Workshop floor advice please

After finally securing planning permission, my new 'proper' workshop, build is proceeding at a good pace with some excellent builders.

The walls are up and the roof is on but one matter I have some concerns about is the floor. It has about 150mm of concrete including some rebar, so its definitely not going to crack with anything I could imagine putting on it. However, I have insisted on it being perfectly level with my garage floor to which the workshop connects. This means we need to add another 40mm or so onto the workshops concrete base. The builder has 'recommended' a self-levelling latex coating applied in several stages.

In my mind the term 'latex' suggests it will be a bit rubbery. Whilst this might be acceptable on a typical coating thickness of say 2~3mm, I fear a 40 mm thickness will indent, either permanently or temporarily, with a heavy pressure.

I have trawled the internet but its difficult to separate salesmanship from fact. And, nowhere can I see anything regarding the performance of 40mm thick coatings! What I do pick up though is that epoxy based are probably stronger. But how with they behave when 40mm thick ?

As usual I therefore return to this excellent group for experience-based advice on the wisdom of using either type of self-levelling materials mentioned above with a thickness of 40mm.

Perhaps some more concrete would be a more sensible solution, but there may be some practical or economic challenges with this.

Your thoughts and comments would be appreciated.

Gerry

Hi Gerry, 40mm thick concrete won't be very strong, even when put on top of new concrete. What you need is a screed compound, e. g. Cement based screed but depending on the area you have, it might be a bit pricey, and you may have to use PVA to bond it to your concrete, it is also recommended to lay a screed the full depth in one go.

Regards Nick.

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

I wonder if the best point of contact might be a concrete supplier, and ask their advice.
Concrete is certainly used in overlays, but I'm not sure exactly what type.
It may be that they suggest something like polyester fibre reinforced screed, such as used for imprinted/patterned concrete; this is different to polyester or polymer concrete.
https://rtmycockandsons.com/floor-screed/ This link is my local supplier, but obviously there will be someone closer to you.

Also, using the above solution might be an ideal opportunity to put in piping for underfloor heating, even if you don't connect it up until the price of heat pumps falls a bit; I didn't but wish I had.

Bill

Edited By peak4 on 13/05/2023 13:35:33

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.

I would also use chipboard flooring. It depends on what you will use the workshop for. If you know where the machinery is going. mark out an area big enough to accomodate the machine and don't put flooring in that area. When I did my workshop, I did half and half. Half with chipboard and half just concrete. The concrete section was for the cars to be worked on (pretty sure the chipboard could have been used there too) and the chipboard half is where I did my woodwork. I also laid vinyl tiles on the chipboard, so it was easy to keep clean and never damaged a sharp tool that was dropped on it.

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

30mm rigid foam foil based insulation, 10mm tongue and groove high grade chipboard on top. Warmer for the feet.

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

Something with a bit of 'give' underfoot is much easier on the feet and legs. Thats one of the reasons old machine shops had duck boards to stand on at each machine.

Why not lift the walking floor level to match the garage, but leave the machines on the concrete.

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.

Many old factory floors were finished with wooden blocks on end and worked well lasting for years although I imagine not cheap to do now. I would prefer a wooden surface even now as it is forgiving with anything dropped and always looks good even with oil residues. Perhaps if you have the kit get some suitable square posts and cut them into pieces and lay with a suitable glue to the concrete. Wood is both comfortable to stand on and sound deadening.

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

My workshop is a pre-cast concrete garage with the door aperture replaced by a 'site office' front. It obviously stands on a concrete plinth. I was just going to paint it with garage floor paint but an old hand told me that there is nothing worse than standing on a concrete floor for any length of time. I had no experience of this because my previous workshop had been a pent shed with a concrete plinth set in the floor where the Myford stood. Because of this advice I put a polythene membrane down and boarded it over with plywood. This lasted for about twenty years but water had seeped in and rotted the wood under one of the machines. As a lock-down project I stripped everything out, put another membrane down and replaced the plywood sheets, this time coated in two layers if thick bitumastic paint. I put a further membrane on top and laid a cheap laminate floor over everything. The Myford stand is again anchored into the concrete plinth through the floor with the holes sealed with silicone sealant. It seems fine but I don't think I will be around long enough to see if will have stood the test of time.

Thanks everyone for you thoughts and comments so far.

The floor has been very robustly made with hardcore, DP membrane and 100mm of Celotex underneath the 150mm of reinforced concrete. Despite the Celotex, that mass of concrete will act as a nice heatsink for the feet and I should consider that.

PEAK4, I had previously dismissed the idea of underfloor heating but your comment has made me rethink this. I have it in the house and its wonderful! You only need a few degrees of warmth in the floor to make the whole room feel warmer. So this could be a useful benefit of a 40mm cement screed. I could finish it with a simple paint coating on top. A latex or epoxy material probably wouldn't let the heat dissipate.

I didn't realise screeds could be self-levelling, so I've learnt something else today!

My concerns about the latex / epoxy was not so much about it cracking, but more about whether it would take on a permanent set or even extrude over time when I raw-bolt my J&S into the concrete that's below the builders proposed 40mm plastic coating. The idea of using solid pads made by a few, could be away around this. Once I know where the machine will be, I could just cut the plastic material away with a hole-saw, insert some steel and sit the machine on this. Lots of food for thought, though.

Gerry

40mm would be ideal for laying granite (granno) concrete and give a very hard wearing surface and can be trowelled to a smooth finish.The firm i worked for always used granno where machinery was stood.

Frank

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

In my workshop I laid 50mm X 50mm tanalised timber battens on the concrete and flooring grade tongue and groove chipboard on top. Then covered it with cheap vinyl flooring. Much warmer and nicer to stand on than the painted concrete floor in the garage next door.

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

My comment about leaving time was not about the strength but moisture as the excess in the concrete evaporates. Also if not dry any rubber based coating might come adrift as water can't get out.
Maybe consider a wood solution still with electric underfloor heating panels driven from a few solar panels on teh garage roof.