self build waterproof basement formwork membrane concrete levelling

Slab Levelling rods.

Anyone can add water to concrete and make it easy to level, but adding water reduces the strength of concrete, causes shrinkage cracking and the excess water pushes the cement grains apart and makes concrete porous.

If you want waterproof concrete, and why waste the opportunity to build a basement that won't leak? the concrete will be thick, sticky and reluctant to move. The vibrator should make a small area move but it won't level the concrete.

My Slab Levelling System. Three benefits. One unique advantage.
  self build basement
  1. The more visual guide you have, the more accurately you can place concrete with just the right amount everywhere, reducing the amount of concrete you need to rake around.

  2. The more guides you have the flatter you can float your concrete.

  3. The flatter the concrete, the fewer and shallower any puddles later that you will be walking around in when you form your walls.
The unique advantage of these rods is they will be waterproof within your concrete for all time.

slab levelling system  
  Very simple.

Buy a 20mm SDS drill bit from Screwfix 1m long. That way you drill into your concrete blinding, between your tied steel bars, without bending over.

Resin glue a fibreglass threaded rod every 2m or so.

Fix them in a bit long and cut them in place to top-of-concrete.

You will need a laser level, a pencil and a small disc cutter with a thin blade.

drilling slab levelling system

slab levelling system glued

slab levelling system detail

slab levelling system

176m³ of concrete. Over 400 tonnes. Placed, levelled and compacted by a team of 6 in one day without overtime. If they had had to rake even 2% they would have failed because it would have been too much.

slab levelling system

This simple solution will always be waterproof.

A fibreglass rod cut accurately to the required concrete level.

It is fast to set up.

Each rod and the resin cost about £2. A typical basement requires about £30 worth.

Without any visual guide you need two extra men to rake more concrete about. Or another man to operate a laser and one more man to rake concrete about.

If you don't pour the concrete in the right place, the concrete can start to go stiff before you finish. The work becomes ten times more knackering and the end result is horrible.

It is vastly better to pour the right amount of concrete in the right place to start with.

Just drill a hole, resin fix a rod, mark it with a pencil and the laser level, use a mini grinder and 1mm thin blade to cut it off at the required level.

slab levelling system

18mm diameter threaded rods made with fibreglass. You only need to get a long drill bit through the steel. I suggest 2m centres.

If you need to lay your concrete to a slight, controlled fall, say to a sump, then these rods will be invaluable.

This slab took 50 cubic metres of concrete. It was poured, compacted, levelled and tamped in only 2 hours or so because, with the rods as a visual guide and the laser to get concrete dead level, they had to rake very little concrete around.

slab levelling system   slab levelling system

These are the more traditional ways.

What's happening in this photo looks all very well until you understand all the issues with it.
  1. The scaffold pole is 50mm diameter, so it exceeds the 40mm cover specified by the engineer. There is an element of cheating, and not following the design is your responsibility not your engineer's.

  2. Support stools would not go through the steel.

    slab levelling stool

    So although it looks like it will be a smooth finish, it won't be a level finish, because the poles are tied to the steel and where the steel is high the concrete will be high. Where the steel is low the concrete will be low and there will be a puddle that the team have to walk through when they form the walls, and wet feet all day are horrible.

  3. As the work continues, someone will have to walk through finished concrete to cut the tying wire and remove the poles.

  4. A steel support stool is in contact with non-waterproof concrete underneath. If it rusts through the slab will leak.
  slab level scaffold

A much easier and better system for a basement slab only costs £2 for every 4 square metres of slab. The labour saving might be 10 times that cost.

A basement floor slab always gets covered in insulation and screed because building regulations say so. Therefore you want it fairly flat and level. It does not need to be the pretty finish obtained with a motor driven tamp rail and Easy Float, as in the photo above.

Another example. 4 people laid this slab. Because they had the visual guides they had time to use an EasiFloat.

simple slab levelling system

The same slab later.

simple slab levelling system result

If you spend less than £50 on some rods and resin and get a level slab with a reasonable finish with 4 men instead of 8, it will be amongst the best £50 you ever spent.

From the beginning of 2021, I VAT registered Basement Expert Ltd (Co. No. 09745193 Registered in England and Wales).

The limited company will supply all products and add VAT at 20%

I, Phillip Sacre, will provide advice free of VAT.

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