self build waterproof basement formwork membrane concrete powder

Waterproofing Readymix concrete.

I can sell you an admixture that makes concrete waterproof.

As good as any of the rest out there.

For less money. £15 a m³. Only while stocks last.

I explain a lot more on this page,
and I go into all the science on this discussion web site
  self build basement

Concrete can be made a million different ways for different advantages.

This concrete is absolutely waterproof.

But it goes stiff quickly.

You cannot get a perfect finish on this concrete

easy float slab nut leveller
  1. You are very experienced with this concrete, and

  2. You bought our slab levelling kit so that you spend very little time raking concrete around before you can try and get a float finish, and

  3. You get your concrete placed by an overhead boom pump, not by a line pump, and

  4. You have 5 hard working guys.
I do not like cement blended with flyash because flyash is hollow and does not react. Therefore there could be capillary pores throughout your concrete and concrete with flyash might never be waterproof.

If you can get concrete with cement blended with GGBS, slag, then this should always be waterproof and that blend will give you more working time.
overhead boom pump

Powder to make drum-delivered readymix concrete* waterproof -
    Added by you.

Making readymix delivered in large trucks waterproof yourself.

* The concrete purchased must be the mix we prescribe.
P350. This means 350kg per m³. (P380 with 10mm aggregate.)
CEM 1. This means pure OPC. Cement blended with GGBS is acceptable but not flyash.
over sanded for pumping
You want to order 60mm slump if you add the product on site.
   120mm slump if you give the additive to the concrete supplier to add at their plant.

no other additives

Tell your readymix supplier that you will be adding and mixing in your own super plasticiser when the concrete arrives.
If you are asked, don't open a can of worms about Health and Safety unnecessarily. The plasticiser will be put in for you by the pump operator who will toss the sachets in from the back of his pump truck, without standing on, climbing up or even touching the concrete truck.

Let them know that it is a very powerful plasticiser so they should only put in the water for 60mm slump - less than usual.

Most important. Mix the powder in 6 revolutions per cubic metre. Any less and the powder won't be thoroughly mixed and the pump will block when it pumps any concrete with too much powder. The clean up or repair bill will be several thousand pounds. YOU MUST COUNT EVERY REVOLUTION YOURSELF. YOU CANNOT TRUST ANYONE ELSE TO MAKE SURE THE POWDER IS PROPERLY MIXED. ESPECIALLY NOT THE TRUCK DRIVER OR THE PUMP OPERATOR.

If the concrete is still dry with the additive in add water cautiously. Only 5 litres at a time.

Be quick with everything. The concrete will start stiffening quickly (if it is pure OPC).

Very occasionally, and usually only in hot weather, if you have had to add more than 20 litres of water and the concrete is still stiff, the batching plant put in way too little water and the concrete is setting prematurely. You have to find and put in water in 50 litre doses as fast as you can. Use the concrete as fast as you can. Try to find somewhere less important for this load, such as the bottom of the slab. (It will be super strong but very difficult to compact and impossible to get a finish.)

Keep your slab wet well into the evening to prevent it drying out too quickly.

If you buy the sachets of powder to put in yourself, you need to know that each sachet is sufficient for 2 cubic metres of concrete.

When the driver complains about cost of diesel, look him straight in the eye and tell him you have paid for mixing. Tell him to mix it or take it away.

You should not be persuaded to add any more water to make the concrete runnier because then you will lose essential grout out of gaps in your formwork and the concrete won't be waterproof. You need all the sand and cement to get the required density. (Don't worry about a thin dribble, but worry about losing half a shovel full.)

Click here to open the Material Safety Data Sheet for this powder.

The admixture for readymix concrete can only go in drum trucks that carry concrete batched back at the batching plant. I cannot waterproof volumetric mixer concrete. Neither can anyone else unless they got a truck specially adapted to suit a particular chemical.

waterproof readymix concrete

It is easy if you are supervising, which you should be to avoid any poor workmanship.