Right now I am looking at 50' x 75' x 18' double wall lumber construction. I have been checking out steel buildings, but not sure I can go that way. We use primarily propane for heating out here in the middle of ag country. I have been thinking 8" on 4" insulation with a water barrier over crushed rock. I like the idea of perforated drain pipe, I can embed that in the crushed rock base. And I will certainly be happy to post pictures when we get things rolling! Thank you gentlemen for all your help and ideas!!!
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Starting a new shop building
- Thread starter Roadhawg
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You definitely want a good layer of crushed rock for drainage. Do the crushed rock in 4" layers, compacted between layers. I did perf drain pipe around the perimeter (not under the slab). Set the drain tile below the depth of the crushed rock to keep groundwater from percolating. Remember, frost heaving is the biggest reason you'll get cracked concrete. Frost heaving requires water. Settling is the other enemy. No fill dirt under your slab, you want undisturbed soil, topsoil removed, capped with crushed rock. Basically no reasonable slab thickness is going to stop cracking if you have settling or frost heaving.
That said, on that size building, I'd want at least 6" of concrete, somewhere down the road a heavy fork lift may be in your building.
I have 7" of concrete (spec'd 6" min). I have several machines that weigh > 8000 lbs. I moved them in with a telehandler that weighed over 30,000 lbs. Concrete has held up fine so far.
That said, on that size building, I'd want at least 6" of concrete, somewhere down the road a heavy fork lift may be in your building.
I have 7" of concrete (spec'd 6" min). I have several machines that weigh > 8000 lbs. I moved them in with a telehandler that weighed over 30,000 lbs. Concrete has held up fine so far.
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I went with 6" in my shop. 4000psi mix with wire mesh throughout the whole pad and I added rebar in the pad where I knew my machines were going to go. My forklift weighs 10500 pounds and loaded moving machines in I have had no issues. Where I plan to put an HBM I dug it out so there is 10" of concrete there.
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Rigid foam insulation for under slabs is rated in pounds per square feet, and the stronger you think you need for concrete, the more rigid the foam - more rigidity means less R value... You can go overboard, and spend way more than you have to.
You have a loader that is x feet wide, that can carry a load of z pounds. The load on the front tires will be the load plus at least half the weight of the loader. for instance, if it can handle 2500 lb load and weighs 5000 pounds , and is 5 feet wide, I'd estimate a 5 foot by 10 foot loading zone, or 50 square feet. so for 5000 lbs (2500 plus half of 5000 lbs, you end up with 100 pounds per square foot.
To give yourself some head room specify 100-120 pounds per square foot foam, and specify the pad on to has to be reinforced for 150 pounds per square foot loading. You can do this for your lathe and mill, and determine your loading factor so they don't exceed your floor. Allow that 2 feet around your machine will also carry some of the load as the pad will flex just enough to distribute some of the weight.
I have a 3800 lb lathe on a 4" floor reinforced with mesh (not rebar - dang, but I wasn't there when it was built) and the floor has been fine for me. But I move everything by hand, so I don't have to account for the weight of a compact loader.
update: I just realized that my 4000lb milling machine has higher floor loading: about 180 lbs per square foot.
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If you do go with hydronic heat, another factor regarding concrete thickness is thermal mass. The more mass in the slab, the greater your thermal storage capacity.
Also, if you do hydronic floor heating, I recommend keeping a very accurate map of the routing of the PEX tubing before the concrete is poured. Accurate dimensions of the PEX layout, to datums that will be accessible in the finished building, would be very nice to have in case future alterations are desired (it's been known to happen). I only have a rough PEX plan from the original construction and I only trust it regarding concept (not dimensional accuracy). I must use an infrared temp sensor to search for PEX locations before planning any alterations. I schedule such surveys for hydronic system startup in the fall when the slab is coldest. God forbid I should want to drill or saw into the slab in the summer.
Another feature I wish my building had is a masonry pony wall (up to the office windows would be nice) supporting the framing of the exterior walls (rather than sills on slab). My building exterior is steel skinned right down to the slab so I have to be careful about keeping weed whackers away and make sure that soil and plant life are not impinging on the steel. If there was a masonry pony wall, with an insulating/decorative exterior treatment, I think it would be more robust than sill-on-slab. If it's applicable to you, a masonry pony wall also provides a non-flammable skirt in welding/fab areas.
Also, if you do hydronic floor heating, I recommend keeping a very accurate map of the routing of the PEX tubing before the concrete is poured. Accurate dimensions of the PEX layout, to datums that will be accessible in the finished building, would be very nice to have in case future alterations are desired (it's been known to happen). I only have a rough PEX plan from the original construction and I only trust it regarding concept (not dimensional accuracy). I must use an infrared temp sensor to search for PEX locations before planning any alterations. I schedule such surveys for hydronic system startup in the fall when the slab is coldest. God forbid I should want to drill or saw into the slab in the summer.
Another feature I wish my building had is a masonry pony wall (up to the office windows would be nice) supporting the framing of the exterior walls (rather than sills on slab). My building exterior is steel skinned right down to the slab so I have to be careful about keeping weed whackers away and make sure that soil and plant life are not impinging on the steel. If there was a masonry pony wall, with an insulating/decorative exterior treatment, I think it would be more robust than sill-on-slab. If it's applicable to you, a masonry pony wall also provides a non-flammable skirt in welding/fab areas.
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Many good suggestions here. I managed concrete placement in my younger years. Often on government jobs. Site prep. Remove all organic matter/top soil (as the organic matter rots it will leave voids!) Uniform support of the concrete is needed. If part of the slab is on sandy soil and the other part is on compacted clay, it is an invitation to crack. It takes quite a thick layer of compacted aggregate to function as an load spreader. Putting down a layer of 6mil poly will keep the moisture at bay. 6-6 x 10-10 welded wire as reinforcing is pretty much a waste of labor and money. Far better off with a 2' X 2' grid of #3 rebar (best to use a US made, graded bar rather than the import stuff from China.) Tie the bars at some of the places they cross and be sure they are supported near the center of the slab thickness on chairs.
Isolate the footings from the slab with expansion joint material. Insulate the footings to below freeze level. 3' around here. A layer of insulation can also be put around the perimeter under the slab. Be sure to dig the insulation layer into the dirt so the slab isn't thinner there.
Concrete mix varies by location. Use 28 day strength 4000psi mix. Do not add water on site! A 4" slump is easily worked but you will end up with stronger concrete using a 3" slump. If the ground is quite dry sprinkle with water just before the pour so the bottom layer of concrete doesn't loose moisture too quickly. Ideally use some method of consolidating the pour. A vibratory screed works OK on a 6" slab. Thicker pours will benefit from concrete vibrators. Do not over work the surface causing an all fines top layer. It will be weak and subject to spalling. You Must properly cure the concrete to end-up with the highest strength you can. As soon as the surface has been finished, cover it with plastic sheeting held down so the wind can't get under it. Leave it covered as long as you can. Week +. If the surface is allowed to dry too soon it will cause stress cracking. After initial set you can use burlap and sprinklers. Moisture must be present for the chemical reaction to set the concrete. Curing compound can be used but it may contain wax that will interfere with clear coats or paints. Remember design strength comes in 28 days. Be carful of heavy loads too soon.
Concrete shrinks as it sets, which will cause cracking. That's why control joints are used. Controlled cracking! Sawn joints work well. Do them soon after the initial set, next day? Go about 2" deep. The rest of the thickness will crack in a jagged manor leaving an interlocking surface. I don't like the plastic joints because of the chipping that always takes place along them. Tooled joints, well done, are Ok but they often leave excessively uneven surfaces or don't go deep enough to be effective. After full cure but before painting, wash down the slab with some dilute acid (HCL) that you can get from the concrete supplier or even the big box stores. It will get rid of the laitance (soft powdery surface) so the paint sticks better. If any oil has gotten into the surface, scrub with Trisodium phosphate or similar. Rinse well!
If you can, figure out the locations where your heavy loads (machines) will be and try to not sit the machine over a joint. Joints may move, messing up that perfect leveling job you've done.
There are a lot of concrete contractors that don't know how to do it correctly. Just because they've poured a million yards of concrete doesn't mean they know the correct methods. The Portland Cement Association has excellent information available. In my area they put on training events about once a year. They are usually sponsored by the major ready mix companies and include tours of the plant, casting facilities etc. Free to the trade around here.
Isolate the footings from the slab with expansion joint material. Insulate the footings to below freeze level. 3' around here. A layer of insulation can also be put around the perimeter under the slab. Be sure to dig the insulation layer into the dirt so the slab isn't thinner there.
Concrete mix varies by location. Use 28 day strength 4000psi mix. Do not add water on site! A 4" slump is easily worked but you will end up with stronger concrete using a 3" slump. If the ground is quite dry sprinkle with water just before the pour so the bottom layer of concrete doesn't loose moisture too quickly. Ideally use some method of consolidating the pour. A vibratory screed works OK on a 6" slab. Thicker pours will benefit from concrete vibrators. Do not over work the surface causing an all fines top layer. It will be weak and subject to spalling. You Must properly cure the concrete to end-up with the highest strength you can. As soon as the surface has been finished, cover it with plastic sheeting held down so the wind can't get under it. Leave it covered as long as you can. Week +. If the surface is allowed to dry too soon it will cause stress cracking. After initial set you can use burlap and sprinklers. Moisture must be present for the chemical reaction to set the concrete. Curing compound can be used but it may contain wax that will interfere with clear coats or paints. Remember design strength comes in 28 days. Be carful of heavy loads too soon.
Concrete shrinks as it sets, which will cause cracking. That's why control joints are used. Controlled cracking! Sawn joints work well. Do them soon after the initial set, next day? Go about 2" deep. The rest of the thickness will crack in a jagged manor leaving an interlocking surface. I don't like the plastic joints because of the chipping that always takes place along them. Tooled joints, well done, are Ok but they often leave excessively uneven surfaces or don't go deep enough to be effective. After full cure but before painting, wash down the slab with some dilute acid (HCL) that you can get from the concrete supplier or even the big box stores. It will get rid of the laitance (soft powdery surface) so the paint sticks better. If any oil has gotten into the surface, scrub with Trisodium phosphate or similar. Rinse well!
If you can, figure out the locations where your heavy loads (machines) will be and try to not sit the machine over a joint. Joints may move, messing up that perfect leveling job you've done.
There are a lot of concrete contractors that don't know how to do it correctly. Just because they've poured a million yards of concrete doesn't mean they know the correct methods. The Portland Cement Association has excellent information available. In my area they put on training events about once a year. They are usually sponsored by the major ready mix companies and include tours of the plant, casting facilities etc. Free to the trade around here.
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yes!!
Yes -in fact everything @Larry$ says +1!! I've seen every downside that he outlines on job sites. It is appalling how uneducated some concrete contractors can be...
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My shop takes up 40' x 32' of a 40' x 56' x 10' pole barn. I have 8" batts in the walls and 12" in the ceiling. My floor is 5" of concrete with no foam underneath. For heat, I have a Mr. Heater MAXX overhead propane heater. I have a Google Nest for a thermostat which lets me turn it on/off from my phone. I leave the thermostat off but it maintains a safety temperature of 40 F. The heater kicks on to maintain that minimum. I would have preferred being able to program the thermostat to maintain 40 F, and manually bump up the temp to 55 F when I head into the shop. On a temporary change, the Nest reverts back to its program at the next programmed temp setting. My logic was if I bumped the temp up to 55 F and forgot to set it back to 40 F, the thermostat would do it for me. Unfortunately, my Google Nest will only allow program temps down to a low of 55 F. Anyway, I usually go through 150-200 gallons of propane through the winter (at $2.60/ gallon in MI this year or ~$500). There's a thread below with my install that goes into my typical "ad nauseum" details.
Bruce
www.hobby-machinist.com
Bruce
Shop Heating
I use a 150000 btu space heater in my pole building when I have to go out in the winter. I also have an infrared heater over my work bench. The space heater is noisy and it raises the temperature so fast everything will start to sweat without the ceiling fans on. I'd prefer to have all infrared...
www.hobby-machinist.com
Gentlemen, thank you all so much, this is a great deal of information and I appreciate all the responses! Clearly I have a great deal of planning to do and I want to get it right! I never thought I would be in a position to build a new workshop, so I want to make sure I plan everything out and get as much as I can afford.
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Please do your research.. putting any coating on concrete should not be done for quite a few years. What happens is the moisture will be leaching out for a long time, and the salts in the concrete will leach too. It will pick up any finish... What you need is time.. and sometimes 20 years is not enough if there is moisture under the concrete or it's able to get in... even or especially if you put down plastic under. That can go both ways. It can help keep new moisture from getting in, or it can trap moisture.. it all depends on your env. If you build the garage elevated and on rock, it will hopefully dry out.
I love a sealed floor, but you need to know before you spend time and money on sealing it. If you lived in AZ desert, you certainly would have a much easier choice to make , after it fully cured. I have seen a good many great seals, and too many poor seals. You may still elect to do it, but at least you'll understand what may happen, and not blame the product or the contractors who poured, or installed anything.