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Checking Subfloor Flatness In Seconds

John Roberts tests the Bosch Professional GSL 2

WHEN Bosch rang me to ask if I thought the flooring trade needed a laser that could easily identify areas of a subfloor with dips or ridges I said I personally would use such an instrument. In fact I already use a laser to check floor levels.

They said the new equipment could quickly and easily scan a whole floor in seconds visually showing areas

of concern.

They offered to send me the new instrument to check out. In a later call from them to check if it had been delivered, they said I could phone if I needed any help. I replied that any tool should come with instructions that could easily be followed!

My first impression was good. The equipment came in a substantial box that held the laser firmly in place during transit and gave it protection.

Safety must be a priority with any laser. The safety instructions provided were clearly stated in bullet points; there were also two labels on the equipment.

The operating instructions are reasonably clear although I found some aspects easier to understand after trying the equipment myself. It is powered by a Lithium ion battery or by four AA batteries, both of which are said to last around 15 hours although I have tested this.

The main advantage of two power sources is that you should never be stranded with a flat Lithium battery as you can insert AA batteries in its place. Three lights on top of the tool indicate battery life so it is easy to see if the battery is low.

A sliding switch projects two laser beams out of two windows on either side of the tool. The beams are at angles that can be seen on the wall in front of the tool (red viewing glasses are provided to help in different lighting conditions filtering out ambient light and making the red beams appear brighter for your eyes).

Note: These are not safety glasses and you should not look into the laser beam directly as the glasses do not protect against laser radiation that could damage your eyesight.

I would recommend telling other people in the area not to look into the laser beams. Also keep the tool away from animals, which may be attracted to the lights.

The beams are low level so in normal practice this should not be a problem with people walking through the area. The laser automatically adjusts the level itself, providing it is placed on a surface not more than ±4deg

off level.

Once the beams stop moving and the tool has self-levelled, it is ready to be adjusted to align the height.

This is done by turning the thumb wheel on the base until the two laser beams become one at the first point in front of the tool which is around 50cm. You are now ready to check the floor level.

When both beams coincide with each other (one line) the floor is the same height as the reference point, but if there are two beams or an interrupted beam the floor surface has deviated from the height of the

reference point.

Evaluating the lines is easy as they arc from the one line to two. Note: when both laser beams run apart at a constant angle on the fl

oor, the surface is inclined. You can still see deviations along these lines but you need to look more closely.
To evaluate the height difference use the laser target plate placed at the middle point (site of greatest deviation) where the beams separate. The plate is positioned so that the beam on the left coincides with the left hand
reference line on the plate. Now push the target plate up or down until the metal tip on the bottom of the plate touches the floor, ensuring the beam is still on the left hand line.

The height variation can now be read off the right hand scale lines. The measurement can then be written on

the floor.

You can also draw around the lines on the floor to show which area needs to be levelled and by how much.
Once I started to use the tool’s full potential, using the remote control to set the tool rotating through 360deg, I realised how quick it was to visually see the variations in floor levels.

The remote has six buttons, two for fast continuous rotation in either clockwise or anticlockwise directions; two for slow continuous rotation either clockwise or anticlockwise; and two for single rotations in either direction.
I scanned around the whole floor at fast speed visually looking for variations, which indicated where the deviations were.

I then scanned at slow speed; when I observed the lines separating I pressed the button once to stop the rotation. That allowed me to use the target plate to take measurements and mark the floor with the extent of the variation.

I said you could check the flatness in seconds which is only partly true. A quick scan takes seconds, but if there are a high number of deviations these will take a little longer, although it is still very quick; far quicker and easier than other methods I have used.

The photos on this page do not do justice to this brilliant tool so come and see a demonstration and have a go on my stand B18 at the Flooring Show in Harrogate (September 2-4).

This would be a very useful tool when discussing subfloor preparations with clients, as they will be able to visually see the variations, helping you to justify the preparation costs.

One piece of advice is that building up dips is fairly easy or should be, but do ground off rises instead of trying to feather them down. Feathering ridges can cause problems with alignment of tiles, wood based products and other ridged materials which could cause wear spots on carpets.

Grinding is always difficult as it can be time consuming, but I will be reviewing a tool that can easily do this in a future issue of CFJ. Look out for it.

John Roberts founder TAOFS (The Academy of Flooring Skills) and prominent consultant in flooring. TAOFS offers training in all types of floorcoverings.


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This article has been reproduced from the Contract Flooring Journal website. You can find them at