Fence posts

[GaryN]

Tony,
I've just completed a short run of fencing (2 x 3' high picket panels with 12" concrete gravel boards and 4 x concrete posts and a 3' picket gate. I'm hoping I haven't made a f--- up here!
I fixed the posts with a damp sharp sand and cement mix as opposed to using cement and ballast, as I had sharp sand on site and I was working to a tight time schedule. Is this likely to provide a strong enough fix? I didn't sink the posts as deep as I normally would as the posts were shorter than I usually use and I figured with the type of panels used wind force against the panels should not present a problem. What's the minimum I should have sunk them. The holes I dug were about 18" deep.

Regards
Gary

[Tony McC]

I reckon you're worrying unnecessarily. As long as the haunching goes hard and is reasonably strong, it's not critical whether it's a mortar or a concrete - it's purpose is to fill the gap between the post and the ground. Having firm and stable ground is more important than whether you used mortar or concrete.

However, the depth is quite important, as there has to be enough of the post shoved into the ground to prevent it being pushed over too easily. Most fence posts are buried to a depth of 450-550mm, so you're just at the lower end on that range.

[GaryN]

Thanks Tony.
For future reference, if I was to use mortar instead of concrete again, should I use the same ratio of cement and sharp sand in the mortar mix as what would be used in concrete with cement and ballast? Looking at a previous post that would appear to be a 9 to 1 mix.
Regards
Gary

[rms]

9:1 mix is fine but I wouldn't recommend using sharp sand. The concrete posts should stay there as it is a picket fence and with the wind blowing through it. Don't try the same thing with a solid fence, even a low one because the concrete posts will soon start leaning when set in normal ground conditions at only 18'' depth.

[GaryN]

Thanks RMS. Any views Tony on the 9 to 1 mix with sharp sand? I wouldn't normally plan to use sharp sand but just in case I get caught short again!
Regards
Gary

[Tony McC]

Yu could, in theory, get away with 9:1 as this is the same ratio as an ST1 concrete (1:3:6). However, because there's no coarse aggregate, I'd prefer to see a mix of, say, 6:1 to compensate for the missing 'gravel'.