Patio porcelain slabs

If the concrete can't be removed I would recommend raising the concrete base to almost the right height and then lay the porcelain with the right materials which is sharp sand and cement mix with all slabs painted with a slurry primer before laying or they will come loose

It would be better to pick up the height with a blinding of concrete to the right height first it will be solid then

Build up the 4.5” height with a semi-dry screed, made of sharp sand and cement (typically at 4:1 or 5:1 ratio).
• Top it with: A suitable exterior-grade tile adhesive to bed the porcelain slabs on top.
• Advantages: Solid, long-lasting base; common in professional paving.
• Tip: Make sure to compact it well and allow it to cure (usually 1–2 days) before tiling.
• Waterproofing: Use a waterproof membrane between the old concrete and new screed layer, especially outdoors.

If the base is okay yes just make sure its damp proofed at least But ideally would be better to go on a screed base.

Build a Suspended Slab (Best for Stability and Durability)
Steps:
1. Install a Waterproofing Membrane (DPM)over the existing concrete.
2. Install solid insulation (e.g. PIR board) if thermal efficiency is needed.
3. Build a reinforced concrete screed (~4" thick) with steel mesh for added strength.
4. Apply adhesive in a thin bed (6-10 mm) on porcelain tiles.

1. Use a Screed or Concrete Overlay
• Raise the level using a concrete screed or a semi-dry mix (1:4 cement:sand) to bring the base up to the desired level.
• Once it’s cured, lay the porcelain slabs using a standard tile adhesive or full bed of exterior-grade mortar (about 20–30mm thick).
• This provides a solid, stable base that won’t shift or crack.

2. Lay Slabs on a Raised Pedestal System
• Especially useful if you want a drainage gap or need access beneath the slabs.
• Adjustable pedestal systems can raise the slabs to the desired height without adding heavy wet materials.
• Works best with 20mm thick outdoor porcelain tiles designed for that purpose.

Avoid: Laying directly on 4.5” of mortar — it’s too thick and won’t perform well over time.

40/50mm mortar bed ideally, consider the size of your porcelaine at 20mm. I suppose you could, you a mortar bed at 100mm but it’s a waste of money. I’d suggest a compacted 50/60mm base of type 1, then mortar, then porcelain, don’t forget the slurry for the tiles. With a non porous sub base, drainage will need to be considered.

A thick mortar bed is fine just mind put plenty slurry on back of tile

Porcelain slabs can be laid on concrete provided the concrete is in good condition. It is recommended that you use a 30- to 40-mm bed to lay the slabs on, if possible. It is recommended to build a brick border around the concrete and fill it with 2 to 3 inches of compacted MOT, leaving enough height to lay the slabs. The purpose of the bricks is to prevent the base from moving on the concrete.

That will be ok mm ake sure you prime the back materials wise be like a wheel barrow full of mortar a slab
Or you could mix up a semi dry concrete and use that the screed 50 mm to save on mortar
Me personally I wood takeo the hit on the big beds

Yes u can leave existing concrete as long as the base is solid make sure it’s all cleaned and apply a primer to the existing concrete base then apply a tick mortar bed or u can put type one down to correct level then apply a bed of mortar

Yes you can lay in a thicker bed the is only a minimum requirement

To raise the base by 4.5" and install porcelain slabs on a concrete subfloor, here are your options:

1. Thick Mortar Bed: You can lay the porcelain slabs on a thick mortar bed (around 30–40mm) to achieve the desired height. This is a common method for raising levels and providing a strong base for the slabs. Make sure the mortar is mixed well and applied evenly for stability.

2. Self-Levelling Compound: Alternatively, you could use a self-levelling compound to raise the floor before laying the porcelain. This can provide a smooth, level surface to work with, and it will bond well to the existing concrete.

3. Tile Adhesive: After preparing the base with mortar or self-levelling compound, use a high-quality, flexible tile adhesive suitable for porcelain to fix the slabs in place.

Make sure to allow enough curing time for the mortar or compound before laying the tiles to ensure a solid and level surface. This method will work to both raise the height and securely install the slabs.

hi , i would recommend using mot type 1 to brings levels up to allow for a 50mm bed of mortar , i would be more than happy to help with your project , many thanks matt

Gently tamp down the ‘wet primed’ porcelain paving onto the mortar bed using the rubber mallet. Adjustment will be necessary to ensure that the paving is fully supported, does not rock or move and use a straight edge with a spirit level repeatedly to check that each paving element achieves the desired level and fall as per the string line.
Immediately wipe off any slurry primer that may have unintentionally found itself of the face of any of the paving as you will not be able to remove this once it has set.
When laying more than one pack of paving, lay tiles from different packs to eliminate colour banding and to obtain the best colour blend.
Use joint spacers or pieces of 6mm plywood to help maintain a regular joint width between the paving elements.

Yeah full mortar , not exceeding 80mm

Laying on top of that is absolutely fine. The only points I would advise you on is making sure you add SBR+ to the mortar mix and definitely put primer on the slabs before laying. It is a positive use don’t look at it as a issue too much.