Generally latex self levelling coatings have a modicum of flexibility helping to reduce cracking should anything move. The epoxy type tend to be much more rigid with a greater load carrying capacity and, often, a tough colour included so no need for subsequent painting.

For your purposes differences are academic. Latex self levelling is amply strong enough and chances of any movement sufficient to crack epoxy are remote. Realistically selection is down to cost and performance down to how well it's laid. Probably the builder is suggesting the material he is most familiar with so odds are he is more likely to do a better job.

I'd not use either.

When I built my big new workshop nearly 20 years ago I was advised to use high quality waterproof tongue and groove flooring board, the green stuff, direct on the concrete.

Which turned out to be good advice.

Still going strong, looks OK despite the mottled green having faded unevenly along with a few oil and paint stains. It's stood up just fine to machine moving but I have put a few scorch marks from welding splatter in. Nicer underfoot than concrete, levelling compound or epoxy too. We took great care when finishing the concrete to get it very level with shallow, close set, tamping grooves. I was told that the board would sit better on shallow tramping grooves being a blessing to accommodate small variations better than on a "levelled" surface.

Splashed out on the best i could find as cheaper breeds aren't as durable. Workshop is 15 ft by 36 ft (ish) and I did the attic space too so I bought an enough to get pallet pricing rather than per board. Leftovers made nice shelves and cold area workbench tops. The slightly rough finish being excellent at slowing dropped parts trying to escape.

Clive

Edited By Clive Foster on 13/05/2023 13:17:18

My concern with a latex screed is that it is not regarded as a finish. Similarly, cement and sharp sand is usually the bed for another finish but it could also be painted.

The traditional screed was was usually 50-75mm thiich bonded to the subfloor by coating with cement grout before laying the screed.. PVA on the subfloor is a better alternative. A good plasterer could achieve a flat and even finish but shrinkage of the screed may mean that it does not bond fully to the subfloor. However, the compressive strength of the screed should to be sufficient to support the machinery as the subfloor will provide the bending strength.

I agree with Clive on this one. As you have 40mm to accommodate, I would use some 18mm battens and 22mm green chipboard with glued joints. Some polystyrene insulation between the battens would make it more comfortable for standing. If you have high point loads for machinery, you could cut a core hole at each point and fill it with a hardwood plug bearing on the subfloor. That would eliminate the deflection of the chipboard floor. Some floor paint would add a finish.

Gerry

You don’t say if you have insulation under the concrete, but it may be worth using a layer of 25mm PIR insulation (Celotex or similar) covered with a layer of water resistant chipboard flooring. You could cast pads using self levelling compound just for where your machines are located. My garage/workshop floor is not level, so I cast a pad using self levelling compound for my Warco WM290 lathe. It varies in depth from about 25 to 40 mm thick. I used this Mapei self levelling compound: **LINK**

I think you could do the whole floor with it but it would be expensive.

Stuart

I've got foam and flooring grade chipboard. All covered in vinyl, where machine feet are going to be I cut a 100mm square hole and insert a block of wood. You don't mention whether you have damp proof membrane. I had my concrete flags covered with mastic asphalt which got it very smooth and keeps the damp in its place

Since you need to let the concrete dry out for a few months you have time to start collecting a lot of pallets and stripping them to provide about 3 layers under a top of chipboard/ply and lino.

Bazyle suggests the concrete will need a few months to properly dry out and reach full stability. Which is standard engineering if you want high strength. But in practice it needs much less time to go off sufficiently to be a stable floor if its not completely hermetically sealed.

My flooring boards went down about a fortnight after the concrete. Just long enough for two of us to build the timber workshop and clad the walls both inside and out. I imagine the need to breathe was why we left the surface with tamping grooves.

Folk buying new build houses a on a small estate just up the road have found out the hard way that building on concrete that hasn't gone off sufficiently. Two years in and major problems with cracks. I doubt if the concert was down three full days before building continued. Big name developer with one of those silo things on site for pumped delivery of the concrete. Oodles of chemical additives no doubt to keep it workable which which doubtless plays merry hob with setting to full strength.

My expensive waterproof tongue and groove chipboard flooring is unfazed by the machines sitting on it. Neither marks or depressions appear if I move things. I have full on workshop machines so the weights are significant. Smart & Brown 1024 lathe at approaching ton and a half, Pratt & Whitney Model B 12" x 14" around a ton and a quarter, Bridgeport mill at about a ton, Elliott 10 M shaper at around half a ton along with a Rapidor saw and Pollard 15 AY drill, both "not light", something in the quarter ton region I guess.

I suspect the economy range and non waterproof versions would not fare as well. The stuff intended for lofts and the like certainly wouldn't be up to the job despite being perfectly satisfactory at what its made for.

Clive

Once the floor is down, something with a bit of fleibility, and insulation will be benficial.

A concrete floor can be hard on the feet, and cold. (In the old days, factories used duckboards because of this. )

My floor is actually 18 mm ply topped with plastic mats whicj have abour 18 – 20 mm of air under them.

Ny fet don't get cold, and about twiice a year, the mats are taken up and the sward, nuts, screws and washers that have fallen through the holes are swept up!

Howard

For that thickness and if you want underfloor pipework, you need a pumped anhydrite screed which will self level pretty much and is hard, harder than you woud think. I think you are at minimum thickness at 40mm

I worked in the large Aircraft Hangar at Brize Norton for a number of years, it has underfloor heating, it mind sound luxurious but it is not pleasant to spend all day standing on it, your feet and ankles do suffer, given a choice I would steer well clear of underfloor heating for any workspace. Dave W