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

[MamaCass]

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]

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]

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]

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]

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