Cement doesn't stick

[chuckchuck]

I have lots of small pieces of bricks that I sprayed with a cement and water mixture (used a garden spray). This looks absolutely perfect, like real rocks. But you can easily wipe the cement of when it's dry, it turns to "powder".

Is there anything I should add to make the cement stick? I thought it becomes really hard. We have lots of white cement in the garage so I prefer to use it up!

This is for a scale model by the way.

 

[Softus]

Cement and water does not bind very well on its own, which is why all concrete has ballast or aggregate mixed into it.

Try adding a little bit of PVA to the water that you use for the cement.

 

[chuckchuck]

That sounds like an excellent suggestion. I will try this when I'm at home tonight!

I do have a lot of wallpaper-glue left, but I guess that will make the mixture too thick to be sprayed.

Thanks for the help so far!

 

[JohnD]

also, cement-based materials benefit from time to "cure" - being kept damp for a few days. You can do this by putting plastic sheet over it, and/or by misting with a water spray.

It does not harden by drying out, like a glue might, but by reacting with the water. As soon as it goes dry it stops hardening, and will not restart.

If you add some fine sand to the mixture you can make a slurry, but you will need a coarse brush to apply it, it won't spray.

 

[chappers]

thats exactly what will happen the cement will just harden but crumble again you need some sand etc as a matrix to bind the set cement together.