The Brew Cabin

I'm presently laying a courtyard patio for a nursing home. It will be trafficked by wheelchairs and pedestrians only. They requested a cheap but stable surface, and opted for 900x600x50mm precast concrete slabs.

I've set up a sub-base of 100mm compacted DoT Type I and am laying on a 30mm wet base of 5parts sharp to 1 of OPC. This has given me a very strong patio indeed.

However, despite my very best efforts, I have noticed in a couple of places that there are 'lips' of 2-3mm at parts of the interfaces between the stones. Looking more closely with a steel straight-edge, I've found that the slabs are actually 'bowed' slightly along their length, making a snooker table finish impossible. They are Marshalls slabs and I hadn't expected this.

Normally I wouldn't worry, but the residents are elderly and tend to shuffle, so 2mm really could be a problem. The Client seems happy enough, but I wonder if it may be flagged up during a later inspection.

Should I try to shave down these problem patchs with some sort of grinder (and if so, what), or is there another solution ?

Any advice would be very much appreciated.

Cheers,

Barry.

In your situation, Barry, I'd take up the bowed flags and get replacements from Marshalls. If these are the A50 flags, they really should not be bowed.

You don't mention what type of jointing you're using. If you're butt-jointing, then any deviation from true will be highlighted, but by using a 10-12mm mortar joint small deviations can be accommodated quite easily and the transition between flags 'smoothed', if you know what I mean.

However, now that the flags are in and on that bedding mix they'll be damned hard to extract, then you might be better off getting a diamond-bladed power saw to "grind" off any lips. It's not a pretty effect, but it's better than having one of the residents trip.

Just how much of a bow are we talking about over the length of the flag? 5mm? 10mm? More??