Retaining Wall Question
I purchased your multitorial a few days ago in preparation for the building of a block wall. Your multitorial is about retaining walls and I am building a fence wall around my lot but I figured you would have some good info. It had a lot of valuable information for me, it was fun read and well put together. But, it didn’t address all my questions. I hope you can give me a bit more advice.
I bought a foreclosure house north Phoenix and figured at the price, I couldn’t go wrong because it had block walls. From talking with the neighbors (and working on it), I discovered that it had been neglected for many years and abused for several. Putting it back in shape has been a labor of love.The house was built in ’78 with a 150’ chain link fence around 2 sides of the lot that I will be replacing. Most of the neighbors have since replaced their fencing with block wall – 4x8x16 blocks in 12’ panels with H-block columns between panels. I’m sure you have the same type of walls in Tucson.
1. Footings. My neighbor’s wall is 10 courses high. I plan to match it. Since the load normal to the wall is limited to wind pressure (substantially less than earth loads), I didn’t think the calculations you provided would apply. It seems to me that reinforced H-block columns can support the normal load; footings just need be strong enough to support the weight of the wall without cracking. As best as I can tell, my neighbor’s wall has a 8” wide by 12″ deep footing. My plan was to use a 12”x12″ footing (with one ½” embedded rebar) but leave the current fence post footings in place (they are 24” deep) and pour concrete around them to include them in the wall footing. Would this be sufficient or do I risk failure in a decade? (The soil is the typical dense sand/clay mix, well drained, minimal organic material). The neighbor has xeriscape with a thin layer of crushed stone. I will likely have the same.)
2. Mortar. I didn’t see a lesson on how much mortar would be needed for setting brick or block. Here’s what I figured. The blocks interlock horizontally so only a bed joint is needed for each block but I’ll wet set the first course as you recommended. So, 3/8” thick joint by 3” wide (the blocks have a hollow center) by 16” long = 18 cu inches of mortar per block. I calculated about 1400 blocks in the wall which is 25,200 cu in = 14.5 cu ft ~= 0.5 cu yards. Mortar is 3:1 sand vs cement; I will need about 0.43 yards of dry sand which is about 860 lbs. If I buy half a ton, I’ll be fine. How many 75 lb bags of mortar cement will I need? (Is the density of cement the same as sand?)
3. Since the interlock blocks are too narrow to pour grout inside, I’m planning to embed “ladder wire” in the bed joints for strength. Should I reinforce each course or alternate courses?
4. Is a single ½” vertical rebar in the center of each H-Block sufficient or do I need two or 5/8”?
5. Weather: Here in Phoenix, we don’t need to worry about rain or frost but HEAT. I hope to start the wall in the next few weeks but know that since I’ll be working on it in the evenings after my day job, it may take several weeks to complete. Do I need to take any precautions to ensure the mortar sets properly?
I’ve included a few pictures of the current fence. It’s pretty pathetic.
Thanks for letting me help.
1) 16×12 – remove existing concrete for a monolithic effect.
2) Very close on mortar. Ask your block company for their yield.
3) Ladder wire every other course
4) 5/8 dead center of hte grout cell.
5) DO not lay in temps over 105 – over 95 degrees DO NOT re-slake the mortar after it is 45 minutes old. DO NOT use mortar over 2 hours old ever and only re-slake (mix in water to a hardening mix) more than twice. Mortar is very critical in T&G block!
Good luck and happy building!
Love & Light,