Cutting concrete blocks

[David WE Roberts]

Getting closer to wall building time now the weather has warmed up a bit; if only it would stop raining!

I will obviously need to cut concrete blocks - I will be using the 'medium density' blocks for external walls with no rendering. [At least I think the normal ones are described as 'medium density' - it does beg the question as to what 'dense' blocks are.]

I see there are some hand saws to cut blocks although most (but not all) of them say they are for lightweight blocks. I have some difficulty visualising cutting the 'medium density' concrete blocks with a hand saw. Is this practical?

Using Google I have seen various descriptions of block cutting methods. Scoring with a cold chisel all round the block seems to be a very slow way. Is scoring all the way round with a small angle grinder a good way to prepare blocks for cutting?

The alternative seems to be the huge and nasty looking stone cutters you see builders using. These look expensive and potentially dangerous. Are these necessary or are there better ways?

I intend to use stretcher bond to build single block walls but will obviously have to cut blocks to fit in doors and windows and also where the wall length is not divisible by the block length.

TIA

Dave R

[NT]

not a hope in hell. Use an angle grinder.

NT

[David WE Roberts]

Any idea how much to allow for wastage? I am not the best cutter of bricks etc.

[The Natural Philosopher]

I just use a bolster and a club hammer.

If I want a pretty result, I don't use concrete blocks ;-)

[Phil L]

medium density aren't packed as tightly in the mould as dense blocks are....I think they just use a dry mix and don't pack it down, wheras a dense block is mixed wet and then vibrated during manufacture to expel air and to strengthen the blocks

you can't cut concrete blocks with any kind of handsaw, these are for the 'thermalite' type of blocks

they can be cut with a bolster chisel but as you say it's time consuming and not very accurate

9 inch diamond disc in large angle grinder, failing that, a small disc in a small grinder will cut an inch into it all the way around and then a few taps with aforementioned bolster will snap it off - the cut isn't clean, but it is at the edges and this is what will be visible IYSWIM

You make the wall length to suit full blocks :-P take a block and use it as a measure, starting at one corner and marking a scratch on the concrete where it ends, then move it along, leaving an inch (or just less) for the joint and make another scratch, continue until you reach the opposite corner - if it works out that you have an odd size left, of say, 6 inches, start your building 3 inches in from where you began, meaning you will have

3 inches of concrete showing at each end. It's entirely up to you of course, but I think pieces in a wall (which will be all the way up to the top) looks hideous, and it is going to be on show. If you are ordering the windows and doors afterwards, build the openings block sized, that is to say you have full and half blocks up each side of the openings, rather than 2 inch pieces on one side and 4 inch peices on the other. It's more economical because obviously you get two usuable pieces with each cut and it looks better, but if yuou already have the windows etc, then you have to build the openings to suit them.,

[Phil L]

I'd order what I needed to be delivered, and then pick up a dozen or so at a time if any extras are required, you are better under ordering with blocks.

Also forgot to ask, are you intending adding any butresses? - if the wall is longer than 4m, you'll need a buttress in the middle, basically just a stack of blocks, tied into the main wall with tie wires on every course

[F Murtz]

use an angle grinder with a diamond blade, they are cheap as chips now

[David WE Roberts]

I will need to add something in the middle of the back wall as it is 7.8m long. The front wall will also need some extra support and I am contemplating how to work this in around windows, doors, and a place for the stove. On the front wall this may end up as a fireplace for the stove to provide sides for protection from the hot metal.

I have more or less decided to go for the maximum length of block wall and ignore the fact that part blocks look less pretty. For three sides this is not an issue as they are facing a fence. The only visible area is the front and the doors are going to make a difference to the number of blocks.

I can always hide stuff behind plant etc, or perhaps render the front wall.

Mainly, I don't mind if it is ugly as long as it is up! [As the actress said to the bishop]

I would like to be able to get concrete blocks at less than £1 per block because I need at least 330 blocks to do the back and sides.

Cheers

Dave R

[Steve Walker]

Correct, but there are disadvantages as well

[JimK]

I'd be wary of enclosing your stove too tightly (if at all) as it'll stifle it and take longer and use more fuel to heat the space up. Could you praps place it in a corner and let it convect and radiate out from there without being "boxed in"?

Cheers JimK

[David WE Roberts]

:-)

[John Rumm]

A proper uk.d-i-y answer ;-)

[David WE Roberts]

I plead special circumstances.........

As I am building up to my 3 rear boundaries I have decided to site the stove pipe as far away from all the neighbours and their washing as possible. This means the location is the middle of the front of the building. As I intend to have work surfaces either side under the windows I need some protection from direct radiation and also contact. I may also make provision for stacking wood either side of the stove to aid the final drying process. It depends on how much room I have.

4 blocks high is 900mm which fits nicely with work surfaces. Air flow will be from a vent by the base of the stove so it won't be stifled. It won't be the most efficient radiator and not the most efficient general heating as I will have two windows on the front wall as well but I do have the stove already and it should certainly keep the chill off the workshop in the winter if required. It should also boil a kettle if required :-)

Question now is will 2 * 900mm high block walls be enough to stabilise the front wall or will I still need a pillar to the roof? I could take the walls all the way up at half a block (or a block stood on end and bonded every other course) or go all the way up at a full block and build the bottom four courses out further than the top six.

Cheers

Dave R

[JimK]

but do they really hang washing out on rainy days or in winter when it's proper cold?!

erm sometimes:-

1) - the definition of "habitable room" is up for grabs to say the least. you're building a luxury shed aren;t you? of a size ISTR that does not involve BRegs or PP? so you can of course do what you like ;>)

2) permanent vents only needed for stoves over 5kw - yours is 4kw from the link you gave, plus BRegs don't apply to your construction so ....

Not in my book no - that will mangle any convection currents you (or at least I :>)) would be looking to create as there would then be less (warm or cool) air movement around the room.

Have a look at your stove and see where the airwash vents are...I expect they'll be at the top on the front so that cold air from outside is going to have to travel a fair way (and get warmed up in the process) before it gets anywhere near where you want it to go...assuming you will be burning wood you'll be using airwash/top fed air all the time.

There are also arguments about air vents doing the opposite of what they're supposed to in unfavourable weather conditions -i.e. working backwards..

Thats beacuse they work by convection rather than true radiation ;>)

could you insulate within it? like a cavity wall?

I still don't understand what you're seeking to protect and from what

- the stove you mention is 4kw peak flat out

However if you take my point and make those 4 block high walls thermally seperate form the rest of the building- *once they have warmed up* they'll then radiate the heat back out for longer than the stove is lit....

Cheers JimK

[David WE Roberts]

Bloody cold at the moment, but not raining. I expect to see washing hanging out soon. They hang washing out any day it is not raining.

Can I ask you in turn if you only heat your house on rainy days or in winter? Or do you heat it when it is cold?

Over time I am bound to want to heat the workshop when they are hanging washing out so I am trying to minimise the impact.

With an oblong room it is logical to put the heat source as near the centre of the long wall as possible. This also puts it (in my case) as far away from the doors as possible. Choice is then rear wall (right next to washing line) or front wall. Simples.

[JimK]

erm yes naturally and obviously I heat it whenever i like - tho of course I am not using a smokey stove in a shed surrounded by other peoples houses, gardens and washing.

The point I am getting at is:- do you seriously believe you will get less complaints (originating) from your neighbours because your smoke stack is a "couple of metres" further away from their washing than it could be?

I suspect someone will complain esp as you appear from what you've described to be in a built up area - is it a smoke control area? - have you asked neighbours what they think of your plan?

Also if you plan on heating it every time its "cold" have you also thought how much fuel you will need to burn? and where to store it? Could be the rest of the garden! :>)

I think you may find those two points worthy of consideration, however, obviously, it's entirely up to you :>)

Cheers JimK

[Nightjar]

David WE Roberts wrote: ...

I find it quicker and easier to use bricks to fill in odd shapes. Some still need to be cut, but that is easily done with a bolster chisel.

Colin Bignell

[David WE Roberts]

I am trying to avoid mixing concrete bricks and blocks as much as possible because of the appearance. I will have to do this around the lintels but as I don't plan to render I want to keep the general appearance of the front as neat as posssible.

[JimK]

could use concrete "commons" (bricks) - same colour as blocks (usually:>)

Cheers JimK

[Nightjar]

It never occurred to me that anyone using blockwork would be concerned about the appearance :-)

Colin Bignell