Advice in converting an outbuilding into a workshop

[public]

Hi all,

I am planning to convert a single-skinned, block-built outbuilding into a workshop. I have read many other posts about this type of project, and know roughly what I need to do, but I have a few specific questions:

1) The building has a rough concrete floor, which I plan to raise slightly (about 5cm), and level off. I need about 0.5 m^3 of concrete. How do I convert this volume into the required bags of concrete, sand and ballast? Are there tables anywhere that I can use?

2) I notice that cement is sold in 25kg bags, but sand and ballast are typically sold in `bags', or `jumbo bags' (big canvas things), with no indication of their weight/volume. If I am ordering material to mix concrete in a specific ratio (e.g., 1:3:6) do I use `bags', or do I have to convert a sand `bag' into the appropriate weight to match the cement weighy, and order by that quantity instead? Is a `jumbo bag' a specific number of `bags'?

3) I am going to dry-line the walls. I have seen two different approaches to putting in the membrane: some people state that it should be placed next to the wall, underneath the battens, and others state that it should go between the battens and the facing material. Which is correct, or should different methods be used for different purposes?

4) Facing material seems to be sold in widths of 600mm, or 1200mm. If I use 3x2 battens, fastened at 600mm centres, then the gap between the battens is about 520mm. I'm curious as to why insulation material isn't sold in these widths, at least for common batten sizes?

5) Insulation: should I use mineral wool, or polystyrene? I haven't been able to find any meaningful comparisons, so what factors determine which is the better option?

thanks,

dan.

[public]

Hi all,

I am planning to convert a single-skinned, block-built outbuilding into a workshop. I have read many other posts about this type of project, and know roughly what I need to do, but I have a few specific questions:

1) The building has a rough concrete floor, which I plan to raise slightly (about 5cm), and level off. I need about 0.5 m^3 of concrete. How do I convert this volume into the required bags of concrete, sand and ballast? Are there tables anywhere that I can use?

2) I notice that cement is sold in 25kg bags, but sand and ballast are typically sold in `bags', or `jumbo bags' (big canvas things), with no indication of their weight/volume. If I am ordering material to mix concrete in a specific ratio (e.g., 1:3:6) do I use `bags', or do I have to convert a sand `bag' into the appropriate weight to match the cement weight, and order by that quantity instead? Is a `jumbo bag' a specific number of `bags'?

3) I am going to dry-line the walls. I have seen two different approaches to putting in the membrane: some people state that it should be placed next to the wall, underneath the battens, and others state that it should go between the battens and the facing material. Which is correct, or should different methods be used for different purposes?

4) Facing material seems to be sold in widths of 600mm, or 1200mm. If I use 3x2 battens, fastened at 600mm centres, then the gap between the battens is about 520mm. I'm curious as to why insulation material isn't sold in these widths, at least for common batten sizes?

5) Insulation: should I use mineral wool, or polystyrene? I haven't been able to find any meaningful comparisons, so what factors determine which is the better option?

thanks,

dan.

[The Natural Philosopher]

Itds about 3 tons per cube meter so thats very close to a ton of ballast.. Mm. probably half in half sand and gravel..and I used to find that a tin bag of sand took about 6 bags of cement to make into a fairly weak mortar..so 6 bags of cement should do it. They aren't so bad - you can always nip down the BM and get another one, but tonne bags of ballast come delivered on 30 ton trucks..

Are you putting a DPM under the new concrete? Or insulation?

Is there a DPC in the blockwork already?

Big bags are 850kg - roughly a ton wet. Frankly if you are concreting that amount, get a 'ton bag' of sand and gravel both..

If you are insulating it ought to go on the inside of the studwork - simple is foil backed plasterboard. A breathable membrane on the outside of the studs is useful if there is any chance of holes in the outer structure with e.g. weatherboarding.

Normal studwork spacing is 400mm. Insulation never fits anyway due to different people using different stud widths. Accept it.

Never use poly in a wall. Its for under concrete use only IMHO.

Rock wool is cheap, but celotex (polyisocyanurate foam board) is better. However running cables/pipes with it is more painful.

[Roger]

The message from " [e-mail]" contains these words:

Concrete ratios are typically specified in terms of volume. 1:3:6 seems a bit thin to me but no doubt you have already taken advice on that.

Buying sand (and you want sharp sand for concrete) and gravel in tiny bags is a very expensive way of doing it. Loose is usually the cheapest but you need a good area to dump it on as it takes more room than a 1 tonne bag and if the surface isn't clean and solid you will have some waste.

FWIW 1 cubic yard of 1:2:4 concrete takes 0.231 tons of cement, 0.513 tons of sand and 0.933 tons of gravel. As this is a diy ng I will leave it to you to convert those figures from Imperial to metric. :-)

[Jerry]

bags of

Err no they don't, unless you meant 20, anything from a 5 ton truck up, although 12 ton is more common.

A 30 ton truck would be a tractor and (medium weight) trailer unit, how many BM's use them for site delivery, although direct deliveries of brick and block work often do.

[The Natural Philosopher]

Mine do :-) Massive great things..I agree they only use the artics for the biggest stuff though..but my 20 tons of gravel didn't come in either a 20 tonne trick OR an artic either. ISTR the tipper had 6 or 8 sets of wheels of which at least two sets were steerable and at least one set were double..

I wish he had come back after I had raked it all out and helped smack it down..

>

[John Rumm]

for the concrete calculators.

The jumbo bags are notionally 1 tonne - but it does depend on the water content. They may contain as little as 800kg, especially if the stuff is very dry.

Mix by volume.... buckets / spades full etc.

Against the wall will save you needing to pierce it ever flush socket box etc.

If you speak to a insulation board supplier you will find that there are many standard sizes available - some designed with exactly this in mind. Note however that unless you insert the insulation as you go you will innevitibly need to do some cutting to make it fit.

Best material is a ridgid PIR foam like celotex or kingspan. PIR foam will give you more insulation for a given thickness than just about any other type. Next would be ridgid polystyrene, semi ridgid rockwoll batts, then at the least desireable end things like fibreglass wool / rockwool.

See

[chris French]

I would avoid expanded polystyrene in this context as any electrical cable run through it etc. would need protecting from it.

[Jerry]

purposes?

socket

It will also save the stud work from damp.

[Jerry]

John

haven't

about any

wool /

electrical

Personally, as this is going to be a workshop, I would opt for surface conduit and or Trunking - makes later alterations far more simple when you need that extra socket or machine supply.

[The Natural Philosopher]

I would say no. If foil backed plasterboard is used, hacking out a section, laying cables using coathangers etc and replacing, making good and painting is VERY quick.

And leaves the walls free to hang cupboards etc.

[Jerry]

more

I would say that drilling a hole in trunking either mounting a socket or dropping a length of conduit is even quicker - installing a new cable or altering an existing cable is certainly quicker. As for leaving the walls clear, that all depends of how you design the installation, trunking / conduit can be mounted above bench level but below cupboard height.

[Peter Parry]

Depending on what the workshop will be used for you might want to consider plywood flooring on top of PIR foam - much kinder on the feet :-).

[public]

Hi all,

Thanks for all your responses.

There is no DPC that I am aware of. I am going to put a membrane down under the concrete, and extend it up the walls. If I use a single sheet, then I am going to get lots of excess in the corners. If I cut the excess away, then what should I use to waterproof the resulting joints? IS having an overlap sufficient, or must the joints be sealed?

I agree that plywood flooring on foam is better under foot, but I want a solid base to which to bolt my metal-working lathe.

thanks once again,

dan.

[The Natural Philosopher]

No. What A DPC does is to make it harder, not impossible, for water to get past. The natural evaporation can take care of any that seeps through.

I am concerned though that the exterior walls are not DPC'ed.

I'd be inclined to line the bottom few feet of the whole thing with DPM before studding out. And use a big overlap running under the concrete.

That way any 'rising damp' in the walls will have to rise a fair way - with the chance of evaporating away first - before it gets to any wood work

Proper workshop I see.

[Andrew Gabriel]

You don't cut the excess away. You fold the corners so it's still sealed. The weight of the concrete pour also helps push it back to whatever is retaining the concrete, but I suggest creasing it deliberately to fold in the right places. Cut the excess off neatly after the concrete has set, if you want to.

BTW, only 5cm thickness on a plastic membrane which isn't going to stick to it sounds a bit dicey to me. I would probably look for one of the paint-on moisture barriers in that case.

[Phil L]

What area is it covering? - if you've worked it out at half a cube that makes the total floor area only 10m2 @ 50mm thick...

There's too may 'bags' in this paragraph to make sense - if you intend using a 1:3:6 ratio, then the 1 is the cement (25kg) the sand will be 75kg and the stone 150kg If you do only require half a metre and you intend putting it down only 50mm thick it will need more cement than this, also you'd be wise to use 10mm chippings, anything larger and you won't get a finish on it. If you have a cement mixer, you'd be better off putting in 3 X 25kg bags of stone, 2 bags of sand and a bag of cement. You'll probably need at least 6 mixes of this size to do half a metre3, meaning that you'll need 18 stone, 12 sand and six cement.