Putting up my shelves

[Rich]

I think I used cement that had partially hydrated 50%. So, in effect, I might have a made a mix that was 6 to 1 or perhaps worse than that. It certainly was not good enough. When I mixed it I did not know about hydration. So, that's why the cement was so sandy and weak.

What's happening is that I have a small room that's 118 Cm wide. I'm putting up shelves 118 Cm wide by x 61 Cm deep. The distance between each shelf is 42 Cm. Each shelf will rest on two pieces of wood one bolted onto the left hand wall and one on the right hand wall. I'm using M6 x 115mm bolts anchor bolts to bolt the wood to the walls.

The right hand wall is a concrete wall. The left hand wall I believe is breese block.

If I chuck out my old cement and get new, I think a 3 sand to 1 cement mix should be good enough, unless anyone says different.

Now the shelves will have books on and a shelf will be be completely filled from top to bottom. So, we have a situation where a shelve has to hold up a volume of books that is 42 Cm high x 118 Cm wide and 61 Cm deep. Not sure of the weight but that would amount to quite a heavy weight on a shelf.

Should I chisel out holes in the breese block and fill these holes with mortar. Then drill that out to hold the anchor bolts? TIA.

[Andy Hall]

A much better solution, because of the weight and the weakness of breeze blocks would be to use resin injection fittings. Using these involves the use of metal studs of size and length suitable for the application. Holes are drilled for them typically 2mm larger than the stud and thoroughly cleaned out. A two part injection resin, which can be applied from a self mixing dispenser or a mastic gun is then injected into each hole and the studs inserted immediately afterwards. After 4 -24 hrs, depending on the resin, you will have fixings that will deal with this application very well and without the attendant risks of a poorly filled or crumbly material.

[Rod]

Suggest resin fixings. Someone else will be along soon to explain more. I think I would try many things including wall bolts, multi monty screws, before using cement.

In the meantime have a look here:

... and lots of related products:

If nothing else, the resin sets quickly (minutes or maybe a few hours) where the cement mix will take much longer to be sound enough to take a heavy load safely.

[Tim S]

Rich coughed up some electrons that declared:

Breeze block or is it thermalite (also aircrete and various other names)?

IME breeze is crumbly and black/dark grey. The other stuff is light grey and tends to powder if it's anything like my house.

I used these on thermalite blocks, with a slight smear of epoxy (araldite) to stop them twisting in the hole when undone:

$MART-HK-$MKAT-HK-$MPG-G2-$MZG-FUR-$MUG-F20&ekat=$EKAT-HK-ENThe context was holding up slotted shelf rail, using about 5 fixings per vertical rail. I would have though they would have been adequate for your use, providing most of the load is downwards shear and not pull. They are very long and have lots of toothed grip area, unlike a lot of cheap frame fixings. They do not have to be used in "frame fixing mode" - I sunk mine flush with the wall, but that only really works providing the screw head to wall distance isn't much over about 1/2".

Regarding expanding bolts, I suspect they will be fine in the bare block. If they actually do up tight rather than letting you turn the bolt forever, it means they are holding rather than pulling through the block.

If it were me, I'd do a trial with a scrap of wood and a couple of fixings to see how they behave.

HTH

Tim

[John Rumm]

Well 6 to 1 is not bad for a bricklaying mortar anyway. Remember cement mixes can take anything up to a month to achieve full cure strength.

A C20 concrete mix (which is a reasonably strong mix) would usually be

1:2:4 using sand and gravel or 1:6 using all in one ballast.

What else is in this wall; Blocks, bricks, rubble etc? If its mostly just cement and rubble, you may need to wait a week or so before you go drilling it - otherwise it will crumble.

The weight is actually not that important in this case - the loading is almost all in shear - i.e. it will attempt to push the fixings down through the wall rather than pull them out. You would probably find fixing simply resting in a hole would keep the shelf and its content up!

Depends on what you mean by "breese block" - there are many things that get called this, ranging from lightweight thermalite blocks to dense concrete ones.

Resin anchors as has been suggested in other posts would work fine. You would probably also be ok with longish screws in plugs - say 4" 12 gauge screws.

[Kevin Poole]

As others have said, the fixings are in almost pure shear, so I think all this exotic resin anchor stuff is ott. Screw the shelves down into the battens and that will remove the last bit of tendency for the battens to twist away from the wall.

Could you use timber sides, so the weight is taken on the floor? And what sort of shelf do you have in mind to take that sort of weight? Could you fit timber uprights between the shelves, again going down to the floor, to halve the span? Even a batten along the rear wall would help, although the front of the shelf might still droop unless you stiffen it with e.g. a bit of 2x1 on edge.

[Andy Hall]

What could be exotic about drilling a hole in the wall, cleaning it, squirting in a resin filler and pushing in a stud?

Very quick, simple and effective.

I would say that all this added carpentry is OTT.

[sm_jamieson]

Very longs screw screwed straight into thermalite is good (e.g.

100mm !) If it comes out the other side, so much the better !! Also, the fancy twist fixings - can't think of the name. They have very good pullout resistance, but you probably dont need this for shelves. Simon.

[Kevin Poole]

Also expensive and requiring PPE to use. An engineer does, for a penny, what any damn fool can do for a pound.

Indeed, if the OP uses an intrinsically stiff enough shelf. If, for reasons of availability, aesthetics, or even (dare I mention it?) cost, he wishes to use materials commonly used for shelves, he may find they sag more than some would regard as acceptable.

[Andy Hall]

One needs to look at the context of the project.

These are not an expensive fixing at all. The whole exercise can be done with one tube of resin and probably two boxes of studs.

The important point is the implication of three shelf loads of books tumbling down and damaging them plus somebody taking down a book.

Mechanical screwed fixings into breeze blocks can easily cause them to crumble or to split. For this amount of weight, it would be very unwise indeed to use them,

That would depend on the material, construction and support.

[stuart noble]

Unwise my arse! A kitchen cupboard full of plates hangs quite happily on a couple of 2" screws.

[Andy Hall]

You would probably hink so if they fell on your bonce.

That I can imagine.

Having very considerably less weight than a shelf full of books.

[stuart noble]

Funny, I always thought china weighed more than paper

[Dave]

An added attraction to this idea is that the stud is only loaded in shear and has no tension on it. I would think your idea would be fine for this job.

Dave

[Rod]

In terms of density, it is usually denser.

(In kg per cubic metre.) Porcelain ? 2403 Paper ? 1201 Cardboard - 689 Couldn't find 'china' - thought porcelain reasonable approximation.)

But it is very rare to see solid china wall-to-wall along a shelf. Most china is hollow or flat-ish and round - neither of which packs particularly well. You might just about manage it with something like bricks. Whereas books can very nearly fill the total space available between two shelves.

What we care about is surely the weight of a shelf-load of books versus china. And I would put a small wager on Andy being right.

[Andy Hall]

Which is heavier? A kilo of feathers or a kilo of lead?

[dennis]

Either depending on how they are stored.

[Rod]

Unless you are playing at quirky things like one being stored on the ISS and the other on the desk, the change in moisture content of feathers, or similar unlikely ideas, I do not understand what storage method has to do with it.

[Steve Walker]

Indeed - you can't beat resin for strong breezeblock fixings.

[dennis]

Well for one a kilo of feathers would be more buoyant than lead in most cases so it would weigh less. For instance a kilo of hydrogen would weigh negative under normal conditions.