What to do with Garage Floor base?

[martysmarty]

hi Guy's an girls!

new here and first post so hi!

Doing some work on our first home and i can see this site being a lot of help!

Our garage is in need of a base. its currently just gravel and mud. its 9.8m x 3m internal built with 440mm concrete blocks. the garage was originally half that size and it's been extended. foundations are quite wide but the problem is the level of the garage floor run's down so the bottom footings are below ground level. the top garage footings are 1 concrete block higher than the bottom half of the garage footings but the roof is obviously level if you know what i mean.

I have had a quote for £570 to pump a 6" base but not sure if i should do it as one whole base or split it into two with some expansion packing to divide the two slabs? also should i pack around the edge against the walls with expansion packing too?

its mostly going to be used for my bikes but may one day in the future have a car in there so best to think ahead! it's a garage after all!

 

[theprinceofdarkness]

I would not bother with expansion joints. The foundations are in the ground and the slab is sitting on the ground, sheltered by the building from the sun.
The base must be leveled up to horizontal or a 1:100 slope towards the door (Err, thats .1m over the whole length), just to make sure that any water getting in (wet vehicles?) will run towards the door and not pool up at the back.
10m X 3m X .15 m = 4.5cu.m, so a good price but make sure that there is enough cement in the mix (C30?) because that stops the base sucking up water from the ground and being damp.
It sounds as though there is a fair amount of earth to be moved about, remember that your finished base has to be at least a couple of inches above the general ground area to stop water getting in.
Just remembered, that 4.5 cu.m is more then you can lay before it goes off, unless you go for self levelling, which in my case was not self leveling. So if its ordinary concrete, you need to move it into the correct position, tamp it down and level it off so I would say you need at least two if not three helpers, you have less then 2 hours to finish it! You must also have some system of getting your slope and your flatness. If you have some 4" X 2" bits of wood say 2.9m long with a hole drilled through at each end and a loop os rope at each end, then two guys can use this to roughly level the concrete.
Once you have sorted out the base, I think you should get a mate or a builder with experience to supervise. You have one chance, and once the stuffs gone off is a s*d to lift it to get it right.
Frank

 

[martysmarty]

Hi Frank, that's cleared up a lot of my questions then thank you for that.

I was slightly concerned the size of the slab and it going off too quick. Would steel mesh need to be lay down with C30 @ 6 inch? or just go with membrane alone? i will definitely be getting help from someone who knows more than me on the day.

 

[theprinceofdarkness]

If the ground is solid (well rolled?) and covered with rolled hardcore , no mesh should be required. I note you are intending to use a membrane. If you use enough cement, you don't need a DPC, mesh or sand blinding for your hardcore. Sounds to me as though you should get some proper details on constructing concrete floors, i am not sure I am the best person to give it even though I have done three garage bases all were successes. listed:-
#1 garage base for a "Marley" type garage, 12" x 12" X 8" wide perimetre strip to carry the walls, 4" over site. all laid on 3" hardcore, 22' X 11'. Mixed by hand just a bit too much for me and a mate (1 : 4 all-in-ballast). Took a car OK, dry.
#2 garage base for another "second hand Marley" garage. Built on 22 9" piles, very exotic design mesh in floor, rods in wall trenches, square box sections in the piles. The steel work cost £120 in 1980. Ready mix, can't remember how much it cost, they delivered far too much (3/4m?) too much to lay for me and two mates.
#3 Barn floor, 4.2m X 5.4m X .1m (OK I have gone metric), ordered as C35 SELF LEVELLING. Ordinary turned up, no tools, no shuttering. . . Grey and smooth, but not flat but waterproof.
#1 and 2 have lasted over 30 years with no degradation and are still dry.
Frank

 

[martysmarty]

Hi frank. Just an update on this. I wont be laying or leveling the cement i have a company doing it for me. I do however have to prep it. The bottom half the garage is fresh and will need 2.5inch of hardcore so i can get my 6 inch slab. The other half (top) has old concrete Floor that i uncovered under some dirt. Very unlevel and cracked This is 6inch away from where the level will be, should i break it up into a hardcore finish or leave that as it is?

 

[theprinceofdarkness]

As its cracked, it shows that it is not very stable, I would break it up and use as part of the hardcore.
Frank