# Forum Home Renovation Fences & Screens  post holes filling with water?

## andyc2005

hi i dug my 11 post holes yesterday for a front fence 1500mm high 
the holes have been dug 700mm into the ground. the founding clay is around 400-500mm deep so we are at least 200mm into the clay.  and the holes are 300mm wide. i was planning on putting in 100mm of gravel in the base then the wooden posts (125x125 spotted gum or cypress gold) and them cement to the top (not rapid set but standard) 
the next day the holes had 100 to 300mm of water in them! 
the water seeps from the top soil. the soild is quite wet. obviously has been a fair bit of rain in melbourne lately so i dont know if its always this wet. but this seems to me to be a problem given i was planning on using wooden posts and i feel that being this wet would compromise the life of the posts?? 
would i be better off going with 100x100 galvanised steel posts?  presumably the water wont affect these as much. also, i notice the thickness of the 100x100 gal posts is from 2mm to 2.5mm to 3mm. what size would be most suitable?  i was thinking using 3mm thick for the 4 gate posts and 2mm for all other posts.

----------


## johnc

Cypress will be fine, posts tend to rot around soil level anyway, the upper and lower sections less so. It is unlikely to have a huge bearing over time plus once you have rammed the earth into place you will hold back some water. Don't use gravel it will create a sump that will hold water refill with the same soil that came out of the hole and ram it in hard. Your steel posts wont like the damp enviroment any more than the wooden ones.

----------


## andyc2005

> Cypress will be fine, posts tend to rot around soil level anyway, the upper and lower sections less so. It is unlikely to have a huge bearing over time plus once you have rammed the earth into place you will hold back some water. Don't use gravel it will create a sump that will hold water refill with the same soil that came out of the hole and ram it in hard. Your steel posts wont like the damp enviroment any more than the wooden ones.

  
thanks john. i have read many debates on using cement vs dirt or gravel to hold the posts in place.  i still feel uneasy about not using cement.  but it seems that many use gravel. the gate posts will be holding a sliding and a passenger gate (both made of 50x50 steel and clad in wood so fairly heavy)  
i have also read many guides saying to use 100mm of gravel at the bottom of the post. is this not generally the case?

----------


## andyc2005

i believe the argument for using gravel is essentially around providing a place for the water to drain to away from the post  however an argument against using gravel is that the post rots at or near the base (not 60cm into the ground)

----------


## johnc

There are different views, and you would have to admit soil type and ground moisture are an issue depending on location. It is the combination of moisture and air that rots which is why posts tend to be effected at ground level with the deeper and upper sections of the post less effected. Disturbed ground tends to hold water more than undisturbed ground which is why I am of the view that placing gravel in the bottom of the hole acts as a sump especially in clay soils. In sandy soils it probably doesn't make much difference.  
As to concrete, if you place the post in the hole first and concrete around it then any water will pass down through the post and get away. If you set the post on a concrete bed and add concrete you create a little bath for the posts to rot in.  
Everyone has there own opinion but I don't have a problem with concreting in but tend to prefer rammed earth as done properly using the original soil you should get a hard mass that hopefully repels moisture especially in loamy soils (well thats the theory anyway). If they are heavy clay ramming is difficult as the clay lumps don't always breakup well in which case concrete may suit better. 
If I was in your position I would avoid gravel as you have wet conditions and just ram the earth spoil back in avoiding any heavy clay balls, you may not have enough soil and you might consider topping the hole with concrete finishing just below ground level with the top of the concrete slopping away slightly so water is directed away from the post. To ram just place back a shovel full at a time and thump in hard with the back of the crowbar, doesn't take long once you get the hang of it.  
We put in rammed earth fence posts thirty years ago which are still holding up well, while trellis post set in concrete at the same time rotted out many years ago. Our soil is a sandy loam which is as hard as the hobs of hell in summer and soft as butter in a wet winter.

----------


## andyc2005

thanks for your reply john 
the first 40cm of the soil and nice sandy loam (similar to what you describe) then its clay which is as hard as hell.  i have dug the holes 20 - 30cm into the clay. the  top soil is very well draining (as all plants grow great in it) and you can see all the water poolling in the top soil just above the clay level when you dig (this is where the water is slowly seeping into the holes overnight.  
i wont bother with the gravel, just put the post into the hole on the clay base and fill with cement to slightly above ground level sloping away from the post (as i already have the cement i may as well use it).  as an expirement i will put a couple of posts in with no cement and see how they go in the years to come 
i also coated the base of the cypress posts (and 10cm above ground level) with 2 coat of a product called diggers eco in-ground protecta (which is supposed to be a creasote alternative)  Products | Diggers Eco In-Ground Timber Protecta | Recochem - Australia

----------


## johnc

Sounds like a plan, Cyprus is supposed to be long lasting and durable, the coating to the base wont hurt either. My FIL had 200 litre drums of sump oil he would soak treated pine posts in for days sometimes weeks before putting in the ground, not eco friendly but pretty effective against almost anything I suspect.

----------

