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Smoothest cement mix ratio

Claudine
Budding Contributor

Smoothest cement mix ratio

Hi everyone,

I've started making planters and have made my own mix using white cement and sand. I'm still finding that it cracks after drying and sealing so I'm looking for a better cement to use or ratio. I'm looking for a smoother finish (as you can see mine is a bit drier). If anyone can recommend a cement similar to Easy Mix Ivory Cement (as I can't purchase it from where I am) that would be really great. Alternatively, if you know of a better ratio mixture using other white cement, that would be great too. 

 

Thank you in advance!

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Smoothest cement mix ratio

Welcome to the Bunnings Workshop community @Claudine. It's wonderful that you've joined us, and many thanks for your question about cement.

 

There are specific techniques like wet curing to help prevent cracks in the cement. This is the process of keeping the pot damp for up to a week whilst the cement hardens. If the water gets sucked out too quickly, as could be the case if the pots are placed in the sun and dry out, you'll see cracks. Don't put your pots out in the sun. They'll cure perfectly fine in the shade, and it will be a much more controlled cure. It's important to remember that the cement doesn't harden by it drying out. It sets by curing over a period of up to two weeks through a chemical reaction that is only active whilst there is water present.

 

Cracks can also be filled after they have occurred, and the surface sanded to blend. So, if this is a personal home craft type project, you could look at doing that. 

 

I recently put together this step-by-step guide on How to make cement planter pots. In it, I used equal parts of quick-set mortar and cement mix. Cement mix is the smoother of the two as mortar includes sand. The size of the sand particles is what will cause the roughness, though having a smooth mould should leave you with a reasonably fine surface. Once again, sandpaper can be used to refine the finish. I believe any white cement you'll find will be of a smooth consistency, though you might like to look for sand that has a particularly fine particle. However, the finer the sand particle, the less resistant to cracks the mix will be. The sand is what joins the cement together and adds strength. 

 

The only type of product that I can think of which you could look into would be a structural grout. These achieve a much higher strength rating than standard types of cement. The issue with these would be they generally need to be poured in thinner layers, and they are most often found in greys, not whites.

 

Our Cement Australia 20kg White Cement should be suitable for your project. What was the cement sand ratio that you've already tried?

 

Please let me know if you have any questions.

 

Mitchell

 

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Claudine
Budding Contributor

Re: Smoothest cement mix ratio

Thank you so much Mitchell! I haven't found anywhere online that has explained it as well and thoroughly as you have. I appreciate your help!

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Claudine
Budding Contributor

Re: Smoothest cement mix ratio

I think I know what the problem is now (partially) which is leaving the pots outside (not in the sun) but whilst I've been spraying them with seal.

 

The ratio I was using was 2 parts cement to 1 part sand. I previously tried 1 part cement to 2 parts sand but the product ended up being too soft in the base and way too much sand coming out of the pot.

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Smoothest cement mix ratio

@Claudine,

 

The mix I used probably worked out around your two parts cement to one part sand. However, I wanted my pots to dry as quick as possible, so I put them out in the hot sun. This resulted in a few fine cracks here and there. Had I kept them in the shade and misted them with a sprayer twice a day for a week, I'm sure the cracking would have been reduced significantly. There was nothing structural, and all the pots are still holding together, but the larger pots have a couple of hairline cracks.

 

You could try adding some BondCrete into your mix. This will assist with binding the cement together.

 

Though it can be a bit challenging, keep at it; once you get that mix right, you'll be set.

 

Mitchell

 

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EricL
Bunnings Team Member
Bunnings Team Member

Re: Smoothest cement mix ratio

Hello @Claudine 

 

After reading what's been happening to your projects I suspect that you are getting accelerated drying as mentioned by my colleague @MitchellMc. I suggest putting your handy work under some black plastic bags to slow down the drying process. On the days where you feel that the air is too dry or it's too windy, I recommend using your garden hose with the mist function on and lightly spraying your projects to cool them off. 

 

We look forward to seeing your creations.

 

Eric

 

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Claudine
Budding Contributor

Re: Smoothest cement mix ratio

Hi Eric,

 

Thank you for your advice! I wanted to ask, if I am going to do the wet curing process, how long would you suggest that I do it for? 

 

My other query is if I was to leave the pots to cure in the garage (dark and no light coming through) wold that work alternatively? 

 

Thank you again!

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MitchellMc
Bunnings Team Member
Bunnings Team Member

Re: Smoothest cement mix ratio

@Claudine,

 

The garage sounds like a great place to put the pots. I'd trial that location and if it doesn't work, try the wet cure process. The curing process can take up to two weeks, but I'd start by keeping them moist for the first week. Even the first few days would be beneficial and might be all you need. You just don't want the moisture being sucked out of them within the first 24 hours.

 

To get this right, you might just have to do a few tests. You'll want to find the method with the least amount of work for you to do, but that still achieves the results you need.

 

Mitchell

 

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