Basement Expert Ltd
Concreting aids you cannot easily get elsewhere
From people who use them themselves
Powder to make drum-delivered readymix concrete* waterproof.
They would also get you spend a lot of money on something to go in the joints. If your workmanship is bad these extras don't work anyway. If your workmanship is good you don't need them. So listening to us and doing as we say will save you money as well as avoid leaks.
£13.50 per m³ is 3 times better because you are getting the same concrete outcome for a third of the price.
* The concrete purchased must be the mix we prescribe.
over sanded for pumping
target slump before additive 60mm
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, this will be done for you by the pump operator who will toss the sachets in from the back of his pump truck.
** Subject to minimum amounts per visit, depending on travel distance
We have lots of information, too much possibly, on other web sites:
Self Build My Basement
We quote science, academic research and books found in university libraries. Concrete with extra cement and less water* will be waterproof if it is properly placed, compacted, cured and reinforced.
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.
You need to mix the powder for 6 revolutions per cubic metre.
So, if you have 8 metres in a truck you need to add 4 sachets and mix them in for 48 revolutions.
You must count the revolutions yourself because you cannot trust anyone else to insist that the mixing is done properly.
Proper mixing is essential, or else you will get some concrete with too much additive that will be too runny and the pressure of the pump will push the liquid forward and leave the stones dry, and stuck very firmly indeed, in the pipes.
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.
If the concrete is still fairly stiff, add a tiny bit of water. Only 5 litres. Mix about 10 revolutions. Once there is enough water the concrete will pour over the drum fins instead of breaking apart. That is when it is ready to use.
You should not be persuaded to add even more water to make the concrete even 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.)
Mixing concrete on site and making it waterproof.You will need to make some gauges. I use two buckets for the ballast and a pot for the sharp sand. I cut bags of cement in half with a hand saw.
Mixing concrete by hand is very expensive compared to full loads of readymix. You should probably only mix by hand where readymix would be too much at once unless you paid a lot extra for a small delivery or extra time on site.
There is no need to buy retarder for hand mixed concrete.
Wash the mixer every hour so that it is easy to keep clean.
Price Each litre of waterproofing plasticiser for hand mixed concrete, sufficient for at least 1 cubic metre, is £10.
All these prices subject to delivery at cost and VAT.
Call me or email me and I can send you a quote.
Concrete left too long before the next truck arrives can start to set.
If it does, you won't be able to compact it properly when it eventually goes in the wall.
Pump-Save retarder is a blend batched in 500g soluble paper bags with the correct dose for maximum retardation of half a cubic metre of waterproof concrete* mix.
The problem is that by the time a truck leaves site, the concrete it left in the pump hopper and in the pump's pipes is already over an hour old. If the next truck doesn't arrive for another hour that concrete in the pump is out of time. It has started to set.
You retard concrete with just the right amount of retarder.
Just the right amount will retard the set for more than 2 hours.
Too little and nothing much will happen.
Too much and very little will happen.
Much too much and you have a disaster, the concrete will set quite quickly, and you don't want the bill for a written-off concrete pump.
So being accurate with the dose is quite important. That is why our small bags are so useful.
You need to judge when there is half a cubic metre of concrete still in the truck's drum. Stop the pump and add the retarder. Mix for 10 revolutions then carry on.
If there is a bit less or a bit more concrete than half a cubic metre you will still get retardation. The driver will show you how to tap the drum.
Price £4.50 per sachet plus delivery and VAT.
You could buy waterproofed concrete with retarder already in it. Such as Xypex. But if all your concrete is retarded for most of the day your formwork will be under much greater strain and more likely to burst.
It is helpful if most of your concrete sets soon after it is placed and compacted because then it is stabilised as more weight goes on top, you won't be losing a lot of grout out of small gaps which would prevent your concrete being waterproof.
So retarding only the concrete left in the pump waiting for the next load is ideal.
High Frequency Internal Vibrators. 110V. The World's Best Type.These pokers have all the moving parts in the head. The hose only contains a cable.
Why the world's best?
The head and hose weigh about 7kgs. That's a third the weight of flex-driven poker heads.
Extremely powerful yet lightweight. That means less knackering. That means that the job gets done better.
One man operation. No one needed to move a petrol engine.
Massive half tonne of excitation force. Effective diameter 800mm.
German design. Made in China. Market leader in the largest concrete market in the world.
Only a cable is in the rubber hose and that is designed to stretch harmlessly when the poker is packed away badly folded up.
So it will last far longer than most electric or petrol driven pokers and it won't stick like air driven pokers.
52mm diameter only.
Either remote control or the switch on the box. We always use the remote control version because then the supervisor decides when enough is enough.
£700 plus delivery and VAT.
Remote control switch £30 extra.
Rods. These are the best things we sell.
18mm dia FRP threaded rods. Stronger in tension than equivalent steel.
Having a rod cast in can make some situations, like a podium floor over a basement, 100 times easier.
Resin the rods into concrete piles and you have two sided formwork not single sided.
We tend to use timber instead of ply. We get more uses out of it, we don't need 4x2 stiffeners and we use roof batten layers so that we don't drill holes. It is easier, we find, to use rods with thin nuts inside to control the wall width if we use timber rather than ply. Treated 6x2 about 3m long is fast and lightweight and doesn't need as much release oil.
However these rods would be no more difficult than steel divi with plywood or hired pans.
We find them fantastic for concreting against CFA piles because you don't need single sided shutters. But be mindful that pile concrete isn't always very strong. Use plenty of rods and consider pouring in at least two lifts.
Sometimes the ability to leave a rod cast in to use again is priceless.
Price Rods are 2m long and can be cut to get the best use out of them. £7 a rod plus delivery and VAT.
Nuts for our 18mm dia FRP threaded rods.
You want to keep the wall forms the correct distance apart.
Slice 8mm to 10mm off whole nuts and use them inside the forms to push apart like plastic tube.
Price £2.20 each plus delivery and VAT.
Slab Levelling Kits.Youtube video here.
The problem with chairs for scaffold tubes is that they don't go in between all the rebars all the time. They won't go through spacing less than their size and they won't go through where mesh overlaps. Neither will they go through where the top mat isn't exactly over the bottom mat. So, they won't usually go where you always want them.
We recently invented the simple solution that will also always be waterproof.
18mm diameter threaded rods made with fibreglass. You only need to get a long drill bit through the steel.
One slab levelling kit comprises 1 rod with a slot cut at one end and 1 thin nut.
You fix 2 rods into your screed,
measure the distance between them,
cut 2x2 to suit and put a 40mm nail in each end,
use the thin nuts to bring the top of the screed rail to finished concrete level,
you can glue the nails and the thin nut to the rod with a drip of resin glue.
As soon as the rail is finished with, rip out the end nearest you then pull it off the far end.
Flush sets have rods 400mm long.
Visible sets have rods 600mm long and longer slots.
Flush sets £2.38 each plus delivery and VAT.
Visible sets £2.79 each plus delivery and VAT.
Just a suggestion
Screwfix code for the quick-setting resin we use
Rawlplug-R-Ker code 85750
External Drainage Membrane.We have a Product Data Sheet available here to print.
Youtube video here. It is 7 years old so a bit out of date. But it might be useful to you.
The membrane we have in stock at the moment is particularly tough, yet cheap.
If you buy either Newton 410 or Wykamol Geotex, their instructions tell you to peel back the geotextile filter layer and overlap the studded plastic layers before overlapping the filter layers.
Both also sell you a plastic covering strip for the top to stop dirt getting down between the two layers.
But the top covering strip doesn't really work across an overlap because the dimples in the two sheets don't marry up well.
It is so much easier, and usually much more effective, to put up the studded sheet first then to cover it in full-width (usually 4.5m) geotextile membrane, simply tucking it over the top to keep the dirt out from above and having plenty at the bottom to wrap over your land drain in one go.
Our rolls are 20m long. The full width is 1.9m. The width with studs is 1.8m. The flat edge at the top means a small overlap to keep the water draining correctly is very simple to achieve - much easier than trying to match up studs in two different sheets.
Price £120 each plus delivery and VAT.
Please Note. You need to buy the filter membrane separately, for instance this. Keyline sell smaller packs as well.
From time to time we will have it in stock and you can ask us to include it with your order.
Call me, Phil Sacre:
We have a number of other pages with information.