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How to get a post plumb using a bolt down anchor?

I want to place some posts on existing concrete using Pryda bolt-down post anchors. https://www.bunnings.com.au/pryda-post-anchor-bolt-down-w-washer-100mm-m10_p1070068 The concrete is slightly sloped but the post needs to be plumb. What is the best way to get it plumb? I have done a similar job in the past just using window spacers under the plate, but that was just for a freestanding screen, nothing weight bearing. I want to do it a bit more professionally this time. Thanks.

Is there a better way to get it plumb?

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MitchellMc

Welcome to the Bunnings Workshop community @mh. It's great to have you join us and many thanks for your question.

I've made contact with Pryda in regards to your question. Since this is a weight-bearing application in order for the post support to function correctly shimming is not an option. You'll need to lay a level bed of structural grout for the post anchor to sit on.

Please let me know if you need further information or had questions.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/10586#Comment_10586

Thanks very much @MitchellMc. Sounds like a good solution that would also look good.

Would you lay the grout first before attaching the bolt down anchor, or put the anchor in first with gaps underneath and pour the grout to fill the gap?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/67649#Comment_67649

@mh,

Forming up a pad, poring and waiting for the grout to fully cure would the correct method. My concern with pouring the grout underneath the anchor is that you won't be able to tell if there are any air gaps and if the post is fully supported.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/96664#Comment_96664

Thanks @MitchellMc .

Sorry for the string of questions... is it OK to drill a hole for the dynabolt right through the grout pad and into the concrete in one go? Without weakening the grout? Or does the dynabolt need to be already in position before the grout goes down?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/114960#Comment_114960

@mh,

Strings of questions are perfectly fine. We're here to help.

You can drill through the grout pad once it has fully cured. If the pad is 10mm or less you might have some cracking issues. I don't see any reason why you couldn't pre-drill the concrete and have the Dynoabolt in position prior to pouring the grout. You might want to run a piece of masking tape around the Dynabolt before inserting to stop the grout getting into the threads of the bolt.

Mitchell

SMOKOTIME

https://www.workshop.bunnings.com.au/discussion/comment/125294#Comment_125294

Hi Mitchell,

Just saw this and had to comment. The whole idea of structural grout is that it expands in it's plastic state as curing to apply tension and fill voids.

Laying a bed of grout and letting it cure to set a post onto is counterproductive for the product.

The feet should be set onto a spacer and the grout packed underneath. It achieves it's preload as it cures.

I use a single 1/2in gal nut in the center of the foot. That gives sufficient gap to pack the grout and allows the post to be leveled on the four chemical anchors. Once the post is plumb pack the grout in with a stick and finish the edges with a small trowel. After 7 days when the grout has reached full strength tension all nuts again.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/132330#Comment_132330

Welcome to the Bunnings Workshop community @SMOKOTIME. It's fantastic to have you join us and many thanks for adding to the conversation.

The advice I've given above was directly relayed from a post support manufacturer's technical assistance team. They are specific requirements for the installation of their post supports on a structural grout base. It was advised that they do not recommend the method you've suggested of packing in the grout when the support is being used in weight-bearing applications. However, they were happy for your method being used in non-weight-bearing applications.

Many thanks for contributing.

Mitchell

SMOKOTIME

https://www.workshop.bunnings.com.au/discussion/comment/136519#Comment_136519

Really???

Not what their technical data says.

That is specifically how the product MUST be used for load bearing applications.

"Designed to undergo controlled expansion in the plastic state, it will ensure positive and
load transfer in structural grouting application. Lanko 702 Durabed has been formulated
to achieve high early strengths with low water addition levels."

Compressive Strength
MPa

Dry Pack 40.7 61.2 70.1
Plastic 25.4 48.6 51.7
Flowable 16.4 36.8 39.8 (What you would use to make a pad.)

Application Techniques
1. Lanko 702 Durabed should be placed within 20 minutes of
mixing to gain the benefit of plastic expansion. During
that time keep material in mixer well agitated. After this
time discard any grout mix that shows signs of stiffening.
2. Flowable Lanko 702 Durabed may be placed with lowpressure cement grouting equipment or may be hand rodded
into restrained sections. High points must be adequately
vented to allow entrapped air to escape.
3. Plastic Lanko 702 Durabed mortar may be rodded into place
or trowel handled where freedom of movement permits.
Consistency can range from thick cream to smooth plastic.
4. Do not vibrate Lanko 702 Durabed into position as this may
cause segregation of the mix.
5. Dry pack Lanko 702 Durabed mortar must be firmly pressed
or rammed into place. Consistency should allow pressuring
into a firm hard ball without cracking.
6. For sealing rebar or steel rods and bolts into bore holes,
adhere to the following guidelines.
7. Lanko 702 Durabed may be pumped for large grouting
installations.
8. All applications require curing. Cover the installed grout with
wet hessian sheets or spray periodically with water.
9. Placing Lanko 702 Durabed in unrestrained environments
will result in lower final compressive and flexural strength.

Kinda means that unless it is under pressure while curing the structural strength is significantly reduced.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/139411#Comment_139411

Hi @SMOKOTIME,

Many thanks for the additional information. Davco has advised that Lanko 702 is suitable to be laid as a pad and then to have the post support fixed on top of it as per Pryda's specifications.

Mitchell

SMOKOTIME

https://www.workshop.bunnings.com.au/discussion/comment/141345#Comment_141345

Sorry I'm just a cranky old Engineer who is very tired of support people who have no practical experience. Their support teem need to set a few posts and see how bad their advice is.

There is NEVER any guarantee that the foot on a post is square to the upright and any discrepancies will be magnified over the length of the post.

There is NEVER any guarantee that the pad will be troweled perfectly level or even flat and any discrepancies will be magnified over the length of the post.

He did mention LOAD BEARING and nobody asked what the load is what it is being clad with and what wind exposure it has.

Better to set the post properly and level with a spirit level and then pack to achieve the best compressive strength.

Otherwise you may as well use tile grout or plastic wedges over an expansion joint.

flywind0329

https://www.workshop.bunnings.com.au/discussion/comment/125294#Comment_125294

Sorry , to ask on old post. What is best size of slave for a 90mm post anchor, and which Dynoabolt Is right product for this application. Thanks!

EricL

https://www.workshop.bunnings.com.au/discussion/comment/134884#Comment_134884

Hello @flywind0329,

Welcome to the Bunnings workshop community. It's wonderful to have you join us.

It's perfectly all right to ask these questions even if it is an old discussion.

Can you please tell us, what is the purpose of your 90mm post? Will it be carrying a heavy load or is it for fencing? Any extra information you can share with us about its purpose will help us give you better advice.

If you have any other questions we can help with, please let us know.

Eric

flywind0329

https://www.workshop.bunnings.com.au/discussion/comment/138291#Comment_138291

I think Diy a pergola 3.5m wide x 5m long , long side attached on the house . Maybe 3 x 90mm post with anchor on the concrete slab (driveway ).

EricL

https://www.workshop.bunnings.com.au/discussion/comment/140575#Comment_140575

Hello @flywind0329

It’s great to see the photos of your proposed pergola location! This will help in determining the best approach for your build. Since your pergola is quite large at 3.5m x 5m, it’s a good idea to check with your local council regarding any size limits or permit requirements. Larger structures often need approval, so it’s best to confirm before starting construction. Given the scale of the project, engaging a draftsperson or engineer would be a smart move. They can create a proper plan that meets council regulations and ensures structural integrity. With a professionally designed drawing, you’ll have confidence when submitting it for approval, as it will include all necessary details, such as the correct fixings you’ll need for your build.

If you're installing a post anchor into a concrete slab, the slab itself should be at least 100mm thick to provide adequate support. Reinforcing the concrete with mesh is recommended if the post will bear significant weight or be exposed to strong winds. When securing the post anchor to the slab, selecting the right Dynabolt size depends on the specific requirements of your structure, including the base plate of the anchor and the slab thickness. Make sure to drill the correct size hole, clean out the dust, and tighten the bolts firmly without over-torquing to ensure a secure hold.

Here is a link to a handy step-by--step guide: How To Build A Pergola Frame

If you need further assistance, please let us know.

Eric

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