using postcrete

Discussion in 'Landscaping and Outdoors' started by hollyb96, Nov 8, 2019.

  1. hollyb96

    hollyb96 Member

    i am currently building a deck and today dug all the holes for the footings. I dug them 85cm deep and 20cm wide. My plan is to add gravel at the bottom for better drainage and then fill the hole completely with concrete. Then once its dry screw in a galvanised post base for the posts to sit on.
    My issue is that i have never worked with concrete before. I have done research and i think postcrete seems to be the easiest option. After doing research though i have found that i will probably need more than one bag per hole (especially because theres not going to be an actual post in the concrete). My questions are:
    I have seen someone adding bricks to the hole so that they dont have to use as much concrete, i dont have any brick but i do have loads of bigger and smaller boulders/stones that i have dug up with the post holes. Could i use them instead? What sort of sizes shall i use, what is too big? How many can i add to each hole?Also when i add them do i add them to the hole first or add them once the postcrete has been poured in?
    Secondly, if i need to use more than one bag (which i probably will have to) how to i do that? Do i add the first bag with the right amount of water and then do the second bag while its still wet or do i wait for it to dry and come back and do the next bag the next day? Also if it takes 1 1/2 bags, how do i know how much more it will need in the hole and how much water to add? Thanks
  2. Wayners

    Wayners Screwfix Select

    Buy sand and gravel with cement (normal or fast setting) You don't need fast setting though. Mix your own is cheapest way. Post create works well as sets quick but you don't need that. Think you may get in trouble with it setting too quick and stuck on kit. Also with post create you dig just enough for one post and bag. The idea is you can move along without fear post will move. Jam post with rubble or use wood brace to hold for 20mins until it sets.

    You should..
    Mix concrete in large builders tub, pours in hole. Can push bricks and rocks in if you want. When empty mix some more. Near enough with mixture is fine. Don't be fussy as colour difference is not a worry.

    Did hole
    Mix concrete
    As setting stiff brush over surface or trowel smooth or just leave as is. Set in 24h Give it few days then get on and finish..

    If you don't mix enough then mix more and pour on.

    You can't add wet concrete to set concrete. It wont stick. But why would you...
  3. hollyb96

    hollyb96 Member

    the only reason i dont want to go with the traditional method is the concrete part of building the decking is kind of stressing me out a bit so i kinda just want to get it done quickly so i dont need to think about it. Also not having to mix the stuff myself and get the ratios right seems way easier. I helped my dad build a pond when i was younger so i know concrete isnt super hard to do but there was 2 of us doing it before and now im going to be doing it all by myself so im just a bit nervous about it
  4. Kas228

    Kas228 Screwfix Select

    Not an expert but just a thought, do the holes need to be 85cm deep? Seems an awful big footing for decking post.
    wiggy likes this.
  5. hollyb96

    hollyb96 Member

    they need to be below the frost line (which is 75cm) so that when the ground freezes the concrete isnt damaged. i then decided to go 85cm down so i can have 10cm of gravel at the bottom for drainage
  6. DIYDave.

    DIYDave. Screwfix Select

    I would consider hiring a cement mixer for the weekend, cost me £22 sat and return mon am, I picked it up in the back of a Renault Scenic but hire shops will deliver if you need (obviously prices will vary around the county)

    Use sacks of ballast from say B&Q (£2.20 sack approx) and mix 6 ballast to 1 cement. With cement mixer it’s easy, and as you say, it’s just ratios and for this type of work, doesn’t need to be super critical accurate

    When I’ve mixed up concrete this way I know that 1 and a ‘bit’ sacks of ballast and a small bucket of cement is good enough to equate to a 6-1 mix (it’s easy to work out really)

    Half fill holes, tamp down with a wooden fence post, fill again, tamp down again and level

    Mixing by hand is hard work !
    Don’t mind a small mix and I use a wheelbarrow to mix in but a larger amount, no way, hire a mixer every time !

    How many holes have you dug ?
    KIAB likes this.
  7. KIAB

    KIAB Super Member

    Shouldn't need the 100mm of gravel at bottom.
  8. Wayners

    Wayners Screwfix Select

    By bags of concrete then. Just add water.. With your plan I think it will set too quickly and not be neat job.jmo
  9. hollyb96

    hollyb96 Member

    DIYDave.: im building this deck for my mum and its already costing way more than we thought it would so i would rather mix by hand than rent a mixer. Is it a lot cheaper to go the traditional concrete route rather than buying postcrete? If its not that much cheaper then i think postcrete might be the easier option.

    KIAB: i read online that gravel is a good idea, why do you think its not?

    Wayners: why do you think it will not be a neat job? There are different kinds of concrete from blue circle (the brand postcrete is from) that takes longer to set. Would i be better with that? The only reason i thought about postcrete as opposed to another kind is its what my posts are going on top of.

    Really appreciate all your advice. Thanks!
  10. DIYDave.

    DIYDave. Screwfix Select

    Postcrete is without doubt the easier option but ....... as you need to reign in the costs, Postcrete is gonna cost you at least twice the price of using ballast and cement and water (that’s free) !

    Agreed, Postcrete you simply cut open bag and tip contents into hole, tamp down - job done, no mixing, no adding anything, sets in 20-30 mins, it is a ‘wonder product’ for sure !

    But, at roughly twice the price of ballast/cement, the speed of setting isn’t really a benefit here as your not setting in posts, so why use it ?

    Even taking into account cement mixer hire for one w end, your still going to save money mixing your own

    You’ve dug all the holes you say (how many ?) so w end hire is all you need. Call some local hire shops (chains and independents) and get some idea of hire costs and delivery if needed

    Your holes are mega deep for this job - I’m only diy me, happy to admit that but 850mm depth ....... ?

    A standard 6’ fence uses 8’ posts set in a 2’ hole (600mm) ... so your gonna use a lot more ‘muck’

    Look online for a building material calculator to help estimate quantities - take a look at ‘The Paving Expert’. Fantastic site for all groundwork information and much more and useful materials calculators

    I suggest you take some time out and cost out materials, suppliers and options to help reign in budget

    Savings can be made but time researching needs to be invested first - good luck
  11. Wayners

    Wayners Screwfix Select

    @hollyb96 not a good job as it sets quickly. If you mix up it will be setting before you pour. Tools and bucket will be covered in set concrete. Guess you will add water and power straight to hole and try get the level right before it sets. Best bet it to try one I guess. Let us know how it goes
  12. wiggy

    wiggy Screwfix Select

    How high is this deck from the ground?
  13. hollyb96

    hollyb96 Member

    i think im going to try one post with postcrete today and see how it goes and if i can level it ok. if not i will switch to traditional cement and ballast. I have 12 holes to fill so might end up being quite expensive but if its the easiest option id rather pay an extra 40 quid to do it the easiest way.
    wiggy: the deck is going on land thats at 2 different heights. on the lower land the posts will be about 80cm and the upper land only about 20cm.
  14. wiggy

    wiggy Screwfix Select

    Sounds like quite a job.
    As kiab said above your holes are too deep, half as deep will be more than enough.
  15. hollyb96

    hollyb96 Member

    the reason it goes so deep is so its below the frost line not for structural stability. i would rather dig a little deeper now than have to replace all the concrete at some point
  16. Dam0n

    Dam0n Screwfix Select

    I would say listen to the advice above.

    Get some ballast and cement, mix and pour.

    6 ballast to one bag of cement. You'll save a a fortune.

    Postcrete isn't really meant to be used that way. You set the posts with the dry mix around it and then add water.

    I also wouldn't be worrying about frost lines for decking.
  17. Kas228

    Kas228 Screwfix Select

    As I mentioned in an earlier post (no pun) 85 cm deep is overkill for decking. Not quite sure why the op is worrying too much about the frost line as presumably there will be concrete to top of dug hole anyway (think he said he will bolt metal post holders into the concrete.
  18. hollyb96

    hollyb96 Member

    i dont really understand how the traditional cement way is cheaper if 6 bags of ballast are about £2 and then cement is £7 on top of that? Will i get way more concrete from it? I think i will need 2 bags of postcrete per hole so if i use the traditional method will i be able to fill up a lot more holes with that?
    I did research and loads of people said to dig down to at least 75cm for frost line so that what i decided to do
  19. hollyb96

    hollyb96 Member

    if i was to go the more traditional route of mixing myself would i need to buy this kind of concrete:
    Also has anyone bought ballast from b&q before because the reviews arent great and it also doesnt say the size of the bags. i dont know if 1 bag would do 1 part of the mix or if 1 bag would do more. If its 1 bag will do 1 part then it would only cost about £25 more to use postcrete and save the hassle of mixing. Although if postcrete isnt great to use if theres no actual post in the hole them i would buy traditional cement.
  20. DIYDave.

    DIYDave. Screwfix Select

    For the size holes you've dug and without posts I recon 2 bags (at least) of either Postcrete or 2 bags ballast/cement mix per hole, 12 holes

    Price for PC varies, as ever shop around but this looks a fair price

    So that's 24 x 20kg bags of PC @ 4.75 = £114.00

    Or ballast

    Poor reviews ? Dunno, not read any reviews and wouldn't bother ........ its ballast, I'm not that fussy, it does the job
    Your right, no weight on bag, assume between 20-25kg, varies depending on how wet the stuff is. Again, as I said in previous post, your mix doesn't need to be super critical, your not baking a cake or building a tower block !

    So that's 24 bags of ballast at 2.20 = £52.80

    Cement, again, for holes in the ground, bog standard cement, cheapest you can find

    So that's 4 bags cement @ 4.02 - £16.08

    Postcrete Total £114.00

    Ballast/Cement £68.88

    All estimated quantities above, please don't quote me on them, as I said earlier, look for an online materials calculator but, I'm always amazed at how much muck a hole in the ground takes to fill

    Also the cost of cement mixer hire, as all holes dug, you only need a 1 day hire or weekend, depends on your time available. No way on earth would I consider mixing 20+ bags of aggregate by hand

    You could consider partly filling holes with hardcore (often given away free on selling sites/local adds) This would reduce amount of concrete needed but you don't seem keen on this idea

    As ever, many different ways to complete any given task .... just depends ,,,,,, etc :)

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