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How to concrete a small area with fall to the fence?

PatDIY_Dad

I need to concrete just a small area that will be next to existing concrete

the area is about 1m wide x 600mm length x 100mm deep

So I have a general idea on what to do but need someone to say yeh thats right or you forget x y z

So After I have removed about 120mm deep of soil:

Put some crushrock down leaving about 100mm for concrete
Drill some holes into the adjacent existing concrete with those steel bars to stop the new concrete from sagging or lifting ( how many mm apart should I put those in?
Do some formwork ( 100mm high) ( wont be much as its going in between a timber fence and existing concrete
Put string line in the direction of where I want the fall to be for water run off. Then get a leveling and rest it against the string to check the fall ( is that how you do that? )
lay concrete and smooth off level with existing concrete and level with string line
Remove string line and smooth off
After concrete is dry, remove form work and so some saw cuts

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Comments

JacobZ

Hi @PatDIY_Dad,

Thank you for your question about how to create fall across a concrete slab.

You've got the basic process down, but there are some small improvements that will make it easier for you.

The easiest way to allow for fall in the concrete is to set the formwork to the grade you are looking to achieve and to screed the concrete directly off of the forms.

Have a look at this render that I've done as a demonstration of how you would set up the forms. Note that the forms are level parallel to the existing slab, but not level perpendicular to the existing slab.

This way, you can run a Masterfinish 1200mm Screed directly across the slab using each side of the formwork as a guide. Please note that this will require you to drive any stakes used to hold the formwork in place below the height of the formwork.

I'd suggest in your application that no less than 3 reinforcing dowels are used approximately 400mm apart, and they are tied to light duty reo mesh installed in the new slab using Jack 0.70mm x 75m Wirepak Galvanised Tie Wire.

You might like to check out How To Pour A Small Concrete Slab for some additional guidance.

Please let me know if you require any further assistance or explanation, I am more than happy to help.

Jacob

PatDIY_Dad

https://www.workshop.bunnings.com.au/discussion/comment/38205#Comment_38205

Thanks yeh I didnt think of that

Dont need string really

Ill make the for work a slight fall angle instead of level and just work off that

Regarding the steel mesh. There building a house next door and its left over so might just go there and take it : )

Easy

PatDIY_Dad

https://www.workshop.bunnings.com.au/discussion/comment/38205#Comment_38205

I've dug out the area that needs to be concreted and moved the hardwood retaining wall over a bit to the left

( It used to be hard up against the right hand side of the existing concrete)

The reason for this is this area is going to be tiled along with a bigger joining area behind the photo ( under cover pergola) see picture

Couple of questions

See the directions of the arrows that's the direction of the fall of the existing concrete

I was thinking of doing the fall to the left but I'll check with my tiler

Ive hammered down a steel star picket to hold the retaining wall better from moving ( I have to add another one today)

Can I just leave it there and concrete over the top?

Should those dots on the side profile of the existing concrete be enough for reinforced dowels and should i put expansion foam along there ?

Can you think of anything else I should do for prep? Apart from crush rock and steel

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/81421#Comment_81421

Hi @PatDIY_Dad,

It's not exactly how I imagined but it should be quite a simple pour regardless.

I'd say confirming the direction of the fall with your tiler is the way to go. Either of your options will work, but it's best to check.

Any time you can work with your tradies so everyone's job is as smooth as possible, you should. It will produce a better end product and tradies will be happier to work with you.

It should be fine to leave the star picket in place, just make sure none of the reinforcing mesh inside the slab comes into contact with it. It's likely over time the star picket will rust. If it is in direct contact with the steel reinforcement inside the slab, it will transfer the rust and weaken the reinforcement over time.

The dowels should be fine, just make sure to aim directly into the centre of the slab and keep your drill level. There's enough concrete there that it won't blow out, but if you aim too high or too low, it's certainly possible.

Expansion foam is probably not needed due to the small size of the slab, but it can't hurt to add some Sika 10 x 100mm x 6m Abelflex Expansion Joint Filler Foam if you'd like to go the extra mile.

You look well prepared, so there's not much else I can add besides to make sure you have all the tools you'll need close by before you start. You don't want to mix your first bag and then realise you haven't got a trowel.

Let me know if you have any other questions.

Jacob

PatDIY_Dad

https://www.workshop.bunnings.com.au/discussion/comment/105442#Comment_105442

Thanks I am more prepared from the help and advice I am getting here!

I worked out the volume its 0.11 cubic meters ( very little)

I have a few more questions 😂

How many bags of cement and crush rock would I need for that ( I just need to mix cement some crush rock and water ? Any sand? )
- I entered those measurements on a concrete calculator and it said I need 13 bags. Way more than I expected ! I only have a wheel barrow to mix it in
Ill try to match the charcoal colour as best I can, Ill buy the grey colour cement ( which I did some at the back for my gate locking pins) but it still a shade too light so might need to add a little bit of black oxide stuff)
I got a straight edge to screed it. I just need the tools to smooth it and finish it with that rough texture as seen in the photo. I also want to groove it next to the existing grey concrete on the right

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/119860#Comment_119860

Hi @PatDIY_Dad,

Since the plan is to tile over the concrete, it's entirely up to you, but do you need to tint the concrete or texture it?

I'd suggest using a premixed concrete such as this Bastion 20kg Concrete Mix will be much easier. That way you can grab 13 bags and have the exact amount you require without any leftovers.

If you want to make your life a bit easier, it's possible to hire a Cement Mixer but make sure to contact your local store beforehand to check availability.

If you want to go ahead with mixing in oxide such as this Dulux Avista Oxide, you might like to do a test run with a small batch before committing to a mixing ratio. You can grab a Sika 5L Measuring Jug so you can measure out your ratios. I'd suggest you work out the ratio required per bag as you'll be unable to mix all 13 in one batch.

Alongside the straight edge, you should grab a Dunlop 80mm Concrete Edger, Dunlop Stainless Steel Finishing Trowel.

Let me know if you have any other questions.

Jacob

PatDIY_Dad

https://www.workshop.bunnings.com.au/discussion/comment/128633#Comment_128633

Thanks

I'll grab those pre mixed bags they sound convenient. Just add water right?

Would I need to put some expansion foam between the charcoal colored existing concrete? Or can I just concrete directly against it ?

Don't want it to crack from movement because we are planning to get tiles put on top

That trowel you linked looks like it do a nice flat surface. I wanted to finish the top of the slab with the same texture as this

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/134245#Comment_134245

Hi @PatDIY_Dad,

Pre-mixed bags only require water and mixing.

You can't have an expansion joint under tiles as it allows movement, causing the tiles to crack. Any expansion joint needs to be added to the tiles as well. In your case, you are rigidly joining the slabs, so I see no point in adding an expansion joint.

That's a brushed texture. So, you'd use the trowel to smooth the surface and, once it's slightly dry, use a coarse bristle brush to add the texture. However, if you're tiling over the area, it doesn't sound like adding the texture would benefit you.

Please let me know if you have any questions.

Mitchell

PatDIY_Dad

https://www.workshop.bunnings.com.au/discussion/comment/137818#Comment_137818

Thanks

I have this trowel already. This should do the job

Ill double check with my tiler about the expansion joint them

When I did speak to him about other matters he said they put flexible silicone on every 4th or so tile to allow for movement to avoid cracking

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/140239#Comment_140239

If you were to create two separate slabs without mechanically connecting them, you'd need an expansion joint. This expansion joint must be directly below one of those flexible silicone joints in the tiles. Either the two slabs float next to each other with an expansion joint without being physically connected, or you add reobar to the existing slab prior to pouring the new slab to mechanically connect them. You wouldn't mechanically connect them and also have an expansion joint, as that really defeats the purpose.

Mitchell

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