How to build an outdoor sunken seating area?

[chloel]

Hi, we are building a sunken seating area in our backyard. We have masonry bricks to do the seat and walls. We want to fill the holes rather than mortar them together. What concrete mix should we use?

thanks! 

[EricL]

Hello @chloel 

I suggest having a look at Australian Builders 20kg High Strength Concrete Mix or similar. This is an easy product to use, simply add the right amount of water mix well and use it to fill the masonry blocks.

My best advice is to make sure to give your wet concrete enough time to dry properly. Painting it or covering it too early will result in cracks forming in the concrete mix.

If you need further assistance, please let us know.  

Eric

[Jason]

Exciting project @chloel! 

I trust Eric's advice was helpful. 

Please keep us updated as the build progresses. I'm sure the community will be really keen to follow along and especially to see the end result.

Jason

[chloel]

Thanks @EricL and @Jason 

Just wondering what you think about using Selleys Liquid Nails for the blocks and then filling the holes with left over sand?

thanks

chloe

[EricL]

Hi @chloel 

Using Selleys Liquid Nails will work but it will not provide the same type of support as concrete. The Liquid Nails will join the edges of the block meaning all the weight bearing support will be on the edges only whereas the concrete will support the interior body of the block joining them together. 

Let me call on our experienced members @Dave-1 and @DIYGnome for their recommendations.

If you need further assistance, please let us know.

Eric

[DIYGnome]

Hello @chloel interesting project, I'm curious what the blocks are resting on gravel, soil, sand or concrete?

I agree with @EricL 100% regarding the use of concrete for structural integrity, the surrounding earth may be fine but it is in essence a mini retaining wall and would need to resist any future potential soil expansion/movement, how is the drainage on your property?

A fellow member built a similar fire pit & seating area project you might find useful/helpful 👍

https://www.workshop.bunnings.com.au/t5/Outdoor/D-I-Y-sunken-fire-pit-with-seating/td-p/159669

[chloel]

@DIYGnome @EricL 

thanks! 

we concreted a little trench so the blocks have a solid base

[Dave-1]

Afternoon @chloel

Your yard seems to be mostly clay and like @DIYGnome I was wondering where the water will go? I have a gabion wall next to a clay area that I dug out and havnt had it shift since so not really concerned about it moving. You could always put a pit (even a solid bucket with holes in the base plus a little gravel and have a sump pump put in if its a concern tho.

Id prefer maybe some of the holes filled with the concrete that @EricL  mentions and then the alternate holes filled with that left over sand, that way it will lock the bessa blocks into place and they wont want to move as easily.

Lastly with the narrow wall closest to the photographer, id definitely be putting concrete in all of them and maybe some reo bars as well. Do you have a concrete footing under that side as well? If you are concerned about using concrete and having to pull it out one day maybe make that thin wall one of the bessa blocks thick and fill the same way with the concrete every second hole? I know I look for alternate ways of securing things instead of concrete but sometimes its wiser to use it.

Dave

[Jason]

How is your project going @chloel?

I'm sure community members will be keen to see an update. 

Jason

[chloel]

Going well so far. Taking its time. Hopefully the decking is done today!

Any advice on mortaring??