Gardening Question From Grant:

A bit of a different question for you…

We have an outdoor radio control car track where the surface is clay, which is ideal for running the cars on as its smooth, grippy, and not abrasive on tyres. The clay is regularly compacted with a 100kg plate compactor at OMC, however we have the issue that when the clay dries out, the top layer starts to break off and the track becomes very loose/broken up. The only way to keep the clay from breaking up is to keep it moist which unfortunately is not feasible.

What would be an ideal product to mix into the top surface of the clay to hold it together when it dries out? I read your article regarding adding sand to clay would make it like cement? Which sand is the least abrasive or what other product would be best to add to ensure the clay holds together when dry? The track has runoff into a drain so drainage through the soil is not required.

We are based in Sydney, Australia where we get very hot days in summer. Our club website is Sydneyrc.com if interested.

Thanks for your assistance!

Answer From Pat:

I don’t think sand would fix your problem. Clay tends to crack on top when it dries, which is natural since the top layer is drying faster than damp layers below which are still expanded by water content. I think you need something that would make the clay on top dry more slowly than the layers beneath, but I cannot imagine what this might be. It occurs to me that if fibers were mixed into the top layer of clay they would hold it together, but who knows? Also a fibrous material might make the track slippery which you don’t want. Puddling of the clay certainly would add to its elasticity, but I don’t think it would completely stop cracking. I wish I could help you, but I don’t have enough expertise to answer your question.

Photo by Doug NC