Concrete Floor Grinder or Power Trowel? Two Different Machines, Two Different Floors

Booking a concrete floor grinder and getting a power trowel delivered is a real and frequent mix-up, because the trade has used the two names interchangeably for years. They are different machines, they work on floors in different states, and neither can do the other's job.

The clearest dividing line is not the name, it is the floor. A grinder works on concrete that has hardened. A power trowel works on concrete that is still fresh, on pour day. If you know whether the floor on site is wet or already cured, you can answer the question immediately.

Getting it wrong costs more than a wasted hire. A trowel put onto a hardened floor does nothing at all; a grinder put onto fresh concrete sinks into it and ruins the surface. Either way that is a working day lost and another delivery run to pay for.

This article separates the two properly and gives you a way to read the site before you call. The rates used throughout are the concrete floor grinder and polisher at 1,000 THB per day and the power trowel at 1,500 THB per day. Those are machine hire; stone and transport are billed separately.

Grinding and stone polishing are the same job: cutting the surface of hardened concrete with abrasive stones fixed under a rotating disc. The machine that does it is the concrete floor grinder, a walk-behind unit with the disc underneath, and the stone grade is changed to suit how fine a finish you want.

Trowelling is the other job: spinning the surface of concrete that has not yet hardened until it is smooth and dense, on the day of the pour. The machine is the power trowel, with several blades fanned out under the body. The Thai name for it, dragonfly, comes from those fanned blades.

Screeding is a third machine again: a vibrating screed that levels fresh concrete before trowelling. AR Rental Tools does not hire one out. That is said plainly here to save you asking. Most sites do this step with a straight edge and manpower.

There is also a catch-all word tradespeople use for both jobs, and it is the single biggest source of wrong bookings. When you call, describe the state of the floor rather than naming a machine: say the slab was poured yesterday and has hardened, or say you are pouring tomorrow morning. That alone gets the right machine on the truck.

The first question to answer is when the concrete was poured. If it has not been poured yet, or goes down today or tomorrow, the job waiting is trowelling. If it went down more than a day ago and you can walk on it without leaving marks, the job waiting is grinding.

The second question is what finish you need. Trowelling produces a smooth, dense surface in the original concrete, suited to factory floors and car parks being poured new. Grinding opens up a surface that has already hardened: stripping old paint, stripping adhesive, flattening a wavy slab, or exposing the aggregate before a coating goes on.

The third question is whether anything is stuck to the existing floor. A slab that had tiles lifted off it usually has ridges of tile adhesive left behind; one that was painted with epoxy usually has film clinging to it. Both are grinder work only, and the stone grade is chosen by how thick the material to remove is.

Those three questions take thirty seconds and remove almost every wrong booking. If you are still unsure, photographing the floor is faster than describing it. The team can look at the picture and tell you which machine and which stone grade you need.

The first job is opening up an old floor before a new surface goes on. A factory or building floor about to be epoxy coated or sealed has to be opened into a porous surface first. A surface left too smooth stops the coating keying in, and it lifts off in sheets within a few months.

The second is stripping what is already there: tile adhesive left after tiles were lifted, old paint film, or staining nothing hand-held will shift. This group eats coarse stone and takes longer than straightforward opening, because the machine has to make several passes before it reaches sound concrete.

The third is terrazzo-style polishing: opening the surface until the aggregate shows, then working up through stone grades from coarse to fine until the floor has a polished sheen. This takes the longest of the three, because every grade has to be walked; skip one and the scratches from the previous grade never come out.

The fourth is flattening an uneven slab. Waves and proud joints can be ground down within a few millimetres. The limit is that a single-head machine corrects large differences slowly. Where levels differ by centimetres rather than millimetres, pouring a levelling layer over the top is better value than grinding down to it.

A power trowel works on concrete that has just been poured and is beginning to set. The usable window opens once the slab has been levelled and the surface has dried back far enough that a footstep only sinks slightly. Earlier than that and the blades sink and bring laitance up; later and the surface is too hard to work.

It suits floors that need to be smooth, dense and easy to clean: factory floors, warehouses, car parks and parking structures. The finish is the original concrete worked until it is tight, not a coating laid over the top, so there is no film to lift off later.

The constraint to plan around is that the machine has to be on site before the pour finishes, because the window is only a few hours long and will not wait. Booking delivery for the afternoon of a pour day is usually already too late. Have it there from the morning of the pour.

People calling to ask for a power trowel to improve an old floor that does not look good is a common case, and it is always a case for changing machine. An old floor is a hard floor, and hard floors are grinder work, whatever name the job is given.

The concrete floor grinder and polisher is 1,000 THB per day and 6,000 THB per week. That figure is machine hire only. The polishing stone is billed separately depending on type, starting at 80 THB each. This is stated on the product page and is the line most often read past.

The power trowel is 1,500 THB per day and 9,000 THB per week, with no separate consumable, because the blades are part of the machine. Comparing the two straight across at 1,000 against 1,500 therefore is not a fair comparison, because the grinder side still has stone to add.

How much stone a job needs comes down to two things: how hard the existing floor is, and how many grades have to be worked through. Straightforward opening takes one grade. A polished finish has to be worked from coarse to fine. The real figure is confirmed at booking, once the floor condition and the target finish are known.

The weekly rate on both machines is six times the daily rate, so a job running a full six days costs the same either way and from day seven the weekly rate is cheaper. Current rates for everything are on the equipment and pricing page.

The job is a 200 square metre old factory floor that had tiles lifted off it, leaving ridges of adhesive across the whole area. It needs opening up flat enough to take an epoxy coating. The slab hardened long ago, so this is grinder work start to finish and has nothing to do with a power trowel.

Working out the days uses the same arithmetic as compaction: effective working width times travel speed times the number of passes. A single-head machine has an effective width of about 0.22 metres and grinds at roughly 5 metres per minute, which is about 1.1 square metres per minute for one pass.

Real running time inside an hour is about 40 minutes once stone changes, vacuuming and lining up are taken out, giving roughly 44 square metres an hour per pass, or about 300 square metres per pass across a seven-hour day. Adhesive removal like this needs about three passes, so roughly 100 square metres a day. Plan on a range of 80 to 120.

Two hundred square metres divided by 100 is two days. Two days of machine hire is 2,000 THB, plus stone by type and quantity from 80 THB each, plus transport charged on distance and piece count. The team confirms the stone and transport figures at booking, once they have seen a photograph of the floor.

The first reason is the shared vocabulary. Suppliers and tradespeople both use one catch-all word for either machine, so the person booking hears a familiar term and assumes it matches. The fix is to stop starting from the machine name and start from the state of the floor.

The second is judging by the photograph on the website. Both are walk-behind machines of similar size and look alike at a glance. The difference is underneath: the grinder has a disc with stones fixed to it, the trowel has several blades fanned out.

The third is booking from what the client asked for. A client asking for a polished floor might mean trowelling on pour day or grinding and then coating. The fix is one question back: is the slab being poured new, or is it an existing floor? That single answer settles it.

Before calling, have three things ready: a photograph of the floor, the area in square metres, and the finish you want, such as epoxy over the top or an exposed-aggregate sheen. The team will confirm which machine, which stone grade, how many days and the total. Contact details are on the contact page.