DIY rapid set cement

This post is about how I use a simple DIY sodium silicate to make DIY rapid set cement (~1.5h) without having the mortar ‘go off’ before it can be placed in the mold.

Introduction

I use portland cement/sand mortar as a filler for many of my projects. It is; simple, quick, cheap, strong, heat resistant and can conform to almost any shape. However, it has one little drawback for an impatient tinkerer like me as it takes many hours to set before I can move on with the next step in the process. DIY rapid set cement can be made by simply adding a DIY sodium silicate liquid to the mix after placement in the mold. The sodium silicate liquid is described in https://timtinker.com/diy-refractories/ and can magically make the mix set very quickly. It can be called an accelerant and my use of the word ‘accelerant’ on other posts has been about gleefully setting things on fire quickly, but in this new context, it is about making cement react to become solid quickly just when required. The magic chemistry of DIY rapid set cement is just as impressive as the flames.

Rapid set cement as a filler for welding tools

As you have probably come to expect (if you read my posts) my first attempt with using this DIY rapid set cement was a spectacular failure (too successful) and a good lesson. The mix ‘went off’ while still trying to mix it in the mixing bowl (I probably 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 of the mold and rodded it to remove entrapped air bubbles. Then I 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 tiny amount of adhering sodium silicate liquid, from the end of the rod, into the mortar. 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 the above mentioned ‘A Render’. 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:

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

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