How to increase height of a small existing concrete slab?

[dant]

Hi,

We are going to replace our aluminium pool fence and add glass fencing directly on the pool slab.  I need to add a small slab in between the existing pool slab and a slab I laid for the filtration equipment.  I didn't have the foresight to ensure this slab was level with the existing pool slab when I did it years ago.  So, it sits around 1cm or more lower than the pool slab. 

• My question is, can I add such a small amount of concrete to this filter slab to level it with the pool slab?

I am adding a slab in between the pool slab and the filter slab, which will be the height of the pool slab.

The filter slab will only have one spigot on it right where the glass fencing will end.

• Or can I just lay an extra thick layer of tiling adhesive as I intend to tile the filter slab and the connecting slab as well?

Yellow dots/lines are the proposed spigots and pool fencing.  I am thinking of joining the filter and pool slabs with the new slab with some embedded reinforced bars. 

Note: the hole in the ground is where I originally laid some conduit from the filter system to run to the other side of the yard and will be filled.

Thanks in advance, Adam

[MitchellMc]

Hi Adam (@dant), 

I can’t see anything wrong with your approach. Provided the new connecting slab is at least around 100mm thick and you tie it into the existing slabs with some reinforcement bars (as you mentioned), it should provide a solid and stable mounting point—especially since it’s only carrying one spigot. Just make sure the ground beneath is well compacted before pouring, to avoid any future movement.

As for the 1cm height difference on the filter slab, while a thick layer of tile adhesive might get you close, it's generally better practice to bring the slab up with concrete or a self-levelling compound if you're aiming for a more structural and long-lasting solution, particularly if it’s part of a fencing anchor point.

Here's a helpful guide: How to pour a concrete slab.

Please let me know if you have any questions.

Mitchell

[dant]

Thanks Mitchell.

RE: the self-levelling concrete.

After installing tiles on top of this, will the new, thicker slab be okay to drill dyna bolts to attach the glass fence spigots?

Do I need to etch, rough up the concrete or add any sort of bonding agent if only pouring an additional 1-2cm?

I'm worried about the strength of the bond between the new concrete and the existing slab, especially if it will crack when drilling through for the bolts.

Any advice on whether this approach is prone to cracking or should hold up fine?

[MitchellMc]

Hi @dant,

The self-leveller is just acting as a non-structural surface layer, and the structural strength of the fixings will come from the original slab as they will penetrate down into it. I think it's unlikely that it will crack when drilling through it.

That said, it’s still important to ensure a good bond between the new layer and the old slab so you don’t end up with cracks or drumming under the tiles over time. To improve adhesion, make sure the surface is thoroughly cleaned and roughened up—grinding or acid etching are common methods. Then, apply a bonding agent such as Bondcrete. This helps ensure the new layer bonds tightly and doesn’t separate down the track. 

Mitchell

[dant]

Thanks @MitchellMc 

Sounds like a plan!