Concrete (shot-crete), June 14, 2015

Last post, I showed you the preparations for the concrete installation at my place in NDG.  As I mentioned, the concrete being used is something called “shot-crete”.  So what is shot-crete? Firstly, it is a really dry mix, with the minimum amount of water/cement ratio.  For those who remember, the less water, the stronger the concrete. This also results in a really small slump, so consolidation of the placed concrete will be difficult. In this case, this is not much of a problem, because secondly, the concrete is actually shot out of a “gun”, so the consolidation actually happens as the layers of concrete are built up. Thirdly, the aggregate is quite small, between 1/4″ and 1/2″ so as to be able to be “shot”.

Before the actual placing of the concrete, the forms had to be made for the window and for the top of the pour.  This photo shows how the existing concrete was so deteriorated, that the columns between the windows had to be removed, and jack posts were installed and are to be left in the concrete:


Now the forms can be constructed:


Note the plywood above the windows that will act as a bulkhead for the top of the wall.

The next day the concrete truck and pump truck arrived. The workers attached the nozzle to the end of the hose.  Note that the hose has been stepped down to 3 inches and then the nozzle again smaller – about 1-1/2″ in diameter. Attached to the side of the “gun” is the hose from a large compressor, which will act as the power to shoot the concrete.


Once all is prepared, the workers take a wee rest before all hell breaks loose.


Then the pump starts to engage and the concrete is shot out of the gun to the surface of the wall:



I was surprised at how much mist there was in the room as they shot the concrete.  The amount of force is quite amazing and I suppose the water is vaporized by the pressure and the contact with the existing wall. There was a ventilator fan running continuously, but it could not keep up:


Once he had built up the layers to about 6 inched thick, the crew moved in to trowel out the surface.


While this was happening, the shooting crew moved outside to instal the opposite surface:


The final look is like this inside:


….and this outside:


After all is said and done, I do have some comments and opinions about this strategy, and of course there are some finishing steps that need to be accomplished before this is completed, so I’ll pick up this topic in a few weeks to tie up loose ends.

Until then,


About jhcarpentry

I am a teacher in the Construction Carpentry Program at the Chateauguay Valley Career Education Centre (CVCEC) for the New Frontiers School board. This blog is a way for me to connect with my students.
This entry was posted in Uncategorized. Bookmark the permalink.

1 Response to Concrete (shot-crete), June 14, 2015

  1. interested to hear how the spots turned out after the paint was applied.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s