I’m planning a freestanding 24′ x 30′ shop to be built this spring. I’ve had several builders say that a “monolithic” or Alaskan slab is normal, and OK to use here in NH, vs. footings that go below the frost line like on my garage attached to my house. Apparently code allows it, and it is cheaper – the building/slab would “float”, is the best way to describe it. Should I be concerned enough to go with a foundation at significantly higher expense? I’d rather use the $ on the shop, if you know what I mean.
Also, my current garage floor gets very damp when it’s wet out. I assume I should look to have plastic sheeting and maybe foam insulation put under the concrete ( I will be heating with a propane unit heater) of the new shop (garage building, basically).
Appreciate any input from anyones that’s been there.
Replies
Over the long term a 4' frostwall will pay for itself, I have friends in N Conway who went with a monlythic slab, and ifailed the first winter. Ground frost anywhere in Nh can go 3-4' easily, any winter. You will also have the opportunity to install dranage around the foundation, so it won't be so damp.
Good Luck
If you post your question over at breaktime they will have a lot of suggestions for your proposed design. Definitely use plastic and insulation for the slab.
J.P.
I've built numerous buildings, much larger than yours, on monolithic slabs here in Maine. We use fiber reinforced concrete, a thick perimeter and pay careful attention to elevations and drainage. I'd recommend applying a concrete sealer. Poly will get poked full of holes during the pour. Propane heaters put a lot of moisture in the air. If your current floor sweats a lot, you probably have poor soil underneath and bad drainage. A good base of compacted, crushed gravel should solve the issue. You don't want to build in a low spot, make sure water drains away from the site.
Beat it to fit / Paint it to match
i have a basement shop and i got very tired of the cold concrete floor, not to mention after a few hours of work, your bones feel it.
i put down a product called delta flooring, which is like a sheet of extruded plastic about 1/2 thick, and i then covered that with 3/4 t&g plywood. the delta flooring did a couple things, acts as a vapor barrier, if the basement ever got a small amout of water it would not ruin anything, and it provided a cushion. with the ply on top it can handle moving of machines no problem, and a is a real pleasure to work on all day. i got the idea from a product named dri-core that I saw at the depot. lastly i painted the floor with a latex floor paint which 1 year into it is fine. makes sweeping easier too!
i did the whole basement which included a rec room, and i tell ya, the flooring alone makes it a very comfortable room to be in. the floor stays warm enough to lay down on, and i don't have that cold dampness of a basement either. wish i put it down in the beginging.
hope it helps
I just noticed your post so I guess I'm a day late but I hope not a dollar short. I think your floor idea is just what I have looking for. Where did you get the Delta flooring underlayment and how do you keep the plywood joint from separating if the floor is floating. I like the idea of no sleepers and foam but how do you attach it to the floor?
The delta flooring is not by Delta woodworking machines. It is just a brand name for the flooring. I bought mine at JTs lumber in North Kingstown, RI. But you can do a net search for your nearest distributor.
To be more specific about the plywood, I used Advantec plywood t&g, it is like a chip board and comes with a fifty year warranty against delaminating. About $50.00 per sheet. 3/4 " thick. I laid that down and then used liquid nails to glue the seams. Where the 4' sections met, i biscuted just for added strength. I drew the sheets tight together by screwing scraps on each edge of the meeting sheets and used wooden clamps to really get the seam tight. let that sit abit and done with that seam. For the seams where i roll the heavy machines around on, i also added some pocket screws too. The floor just floats. Definetly leave at least a 1/2 " from all walls to allow for expansion-contraction.
I rolled on three HEAVEY coats of latex (becuase i got cheap at the end and I love water cleanup) and let cure. Sweeps very easy now too. MERRY CHRISTMAS TOO!!
Joe,
Thanks for the information. I had an idea that you used construction adhesive on the joints. I even considered narrow crown staples in addition to the adhesive. I went to Lowes today and asked about your floor design and they had no clue. I'll try to find the products locally (Ann Arbor, MI) or look online for distributors. Thanks again for all your help. I hope you and your family have a MERRY CHRISTMAS!
I have a 24 x 32 shop on a monolithic slab. I have one substantial issue with the whole thing. The roof pitch on my shop is 12 - 12 and when it rains the water comes down fast. This is ok on the back of the shop where the grade is down, but on the front where the side walk is, water bounces of the sidewalk to the siding, seeps down and under the floor plate. I have added gutters, and that has helped a lot, but I still see a little seepage when it rains very hard. My only suggestion is to make sure the slab is above grade (3 to 4 inches) and if you do have a walkway it is below the slab as well.
I gotta agree with Hammer on the issue of the poly sheeting - finishers don't like it 'cause it inhibits drainage of excess mix water under the slab and most will poke holes in it intentionally. Concrete has to be a lot wetter than need be just to place and grade it. Thus you get what's called "bleed" water that has to go somewhere. With an essentially waterproof membrane directly under the slab, it comes to the top and you have to wait for it to evaporate.
In my humble yet closely held opinion, a much better vapor barrier is a 6" lift of either 3/4" drain rock or pea gravel. Pea gravel is a lot easier to handle and spread than the drain rock but I don't think it provides as good a capillary break as the 3/4" material.
By all means install at least 2" of polyiso (rigid) type foam insulation under the slab. That would be the minimum here in the NW where I live, you'd probably want more there in NH. If I were doing it (easy to spend your money -hahaha-) I'd put in the foundation wall well below the frost line for your area. I'd also add at least a 2" wide strip of the same under slab insulation all around the perimeter of the slab as a thermal break as well. While you're at it, put in some PEX tubing with the thought that some day you might want to set up a small heating boiler or even a hot water heater to provide heat to the cold concrete floor.
If you haven't considered it already, lay out your shop and get the positions of the major machines located so you can address power to those that sit out in the open. Specifically the table saw and any other piece of equipment you need to work around from all sides. Then have power brought under the slab so you won't have to have cords running across the floor presenting a traffic hazard.
Planning a shop is almost as much fun as working in one.
Almost.
A year ago last Oct. I had a 30" X 40' shop built. I had 135 yards of sand trucked in to get a 20" lift above grade. It's sitting on a monolithic slab and last year here in NW Wisconsin we had frost nearly 6' deep. Had absolutely no problem. There is a double layer of 1" PSF under the slab. I laid down tubing for inslab heat and then a 2' grid of 3/8" rebar was set down and then 5" of concrete was poured. I believe it's important to get that slab high enough so you get good drainage away from the building.
Go with the frost wall, foundation drain, crushed stone / poly / crushed stone below the slab. It wouldn't hurt to put 2" blue-board insulation below the slab either.
If you intend to pour this time of year, make sure use have blankets for the slab. Remember to saw construction joints when the concrete is still green.
Dave -Good advice on cutting the construction joints once the slab's poured and before it's gotten too well cured. Best the next day if possible. Few people realize how much concrete will shrink as it dries and cures out.Of course we only saw cut the top 1 - 2" to avoid cutting through the rebar and, if it's there, the in-floor tubing for slab heat! (grin)The rule of thumb in my area (Pacific Northwest of the states) is 20' in each direction as the maximum distance between construction joints. I pushed it to 24' for the width of my shop and fortunately haven't had much in the way of shrinkage cracks. But it's definitely something to keep in mind for the long dimensions of a rectangular slab.
Dennis
I'm a full time concrete contractor in the Chicago (Northern Illinois) area. Your advice is good, but a little off. If you're gonna cut green concrete, which is what we do in ALL commercial applications, you can do it with a soft-cut saw about 10 minutes after you're done finishing it. The sooner the better. Large slabs, if not finished correctly, or with an improperly packed base, can crack badly in the first 24 hours. Also, make sure you seal the concrete right after you cut it. It will slow down the curing process, and help the strength of the slab in the long run.
Also, in any slab situation where heavy machinery is going to be moved around, 20-24 feet between expansion joints/cut lines is way too much. We cut them into 12' squares. My shop is 36' X 45', and is a 3 x 4 grid, 2 cuts on the width, and 3 on the length.
Laying down poly does cause the water to go up, but that's a good thing, too. Takes longer to cure, but that's always better than fast curing concrete. Curing concrete creates heat, which causes internal stress cracks. And, if done correctly by a professional crew, there isn't that much water in the concrete anyway. I poured my slab with 4 of my guys, 5" thick, 22 yards of concrete, in 6 hours. Done, finished, cut and sealed. Any contractor worth his weight in salt doesn't want the ready mix to be too wet, cause they'll be there all day.
Just my .02.
Merry Christmas.
Jeff
Jeff -I would certainly defer to your expertise - mine is only second hand from being around concrete work, not in the actual doing of it. The recommendation of 20'max for control joints has to do with controlling shrinkage cracks moreso than weight distribution of support. But I can't help wondering .... why would a 12" grid of sawcuts be better for a floor subject to heavy machinery loads and movement?I would agree that keeping the slab as damp as possible as long as possible is a good thing. But most finishers I've worked around don't agree (grin). I just last week had a curb & gutter poured alongside my driveway while I had them order a bit extra mud with which to pour a few little projects around the garden. Unbeknownst to me, they'd called for 2% calcium in the mix. Of course my work was the last to come out of the truck. By the time I got a little 4' square pad placed and rodded off, bleed water was the last of my worries! (hahaha)
Dennis
Calcium??? I hate the stuff, never ever use it. Best way to ruin a slab.
Anyway, the 20' strike lines leave the possibility of cracking from any kind of movement, be it from heavy machinery, or mainly, from frost getting under the slab. Controlling the cracks in a straight line is far better than having them spider all over the place.
Oh, and by the way, I have no expertise in anything other than beer drinking, LOL.
Merry Christmas
Jeff
Can't say much about the way long terms of calcium - my shop slab's only been down 2 1/2 years but hasn't shown any effects from the 1% that was used. I see you're point about the close spacing of control joints but 1) there's little danger of frost under a slab in an occupied space here in WA state and 2) if my Unisaw cracks my 6" slab with 6x6/10-10 mesh accurately chaired in the middle of the slab, I've got more than a few stress cracks to worry about (grin).
Dennis
The effects of calcium in concrete are more evident in outdoor flatwork, especially stairs. The yellowing effect, and loss of top integrity over time are the biggest issues. There are liquid alternative additives which are newer (technology), and much better for the finish.
With regards to weight, I guess I was a little narrow minded with those remarks. My machinery in my shop is mostly industrial old woodworking stuff. My bandsaw weighs 2200 lbs., my planer about 3500 lbs., and jointer weighs about 1800 lbs.. I have to move them (rarely) with my bobcat with forklifts. The bobcat weights about 7500 lbs. Also, I take and pick up logs to and from the mill that are too large for me to cut with an International Dump Truck with a 16' dump bed, and I sometimes park that in the last stall of my shop. These items are just a wee bit heavier than my cabinet saw, also. (LOL)
Merry Christmas,
Jeff
<I poured my slab with 4 of my guys, 5" thick, 22 yards of concrete, in 6 hours. Done, finished, cut and sealed. Any contractor worth his weight in salt doesn't want the ready mix to be too wet, cause they'll be there all day.>Wow, Jeff, 81 yards here, 6 inches with rebar cages for the steel columns 4'x4'x4'...... They were there all day.....$29,000. That part was an insult but the shop sure is cool. aloha, mike
Mike
The key to large pours is having more 'finishers' on the job, and a very good and experienced Foreman to make sure everybody is doing there job quickly. Large jobs are broken into grids. The size of each section is determined by the equipment on hand. With "Handraulic" power, one finisher stays behind to finish the surface, and the laborers move on to the next section of the grid.
A good friend of mine is one of the largest concrete contractors in Chicago. That's saying quite a bit. He consistantly pours 200 to 300 cubic yards per day. He's so large, he has to order the concrete from 4 or 5 ready mix companies at the same time to get the volume on the job. It's pretty funny showing up on one of his jobsites, and there are 15 to 20 ready mix trucks waiting to unload. $$$$$$$$$$$$$$$$$$$$$$$$
Jeff
The concrete guys on my job said there are two hard (hehe) facts about concrete.
1.) It will get hard!
2.) It will crack!
And it did get hard and I do have a few spider web surface cracks.
Just my experience.
A bad day woodworking is better than a good day working -- yes, I'm retired!
Stumpy, I live in Hawaii and have a new shop almost finished. I have a clear span 51 X 49 slab with 4'x4'x4' steel cage footings under the columns and 6" slab. There is no frost here but machinery is heavy and with 12' walls I built for windload. What I am getting at is I dont want to do it again and that is the best advice I can give-make sure your building is adequate to the job you want it to do so you dont have to do redo it. aloha, mike
The other problem I have seen with mono-slabs is rotten lower wall plates from poor draining and/or grading issues. I have seen alot of these issues, they all could have been prevented, but IMO a foundation is the way to go
MikeD
I built a 24 x 34 shop using a slab on grade with built in beams around the perimeter. We do the same thing with single family homes that we build for our Habitat chapter. We're in central Wisconsin with all the freeze and thaw problems and the houses and my shop work out just fine. We intall two inches of foam under the slabs and use rebar to reinforce the perimeter beams and wire mesh installed to reinforce the slab. I should add that we put down some poly under the whole thing do keep out the dampness.
In my shop, I installed 2 x 6 treated stringers with 16" centers covered with 3/4" plywood so I could put the air filter collectors and some of the electric wiring under the floor. So far, everything is working as I hoped it would.
If I can get up the ambition to learn to use my wife's digital camera, I'll post some pictures of the shop. I love it. I can disappear into it, I don't have to sweep every time I use it, and, if the tools and material aren't always put away neatly, no one cares.
Edited 12/13/2005 9:02 pm ET by donshop
Stumpy
Been there done that. Go with foundation and crawl space, and wood floor. A little more expencive but well worth the extra. I have a DC system with pvc pipi under the floor and out the side to my DC. The wood floor is easer on these tired old leggs.
DusterBuster
Dusty, Good call on the wood floor. Its like night and day on the knees and I'm only 38. I used 1-1/2 tg maple flooring I bought from the classifieds, It was supposed to be used in a fabric mill in 1935. it was in storage in the building for all these years banded and straight as an arrow.Beleive it or not I paid 50 cents a sq ft. Its nice stuff.
-Lou
Good job enjoy.
I've seen that you have gotten a lot of advice on your "potential" concrete slab. Hope you don't mind one more opinion...
I'm in the concrete business. If you do go with a monolithic slab, you definately want to make sure there are control joints in your floor. The rule is... your joint spacing should not exceed three-times the floor's thickness (inches) in feet. If the floor is four inches thick, the control joint spacing should not exceed 12 (4 X 3) feet in either direction. Anything greater than that and you are tempting the "Crack Gods". If your subgrade is done properly, you shouldn't need rebar reinforcement for your shop. The floor will "float". Depending on your site conditions, poly may not be necessary. If you keep the subgrade dry, the concrete floor can never get wet. Draining water away during rain events is the best preventative method. Keep your floor above the water. If you do use poly, you should not place concrete directly on the plastic. Proper placement techniques prescribe putting poly over a properly compacted subgrade (pea gravel, crusher fines, etc.) then covering the poly with a bed of compacted sand (4-6 inches). The sand allows the bleed water of the concrete to be "wicked" into the sand. Most finishers never do this. This prevents all of the bleed water from having to go up. If you force the bleed water to the surface, you will likely end up with a poor finished surface prone to dusting and crazing (tiny cracks). Bleed water is increased as the slump of the concrete is increased. Slump is a measure of the concrete's workability. The stiffer the concrete, the lower the slump and vice versa. Most finishers prefer a high slump for ease of placement. If they make it too "wet", they will be lowering the compressive strength of the hardened concrete. If you order a 4000 psi, air-entrained mix, you will minimize the damage caused by finishers who dump a bunch of water in the truck to make it easy to place.
There's no question that wood is easier on your body than concrete, but a couple of anti-fatigue mats in front of your bench will take care of your feet and legs.
Good luck.
Stumpy, I use to work on a concrete floor "use to work"! I hated it. Living in the north east, the cold and the hardness of the floor would just kill my old feet. Getting older, I also don't hold on to things like I use to. Hone a fine cutting edge on a cutting tool, only to have it drop to the concrete floor, would just make me cry! I have just finished building a new attache shop/garage this summer. The shop floor is of 2 x 8 pressure treated construction, covered with presure treated 1/2" ply, and finished with 2 x 6 T&G yellow pine, upside down, I wanted a smooth surface. All wiring will run under the floor, and the DC will also be located under the floor. There is a three foot crawl space. There is no transional diffrence between the concrete parking space and the wood shop floor, allowing me to move equipment freely from one side to another, as projects increase in size. The concrete floor in insulated with radiant heat. It should keep the shop from freezing during the winter months. The wood floor is great, I don't mind seeing one of my wood cutting tool sticking up from the floor after it has been droped. I am very disapointed to find water in the crawl space this winter, I live on a side of a hill. Next spring or when the carwl space dries up, French drains go in along with some kind of rubber membrain glued to the foundation. I will be asking for some help from you guys later on this subject. Consider wood, it will allow greater flexability in the location of your equipment and electrical needs in the future, nothing remains the same!
Good luck Pop
Good info, I have worked on concrete a lot too, and built a new shop recently, and once again put in concrete. I thought very seriously about wood, and even went so far as pricing the job both with concrete and with wood, and the price difference was almost none. Concrete here in North Carolina is real high right now. The reason I did concrete is I want to keep my own cars up and need a place to work on them as needed, but other than that one reason, I would have done wood for the comfort and the lack of cold slab in the winter. I did buy a bunch of rubber mats that will help out some with my aging feet and knees, but nothing replaces a softer floor in a wood shop.
Hi Coop!
Yes, I went through the same thought process. But my fresh water well head was located right where I wanted the shop. I did think about those rubber matt's used in horse stalls, I have installed them once, as "Head Mucker". LOL I also wanted to get under the floor to install saw dust removel ducts and of course, wiring. That will be completed much later, as I want to work the shop for a few years, and let my equipment find their permanent spot, or not. Flexability is so important with small shops.
As you know, the parking area for WIFE, (concrete)13' wide, is at the same level of the wooden shop floor, makes expanding of the shop space very easy, and if I still need more room, I open the double garage door, and expaned even more into the carport, which is another 15' X 18 foot. I should send you a picture.
My problem now, is water! With the great advice I have gotten from this net, I think I will have a good fix, and will start that project when the ground dries out.
Take it easy and good luck Coop.....................Pop
I thought about my shop for months before actually starting it, and with equipment I figured my old shop was a good start for layout, but knew that this one would be different in some ways too. I put enough power outlets around that there is no shortage no matter where stuff goes, and the dust collection is figured so that very little of it actually had to go very far, hopefully it will work out ok. We have a carport to park on, but working on a broken down car in the cold on a carport wasn't for me, so that was why I went with the hard floor. I used to be a auto tech for a Ford dealer until about a year an a half ago, decided to work as an instructor for auto and work more on my wood stuff, so I can't get away from working on my own cars. After it was all done and too late to change anything, I figured out a way to make the floor wood and still be able to park on it, so now I wish I had a way of going back in time and redoing some of it. My wife says the next shop can be done that way, well, hopefully there won't be a next one. My shop is about a thousand square feet, which as I have seen isn't all that small compared to many. I'd like to see any pictures of shops anyone posts, I get ideas from every one I see, and when my shop is set up and going, hopefully will post some for you to see as well.
Hello Coop,
Well, wood floor, or concrete floor, you have your new shop, and that is great. A place of solitude, your area, your music, your noise, the smell of fresh cut lumber, what could be better, for me, warm and the noise of rain on the roof! We all need a place for our sanity, and maybe a cold beer while looking over the plans of the next project.
I tried to attached a few pictures, but I'm not all that skillful with this dang computer thing, as yet. If you have this attachment thing figured out maybe you could lend a hand?.....................Pop
I haven't figured out how to do the picture thing either. I tried last night on another post and didn't get it right. I know that there are some others that have it down pat, if they will be kind enough to lend a hand here, I know we would be very happy and thankful!!
Hey Coop, I say "Onward, through the fog"! Don't stop until you step on a nail!
I live in Toronto so we have similar winters. Slab on grade is ok. I would consider an in floor heating system,glycol based,this would reduce the moist air you get from propane heaters. Also once the slab heats up because of the huge thermal mass of the cocrete you can us less heat to keep it warm.
spiff,
When you say glycol based, do you mean a solution of water and glycol in coils of the concrete floor? If so, would you elaborate? I am building a new shop with a suspended concrete floor. The tubing is imbedded in the concrete for heating purposes, but I don't have a heat source yet. Since I have decided to not put the house on this heating system, I have wondered about freezing. The house uses methanol so I am wondering if glycol would be used for the same purpose and if so the advantages, disadvantages etc? Also, do you mean a compound of glycol like ethylene glycol( Prestone)?
Edited 1/21/2006 7:18 pm ET by tinkerer2
Edited 1/21/2006 7:18 pm ET by tinkerer2
The solution is just like prestone. The heat source can be a small electric or propane hot water heater with a small pump attached to circulate the solution. If your thinking of using this for your home then water is all you need. Many new homes are now moving in this direction, more even heat and cleaner air. If your interested in more info look into the forum section of fine home building.
I hope this helps.
Spiff,
I noticed on TOH that with their floor they had four zones....the reason being that heat loss is greatest near the outside walls. Perhaps a small manifold with appropriate valves attached to that water heater would save money and keep it more comfortable.
Whats TOH ?
spiff,
Sorry, TOH = This Old House....currently they are working on renovating a house in Cambridge, MA. and have the tubing in the floor for the heating.
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