- This topic has 5 replies, 4 voices, and was last updated 4 years, 9 months ago by harry wheeler.
30 August 2018 at 4:50 pm #550775
I’m moving soon and hope to build a new workshop.
I’m currently working from a shed which sits on a frame directly onto my concrete patio.
My new workshop base will have to hold a bandsaw and lathe as well as my bench.
Here in the UK the common solution is to lay a concrete block, having dug a pit and lined it with sand, put a damp proofing membrane down and then pour concrete on. Then maybe build a low brick wall and stick the walls onto the brickwork.
I suppose this has the advantage of being strong and weed resistant. However, laying the concrete etc isn’t something I’m experienced at and it looks like a palaver.
Most of the US based shed builds use either concrete piers or railway sleeper sized posts laid onto the ground or shingle and then a wood frame buit onto this. It seems to make sense and is a whole lot easier looking.
Is such a floor capable of taking the weight of machinery? can you insulate it? What about damp and weeds on the underside, is this an issue?
Anyone have experience of this?
I am based in the US and yes it is easier here then say the UK or Australia I lived there for 15 years. If you are wanting to put pavers down as opposed concrete, it can be done. Here is what I did in Australia. I put 2ft by 2ft concrete blocks down. I had machines on top of them. What I do suggest is you put down black plastic first use as thick as you can I used 20Miles thick. You do want to make sure the ground is level that is very important. I am sure you can get what they call dead sand to put down as well that will form a very hard base to put your blocks on. Concrete is not that hard either build a form and mix it up and pour it in sir that is it. I hope I helped.. All the best with the new shop.30 August 2018 at 7:35 pm #550784
A concrete foundation may very well make for the easiest remaining construction. That was what I was told when planning to add a bathroom to our croft (early 19th century).
It might be a good idea to dig channels for electricity, and definitely for rain drainage.
To protect against ground frost, I added a 200 mm thick layer of styrofoam sheets, held together by brackets, on top of the moisture proof. To prevent the concrete from fracturing, I then laid out iron armour nets, spaced by distancers. I used ordinary construction wood with plenty of supporting pegs to keep the mould set while the concrete burned.
Finding concrete was surprisingly easy. It seems that at the end of the day concrete lorries usually have some left, tumbling around, and the company I contacted was happy to, at no cost, discharge it directly into my mould form.
London, UK; Boston, MA30 August 2018 at 9:43 pm #550788
Hello Rowly, as Rich said, one possible solution is a sand bed with concrete or walk stones or laid on top of it. That is a possible solution for the walk surface but you still have to build the structure and that can take many forms from pole barn construction to a full fledged conventional framed structure to a prefabricated steel building. It would be pointless to anchor any of these to walk stones. Some type of solid connection to mother earth is necessary to resist wind loads and that can be poles in the ground, CMU’s laid on top of a concrete footer or a monolithic pad/footer which is pretty common in the southern US where frost levels are shallow.
Having been a general contractor, I would prefer a poured concrete solution and that isn’t usually hard for a contractor to do. A couple of tips if you go that way though. Concrete should be poured over a gravel bed about 4″ to 6″ thick with a vapor barrier (20 mil polypropylene sheet) on top of the gravel. The gravel acts like a french drain. No form of insulation is needed nor will it really do anything. You can do the forming and gravel spreading yourself. Unless you’ve done it before, I don’t recommend trying to finish lay and finish the concrete yourself. Hire a professional for that. As Sven-Olof points out, concrete suppliers usually have excess material in their trucks that they are more than willing to dispose of but it would be hard to find enough surplus for an entire pour. A 20’x20′ slab will need about 5 yards of concrete and that’s a little over 1/2 a truck load. If you try to do it in multiple pours, you would need to break the pad into sections with expansion joints to avoid having cold joints in the finished floor. Left over concrete can be difficult (maybe impossible) to work with because it’s been in the truck so long. Even expert finishers cringe at the thought of trying to deal with it.
If you decide to build a wood floor just be sure that it has some clearance to the ground, cover the ground with a vapor barrier and any wood touching masonry has to be treated lumber. Insulation can be put in if there is enough room under the floor to work but it really won’t be of much help as long as a vapor barrier is put down and the crawl space is ventilated. Load wise, a properly designed wood floor would have no problem with the weight of the machines we use if it has the equivalent of a 3/4″ subfloor with a 3/4″ hardwood walk surface laid perpendicular to the joists. Cost wise, a wood floor would be the most expensive option though. And don’t worry about weeds – worry about termites. Be sure the ground has been treated before any concrete is poured. Hope that helps.
Harry31 August 2018 at 7:32 am #550792
Rich, Sven-Olof and Harry,
All good, encouraging advice, thanks. It looks like I will go down concrete base route, particularly as the mix could come from a lorry (It may even equal the cost but I had read that a company may not deliver small quantities- you have put that to bed).
What is the frost line? I can’t work out wether it’s a thing here in the UK, Harry as you say most instructions say to pour 4 inches or so.
Rowly31 August 2018 at 12:15 pm #550799
The frost line is the maximum depth the ground will freeze in a particular area or region and there may not be one where you are if the ground never freezes Rowly. Check with your local building codes officials and they can tell you. And yes, 4″ is a normal thickness for a concrete pad. Sven-Olof gave some good advice for steel reinforcing wire that I would agree with. It helps prevent cracking. If you make the perimeter of the slab thicker, say 12″ or so deep and about 12″ wide that forms an integral footer. You can anchor your walls directly to a slab made like that and be certain it will support the weight of the structure but you have to make wood forms for the perimeter. That’s no big deal to do. You can lay concrete blocks (CMU’s) on a conventional footer if you like and let them be the form for the slab. Lots of ways to do it. Good luck!
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