Roger Bisby gave a new ARDEX screeding cement a try on his current extension job and was delighted with the result.
Let’s be honest: screeds can be problematic, they slow the job down, and leave you with a no go area. Traditional sand/cement and anhydrite screeds dry at a rate of 1mm per day, which can leave you with months of waiting before you can lay tiles or other floor coverings. ARDEX solves this problem by giving you a fast track solution that is easy to lay, and tileable within 48 hours – or 7 days if you are using natural stone or laying resilient floorcoverings.
It’s called ARDEX A 29 and it comes in 20 kilo bags. You mix it with your normal sharp sand, but it is a cement on steroids so you only need a 1 to 7 mix – yes, really; 1 to 7. In order to get the even dispersal of the cement through the sand you need a forced action mixer. Actually you really need this for any screed because a conventional mixer doesn’t move the dry-ish material properly and it balls up in the back – we have all been there.
You can, of course, get a screed pump in but they are big noisy affairs and I really don’t like it when the hose jumps and bangs about on the underfloor heating and insulation. It can make a real mess of it, so we used a Baron M200 mixer and barrowed it in the old fashioned way. The mixer will take a bag of A 29 and 18 shovels of sand with room to spare, and it is plenty fast enough to keep up with me. Your local hire merchant can get this mixer in for you on a cross hire and they deliver nationally.
The screed is a rapid set, but don’t let that worry you unduly because you still have a good hour to get the screed from the mixer to the floor. I have to tell you that I am no screeder but by setting up rails scaffold tubes and edge guides I can get a flat screed, certainly flatter than many of the bash crash cowboys I have used in the past who come in and ignore my datum lines as they trowel through with an 8 foot level.
I ran down one bay with my Refina screed rule and, after lunch (how civilised) I primed up the day joint with a lovely green slurry (ARDEX A 18) which allows you to join on to your existing screed work, even the next day. The ARDEX A 29 trowels up beautifully and has more fat than a standard sand and cement mix. You can also mix it slightly wetter because it is shrinkage compensated. It holds the water in the mix as it cures, so no need for my usual polythene sheet to hold the moisture in. The big payoff, however, is that you can walk on it after 8 hours, and after two days get on with the tiling. I like this because I prefer a clear run for wall-to-wall floor tiles before the units go in.
Now I know the question on your lips is “how much?” and the answer is that those bags are around four times the price of OPC, but you only need half the quantity, so the premium is to double the cement cost. For me the payoff is that you get a super-tough screed that is ideal for underfloor heating and it is easier to trowel up. I will certainly use it for my next screeding job, knowing that my client will get their floor back faster and I can crack on with my next job, which is the tiling.