workshop floor - strength question

With impending retirement I plan to build a small extension onto my garage to become a dedicated workshop. The structure will be well insulated and should need only a low level of heat input to keep it warm. To provide this I plan to embed a low-power electric heating element into the floor.

The heating elements need to be embedded in 50mm of concrete screed which would sit on top of 100mm thick polystyrene blocks.

My question is this: Is 50mm of concrete sitting on top of a relatively soft base material going to be strong enough to support machines weighing up to a ton ? Any thoughts or experience anybody?

A crack in the concrete would be a bit of disaster for the heating elements as one might imagine

Gerry

No

Mainly due to the polystyrene

All disturbed soil settles so you need to spread the load big time.

It would be normal to use 100-150mm of concrete (not screed) with reinforcing mesh as the structural floor. This can be above the insulation. If below you need a similar thickness concrete top layer.

Screed is not good for bending loads and would not be considered structural in this sense but its fine for making a smooth surface and wrapping around the pipes/wires of your heater.

Good luck, just get a builder in.

Being a graduate of the "Brick mausoleum" school, my thought was to lay a 50 mm layer of concrete around a steel reinforcing mesh, to minimise the risk of deflection of the 50 mm of concrete containing the heating elements.

But the increased weight, although a uniformly distributed load, might crush the cells in the polystyrene and so reduce its effectiveness as an insulator.

Maybe the edges of the reinforcing mesh could be turned down to keep the weight off the polystyrene, at a slight expense of the insulation factor.

Howard

I like underfloor heating, got in our Kitchen living area 40 m2, pipes off the combi boiler, its great, but for a workshop it would not be my choice. Don't forget there is a big lag time to get up to heat and if you are out there for a few hours IMO wouldn't work out well, especially with a thick chunk of concrete on top, to heat up first. I believe those electric heat meshes are 80 -120 watts per m2, not sure how long they would take to get the workshop up to working heat or how long to be on to keep it there?

Insulation is the answer these days as you say, hardcore, 100 mm insulation slab, concrete slab on top, with "air" electic heating of some sort, would be my option.

I like my workshop wood stove, but I am being woked out, should see me though .

Pete

Hy shed has actually got 200mm of concrete on top of 100mm of EPS foam (one layer of badly positioned mesh). The specified strength of the foam is more than enough to support the concrete and the machines. Concrete's quite cheap in the grand scheme of things and a good thickness on top of the foam does a wonderful job at keeping the temperature stable.

Instead of the electric wires look at water pipe type of underfloor heating. You might find an offcut available cheap for a small shed area. Then you can have a variety of heat sources to warm the water tank. You can embed the pipe in/under the 4in reinforced concrete without wasting thickness on a low strength screed.

Would you be bolting down machinery? as a pillar drill or a pedestal grinder defiantly need bolting to the floor which possibly could damaged under floor heating. I would think at least 150mm steel reinforced and fiber mixed concrete would be my minimum. I have a wall mounted electric heater and a dehumidifier which makes it warm and dry in my workshop.

David

Edited By David George 1 on 07/02/2022 07:55:53

I have 100mm rigid insulating foam in all the walls and roof. The base is reinforced concrete then a thin underfloor insulating foam and chipboard flooring on top of that. I initially heat it with a small fan heater that takes the chill off then if I am using machinery for a few hours the heat from the machines maintains the temperature.

The most important thing in cold weather is warm socks to keep comfortable, the warm air tends to rise

Martin C

I found underfloor heating in a work area to be punishing on my feet and ankles, this was an aircraft hangar and we were in there for a full working day, every day, the underfloor heat makes your feet sweat and ache. I wasn’t alone in complaining about the problem almost everyone who worked in there felt the same. I wouldn’t by choice work again in an area with underfloor heating. With the problems already highlighted with bolting down machines I would go for heating above ground level, if the workshop is well insulated then a small oil filled radiator will work fine, that’s all I have in my workshop, which is well insulated, and I leave it on overnight on a low setting and it keeps the temperature to about 10 degrees, when I am working in there I crank up the thermostat to an acceptable level, this radiator is used in conjunction with a dehumidifier. Dave W

Current building regs go along the lines of this:-

Add reinforcing mesh to concrete slab for extra load bearing. Infill layer would be hardcore with a sand blinding on top. Heating if required in the top screed. If machines need fixing to floor heating element position needs careful planning.

John

Insulation is most important. Mine has at least 100mm on all sides and top - but not the floor. It would, if it was poured these days, but not 30 years ago as a base for a garage.

Electricity is the most expensive energy source for thermal energy - unless you can generate your own using PV or wind - or use a cheap night-time tariff. I have just installed a chinese diesel hot air heater and it is cheap to run. Ignoring the ridiculously hyped-up claims by the suppliers, they do the job.

We have no details of electrical loads, TOU, etc. My little “claimed” 5kW heater is far more than I need in my workshop, except, perhaps, heating it quickly from a close-to-zero Celsius start. Machines remain cold, lagging far behind air temperature, mind. Once up to workable temp my workshop needs , I would say, likely less than a kW to maintain a reasonable working environment under most conditions.

What about those proper workshop mats, sited where you stand?

Those diesel heaters mentioned are good, got a couple of mates happy with those, thinking of getting one myself . There were problems when the exhaust was lengthened, so becareful there.

Pete

I have a chinese diesel heater in an insulated garage 20 ft * 12 ft * average 9 ft high & I find it next to useless. I have to use a calor gas radiant heater to suplement it & i find the gas heater far more effective & cheaper. The chinese thing uses lots of fuel ( cost seems to be running double calor gas) & I have tried different temp settings. Having to run it off 12 volts is an issue as well as I have to have a battery charger on the battery at the same time, otherwise the battery goes flat in a short time -

When I had my Joinery works, one of the buildings had 15 electric radiant heaters aimed at each work station. They were very effective & the workforce had no complaints. However, electricity was cheaper then, so I am not sure how they would stack up now with one each aimed at the lathe, mill & work bench.

The wife pays the bills so it might be a massive no no.

As for under floor heating, one only needs to decide where one wants the machinery, Omit the insulation & fill that part in with concrete. There is no point in heating a machine so go round it. . No need to put it under side benches if you are going to stack boxes & tool chests there either. One needs to plan the layout first.

Edited By Sam Longley 1 on 07/02/2022 11:19:32

I have electric element underfloor heating in a bathroom floor. The element is in the floor set in the adhesive. With a second layer of adhesive over the top for the tiles as per manufacturers instructions. It takes at least 8 hours to feel any heat in the tiles. God knows how long to heat through a 50mm screed. The floor is meant to be permanently on. If you use a programmer it will be full on when timed on and at 80% when off.

If it fails then nothing you can do except change a thermostat. If electricity prices continue to rise I guarantee you will put another form of heating in there. Wet heating pipes differ in that they use a special conductive concrete screed which allows the heat through

Brian

When installing, one is advised to follow the Webasto or Eberspacher installation details as pipe/duct sizes are important. The chinese instructions often leave a great deal to be desired - either factually, or language problems.

The Eberspacher manual can be found at:

**LINK**

132 pages, of which few are relevant to a simple installation but, nevertheless, useful for those that want to be sure they install the heater correctly.

The advantages of these heaters are: No water vapour is produced, or introduced, within the area heated. They do not need draughts to be sure of proper combustion (ie they are can be completely draught-proofed - my workshop is such, with no windows. Minimum fuel delivery (152ml/h) soon gets my workshop to a reasonable temperature for working, even if the machine temperatures lag behind. Full-chat would soon have been simply too hot in a short time.

I suspect that Sam’s garage is neither fully insulated nor draught-proofed. Also he may be procuring his fuel at inflated cost. He might be drawing in cold air from outside, for all we know.

Gross energy cost for gas oil is currently about 7p/kWh tops? (mine is currently a lot lower than that🙂 ) - unless bought in inappropriate volumes from convenience sources.

I run mine from the mains (practically). The 12 volt battery (needed as the power supply in case there is a power cut) is simply float charged from a lidl battery charger. My battery returns to ‘float’ charge only a few minutes after the heater is turned off, even though the controller is a permanent draw. Electricity draw is, I believe, 36-40W at full output but only around 12-15W at minimum fuelling.

I have 75mm insulation in walls, a lot in the roof, and 25mm under the floor. A 2kw gas balanced flue heater is more than adequate, warms up quickly then turn it down to 1kw.

my workshop has 3 to 4 inch concrete floor (no reinforcing) laid on a foot of rubble, with a membrane in between,then 18mm shuttering ply with top layer of 18 mm chipboard,ordinary diy quality. No problems with cold feet and the floor supports a 6 inch Colchester,and in the past has supported a 35 cwt turret mill. In cases with large long bed lathes ie 7.5 ch eg colchester triumph I would use in future 6 to 8 ins of reinforced concrete,and the lathe directly mounted on the concrete,as over a year the concrete will move depending on ground conditions ,my triumph was mounted on 4 ins on concrete over a 9 inches of crushed concrete and the movement in the ground conditions did affect the accuracy,it has now departed as I have got to old as a big lathe can be hard work.If I want my workshop warm I use a 3 kw fan heater,the walls and ceiling are insulated and windows are old double glazing

That is about as cheap, per kWh, as one can get at the moment, short of home renewable generation. Combustion air from outside and inlet air to the combustion chamber preheated by the exhaust gases. No water vapour from a fuel burning in the heated area.

That would cost me 5p/h at 1kW (assuming 80% efficiency) whereas an electric fan heater would cost me over 25p/h during the day. No contest!

Thankyou for the link, these heaters are getting some good reports, will be getting one fitted and runner for next winter. Apparently there is quite alot of information on Utube, as usual.