Using concrete to anchor posts provides a very solid foundation and will help to make your fence and other garden structures more durable.
Fixing wooden posts with concrete will give your structure a much firmer footing than using a post spike would, particularly if working with light soil or areas of high wind.
Bear in mind that using concrete will add a couple of days to the overall completion time of the project, as you will need to allow time for it to set properly.
Tools You will need:
– Narrow Spade or Large Trowel
– Spirit Level
– Wood Preservative (optional)
Digging The Post Holes
Carefully check and mark out where the holes need to go. Using a narrow spade, dig a hole roughly 100mm wider on all sides than the post (for a 100mm square post, make your hole 300mm square) and at least 600mm deep.
To help to stop the bottom of the post rotting over time, paint the part which will be buried with Wood Preservative and let this dry. You should also put a 100mm layer of gravel in the bottom of the hole to aid drainage.
If you are going to need several holes (for fencing posts, etc), measure from the middle of the first hole to required position of the next.
Dig this second hole out and repeat until all holes are dug and ready for posts to be inserted. This helps you to avoid wasting concrete.
Mixing the Concrete
Make up a fairly dry concrete mix using 1 part cement, 2 parts sand and 3 parts aggregate (1:2:3 mix) in a cement mixer, if you have that luxury, or on a board or wheelbarrow if not.
Your mix should not be too wet as this will not support the posts whilst it hardens as well as a dryer mix will.
Setting The Posts in Concrete
Set the post firmly into the hole and hold it upright whilst you shovel in concrete evenly around it. If you have some helping hands to hold the post (or shovel), so much the better.
If not you can clamp lengths of wood to the post to act as temporary braces. Be careful to check that the post is upright with your spirit level before and whilst you add the concrete.
Aim to leave the surface of the concrete slightly below ground level so that you can cover it with soil when it is set.
Tamp the wet concrete around the post to knock out any air bubbles and to firm it down. If possible, slope the surface of the concrete away from the post slightly to stop water pooling around it.
Double check that the post is upright and then leave it braced in position for 2 or 3 days. Check that the concrete has set fully before removing the braces and continuing with the construction of the rest of the fence/structure.