Concrete/Mortar for laying rock garden bed -what type do I buy?

[makka619]

So I want to lay a rock garden bed border. I want to use concrete to do it.

I have never worked with concrete so I need your help on choosing the right one. Do I choose a concrete mix or mortar? I don't know what the differences are. I want to know exactly what to get before I go to the store. Less complicated the better

I found an old 5kg bag of MORTAR (Mitre 10 brand). It says on the bag "A ready to use premix, ideal for brickwork, stonework, cement blocks and paved areas. Contains sand, cement and lime." Can I use this on top of soil?


I don't expect you to read all of this . I am just putting it here to give you an idea of how exactly I plan to use it. You can probably skim over it to get the idea and hopefully it will help you direct me in what concrete or mortar to get.

This is what I need the concrete or mortar for:




Prep<o></o>
<o></o>
<!--[if !supportLists]--><!--[endif]-->1.If you are not working against an existing surface, establish the line by setting a string line.<o></o>
<!--[if !supportLists]--><!--[endif]-->2.Excavate approximately 100mm (10cm) below ground level so that all grass and vegetation are removed. The width of the excavation should be approximately 300mm (30cm) but will vary according to the size of the stone.<o></o>

Laying the stone
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3. Lay out the stone approximately 500mm (50cm) in front of the excavated edge. This will give you a rough idea of how the edging will look. Reposition individual pieces of stone, turning them over or around or swapping them with other pieces until you are satisfied with how they will butt together. If you want the top edge of the stones to be level, adjust the depth of the trench to suit each stone. If the top of the edging is to be irregular, however, the stones can be placed on a flat bed.<o></o>
4. Prepare the ground for concrete by wetting it to prevent the concrete bed drying and hardening too quickly. It is advisable to mix your own concrete so that small sections can be laid at a time. This avoids the problem of a whole load of commercially delivered concrete going hard before all the stone is laid.<o></o>
5. Spread a bed of 50mm (50cm) thick concrete approximately 1m long. Position each stone in turn, using the string line as a guide for an even top edge. Give each stone two or three twists to bed it firmly in place. Make sure each stone is hard up against the edge and also closely butted against the last stone.<o></o>
6. Fill any gaps with small pieces of stone. Cut them to fit with a lump hammer and bolster and tap them in place. Use concrete at the back of each joint to prevent soil washing out through the joints.

TIP: Using mortared joints
To mortar the joints between the stones, space the stones approximately 50mm (5cm) apart.
Mix a fairly stiff mortar mix of four parts sand and one part cement. Coloured oxides can be added to the mortar so the joints blend naturally with the rock.
Wearing protective gloves, roll the mix in your hands to make large sausage shapes of mortar. Place each 'sausage' in a joint and use a small trowel to work the mortar in and round the joint.
Use a small paint brush to finish the surface of the joints and then sponge the face of the stone until it is clean.
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To finish<o></o>

Fill any narrow gaps between the stones and the hard edge with a sand and cement grout, or sand. Allow the concrete to dry before filling in behind the edging with garden soil.<o></o>

[SilentButDeadly]

Personally I wouldn't bother with the concrete/cement/whatever....unless it is reinforced and there's a tonne of it it'll crack up in no time and you end up with a procession of bigger rocks than you started with.....

However, if you feeld the need then plain old mortar will probably be fine. Bear in mind that a 20kg bag won't go a very long way in a footing - no more than a metre a bag assuming a 100mm x 100mm footing. So if you have many metres of rocks.....that's many metres of $6 a bag.

If thee were me I'd place your rocks in a bed of crusher dust (dig a trench and backfill a bit with the crusher dust), lean them slightly into the slope of the rock garden then completley fill the trench with crusher dust, packing it in around the stone....

[makka619]

Cool. Or should I just stick the rocks in without anything? That should work do you think?

[GTWAGN]

I finished a similar project at my place a few months ago. I used recycled Bluestone and pre mix mortar to which I added some black oxide to try roughly match the colour to the bluestone. I also built a 150mm concrete footing which in hindsight completely over engineered the project as I only had one layer of stone. Nonetheless, 4 months post compleion I do not have even a hairline fracture in the mortar!

I suspect that for a single layer of rock you could dig a small trench to house the footing (compact down some sand), lay 150mm-200mm of mortar and away you go!

Also, you must use a string line if you want your edge to be straight!

[falcon]

I agree, if your only doing a rock edge, you wouldn't really need to bed them into concrete. Simply dig your trench and use some sort of fill, such as crusher dust, to level trench and place the rock in and backfill.

If you want to use concrete, Id use a concrete blend mix eg, sand, cement and gravel and place the rock into in whilst still wet. Mortar mix is mainly used to join layers of material together. If you were going more then one rock high, you would use this.

Hope that makes sense.

[makka619]

Makes sense, thanks guys.

I was keen to do it with mortar, but I now that I think about it, isn't necessary.

Will look into those dust fillers.

Cheers.