Cement and sodium silicate accelerant

This page is about how I use and sodium silicate accelerant to rapidly set cement mortar (1.5h) without having the mortar ‘go off’ before it can be placed in the mold.

I use portland cement/sand mortar as a filler for many of my projects. It is; simple, quick, cheap, strong and can conform to almost any shape.

It has one little drawback for an impatient tinkerer like me. It takes hours to set before I can move on with the next step in the project. Addition of liquid DIY Sodium silicate can magically make the mix set very quickly.

An example of the use of sodium silicate accelerant

My use of the word ‘accelerant’ on other pages has been about gleefully promoting small fires in cooking/heating stoves. In this new context, it is about making cement react to become solid quickly. So this is my opportunity for an ode:

Search for the right word for a cement accelerant,
Not a pyromaniac  flames when fuel he did decant,
Just to make boring cement set as fast as a jet,
About as meaningful as the term civil celebrant.

“This magic chemistry is almost as impressive as is that of fire.”

As you have come to expect (if you read my pages) my first attempt with experiments often don’t work out. Using this cement and sodium silicate accelerant was a spectacular failure and great lesson. The mix ‘went off’ while still trying to mix it in the mixing bowl. “I assumed I used too much silicate. With this experience, the next attempt was a great success.”

The second time around I mixed the sand cement and water to get the right texture in the mixing bowl. I filled the cavity with it Following that I ‘rodded’ it to remove entrapped air bubbles and then use the rod (in the background in the above photo) to dip (~20mm) into the pigmented sodium silicate ‘A-Render’ as described in the above link. I rapidly mixed this adhering accelerant, from the end of the rod, into the mortar and the mortar started to thicken noticeably as I mixed it in. The clear stock sodium silicate in the above link would also suffice, but I found that the dark colour of A Render was helpful in showing the extent of mixing of the silicate with the mortar.

Rapid set cement as a filler for garden poles made from discarded galvanized water pipes

I have just been sealing off the ends of galvanised pipes that I use as posts in my garden. I do this to keep water out of the pipes and deprive pest insects of a nice home.

I press a plug of newspaper a little way into the pipe and then pack a sand, cement and water mortar mix on top of the paper. I experimented with just painting on a coating of my silicate ‘A Render’ as described in DIY Sodium silicate refractory. It set the mortar immediately (within 2min) without any need to mix it in below the surface. So that’s another easy way to use the sodium silicate accelerant.

After a little more literature research I found a reference to this ‘accelerant effect of sodium silicate‘ and it even mentioned the issue of requiring special mixing to prevent premature setting.

An ode to sodium silicate to finish with:

Sodium silicate will make it quickly go thick,
Portland cement that will go as hard as a brick,
If you want hard fast, stick it in last,
With mix stick that should be pulled out quick.

Tim

Addendum 1

I have had a cautionary comment from a subscriber who is a concrete expert (Greymatter) and indicated that the use of sodium silicate could make the cement strength weaker. This reference on acceleration of Portland cement indicates that low sodium silicate addition (1%) can cause retardation, while 2-10% addition gave remarkable acceleration but a decrease in strength. “I must have been lucky to just get it right with my rough bucket chemistry.” However, for all my farm and tinkering projects, achieving maximum strength has not been an issue and everything has held up over time. Having a quick set is often the priority to stop procrastinating and get the job done.