In Rack It 16 we looked at floors, their influence on the efficiency of a high density storage system and how a poor floor affects lift truck performance. In this issue we are going to look more closely at how to deal with an existing floor that may not be appropriate for its intended use: How to measure it and how to fix it?
If an existing floor is not flat enough for its intended or actual use there are two options; raise the low spots or eliminate the high spots. Simple in principle but how do you find the exact areas to work on and how much do you add or remove? Is localised patching or grinding the only option, or can I resurface the whole floor?
Renovating a floor starts with identifying your problem. If your lift trucks are swaying around as they travel through the warehouse then it doesn’t take a genius to spot that the floor is out of level. But beware, this is only a problem if the sway has operational implications. Are your truck drivers being forced to slow down or are the trucks hitting the racks? Yes – then you have an operational problem.
To fix a floor you must identify its faulty areas. So how do you check the flatness of a floor? British Standard BS8204 Part 2 1987 specifies floor flatness, or surface regularity, as a gap under a three metre straight edge. Various classes of floor have different gaps; 10mm for a general purpose floor down to 3mm for a special purpose floor. However, this means of checking is rarely used because of the difficulty of applying such a measure over any significant area.
The Concrete Society’s Technical Report 34 (TR34) sets out to provide more usable measures, specifically for new floors. It does this by dividing floor areas into two categories, those where forklift traffic roams free and those where the truck’s path is fixed i.e. in aisles.
In areas of free movement a tolerance is specified relating to measurements taken at points on a three-metre grid running across the floor. FM1 floors, the flattest, should have a variance in elevation of less than 3mm between the points. TR34 specifies three other tolerances to be applied to the floor within the aisles: Difference in level, difference in slope and maximum difference across the wheel tracks of the trucks. These tolerances are based on a 300mm gauge length or the track of the FLT and are easily checked.
Going back to our existing floor, having decided to improve its performance you must first categorise your usage. An FM1 floor is a special purpose floor, for example the type you would need in a VNA warehouse. An FM3 floor is a general purpose floor. Obviously an FM1 floor is more expensive to construct than an FM3 floor, so only specify what you really need.
Categorising the floor will enable you to set a specification for flatness in both the free movement areas and the defined movement areas. Now measure the floor at the prescribed points using traditional surveying equipment to identify the nature and severity of your problem. If you have severe problems then an alternative surveying methods might be appropriate. Specialist companies offer a profilograph service. These strange machines travel along the aisles measuring changes in level in two directions. They produce instant print-outs identifying problem areas precisely.
If, within the critical defined movement areas, your floor is out of tolerance you will need to arrange rectification. Here you have other choices. Do you rectify by localised grinding and filling or do you attempt to resurface the floor, either within the aisle or totally?
Your decision will be influenced by the severity of your problem. Laying a new surface can provide the most effective solution. However, can you afford to have your warehouse out of action for the time involved? The cost can also be prohibitive and you may have problems in the future with debonding, where the new surface parts company with the old. You may also cause yourself operational problems if you raise the floor level by applying a new surface to only part of the floor.
The alternative to a new surface is to grind the existing surface. There are two methods of grinding: manual using push along grinding machines or automatically using one of the new highly accurate laser guided vehicles. The manual approach can be messy and time consuming. It is really only applicable to small areas in empty warehouses.
Laser guided grinding machines are better if larger areas must be rectified. The latest machines are environmentally friendly, and don’t produce clouds of dust. So, they can work in one aisle while the rest of the warehouse remains operational.
The advantage of grinding, is that it works by removing high spots. This means that you won’t get a step change in level from other areas of the floor. Also, once ground, the surface is immediately usable. But beware, TR34 was not written to cover renovation of existing floors. Grinding can produce situations not possible in new floor construction, for example you can grind the wheel tracks within an aisle and produce two channels in the floor. This is something that would never happen during the pouring of a new floor and so is not catered for in TR34.
So, if you think you have a problem floor get a copy of the Concrete Society’s TR34, decide what classification of floor you need and measure your floor. Remember that TR34 was written for new floor construction, not rectification of existing floors. If you need to rectify your floor choose your method. Get a competent contractor and ensure that they work to the tolerances set out in TR34 for the standard of floor you need. Floored thinking? We don’t think so!