How to use Postcrete

79 Comments

  1. Kevin Nolan

    Can I use postcrete to install sleepers as fence posts with the dimensions 2400 x 200 x 100
    buried 600 into the ground with a 300 diameter round hole? If so how many bags do you suggest?

    Reply
    • Olga Waterhouse

      For your particular use we would suggest 4 bags per post, this will ensure the hole is completely filled with Postcrete, and should
      reduce the chances of the posts ‘slipping’ over time under the weight of the sleepers and any soil they may be retaining.

      Reply
  2. j wilson

    I am installing a 240cm ×10cm fencepost.
    how much postcrete do i use?

    Reply
    • Olga Waterhouse

      With a 240cm x 10cm post typically 60cm will be below the ground, the width of the hole would be 30cm.
      2 bags of Postcrete will fill the hole approximately half full, once the post is level you can backfill the hole and compact it.

      Reply
  3. Keith

    I am installing a 5cm square post how deep and how big an opening

    Reply
    • Olga Waterhouse

      Typically for a 5cm (2.5 inch) post the minimum hole width would be 15cm (6 inches), so you would need a narrow trenching spade or a post hole / split shovel. The depth is dependent on the height of the fence (post) required above ground, as a guide a minimum of 1/3 of the above ground height should be below ground e.g. if the post has to be 180cm (6ft) above the ground 60cm (2ft) should be below the ground.

      Reply
  4. C Jordan

    How long do you have to wait before you can hammer nails in postcrete?

    Reply
    • C Jordan

      I mean how long before you can hammer nails into posts set in postcrete?

      Reply
      • Olga Waterhouse

        Good question, we suggest a panel can be hung in as little as 10 minutes using Postcrete (weather permitting of course).
        There is a good technique for nailing in to a vertical post, if you start the nail as normal with a couple of light taps and then hold a second hammer or in fact anything heavy (a brick works well for example) in constant contact with the opposite face of the post to where you are nailing, this simple action will reduce the vibrations or wobble in long posts and make your job of nailing the panel or panel clips far easier with less force needing to be exerted through the post with the hammer… Alternatively you can screw the clips or panels to the post, this way you can take them down if you ever need to without damaging them.

        Reply
  5. Alan CARDWELL

    I’m using 3-inch posts with 6ft above ground and 2ft below. How wide should the hole be, please?

    Reply
    • Olga Waterhouse

      Thank you for the question, typically the width of the hole should be three times the width of the post; so in your example the hole would need to be 9″x9″ (22.5cm x 22.5cm). This may be a little narrow to dig with a standard spade so if you have to do lots of posts it could be worth investing in a ‘split shovel’ or narrow trenching spade.

      Reply
  6. Russ

    Can I drill a fixing into post crete to secure deck post foot plate as I have used post crete to create strong flat base on uneven soft ground.
    Thanks

    Reply
    • Blue Circle Products

      Thank you for your question.

      Although we are aware of Postcrete being successfully drilled for fixings, Postcrete has been designed and formulated specifically for the erection of fencing and smaller gate posts to be embedded within the material; as such, we would not consider it to be the best option for your particular application.

      Assuming speed is one of your primary concerns, best practice would be to use our Extra Rapid Cement (https://tarmac-bluecircle.co.uk/product/extra-rapid-cement/) mixed with an all in ballast. The lager aggregate of the ballast (typically upto 20mm) reduces the chance of cracks forming while drilling the holes and/or tightening the fixing(s). Concrete made using Extra Rapid Cement will provide an excellent long term durable solution in your particular application while still gaining strength considerably faster than a concrete produced with a conventional cement.

      I hope this information helps.

      Kind regards

      Reply
  7. Dave

    Hello, I am building a kids climbing fort and using 10cm x 10cm x 360cm posts. The hole to bury them in is 30cm x 30cm x 120cm.
    How many bags to you suggest per post this seeing as these are the supporting legs of the climbing frame.
    I take it if takes 4 bags you fill the hole with 4xWater then all 4 bags at once, you don’t wait for one bag to set before layering in the next bag on top?
    Also do you recommend filling the holes to the top for extra support or is back filling the top 1/3 of the hole with soil okay?
    Thank you

    Reply
    • Blue Circle Products

      As best practice we would not suggest using Postcrete for a child’s climbing frame as there is no guaranteed compressive strength – it is ideal for supporting fence posts and smaller gateposts.

      We would suggest using your High Strength Concrete instead which is guaranteed 40N, again ready to use just add water but is not fast setting and normally takes 2-3 hours to set. Based on measurements given you would need just over 11 bags per hole.

      Kind regards

      Reply
      • David Steen

        Can you help me with amounts I will need please?? I am building a kids swing and slide set in the garden with pegs securing the bottom of the wooden frames to the floor. There with be 6 mounts to the floor. The holes for the pegs it asks for 15cm diameter circular hole 30 cm deep. They are small ancher pegs for the wood to screw to. How much High Strength Concrete (40N) would I need?

        Reply
        • Blue Circle Products

          Hi David,

          Thank you for your enquiry, If you choose the ‘Blue Circle High Strength Concrete (40N)’ on our website you are taken to https://tarmac-bluecircle.co.uk/product/high-strength-concrete-40n/ where there is a handy volume calculator for the product. Based on your measurements you will require just under half a bag per hole (so three in total for your six “mounting points”).

          Reply
  8. Alex Knight

    Would postcrete be ideal for setting 150mm x 150mm green oak posts into the ground for a gazebo?

    Reply
  9. Howard

    I’m building a slightly raised deck over an old rockery to put a greenhouse on. How deep a hole should I dig for the posts?
    Thanks

    Reply
    • Blue Circle Products

      Hi Howard,

      We would not suggest using Postcrete for this project as there is no guaranteed compressive strength. It is ideal for fence posts and smaller applications such as small gateposts and rotary lines however not to support sheds or similar structures. In this instance we would suggest our Multi Purpose Concrete or High Strength Concrete. Both are ready to use however not quick setting like Postcrete (normally 2 -3 hours)

      The size of the hole is dependent on the posts but would suggest narrow and deep with approx 25% of the post below ground.

      Reply
  10. Marc

    I have 16 4ft posts and want to bury them 1ft, how much postcrete will i need?

    Reply
  11. terry bryan

    hi – i am assuming i can use this for traditional purposes? I have some left and need to fill in a narrow ‘hole- in an internal floor before covering with carpet. This OK to do?

    Reply
  12. Kevin

    Hi,

    I have a section of Estate Fencing to erect. The posts are 50mm x 12mm flat iron and will be sunk 600mm into the ground with 1200mm above ground. What size diameter hole would I need to suit this type of post?

    Reply
    • Blue Circle Products

      Thank you for your enquiry,

      I would be inclined to dig a 150mm x 150mm purely because anything smaller than this is not practical to dig down to 600mm as the chances are the sides will keep collapsing in. If you have to do several holes to dig I would invest in a split shovel or a narrow trenching spade as this will make digging a narrow deep hole much much easier. If your hole ends up 150mm x 150mm x 600mm you will need one bag per post if you end up with a 200mm x 200mm x 600mm you will require 2 bags per post hole.

      I hope you find this information useful.

      Reply
  13. David

    I’m laying wooden sleepers in my garden what is the best way to do this.

    Reply
  14. Jordan Brocklehurst

    Good morning,

    I have a frame built from 3x 150mm diameter posts (2 uprights, 1 crossbar) – for a hammock – the hole is quite substantial: 450mm x 450mm x 900mm deep…

    I’ve read that you shouldn’t mix postcrete, or let concrete ‘fall’ through water (so that the elements aren’t separated)… if this hole is filled with a 3rd water, the first few bags will fall through the water – would I be better off pouring a little water in, then a bag, then a bit of water, then a bag etc etc so nothing is saturated / separated / mixed?

    thank you

    Reply
  15. Richard Herring

    Using 2m 100x100mm oak posts on galvanised post anchors for a close board fence, how much postcrete will I need?

    Reply
    • Blue Circle Products

      Hi Richard,

      Depending on the design of your chosen ‘post anchors’ Postcrete may not be the best choice of product. If the anchors are to be embedded within the concrete (e.g. a spike with a socket on top to accept the post) Postcrete should be fine. This being the case the hole will need to be 200mm square and 650mm deep as a minimum; this volume would require just over two bags per post.

      If the anchors are a ‘bolt down’ type we would not suggest using Postcrete. Although Postcrete has been used successfully in many such applications, a conventional concrete mixed at a 1:4 ratio (Cement : Ballast) using a fixed volume container such as a bucket to gauge your mix; or alternatively, if you would like a ‘ready to use’ product our ‘High Strength Concrete (40N)’ would be an ideal choice, either of these two options of conventional concretes would be considered the best practice.

      Below are links to our High Strength Concrete (40N) and our ‘Builder’s Guide’

      High Strength Concrete (40N) – https://tarmac-bluecircle.co.uk/product/high-strength-concrete-trade/

      Buidler’s Guide – https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  16. Dan Ross

    Can this be used for putting in goal posts?

    Thanks

    Reply
    • Blue Circle Products

      Hi Dan

      Thanks for your question.

      This is not a normal use for Postcrete (primarily for domestic fence posts) however it has been used for this purpose in the past we believe without any any problems. Obviously bear in mind if the goals need to be moved in the future the implications of concreting the posts into the ground.

      Reply
  17. David Woof

    I am using steel ‘I’ beams, size 123 x 76, as posts, to build a low retaining wall with sleepers. The wall will be 600 above ground level and 900 into ground (because of slope). What size hole would you recommend and how Many bags of Postcrete will I need per hole?

    Reply
    • Blue Circle Products

      Thank you for your enquiry,

      Although we are aware of Postcrete being used successfully to support posts retaining soil, Postcrete was designed purely for fencing so we would not consider its use for anything else to be best practice. This would make it a matter for your own engineering judgment. If you do decide to use Postcrete your holes will need to be 250mm x 250mm x 900mm (250mm is a typical spade width) holes with these dimensions will require just under 5 bags of Postcrete per hole to fill them to the top.

      As best practice we would suggest a more conventional concrete such as our High Strength or Multipurpose Concrete, if you choose this option you will require approximately 6 bags per hole. Alternatively you could batch your own concrete and use our Extra Rapid Cement (or if speed of set is not a primary concern any of our bagged cements) at a ratio of 1 : 4 (cement : ballast) by volume; if you choose this option you will require approximately 20kg of cement and 110kg of all in ballast per hole.

      If you require further guidance please contact the Technical Helpdesk (info-cement@tarmac.com) and we will endeavour to help you further.

      Reply
  18. Ryan

    Hi.

    I’m going to be using your postcrete for concrete fencing. Will be using 2 bags a hole. How much water will I need if using 2 bags at once please?

    Reply
    • Blue Circle Products

      Hi Ryan

      Thanks for your question.

      Please refer to the calculator available on the website https://tarmac-bluecircle.co.uk/product/postcrete-trade/.

      As a guideline the water should fill approximately one third of the post hole (3.3 litres of water per bag).

      Reply
  19. Jason

    Hi I am installing fence posts of 100 x 100mmx 2.1m how much postcrete will I need to install the post
    Thank you for your help

    Reply
    • Blue Circle Products

      Hi Jason

      Thanks for your question. Please refer to our product calculator on the Postcrete page for exact measurements!

      Reply
  20. John

    Can postcrete be used to lay a block 8.3m x 0.2m x0.2m? If so? How many bags?

    Reply
    • Blue Circle Products

      Hi John,

      Thanks for your question.
      Postcrete should not be used for this application. It is designed primarily for fenceposts.

      Many thanks and best regards
      Nick

      Reply
  21. Michael

    I will be putting 8 concrete fence posts, which will also be used for a retaining wall with 4ft fence panels on top. I am putting 3-4ft of post into the ground how much postcrete will I need?

    Reply
    • Blue Circle Products

      Hello Michael,

      Thanks for your question. Assuming your holes are 30cm x 30cm x 100cm (1′ x 1′ x 3’6″) you will require approximately 5 bags per hole, this will leave a few inches at the top of each hole that can be cak filled with soil; if you wish to fill the hole all the way with concrete you will require approximately 6.5 bags per post. You could reduce the Postcrete required by making the holes narrower (25cm x 25cm x 100cm) this would mean you could use 3 bags per hole with a little soil back filled on top or approximately 4.5 bags per hole if you wished to completely fill the hole to the top.

      Reply
      • Michael

        Thank you appreciate the help

        Reply
  22. James

    When using multiple bags of postcrete per hole how much water would you use? And would you pour one bag in, then more water and then the next bag?

    Reply
    • Blue Circle Products

      Hi James, long one, so brace yourself!

      Ideally you fill the hole 1/3 to 1/2 with water (depending on soil conditions) and pour in the Postcrete until dry powder is visible on the surface, this will give you the optimum result of producing one homogeneous mass of concrete. As a rough guide however; you can use around 3.3 litres of water per bag, please note this measurement does assume that none is lot to the surrounding environment, if you find you have Postcrete left to pour and already have dry powder on the surface, stop at that point, level the post and hold it in position until is if free standing (usually around one minute) and then repeat the previous process (fill remaining hole 1/3 to 1/2 with water add Postcrete until powder is visible). Although multiple layers of Postcrete is not considered the ‘best practice application’ in the real world for domestic fencing we have seen no issues in our many years of experience. Another good tip is to get prepped! Have all of the bags you want to put in the hole open and within easy reach (I lay mine by the hole with the open end pointing to the holes) before you start and ensure you have your spirit level to hand before you start, if you need to scramble to get bags two three or four open or to find your level the first bags will have begun setting and you may end up with a wonky post or a large arduous job in digging them back out, it sounds silly but you would be amazed the amount of people who don’t realise just how fast Postcrete initially sets.

      Thanks and kind regards

      Reply
  23. Bill March

    Will there be any problem using this for metal plant screens – diameter of supports approx 2.5 cms

    Reply
    • Blue Circle Products

      Hi Bill

      Although Postcrete was designed for supporting fencing we can see no reason that it should not work effectively to hold a plant screen in place permanently.

      Kind regards

      Reply
  24. Stuart

    How many 20kg bags of postcrete would i need for one 8″ x 8″ (200mm x 200mm) gate post approx 116cm in the ground this is to hang a 6ft by 6ft gate?

    Reply
    • Blue Circle Products

      Thank you for your question. As per the calculator tool on the website you will require 8 bags of Postcrete, this is based on the hole being 40cm x 40cm x 60cm.

      Reply
  25. Dave

    I am wanting to cement in steel feet to hold pergola posts. The pergola posts are 100mm square (2.3m high. How deep/wide should the holes be and how many bags of postcrete will I need for each?
    Thanks

    Reply
  26. Trevor Wilson

    Hi

    Can pea gravel be added to Postcrete in order to bulk it out and form a stronger concrete base for fencing posts?

    Reply
    • Blue Circle Products

      Thank you for your question.

      No, if you add pea gravel to Postcrete it will actually make it weaker, cause voids and probably all sink to the bottom. The specially graded 0-5mm aggregate in Postcrete was chosen as it will self mix when it falls through the water with the cement, adjusting our formulae has always provided less than satisfactory results.

      Please see our Builders Guide here for any more information; https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  27. Patrick Kearney

    Hi, I am building a table with sleepers. The four legs will be 1200 x 200 x 100. On top will be three sleepers 2400 x 200 x 100. Is Postcrete suitable? If yes how much will I need if no what is the best product?

    Also would I need to protect sleepers form concrete? Thanks.

    Reply
    • Blue Circle Products

      Thank you for your question. Personally I would be inclined to use a more conventional concrete (1:4 Cement : ‘All in Ballast’ if gauging it yourself) ; if you do not want to gauge out the cement and ballast with a builders bucket you could use our Multipurpose or High Strength concrete. You don’t need to protect the wood from the concrete, but it should be treated with something to prevent rot and fungi.

      Please see our Builders Guide here for any more information; https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  28. Jamie

    How many bags do I need please per post? my posts are 10cmx10cm and Iv dug 40cm down and the hole is 30cm x30cm wide. Thanks

    Reply
  29. Christian

    Hello,

    I am building a fence in an area that can have strong cross winds.

    The fence will will be around 2.2m above ground. I was planning to use 3m (10×10) posts to support this and bury each post 1m in the ground (so that a third of the post is buried). Does this sound ok to you?

    The hole will therefore be 30x30x100. How many bags would I need please?

    And do I fill the hole with 1/2 or 1/3 of water before pouring all the bags in at once?

    Thanks for your help.

    Reply
    • Blue Circle Products

      Thank you for your question.

      As a guide posts should be buried between a quarter to a third below the ground depending on the soil conditions; so your suggestion seems fine based on the limited information provided. the amount of water is also dependant on the soil conditions, in an ideal world you will finish with dry powder on the surface. If you can try to get your holes to be 25 x 25 as this will save you a considerable amount of money in product and still be more than sufficient to support your post fully. If you can achieve this new dimension you will need approximately 4.5 bags of Postcrete per hole.

      Please see our Builders Guide here for any more information; https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  30. Nick

    Can I use postcrete for a 6’galvanised steel gate post which is hollow?

    Reply
  31. James

    Hi I have a post 9ft high, I plan on going 3ft into the ground size of the hole 900 deep X 600 wide
    How many bags of postcrete do I need?

    Reply
    • Blue Circle Products

      Thank you for your question.

      That is a very large hole to fill with Postcrete! If you wanted to do it you will be looking at approximately 27 bags of Postcrete. If you were to use a conventional mix at 1 : 5 (cement : ‘All in Ballast’ by volume) you would require approximately 4 bags of cement (25kg) and 610kg of ‘All in Ballast’

      Good luck with your project!

      Please see our Builders Guide here for any more information; https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  32. Uppal

    I am looking to build a 2.4m x 2.4 pergola over soil ground. I will be using 4 x posts at 2.4m height at 150mm x 150mm dimensions. Posts will be bolted to adjustable post anchors (APB100/150 Simpsons), and such anchors bolted to concrete base. I was going to dig a hole of approx 600mm deep and 450mm square width and fill with postcrete. However, sounds like I may need to use your High/Super Strength Mix (40Nm)… is that correct? Should I be adding anything else to this… maybe rebars into the mix also?

    Reply
    • Blue Circle Products

      Thank you for your enquiry, although those are some pretty substantial volumes of concrete you are producing for each leg there is probably on need to add rebar to your concrete for the pergola footings but as you are planning to drill and fix in to it a more conventional concrete than Postcrete would be beneficial.

      If you are after a product that only needs the addition of water and mixing then either our High Strength Concrete (40N) or our Multipurpose Concrete would be ideal, based on the measurements you have provided you would require approximately 12 bags per hole; although this is a sound option it will certainly not be the most cost effective for you.

      If you are happy with doing some gauging and mixing you could use either our Extra Rapid cement (if you want it all to set nice and quick) or our Mastercrete cement we would suggest a 1 : 4 (cement : ‘All in Ballast’) by volume, this should mean for each hole you will need approximately 1.5 (25kg) bags of cement and 5 (25kg) bags of ‘All in Ballast’ per hole.

      Either of these options would be equally as acceptable for a free standing garden structure.

      Hope the pergola construction all goes to plan!

      Please see our Builders Guide here for any more information; https://tarmac-bluecircle.co.uk/wp-content/uploads/2018/01/Builders-Guide-170118a.pdf

      Reply
  33. Phil S

    Hi there. I am looking to anchor a swing set using postcrete. The instructions suggest embedding the anchors in 30cmx30cmx30cm hole. How much postcrete would I need per hole please?

    Reply
    • Blue Circle Products

      Hi,

      We would not suggest Postcrete for this application, although we are not aware of any occasions where Postcrete has been used for a swing and failed the product is designed specifically for domestic fencing and small gates. A more conventional concrete would be (in our opinion) better suited for the task.

      If speed is your primary concern may I suggest Extra Rapid cement (yellow and green bag) mixed with ballast at a ratio of 1:4 although not quite as fast as Postcrete the initial set of this product is around 30 minutes.

      Please visit https://tarmac-bluecircle.co.uk/product/extra-rapid-cement-trade/ for further details and a useful volume calculator.

      Reply
  34. Alexandru Raznoveanu

    I’m planning to build 6 by 6 gazebo with 6by6 posts that will be mounted on some concrete in metal supports.
    What will be the better ready mixture concrete to fix the metal supports? Thank you!

    Reply
    • Blue Circle Products

      Hi,

      Thank you for your enquiry, a 1 : 5 (Cement : Sand) mix by volume should be sufficient for your post metal post supports, this mix will want to be fairly stiff so foe every bucket of cement in your mix use approximately half a bucket of water.

      Reply
  35. Ian

    I am looking to install a 4 metre long screen of 1800mm x 100mm poles with 60mm between each post. They will not be supporting anything so I wouldn’t expect that that they need to be buried too deeply and I am therefore planning to have 1500mm above ground and 300mm below. I plan on digging a trench and then knocking each post enough into the ground to support itself and then filling the trench with concrete. Would postcrete do the job and how much would I require. Thanks

    Reply
    • Blue Circle Products

      Hi Ian,

      We would not suggest using Postcrete in a trench as the product relies on self mixing which may not occur effectively when poured in you a trench rather than a vertical hole. If however your engineering judgement leads you to use Postcrete you will require approximately 30 bags, although I must stress this is not the option we would recommend.

      A better option would be to mix a conventional concrete but use our Extra Rapid Cement and mix it with an all in ballast at a ratio of 1:4 (by volume e.g. 1 bucket of cement to 4 buckets of ballast).

      If you choose this option you will require 6 x 25kg bags of Extra Rapid and 750kg of all ballast.

      Below are links to our Postcrete and Extra Rapid datasheets and additionally a link to our ‘Builder’s Guide’

      Postcrete
      Extra Rapid
      Builder’s Guide

      Good luck with your project.

      Reply
  36. Ian

    Thanks for that but are you sure they are the right quantities for 0.25 cubic metres of concrete? i.e. 125kg of cement and 750kg of ballast
    many thanks

    Reply
    • Blue Circle Products

      Thank you for your follow up question…. a trench of 30cm x 30cm x 400cm has a volume of 0.36 cubic meters, with any soil dug trench it is common practice in construction round up. This allows for inaccuracy in digging, tree roots, stones etc. The figures I provided were for 0.4 cubic meters; having some left over material is a lot less of an issue than not having enough to complete the job. 0.25 cubic meters of concrete requires 4 bags of cement and 475k of all in ballast.

      Kind regards,

      Aisling

      Reply
  37. Ross Mitchell

    I am planning on using post crete for a 150mm square 3.0m long gate post to a depth of 700mm. The data sheet does not show 6 inch posts and the calculator asks for post width stating 6 bags would be sufficient. Can you confirm this is correct?

    Reply
    • Blue Circle Products

      Thank you for your enquiry. The calculation of 6 bags is correct based on a third of the post being below ground i.e 100 cm.

      Kind regards,

      Aisling

      Reply
  38. Peter Neale

    Hi,
    I need to repair a fence post, so I am planning to use a 75mm x 75mm x 1000mm spur post, set in postcrete. I may need to repair another post soon, but I don’t know which one or when. If I buy spare spur posts and bags of postcrete to hold ready, how long can I keep the postcrete in a dry garage or shed before it deteriorates?

    Reply
    • Philip Dodding

      Hi There,

      The shelf life of Postcrete is 8 months from the production date, so as long as you’re using it before that end date it will be fine.

      Kind regards,
      Phil

      Reply
  39. Mr Theo Tramblinas

    I am not looking at filling the entire hole with post-Crete, as the holes are 30 inches deep. I have purposefully made the holes nice and tight with room around the edge to be backfilled. I’m thinking of using half a bag per hole. Are there any problems think I might run into?

    Reply
    • Philip Dodding

      Hi There,

      It sounds like with a hole that deep you may need a bag per hole, however we recommend that you use our product calculator as a guide, it’s found here on the Postcrete page: https://tarmac-bluecircle.co.uk/product/postcrete-trade/

      Kind regards,

      Phil

      Reply

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