How to anchor cinder blocks to exisiting slab for a bench seat?

Hi There,

I am using 190x190x390 cinder blocks to build a bench seat that will be topped off with inset 18mm ply and a piece of custom foam. I am only building it 2 blocks high and then capping it off and putting a foam cushion on top. Total cinder block + cap Height is 420mm (not including cushion).

I will be laying the blocks on an existing concrete slab. How do i anchor the blocks to the slab? Is morter alone enough? I was also going to construct a internal frame using 900 x 45 on the inside for added stability and so there is a platform to put the cushion on. This will prevent the blocks from falling inwards but not outwards. Can i bolt the timber frame to the blocks from inside? I have a tendancy to over engineer things because i have 3 small children, is this overkill?

Also, I was considering adding another section that would be 4 blocks height for the BBQ and some bench seating, for this add on the blocks will be much higher, perhaps 800mm high including caps. How should i ensure it is stable?

Please see my design images, they are images of the blocks roughly arranged WITHOUT caps. This is not the final arrangement but it gives you an idea of the basic shape. Its a very wide daybed, bench seating and then staggers up to become an L shaped bench top height for BBQ and outdoor cooking space.

Lastly, I wanted to render is white to have that Spanish look (I have included lots of inspiration shots), can you please assist me with what products i might need to achive that look and can i render on to wood or ply or does that need a primer first?

Screen Shot 2024-04-18 at 11.55.07 am.png

THANK YOU SO MUCH!

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Comments

EricL

Hello @MamaCass

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your cinder block seating project.

I propose drilling into the concrete base and anchoring threaded rods using Sika 300ml Grey Anchorfix 1 Adhesive. You then place the cinder blocks into place and filling the holes with builder's mix. The threaded rods will serve as the anchor to the base.

Building a timber frame inside the cinder block structure is a plus as it adds structural support. Anchoring the cinder blocks to the frame is perfectly fine. For the higher sections make sure that each section of the cinder block is supported with a Reo bar anchored to the concrete base.

Make sure that all the holes of the cinder block are filled with builder's mix. In order to get that Spanish look, I propose rendering the entire surface to a fine finish and painting the surface in an off-white colour.

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

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

Eric

Dave-1

Evening @MamaCass

@EricL took the words/suggestions straight out of my mouth. I was thinking first that mortar would be fine until I realkise dthat some of the structure would be 800mm high. Like you I tend to over engineer stuff, better to be safe then have to worry is usually the way I think.

Attaching the timber to the inside of the blocks - I never know if I trust the blocks to hold together while drilling, however if they are filled with a builders mix of concrete it does sound like it would work. I would use masonary screws to fasten the timber for sure in this instance.

I havnt rendered anything .... yet 🙂 I do have an retaining wall that has a long horizontal crack on it that I will need to repair but thats the closest I have come to answering that question

Looking forward to seeing your project, It sounds like it will be an interesting and well worked out one 🙂

Dave

Nailbag

Hi @MamaCass Sounds like you very well planned out and it looks like it's going to be w terrific entertainment space once completed. I have nothing to add over and above both @EricL & @Dave-1 suggestions 👍

Nailbag

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/36779#Comment_36779

HI DAVE,

Thank you for your reply! Sorry my my delay in responding.

Can I ask, Do i need to use mortar to bond the blocks to eachother (like in bricklaying)? or will the anchor threads and builders mix be enough to keep them put?

Thank you.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/84121#Comment_84121

Afternoon @MamaCass

Definently Mortar should be used. And yes like brick laying. If I am putting a cake together with seperate layers I use cream, jam or an icing mixture to hold them together. To give a base and also to stop them sliding of each other. Bricks or bessa blocks are the same.

Dave

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/107063#Comment_107063

Hi Dave,

It’s taken a long time but I am approaching the render portion of my project. I am using cement board for the counter tops and wanted to render right on the top so the bench top is render finish as well as the sides. (I don’t have the budget for a stone or tile bench top) I have seen the benchtop render done on Pinterest and I have attached images. What product should I use? I want the render to seamlessly

go on the sides edges and bench top.

Also, for that white Spanish look, can I paint the render? I know the cement blocks are porous and will get wet when it rains and so will the render, so Is there a paint product that won’t flake off over time?

thank you.

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/121931#Comment_121931

Good Evening @MamaCass

That is looking good and looking solid! I dont have a lot of experience with rendering but think @Nailbag (He may be a little slow to reply atm as he is busy) and @EricL have knowledge.

I like the idea of the cement sheeting as a cheaper alternative. You may need support on the underside as structually I dont know what load it can carry. The support would be timber either side of the interior of the cavity with a piece of timber between them.

Dave

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/130007#Comment_130007

Thanks Dave.
I was going to put timber supports inside to support the cement board. How best to attach the timber to the blocks without the blocks chipping or breakage?

Thank you.

EricL

https://www.workshop.bunnings.com.au/discussion/comment/135074#Comment_135074

Hello @MamaCass

To make it easy why not just install the timber frame on top of the blocks rather than drilling through them. You can use liquid nails to stick the timber frame onto your blocks. You can then cover the timber frame with cement sheeting and render the whole top to disguise it. I suggest using the Dunlop 20kg Multipurpose Acrylic Render to render the entire structure.

Here is a handy step-by-step guide: How To Render.

If you need further assistance, please let us know.

Eric

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/138429#Comment_138429

Morning @MamaCass

I do like @EricL 's suggestion tho if you really want to drill the bessa blocks I would sugest to drill throgh the middle of them more so then the edges. Have you filled the blocks with concrete yet? I think you may have mentioned that earlier? If the blocks are hollow I would drill through with a 6mm or maybe 8mm masonary drill slowly and then attach your timber via a long bolt. That way its secure with less chance of fracturing the block. Having the timber sit on top would definently make it easier but then you are adding a little more height that you havnt factored in. "Wiggles hands"

Maybe practice drilling on a spare block and then make a call?

Zenith M8 x 100mm Hot Dipped Galvanised Hex Head Bolt And Nut is the bolts I am thinking of, they are cheaper when you purchase a box 🙂

Dave

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/138429#Comment_138429

Thank you.

there are some areas on the bench top and seating where the cement board might be prone to sag, so additional internal timber frame supports will be required.

I wondered how best to attach the timber frame to the blocks. Once the supports are attached I can cover the whole thing in cement board and render.

thank you.

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/140663#Comment_140663

Hi @MamaCass,

In any areas where you need to attach timber to the cinder blocks with an anchor, it is important that the cinder blocks are core-filled with concrete.

You can then use AnkaScrews or DynaBolts to attach your timber to the cinder blocks. Without the concrete core fill, there is the risk that the blocks will crack or blow out when the masonry anchor is set in place.

Let me know if you have any further questions.

Jacob

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/142301#Comment_142301

Really helpful. Thank you.

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/121931#Comment_121931

Hi @MamaCass (loved her music BTW)

If you seal the blocks you should be able to then apply a render coating over them. This is one I have used before, though not an expert in this area I'll tag in @JacobZ who will be better placed and qualified to confirm or suggest a more suitable sealer.

Regards Nailbag

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/130021#Comment_130021

Hi There,

you have been such great help so far. I’m moving on to the pergola section of the project. I got 2x 9 meter LVLs (42mmx240mm) and they are just too heavy and awkward to lift up on to the posts I’ve anchored. Can I cut it in half and attach it with two bolts on either side of the LVL to the post? I intend to attach the LVL using a half lap join on each of the 6 Posts.

the span between each post is 4 meters. With a 50cm over hang on either side to make up the full 9 meters length.

Please see my images. Thank you.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/135553#Comment_135553

Hi @MamaCass,

You certainly can cut the LVLs in half and fix them with bolts through the posts, but just be mindful that any joint you introduce has the potential to reduce the strength of the timber and create a weak point.

The ideal solution is to keep the LVL continuous if at all possible. Maybe consider turning it into a bit of a weekend BBQ project. Invite a couple of friends or neighbours over and have a hoisting event. With a few extra hands, it becomes much more manageable to get those beams in place without cutting.

That said, if you do cut the LVLs, as long as the half-lap joins are done neatly and the sections are well secured with bolts through the posts, you shouldn’t have any issues spanning the 4m bays. Just ensure that your fixings are solid and everything is tightened properly so that the beams act as one.

If you've had this structure engineered, it would be best to confirm with the designer as to how this split LVL would affect the load capacities.

Please let me know if you have any questions.

Mitchell

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/138756#Comment_138756

Good afternoon @MamaCass

I like the suggest of a BBQ to get a couple of extra hands 🙂 I much prefer keeping the lengths continuious all the way across the structure if possible.

Another way to raise the timber lengths is to "work" your way up a laddr or between two ladders. It is problematic but once you start you soon find where to place the next lift. Just remember if it feels sketchy then it is sketchy and prob shouldnt be done 🙂

If you set everything up for raising the two lengths that you want before hand, then getting someone over for half hr/hr's work might be an option. All you need them for is to get them up, then you can continue the next day with no one watching 🙂 Been there and done that a few times.

I have done a few lap joins and horizontal ones were easier. The vertical ones I have done, well "screwed up nose" is a good way to describe it 🙂

Looking forward to your solution.

Dave

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/140884#Comment_140884

Thanks @dave1,

Can you please tell me what you mean when you say a "horizontal" one?

In my mind (and limited capentry knowledge) the lap groove is cut out of the post at a depth of 42mm to match the depth of the

LVL so that the LVL can fit snug into the lap groove. Are you talking about something different? I am excited by your use of the word "easier" haha!

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/142464#Comment_142464

Good Afternoon @MamaCass

hahahah Well I have probarlly worse terminology then you 🙂

A "lap join" In my mind was two of the same pieces of timber, Where they are partially cut using a saw and chisel. They are reversed so when you bring them together it looks like one continuious piece of timber (Think two people shaking hands)

Pool deck stage 2 will show you some notches I did to hold the beams. The beams are what you have and the lap join would sit away from the post and overlap. (If its on the post then you have two lots of timber trying to be bolted to part of a post, instead of 1 piece bolted to the post) I figure it makes for a stronger support point.

Pool deck stage 1 Just to show some other notches.

I can draw it up if you cant picture it but wont be able to do so until later or most likely tomorrow afternoon. 😕

Dave

MamaCass

https://www.workshop.bunnings.com.au/discussion/comment/143585#Comment_143585

Ah, I think my terminology is wrong but we are on the same page. Rather than both pieces of wood shaking hands, I only intend to cut a lap in the 90 x 90 post and then rest the LVL on and in that lap.

The LVL is only 42mm x 240mm so I can’t afford to cut into it because it would weaken it too much (I assume).

EricL

https://www.workshop.bunnings.com.au/discussion/comment/144438#Comment_144438

Hello @MamaCass

Cutting the 90x90 and having the LVL sit on the post will transfer the load to the post. If you are fixing it with a nut and bolt configuration it's definitely a plus as the nut and bolt will not be carrying all the load of the assembly.

Eric

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