Setting mortar blocks on a sloping slab
andyman
| Posted in Construction Techniques on
I will be building a 16″ tall concrete block wall around the perimeter of a concrete patio slab (purpose is to visually define the space and also to serve as a seating wall). Between two corners spanning 12 feet, the slab has a fall of 2″. Would it be alright if I merely build up the difference with mortar under the first coarse of blocks? Or, will a 2″ thick mortar joint on the far end between the slab and first row of blocks lead to a structural problem later on? Any advise is greatly appreciated.
Replies
I'm not a block-layer, but i have seen it done. Your job will look much better if you take the time to saw the blocks on the first course. Structurally, the blocks will probably be OK if bedded in the mortar, even if the mortar is 2 inches thick. If this is an out side slab, you may want to place one or two PVC pipes{small diameter} under the first course at right angles to the wall to drain off rain water.
IBEWChuck,
Thanks for your input. I think you are right - I will take the time to saw cut a couple dozen blocks rather than build up the mortar. The pvc pipe is a good suggestion too. Fortunately, I planned for drainage and poured the slab so that water will flow away from the block walls and into our garden area. Thanks again!
It's your own patio?
Cut the blocks so you don't have to look at it everytime you go out there and think "Wish I'd have done it right."
They cut easily, just a lot of dust.
Joe H
I have to agree with JoeH.
The easiest way is to lay the first course on a normal 1/2 to 3/8" bed of mortar following the fall of the slab. After it has set, chalk a level line on both sides of the block and use a diamond dry cut blade in a circular saw or angle grinder the cut the block. You will have a small center of each block that did not get cut because to the limited depth of the blade. On all but the end block you can just chip that part out with a hammer. On the exposed end block, another cut is made to dress it up.
Lay the next course of block on a now dead level first course. Much better looking than a 2" thick bead joint.
Dave
Dave,
That's an excellent idea! It sounds much easier than cutting each block individually before placing in mortar.I do have a question about this method, though. If I set each block in the first layer allowing for the 2" fall, in theory, each block will not sit "plumb". Do you think I will have a problem with my corner blocks NOT sitting plumb? (Did I explain that properly?)Thanks!
Andy
JoeH,
Thanks also for your input. I was hoping to avoid cutting the blocks, but cutting them does seem to be the best method. I do plan on applying a stucco finish when done, and thought perhaps the thick mortar wouldn't be a 'visual' issue. I had doubts as to whether or not a 2" thick mortar joint would shrink as it dried or otherwise become weak.I have a new diamond blade on my grinder so it should go fast. I think I'm going to plug in my floor fan a few feet away and blow the dust away while I cut.Andy
If you plan to stucco it, build it up with mortar.
Joe H
No, No, No, No, No, don't listen to any of these other guys.
I do this stuff, (among other things) for a living. Use the 2" bed of mud. Set your first course of block level......................avoid cutting block at all costs. Too much trouble.
Set your first block on 2" of mud level..............set the other end block at the right height. Run a string line between them and set all the other blocks according to the string line.....making up the difference in mortar (mud, we masons call it).
Don't use homeowner Sacrete crap. Go to a mason supply store and get masonry cement (70 lb bags) Mix 1 bag with 4 buckets of sand (5 gallon buckets) Sometimes it's easier to mix half batches.
Make your first batch thick to support the block at 2" deep. Let it spread out, you can wait till it stiffens a bit and cut off the excess.
Keep in mind I say this because you say that you'll cover the block after. If I had to look at it everyday............different story.
Rod
Edited 8/26/2005 9:51 am ET by notagain
What about approaching it from this angle -- lay the block as you usually would with a half inch bed joint and level things off from the top like you would normally do -- clamp a 2x4 or 6 to both sides, level and fill the portion in-between with concrete -- result is a level top and a pretty strong set up -- all the best - Dudley