concrete floors, how strong?

[chunkolini]

Hi guys a problem developing here.
I have a farmer building me a workshop on his farm, at last I get to escape from my garage.

They have laid the concrete slab, 28x22ft.

I mentioned to the guy who laid it that I would be bolting a big vice stand down and asked how would he reccomend doing it.

His response was ''the concrete is not reinforced so dont.'' he said it is 4" thick and would crack if I started swinging around on the vice and hitting it.

I know that this is only a potential problem, I dont want to nark my new landlord and his crew before I move in.

I dont want the vice on a workbench as everything jumps off the bench when you hit, and the bench can still move.

Plan A is I go ahead and fit the thing and see what happens, the base is spread over a rectangle about 26x30" I was planning on using expansion bolts on the corners and in the middle of the sides, going through plates around 6" wide to spread the load.

Anybody got any ideas?

chunko'.

 

[Tusses]

if its not reinforced it will likely crack anyway !

 

[OLD]

concrete is strong in compression to break it you force a chisel in to fracture the structure , so expanding fixings may not be a good idea you could resin glue threaded rod into the floor to give a good fixing without side force. Clean holes out well for a good fixing and spread the load.

 

[RogerS]

The stability of the concrete base is going to depend on the underlying foundations - how compacted they are, what sort of soil are they sitting on etc. That size slab without rebar is just asking to crack ....

Roger

 

[adzeman]

Tusses is dead right it will crack anyway. 100 thick is not that substantial anyway. So you could mark out the area about 150 all round to what you need, cut it with a Stil saw, remove the slab, dig down another 270 say plus hard core of 100, line with an expansion board,(Celotex would do), re-concrete casting in your holding down bolts and Bobs your Uncle.

 

[RogerS]

Tusses is dead right it will crack anyway. 100 thick is not that substantial anyway. So you could mark out the area about 150 all round to what you need, cut it with a Stil saw, remove the slab, dig down another 270 say plus hard core of 100, line with an expansion board,(Celotex would do), re-concrete casting in your holding down bolts and Bobs your Uncle.

What about his dpc - assuming he's got one? Do you mean line the sides or the base with cellotex?

Chunko - if you need some cellotex I have surplus kinsgpan but may be a bit too thick for you (it's 75mm). Actually quick plug...I have 30 odd sheets spare

 

[Anonymous]

Actually quick plug...I have 30 odd sheets spare

I need some but I doubt you will get them in an envelope to post them down here.

Regards floor, yes it will crack sooner or later so I'd just go ahead and bolt it down for now, using resin fixings - not expanding ones.

 

[chunkolini]

Some useful stuff here, as usual.
For starters I have revised the plan. I have welded up a stand and mounted it on a plate about 28x24", and will put studding in the floor with epoxy.

There are other long term plans, slip rollers among others that depend o a decent floor.

I am hoping to catch up with Farmer Palmer today to let him know my concerns and see what they can do before the building goes up next week.

I am off on holiday for two weeks on Saturday so I need to get this sorted before I disappear.

Chunko'.

 

[adzeman]

RogerS wrote
[What about his dpc - assuming he's got one? Do you mean line the sides or the base with cellotex? ]

Its difficult giving a meaningful spec' in a few lines when normally it would be a 16 pager.

My initial thoughts were, anticipate the slab was laid in one go as it has no reinforcement, a dodgy slab. Will it have a mebrane? does it have a sound hardcore base? Is the concrete 100mm thick ? or was told it was. Is it level? anticipate the worst. If the slab is cheap and cheerful then isolate an area for the vice base. The celotex a cheap option round the sides, if there is a membrane put one in say using polythene, cast the base. The slabs going to crack any way, maybe cut some crack inducers into it, so when it does crack they will be or look uniform. Discuss it with the farmer get him to do it.
[/quote]

 

[Gary]

Chunko - if you need some cellotex I have surplus kinsgpan but may be a bit too thick for you (it's 75mm). Actually quick plug...I have 30 odd sheets spare

Roger do you mean insulation, if so what size are the sheets? I need to insulated a double garage roof.

 

[RogerS]

Chunko - if you need some cellotex I have surplus kinsgpan but may be a bit too thick for you (it's 75mm). Actually quick plug...I have 30 odd sheets spare

Roger do you mean insulation, if so what size are the sheets? I need to insulated a double garage roof.

1200 x 2400 mm, Gary.

 

[Gary]

In that case I could take some off your hands.

 

[RogerS]

Gary...pm sent

Roger

 

[Losos]

The slabs going to crack any way, maybe cut some crack inducers into it, so when it does crack they will be or look uniform.

What are 'crack inducers' :?:

I'm also planning to lay a concrete slab in my barn 'lean to' it's about 3 x 10 Mtrs.

I assume from the above posts that this size will crack, should I get the slab laid in smaller sections :?:

Also, am planning to put a very heavy bandsaw on it so I would imagine that rebar under this area is a must. :?:

 

[whoops!]

Chunko
how about making a former (simple wooden box), putting some rebar in it, and then pouring a mini slab.If its not too close to the edge of the main slab you should have no real problem with the weight (again depending as to wether the guy has use hard-core. You wouldn't need to start thinking about cutting holes etc into the existing slab, you can drill all the holes you want, and if the mini slab is big enough should spread the load. there will of course be the height difference to consider unless you make it big enough to stand on as well. Just DONT do it close to the edge.

If there is only soil underneath that may have gullies due to inadaquate drainage, that may cause cracking. But if the farmer knew you were going to use it as a workshop....

Decklan

 

[adzeman]

Losos asked about crack inducers. Even when reinforced, concrete will crack, the trick is to make it crack where you want it to go. Its all to do with shrinkage and curing. The current trend is to go for long bay casting and dividing its length with crack inducers about 10M, not critical but fits in with the lap on the reinforcement. These can be triangular lengths of timber or purpose made plastic triangular sections. I think the trade name is schliger? Make sure the slab is not locked in say at door entrances columns etc. After floating (power floating is best) cut the slab with a diamond saw or press in a small section timber about 12mm x 12 mm directly above the triangles you will have to mark where you positioned them. Oh stagger them like joints in floor board. When the concrete cure it will crack at the edges on the width of the bay and across where you put in the crack inducers. Google crack inducers or Schigel which should give you some pictures. don't make the bays too small as the concrete will curl up at the edges.

 

[Deejay]

Hello Losos

If you want more information about laying concrete, have a look at

http://www.pavingexpert.com/

(No offence Adzeman)

Cheers

Dave

 

[Losos]

Thanks Mike B and Dave

You learn a lot on this forum and not just about woodworking, not sure when the floor will be done (It's a real b****r trying to get people to do building work where we live right now) but I will make sure they know what you've said and do it that way.