New workshop project

[Retroanaconda]

It's about 25m from the closest accessible point.

Smallest available truck locally is a 6-wheeler, but it's still too high and wide to go down the side of the house. And the weight may be an issue for buried services under the drive. Using a dumper won't be a big issue - will take a bit of time but a hell of a lot faster than barrowing it.

Alas the reality of living in the Highlands is that things like mini-mix simply don't exist locally, the closest is Glasgow which is 100 miles away. There are a few normal concrete batching plants about but they all just offer the standard mix trucks.

[Arjan]

Easier to use a pump me thinks

 

[Blanco]

Beware that they do encourage anything that makes their own delivery quicker and simpler, they are naturally wary of small DIY jobs because the lories spend more time in general on site.

I really wouldn't be tempted on your sloping site to go without steel mesh, it helps insure against inconsistancies in the laying technique, almost inevitable unless you get in skilled labour.

If you have some choice of supplier in your location then do enquire what vehicles are available, I had a combination 6m³ mixer and pump wagon combined on my last big floor job, probably rare enough to find though. More common are the small lorries and the 'We mix-You lay' pan mixer tippers which would probably be more cost effective.

Lastly water, ... don't agree to extra water being added unless you have a genuine difficulty, some drivers are over keen to make their own job easy at your expense. Too much water can seriously damage the strength of your slab. Unless you are dealing with modern self levelling gypsum recipes and the like (which I presume you aren't) then water is your enemy. Same goes for washing out, think before hand where the lorry can wash down and make sure it is well away from anything important.

At the end of the day, the slab is the foundation, very difficult to re-visit and improve after the event, an extra £400 (guessing) on a pump lorry might seem like a lot but it will make the job so much easier, the pump operator will place the concrete precisely and quickly exactly where required and massively reduce the physical effortrequired from you/your team, leaving you free to concentrate on tamping and floating.

 

[Blanco]

Crossed posts, I did wonder how much choice there would be in supplier when I saw your location. If you do go the dumper route you don't necessarily need a big machine, but keep keep in mind the reduced stability of narrow track machines in the tipping phase, and don't be tempted to overfill. With a dryish mix you can still drive over the mesh and pull it up into the concrete as you go.

[Retroanaconda]

I think I've come to the same conclusion that I would rather have the mesh in than not. For the tiny extra cost it will add more strength to the slab.

After all that I had another call back from a concrete company who reckon I'm looking at around £500 for a day's pump hire including travel from Glasgow. That's about £1,000 less than the other quote I had and changes things completely - happy to spend that on making my life easier.

I'll check with them further, biggest issue will be getting space for the pump to sit on the drive in a location that will allow the mix truck in to feed it. I'm on a dead-end road so can't block it.

[Arjan]

Most serious concrete pumptrucks bring about 6 M3 and a 30 mtr. boom.

Looking at your floorplan, he'll need more time to set up his legs and unfold the boom than to pour..

Do not do this floor without netting / armour - you'll more than regret it.

 

[Gazzar]

Agreed, mesh is cheap and stops all manner of ills.

When I did mine the concrete finish ended up very rough, so I topped the slab with the self leveling compounds. The thing to look for is the compressive "strength" of the compound.

Avoid the latex stuff, it levels brilliantly but has no strength, I think the number is about 7.

You need at least 25, which is what good concrete is.

I used sika floor rapid 300, which is stronger than general purpose concrete and it has taken serious abuse. It does chip when big heavy pointy things are dropped on it, but I think that concrete would have been damaged more in the same circumstances.

 

One other thing, are you building your walls on the slab?

[Gazzar]

Forgot to say, the leveling compounds can be applied without expensive kit, I used a Lidl plaster mixer, two plastic trug buckets and a spiky roller on a long handle to do mine. 

[Retroanaconda]

The walls will be on the slab yes. Two courses of engineering brick and then timber walls on top.

[Gazzar]

One thing caught me out with my first workshop build was building on the slab, the rain runs down the wall to the slab, where it wicks into the building. I set the blocks in from the edge of the slab about 1/2 an inch, to fit in with the steelworks. This ledge allowed the rain to rest.

Mistake.

I fixed it by grinding off the lip and plastering/rendering the outside.

 

[Retroanaconda]

I won't have a ledge - the brickwork will be right up to the edge of the slab. The studs of the timber walls on top will be the same and then will have battens and cladding which will put the finished wall surface around 50mm further out, so the bottom piece of cladding will therefore drip rainwater down away from the slab directly onto the ground.

I'm hoping that the c. 150mm of exposed brickwork will not receive too much rain given the shelter from above, and that any it does get will not be sufficient to drive water through the mortar joints given it won't have a ledge to sit on. If I get issues I can always paint the blockwork and exposed part of the slab to seal it if needed.

That's the plan anyway!

[Gazzar]

That should work, my first workshop was quite exposed and the wind drove the water through the jointing.

[Retroanaconda]

A fun morning with a pick digging and removing seemingly endless amounts of slate leaves me with a nice deep trench for the cable duct. 

Once I’ve had a sparky round to okay it I’ll stick the duct in, backfill, compact and then can complete the preparations for pouring the slab. Slot the last bit of formwork in, fully peg it all and add some type 1 behind some more areas for further reinforcement. Then DPM and mesh.

This is the pile of bigger pieces of slate that came out of that trench. Should start my own quarry.

[Arjan]

May I suggest you put in a tube ?

Fit a "pull through cord" in them and putting in additional wiring in the future is  so much easier.....

Being Dutch etc. means we're a bit weird, but out here I have put in over 800 mtrs. of underground ducting (France has 5 x more lightning into the ground than Holland) and it makes life so much easier....

 

[Retroanaconda]

Proper twinwall cable duct all ready to go 👍🏻

[Arjan]

Well done !

[FridgeFreezer]

You don't need a sparky to OK your duct, only the wiring as far as I'm aware.

[Retroanaconda]

It’s only fair to let him see the trench first if I’m later asking him to pull a cable through a duct he hasn’t installed. There is no specified depth for external cables in the regulations, it’s down to a what is deemed appropriate by the installer and this depends on both the environment/risk to the cable and the soil type etc.

There’s no Part P here so I can do it all myself if I wanted to, but I’d rather have a pro do the hooking up into the house CU and then I’ll run all the circuits in the workshop itself.

[Cynic-al]

Do you need a tracer tape above the duct?

[Bowie69]

If outside of part P, then he doesn't *need* anything, but it is one of the more sensible things to do....

[Retroanaconda]

It still has to be in line with the regulations and building standards, even though the building is not big enough to require a formal building warrant (<30m²).

I've got buried cable warning tape and that will go in yes.

[jason110]

We alway bury stuff to 300mm deep unless on agricultural land then it’s 600mm deep. Bury with crushed slate or something 20mm to dust and then tape above that. 

[Retroanaconda]

Sparky said 500mm is plenty so I'll put the duct in and backfill it this weekend. A pump plus 7m³ of concrete is due next Wednesday morning, so will hopefully have time to get all the rest of the prep done in terms of reinforcement and DPM etc.

Expensive part of the build now, but hopefully worth it for a solid foundation. Unfortunately because I've dragged my feet over the summer we are now into frosty nights and so I will have to protect the slab for the first few days once it's poured. It would need protecting from rain/rabbits/cats anyway but I'll add some blankets as well as a tarp to keep the frost off.

[Gazzar]

Like you I missed the summer. This was when pouring the pads for the pillars of my workshop.

The night was a lot colder than I expected, so I heated engineering bricks in the oven, wrapped them with old dust sheets and put them under the frost covers. It did the trick.

Anything that holds heat will make a big difference.

[Retroanaconda]

Nearly ready, just the DPM and reinforcement to add tomorrow - weather permitting. I’ll pile a load of type 1 against the front section of shuttering as I can’t find a single area there where I can knock a stake in firmly or more than about 6”.

 

Needed to move the pile of waste slate out of the way so decided to pile it up behind the tallest part of the shuttering as extra mass to help stop it moving. It’s all braced quite heavily but better safe than sorry.