by James on April 26, 2012
The following is Part 2 of a photo guide showing one method for building a raised planter out of masonry. You can find Part I of this article here. This example comes from our backyard. Please read the Disclaimers from Part I before even thinking about starting this project because some things you may want to do differently.
In Part I, I covered how to build the footing for your Raised Planter and by now you should have laid out the first course of blocks onto that footing as seen below.
Beginning Part II
10. Lay the first course of blocks out “dry”. I’m not saying you can’t have a sip of your favorite whiskey. What I mean by “dry” is without any mortar. Just set them in place. Having a beer beforehand may improve your enjoyment of building this planter but not necessarily the quality.
You could use a string line to make sure your wall is straight or if you’re not fussy and want something more rustic and hand-made looking, just use your eyeball to sight along the wall for straightness. In the photo, this particular planter has to line up with other existing planters. If you’re only building one planter, you might not have to worry about lining things up with other existing objects.
If you’ve had one too many beers and are seeing double, then always pick the row of blocks on the right (or left, just stay consistent).
The same goes for squareness. You could create a 3-4-5 triangle to check for squareness or just eyeball it for a more ‘human’ (i.e. imperfect) look. Or you could use a large carpenter’s square if it makes you feel better.
Don’t forget the wall is going to “grow” in thickness by about 1/2” after bonding and finish stucco coats. So, if you’re lining things up with other objects, don’t forget about that extra poundage that goes on the wall.
Variations in the bottom of the blocks and foundation may cause some blocks to tip a little, side-to-side. It’s OK, we’ve all been a little tipsy now and then. A little tippiness (let’s just say up to 1/16”) is generally OK and will be fixed when stuccoing the blocks in a later Step. You can even out tippy blocks using mortar or grind the bottoms if it’s really bad.
The only problem seems to be if you’ve got one tippy block atop another, atop another, etc which wont happen until Step 14 when you start stacking blocks. Then, it’s like a pig-pile at a college frat party and will likely end in the same way – collapsed on the ground and a big mess to clean up. Be a block cop and make sure the tippy blocks aren’t atop other tippy blocks or get them rehabilitated so they don’t tip.
11. Here’s one brand of Surface Bonding (SB) cement that is available locally through special order. It comes in grey or white, sanded or unsanded. Get the grey sanded version because it is the easiest to use and gives a good appearance (if you choose to use it as the final coat). The white seems just slightly harder to work with but maybe I got a bad batch. Get the sanded finish because it presents a rough surface for subsequent coats to stick to. One 50lb bag covers about 50sqft conservatively and costs $17-21 per bag.
Buy extra bags because you never know what might happen and they usually take about a week to order in. You don’t want to be caught a bag short and a week away from another one or you will feel like a meth-addict stuck without a fix. So order extra, it’s relatively cheap compared to the consequences not having enough to finish.
Since SB cement hasn’t become wildly popular, they tend to sit around the warehouse (I suspect) and some absorb a little water and become chunky and hard to use. Another reason to buy extra bags. You will need to throw out the chunks, they will just cause you trouble when you apply it. Or you can whine complain and scream mightily until your Supplier gets you some fresh bags.
12. Mix your SB cement to a thick slurry as shown in the video (produced by Quikrete). Unlike the video, I’d recommend using a heavy-duty, low-speed drill (about $130) and a paddle mixer ($15) in a 5 gallon bucket.
I’d also recommend only mixing a small amount at a time, such as 10-15 lbs, and not a whole bag at once, especially if it’s your first time and you don’t have an assistant. This stuff sets up fast (you have maybe 25-40 minutes) so don’t mix a whole bag at once like they show unless you know you can do it. Otherwise, you might end up with a bucket full SB cement the consistency of bread dough, unable to spread on the wall, only good for molding into an amorphous block (art project) or for making a relief impression of your butt which you can then gift to your friends and frenemies.
The set period depends on the weather. Hot weather is difficult to work in. We’re so very lucky that we have many, many dreary days in the NW. So lucky. Makes it easier to mix SB cement. Take that California.
SB cement is very sensitive to the amount of water you add. You may think you need more water, but if you don’t thoroughly mix in the water that is there, it might suddenly get very soupy with the addition of more water. And you can’t take water away. You can only add more mix to thicken it up or let it set a bit if it’s not too bad.
To make it even trickier, the manufacturer’s instructions recommend not to over mix the cement either, or you will “filamentize” the reinforcing fibers (break them). I honestly don’t know at what point filamentization happens or how you would know it happened. Best to just stop mixing when it looks ready I guess.
The SB mix will go into an initial set after about 10 minutes and start to get very stiff; too stiff to spread against the wall. What you need to do is re-mix it with a small amount of water. This is called “tempering” the mix. After this first temper, it will be easier to work for a longer period of time. Don’t temper too many times or the mix will lose strength; maybe twice max depending how much time has elapsed. Like I said above the manufacturer’ instructions say not to overmix but doesn’t give specifics.
Butter the footing about 1/4″ thick with SB cement using a trowel. Choose a small trowel, like an edging trowel because it’s very versatile and you can scoop right out of the bucket with it. The method is to pick up one or two blocks at a time out of your layout, being careful not to disturb adjacent blocks. This way, you can use the adjacent blocks as your guide, since you already laid them out. After buttering the footing, replace the blocks you just removed, lining them up with adjacent blocks as guides. The video above shows them using a chalk line to align blocks. The problem with that is your chalk line becomes obliterated
by the slurry you’re buttering the footing with. You can also use a string line set between stakes.
The video shows fine-leveling every few blocks with a bubble level. If you spent the time to make sure your footing was level, with no bumps or dips, then leveling every block in the first course is not necessary. Just press the blocks into the slurry as far down onto the footing as they will go. If you do try to level the first course of blocks, then you must also make sure the tops of the blocks are at the same height too, since the leveling mortar adds height. In my method, I make sure the footing is reasonably level and any minor imperfections will be compensated by averaging of the block imperfections, adjusting at the wall cap at the top, and concealed by the stucco.
Keep the surfaces moist that you’re applying the SB cement to. If the blocks or concrete footing is too dry, it will suck the moisture right out of your SB cement mix making for a weak, incomplete cure. However, don’t overdo it and have puddles of water either. I recommend getting one or two good water sprayer bottles to wet down dry surfaces during SB cement application. Trying to mist from a garden hose tends to get out of hand when your working with the mix. The garden hose is great for initial wet down and post cure wet down. But if you’re dealing with a wet cement mix, an errant squirt of the hose can really destroy a portion of your work pretty quickly.
After bonding the first two blocks to the footing, repeat the procedure for the next one or two blocks and work your way around the wall. When you complete a side, double check your blocks for straightness, just in case something got knocked out of place. After you made your way all the way around, clean your tools, sit back, and let the SB cement fully cure.
Some final notes on the video:
A) Too much colorant can reduce the strength of the SB cement. If you’re going for a really saturated color, you will need to do that in a finish coat that goes over the top of the SB mix. Follow the manufacturer’s instructions for maximum allowable dosage of colorant.
B) SB cement makes a pretty good final finish coat, but you will still see the reinforcing fibers in the final product. Some people don’t like the look of little glass fibers in the final finish. However, it does save you money and time for the SB coat to be the structural and finish coat all in one.
13. This is what your planter should look like after the first course has been buttered and bonded to the footing. After the slurry for the base row has fully cured, it’s time to dry-stack your blocks. This is when the wall really starts taking shape fast.
14. See how fast that was. Start grabbing blocks and “dry stacking” them in a “running bond” pattern where the joint between two blocks always lands in the middle of a block below as shown in the picture above. If you have any seams that line up with the row above or below it, you’re doing it wrong, adjust your pattern. Otherwise, it will create a weak spot in the final product.
Don’t worry too much about blocks that are a little tipsy. Remember what I said about being a ‘block cop’ way back in step 10? Again, the bottoms of your typical concrete block are a little uneven because they are meant to be laid in a bed of mortar. A little bit if tippiness (about 1/16” gap) will be fixed when you apply the SB cement. If you have a really tippy block, you can level it using mortar or SB cement. Or you can grind down unnecessary protrusions on the bottoms of blocks with a grinder fitted with a concrete cutting blade or grinding wheel or a by hand using a grinding/finishing block available at any big box or concrete supply store.
15. After dry stacking a row, site down the blocks again to make sure the wall is still straight. In the wall above, you can see how it is aligned with the adjacent planter and there is a slight bow inward.
Chances are you wont be able to get a perfectly straight line because of a combination of variations in the blocks and footing. However, it’s going to be OK, folks. It all depends how you want it to look and whether that additional effort required for perfection really pays off. If you intend to put a cap on the wall that is wider than the wall itself, then you can make up for small imperfections by making sure the cap is straight.
If you have a little bowing of the wall, just make sure it bows inward toward the center of the planter. Then, it will actually strengthen the ability of the wall to resist internal soil pressure. And a slight bow will not be seen once the wall is capped.
16. Follow the directions for the SB cement (above in step 12) and stucco the outside of the wall. Be sure to spread it to the proper thickness (min 1/8″ thick). You can do a wall of this size using the edge trowel mentioned in combination with a pool trowel. A pool trowel is similar to the rectangular trowel shown in the step 12 video except it’s oval – so there’s less chance of catching a corner. Have your spray bottle handy to lightly mist the wall and stucco as necessary to keep it from drying too soon.
17. After the outside coat has fully cured you can carefully climb over the wall to do the inside coat. Set up some blocks to be able to step over the wall without placing weight on the wall and possibly damaging the outer skin. Note that little pipe sticking out of the ground is for irrigation.
First fill in the inside corners with either SB cement or mortar to create a fillet relief. This will help prevent cracking of the SB cement at this sharp transition. Let it cure and then go over with the skin of SB cement.
18. After the SB cement has cured, fill the block cores that had the rebar “pins” in them (see Part I) with a wet concrete or mortar mix and stick a piece of 1/2 rebar inside for reinforcement. The rebar should extend from the top of the footing through all the blocks and be about 1 inch shorter than the wall height.
Concrete and cement products based on Portland Cement (everything you see here) require about 28 days to reach full strength. During that time, these products also need moisture to cure and gain strength properly. Not having enough moisture can lead to cracking and/or a weak mix that will deteriorate faster. Keep your planter moist for 1 to 4 weeks by watering daily for the first week or two (especially if the weather is dry). If you can spare the expense, covering the whole thing with plastic also helps to retain moisture.
Congratulations, your planter is almost finished! In Part 3, we will cover capping the wall and adding a finish coat.