Concrete Shed Base Problems

[DigitalM]

Feel a bit ashamed asking this after looking at some of the fabulous workshop builds but I could use some good advice.

I have a concrete shed base that is something like 14' by 8'. A friend (experienced landscape gardener) poured/made it as a return favour for some work that I'd done for him. Problem is it's up to something like 25mm higher in one corner and simply not flat (I checked it using a levelling laser thing). Something clearly went wrong during the form-making/pouring phases. I don't want to call him back and jeopardise/stress the friendship, you may think I should/shouldn't but, no, I'm not - don't make me explain, I know he meant well and tried his best.

Anyway, I was going to buy one of those prefab workshop things. I know some of you are super awesome and knock up your own and I could too, but frankly I'm just time poor and would rather put my time into tinkering in the workshop rather than making one (though I've thought about it).

I was kind of hoping to have the floor be resin over the concrete but 25mm is likely

What are my options other than hiring a breaker and starting again? Can it be ground/leveled somehow? I see they have 'scarifiers' at the hire shop but have no experience with them.

How bad is 25mm out from one diagonal to the other (and various places in between!)?

 

[Lefley]

order the prefab shed. And rip a 2by 4 starting at zero.” The high spot’ and chase it around until, it’s 25 mm thick the low spot. Now you have a level base to sit your prefab shed on top of it.. put glue or something under shed. Or put a coarse of bricks around with mortar under to level yourself up then sit shed on that, or set a form aro7nd perimeter the size of shed and pour a little short wall a few inches high to have something level to sit shed onto.

 

[Jameshow]

I'd buy a dozen engineering bricks and a bag of sand cement lay the bricks a meter apart bedded into the cement with the bigger mortar bed where the slab is lowest.

That way your shed if off the ground completely and much less likely to rot!

Also don't forget some guttering and the stain that factory applied is rubbish it needs additional staining asap.

Cheers James

 

[Digger58]

Just pour another base over that, set up your forms and allow an extra 25/30 over the high spot which means about 50/55 mm at the lowest part. you can get a fibre to put in concrete to prevent cracking of the base where its thin. Forget wood on a shed floor, not a good base for resting machines on, traps moisture and can warp. Is there a damp proof membrane in the current base, if not you could put one in under the subfloor.

 

[Old.bodger]

One or two courses of engineering bricks would enable you to sort it, to construct the shed. Then you can level the floor with taper beams, or just live with the floor out of level. I doubt you would even notice it in use.

 

[Stigmorgan]

As @Jameshow and @Old.bodger said, a course or 2 of engineering bricks with a dpc membrane between the brick and timber would be your best bet, tbh I'd recommend it even if the slab was perfectly level, it will stop any standing water from getting into the woodwork.

 

[Sheptonphil]

Agreed, two courses laid by a brickie will see the perimeter spot on level. if you’ve already got DPM in the construction, float the floor with a screed or levelling compound depending on what you are going to use it for.

 

[hairy]

From memory plus or minus 10mm for a footing is probably within the allowable tolerance normally (within a certain distance of each measurement, seperate and in addition to how far from required level, etc)? There will be some error in whoever measured it, in the laser, more etcs Obviously 25mm is a little outside that, better would be good and some good ideas on how to fix it above, but maybe not enough to go pointing fingers? The person who did it may not know it is that far out and be keen to assist?
Also, prefab concrete can be really bad itself in my experience, disc cutter and sledge hammer required from the people who install car park type things for a living

 

[Adam W.]

Screed is your friend.

 

[Jameshow]

Feel a bit ashamed asking this after looking at some of the fabulous workshop builds but I could use some good advice.

I have a concrete shed base that is something like 14' by 8'. A friend (experienced landscape gardener) poured/made it as a return favour for some work that I'd done for him. Problem is it's up to something like 25mm higher in one corner and simply not flat (I checked it using a levelling laser thing). Something clearly went wrong during the form-making/pouring phases. I don't want to call him back and jeopardise/stress the friendship, you may think I should/shouldn't but, no, I'm not - don't make me explain, I know he meant well and tried his best.

Anyway, I was going to buy one of those prefab workshop things. I know some of you are super awesome and knock up your own and I could too, but frankly I'm just time poor and would rather put my time into tinkering in the workshop rather than making one (though I've thought about it).

I was kind of hoping to have the floor be resin over the concrete but 25mm is likely

What are my options other than hiring a breaker and starting again? Can it be ground/leveled somehow? I see they have 'scarifiers' at the hire shop but have no experience with them.

How bad is 25mm out from one diagonal to the other (and various places in between!)?

Maybe get him a spirit level for his birthday!!

 

[Bristol_Rob]

Call your friend back and ask him what he recommends - he may feel embarrassed enough to fix the problem for you?

 

[Jones]

Maybe your friend put a slope in for drainage ? Like others suggest two courses of bricks with thick/ thin mortar beds should bring you level. Then lay DPM over and put insulation in with a floating floor over. This will give you a good flat floor, level as well if you spend time shaving the insulation. An insulated floor is much more comfortable underfoot if you spend much time in there. You can use polystyrene ( jablite) which is adequate for a shed and cheaper than PIR.

 

[Spectric]

and simply not flat (I checked it using a levelling laser thing).

Have you checked using an old fashioned level? If the shuttering was level and sturdy then what may have happened is that as your freind leveled it and got to the last bit, rather than removing any excess concrete he tried to just spread it out which does not work and can leave a raised area. But give him his due, that is quiet level when you see how modern house floors can be out by a lot more.

 

[MARK.B.]

You might want to mention it to your friend anyway because he may be using a level that is out of true without even knowing it, at the very least it could stop him making the same mistake with a customer who may not be as obliging as you

 

[hairy]

Another idea could be to ask your local friendly metal fabricating shop for something like 2mm, 5mm and 10mm shims to level the bottom sections of your precast workshop, then non-shrink grout just under the walls to fill the gap and give a nice bearing surface?