar, I got no clue - I'm just asking.)

If I recall correctly (asking a lot from a tiny brain), the one article I saw where they were straight stacking and not staggering (okay, that part stood out - I know just enough that straight lines up look really scary to me) they were using interlocking (mortarless) block. The blocks were subsequently filled with concrete before the walls were capped (the thing was a house. I would never buy a house like that because you would never, ever convince me that was safe! But, whatta I know?) and rebar was running up through them.

I'm not suggesting anything here - I'm asking only because there's a similarity and I'm curious. The extent of my masonry experience was watching my cousins and my Dad put up our basement walls (very well, actually - my cousins were all in the construction business and Dad could do anything that involved tools). My one contribution was taking a shovel and scraping the mortar splatters off the slab. Dad said I did a good job.
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  #20  
Old 07-26-2007, 11:19 PM
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Default Re: Oven support wall cracking

I'm just curious. You mentioned that the proportions were wrong for standard block, but from what I've been able to learn (remember that incompetent part - 'cause I am) mortar-less block at least sometimes comes in exact sizes and not the standard, adjusted for the mortar, size (i.e. 16 in. block are really 16 in). I'm just wondering if maybe he used that kind instead? (Why the mortar, I got no clue - I'm just asking.)

>>> I see your logic but 5' still doesn't work out for 16" it would be 5'4" I dont know what he did..
If I recall correctly (asking a lot from a tiny brain), the one article I saw where they were straight stacking and not staggering (okay, that part stood out - I know just enough that straight lines up look really scary to me) they were using interlocking (mortar-less) block. The blocks were subsequently filled with concrete before the walls were capped (the thing was a house. I would never buy a house like that because you would never, ever convince me that was safe! But, whatta I know?) and rebar was running up through them.
>>>Vertical steel in CMU (concrete masonry units) is something that is very common here in CA and engineered buildings in other parts of the world. As I mentioned somewhere in this thread if the block were bond beam block (standard block with the top half of the sides and webs missing) even stacked in this manor they could work but it still wouldnt be right. The missing web create a continuous (beam) through each series of blocks and is extremely strong especially with the addition of horizontal steel. Bond beam block are designed to hold steel in the missing web cavity.

I'm not suggesting anything here - I'm asking only because there's a similarity and I'm curious. The extent of my masonry experience was watching my cousins and my Dad put up our basement walls (very well, actually - my cousins were all in the construction business and Dad could do anything that involved tools). My one contribution was taking a shovel and scraping the mortar splatters off the slab. Dad said I did a good job.

>>>that was always the funnest part I remember going with my Dad when I was small, the mortar that fell on the sand he put on the concrete was always in strange stalactites or is it stalagmite (can never remember which it is). Just a light sprinkling of sand protected the slab from stains and the mortar sticking to the floor, when your done you just run a flat shovel on the floor against the wall and it comes off with no problems...Just another one of those invaluable, old-timer tricks. Its funny how we see our fathers differently as we mature, the more I experience in this craft and the older I get the more I see him as a masonry GOD...
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