This blog is dedicated to my good friend and concrete colleague Elaine Toogood. She recently inspired me to ‘get off my horse and write my blog.’ This came about through a discussion on sandpaper of all things.
"80 grit? 120 grit or indeed True Grit?" That was the question.
Of course we weren’t discussing the thespian talents of John Wayne or even listening to Glen Campbell... because the usual focus was on Visual Concrete of course. The subject in Elaine's holster was if sandpaper was a good idea to use for cleaning concrete surfaces…
We never got round to having that shoot out before, during or even after Eco Build. So in the spirit of sharing and, as John Wayne once said, “Tomorrow hopes we have learned something from yesterday.” here's what I think:
Ok, so if you want to find your True Grit for dry or wet cleaning concrete then Diamonds are a concrete’s best friend. Flexible Nickel encrusted Diamond hand pads or 3M diamond encrusted floor pads are the trail blazers.
So why is your 120 or 80 sandpaper not your True Grit?
Here are my reasons:
Sandpaper essentially a FLAT sheet of paper which is not flexible and relies on the operative holding it flat, with a block or on a sanding machine. If you sand concrete flat it will abrade the high spots and leave the ‘valleys’ alone. This will accentuate the natural ply grain in the formwork making the high spots darker and the low spots lighter. I’ve seen this dramatically change the aspect of concrete, especially in soffits. At first glance the concrete looks so gorgeously bright… but’s it’s covered in a fine dusting of the cement and latency you’ve just removed. Upon dusting down it’s a different matter and you can find yourself looking at heavily grained ply imprint. Hmm.
Sandpaper is particularly aggressive. This is because it runs out. It’s a sort of ‘all or nothing’ mechanical abrading system. New abrasion will make surfaces dull and scratchy and worn out paper will make them VERY shiny. So there is no happy medium. Light reflectivity, when cleaning concrete, is so fundamentally important and if you don’t check this regularly you can find that the surface may look good from a perpendicular angle (directly at you) with diffused lighting. However from an acute angle in direct sunlight it can look awful. By awful I mean you can SERIOUSLY ruin it. Sandpaper does not have the subtle degradation of abrasion that diamond has and as such is very aggressive.
Thirdly and very importantly...
There is the psychology of it all. Proper cleaning can greatly increase the aesthetic value of visual concrete. It can also get PC on concrete that may have potentially run the defective gauntlet prior to cleaning. So this fundamentally important activity is so worth investing time, money and investigation in. It reduces defects and it is remiss to think that a quick rub will do. Sandpaper is a cheap solution which will ultimately be used as such; In abundance and without the consideration the concrete should be due.
On my most recent project I found I needed to wet clean all the walls in general with a flexible diamond encrusted 3M pad. Then remove the remaining superficial white efflorescence with a 200 Nickel Diamond pad carefully in wet (at angles and using the base of the palm to push the flexible pad into the valleys).Then I had to slice off incredibly hard orange calcium carbonate striations with a razor blade to ultimately revert back to the 3m pad to give an even reflectivity to the concrete. Some of the concrete needed to be subsequently dry diamond abraded as well. Sandpaper would never have been able to achieve this.
For Decent flexible Diamond Pads look to DK Holdings. www.dk-holdings.co.uk. A 200 nickel is best for matt concrete. If you can talk to Derek Sweetman do so as he’s brilliant. The 3M pads are harder to get hold of but you can at http://www.janitorialexpress.co.uk. if you are in London. Go for a ‘Sienna Pad’. Or…. if you like you can contact me of course.
My conclusion to all this is that If you chuck some True Grit at such a sensitive material as Visual Concrete you may finish up being the Grindstone Cowboy!riding a Bucking Bronco!
Thanks Elaine for getting me off my donkey and back on the Blog.