Unlevel concrete floor nightmare!

D

dunvale

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Hi there,
Yesterday we laid a concrete floor for a workshop im building. The size of the slap is 20x20 foot and 5.5 inches deep. Im not an expert but have done some building in the past so im not a total novice.
We have laid some other smaller slabs and there has been no problems,
after we tamped the slap I floated it with a bull float and obtained a really smooth finish.
When I had a look at it this morning its quite noticable that there is hump in the middle of the slap, its not noticable at first glance but when you put a straight edge across it you can see the problem. Since this is going to be a workshop floor where I want to do welding etc. this floor will just not be acceptable.
I dont know what went wrong it looked fine last night, all I can say is that the driver made the mix very wet maybe that had an effect on the slab as it cured.
You can only imagine my dissapointment!
What is the best solution to this problem, cut off a layer and relay?
Someone mentioned concrete planers to me, that mill the concrete down, I presume this would leave a rough finish?
Any suggestions would be great. Thanks.
 
I presume this building is just at the floor/sub floor stage.
I would finish the floor off when built with a layer of insulation and finished screed.
Just regard what you have done as a sub floor and leave it.
It will make a better more comfortable workshop especially in Winter, as when welding you will be on the floor a lot laying out steel.
It will cost a bit extra, but it is not very big.
 
Alternatively if this is the finished floor you could have it ground and polished to a very fine finish and seal it with an acrylic concrete sealer, something like Sika Proseal?
 
Sailor, I respect your suggestion and I had thought about that, unfortunately this is the finished floor level and the way things are planned out, I'd rather not raise the floor.
Carpenter, your suggestion sounds interesting. Can you elaborate a bit more? do you know of any companies around Ireland I could talk to about the issue?
Thanks for reply lads.
 
The guys at [broken link removed] have the Sika approved logo on their van if that is any help to you
 
Flicking through the HSS catalog I see they rent out a high speed Grinder that uses big Diamond discs to level out high spots, it looks like a big floor sander but it has an 11hp petrol motor.
Catalog item no. 452.

No affiliation with HSS ,I just rent a lot of gear from them.
 
Mulvany Hire & Sales (Glasnevin) would specialise in renting out floor grinding/scabbling/finishing equipment. They are not cheap but they are experts in this kind of thing. A wide range of options available.

No connectction, just a customer...etc.
 
Dunvale

I know you don't want to raise the floor level but a screed done by someone with experience will be far and away the quickest and most satisfactory solution

Incidentally ( for the next slab pour ) - if there is hump in the slab then I am afraid that you made it. wet concrete etc cannot be blamed as this is more likely to be self levelling. My guess is that you needed to tamp and level it a second or third time to achieve the correct levels and then be careful not to affect the levels when floating. It is a considerable skill to lay a very level slab of that size.
 
Badge55, I think your right. looks like we took on more than we could handle, ignorance is bliss!, If I were to go with the option of getting a screed done properly what is the min height I could afford to raise it? and what type of mix would you use? bearing in mind that this is a workshop floor.
thanks to everyone else for info, I will give apolloscreed a buzz.
 
Depending on the sixe of the hump in question - a heavy scabbler/planner from a plant hire company would work. This could potentially take a long, long time to grind out. The finish would be smooth, as these machines only grind out a dust film layer at a time. If the level difference between hump and surrounding area is greater than say 10mm, I don't think this would be a viable option for you, it would just take too long.
 
Thanks roundy,
I'm going to talk to one of the companies that rent these machines, I might get away with using one to sort out the issue. The hump is not noticable until I put a straight edge across. I'd be confident the difference is less than 10mm. it might work
 
I've used a concrete grinder in the past. Its not the easiest machine to use. Can go heavy in spots if not careful. I've rented it from Daly industrial. www.disc.ie Find the lads there helpful. This will certainly solve your problem. Your can't use it on fresh concrete tho. It takes 28 days for concrete to properly cure.
 
how noticeable is 'noticeable'........?

If this is a workshop floor, well I've yet to see a truly flat one, so unless yours is particularly bad.......what is the issue?

I see you say you do welding, etc, even if this is so, you can't rely on a floor to give you a good enough finish to suffice as a surface plate for straightness etc.............
 
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