Putting up Stucco with the Mortar Sprayer

I needed to mount an electrical panel in the mechanical room in the basement.  But first, I needed to stucco those walls.  The walls were really too rough to use metal tools (the stucco just falls off between the lumps and tool) and packing it by hand was too slow.  After trying both, we decided to spend the money to buy a Mortar Sprayer from Tool Crete.

Here is the video

Enough Air?

These mortar sprayers use air pressure to blast wet concrete/stucco/mortar from the bottom of the hopper on to the wall, so obviously having enough air is critical.  For maximum flow, I would need a decent air compressor and high flow fittings and hoses, but without spending too much money.

My little pancake compressor, with its quarter inch fittings, definitely wasn’t going to be sufficient. Larger compressors can get expensive and the mortar sprayer was expensive enough on its own. Fortunately, my father let me have his old compressor.  He must have had that thing for about 30 years and I remember hating it as a child… Not just because it was annoyingly loud, but because he would sometimes ask me to turn it on or off and the switch was strangely placed on the inside and I would have to reach blindly under the bench over the electrical connections, between the motor and compressor and way too close to the spinning belt that connected them…  Regardless of my past (totally reasonable) fears, I was quite happy to get it now.

Next, I would need to find the right fittings.  Larger is better, so I was looking for 1/2 inch fittings. These are not available at any hardware stores near me, so I was checking out places like Grainger industrial supply and they were pricey.  Fortunately, I didn’t get around to buying anything before I realized that the compressor outlet was only 3/8ths of an inch.  There is no sense in having larger connections downstream of a smaller one, so the compressor outlet diameter limited my max fitting size to 3/8ths inch. I found that Home Depot had plenty in stock and they were much more affordable than the 1/2 inch ones.  My fathers old hoses were also 3/8ths, but with 1/4 inch fittings, so, I just swapped out all the fittings.

The last hurdle was the 220 volts required.  My generator has a 220 plug, but it couldn’t keep up with the demand I expected from the compressor.  This meant I needed to wire in a 220 plug and make up a long enough extension chord. At least that was pretty straight forward. I also had to swap out the plug on the compressor to match. While rewiring the generator, I discovered that the original wiring didn’t have a properly connected ground, somewhat further justifying my childhood fears.

Once that was all done, I bought the stucco and waited for a rainy day.  No sense wasting a good sunny day down in the basement.

Mortar Sprayer Tips

I found the mortar sprayer pretty easy to use, and you would probably figure these things out yourself if you picked one up, but I will write them down anyway.

1) It is clearly designed to scoop from a wheelbarrow, so you might as well just mix the stucco right in the wheelbarrow.  I do have a paddle mixer (attaches to my drill), and a barrel mixer, but it just seemed easier to do it directly with a hoe in a wheelbarrow.  Proper “mixing hoes” have two big holes in the blade to help reduce drag and improve the mixing, but the light weight stucco mixed easily with a standard garden hoe.

2) Mix consistency is important.  If the mix is too thick it doesn’t slide down the hopper to where the air nozzles are.  I found I could sometimes shake it down, but that was tiring.  On the other extreme, if the mix is too thin, it slides down the hopper and some of it starts to drain out the holes before you can shoot it on the wall.  With a little trial and error, we worked out a water ratio and mixing process that worked pretty well for our conditions.

3) Ladder work is sometimes required.  The hopper empties quickly and climbing up and down the ladder with the mortar sprayer and hose is a bit tiring.  We found it worked best to stay up on the ladder and pass the sprayer down to someone who could scoop it and pass it back up.

Shooting the Scratch Coat onto the wall

4) The scoop action is easy if the mortar is all piled in the right place in the wheelbarrow, but near the end of each load, we found it saved time if the second man used a trowel to help push the mortar from the corners into the “scoop zone” while the sprayer was shooting onto the wall.

5) The sprayer does make a bit of a mess and things are much easier to clean up if you can put down some plastic, etc.  In the video, you can see I even covered the water pressure tank in a garbage bag.

6) After getting the mortar up and smoothing it off (with a tool or by hand), you should let it set for several hours (depending on environmental factors) and then come back with a grout sponge when it feels pretty stiff.  These are tougher than a regular sponge and you can find these in the tile section of the hardware store.  I used a bucket of water to keep in wet and wiped down the walls to smooth them significantly.  The difference between the sponge smoothed walls and the walls I didn’t smooth is pretty dramatic.  I am just glad that I will be putting a lot of duct work, etc. in front of the rougher walls.

Gallery

A gallery of pics.

Shooting the Scratch Coat onto the wall

Here, you can see the horizontal lines of the scratch coat… And a hint of how rough the underlying shotcrete was.

Left half is final coat stucco, right half is scratch coat. The tubes are 8″ diameter earth tubes.

Final finish coat. Just plain white stucco.

After the stucco set, we mounted this plywood with tapcon screws as a base for the electrical panel.