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

[MamaCass]

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?

THANK YOU SO MUCH!

[Dave-1]

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]

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]

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]

Really helpful. Thank you. 

[Nailbag]

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