Footings slightly uneven

[pippo]

Hi all,

I had my garage footings poured yesterday and there is a low spot in one of the corners (my fault cos im crap and it was I who pegged and levelled it). Its a difference of around an inch maybe 1.5 inch. So im a bit worried. I plan on laying 2 courses of block which will take me up to dpc and fill the middle with hardcore and slab. Can I make this difference up by using more mortar under the first course or will this weaken the blockwork?

Thanks for any help

Pippo

 

[noseall]

Lay some muck out on the low end and let it go off or stiffen, then build off this. You could get it out with a bit of semi-dry screed also.

 

[pippo]

Thats sound thanks noseall,

I take it the "muck" is just standard mortar mix? should I fill the low spot 10mm at a time or just level it at once?

Pippo

 

[noseall]

Standard 3:1 mortar mix - all in one hit if you can.

 

[pippo]

Hi again,

Sorry to bring this back up. I am hoping to lay this bed of mortar down on Sunday so I have a couple more questions then I will leave you alone, honest

I have worked out I need 0.27m3 of it as it needs levelled more in some areas than i initially thought. Infact the lowest point is 70mm lower than the highest point which I am worried about. Can a bed of mortar be used at this thickness? If so:

1) If I am mixing 1 part cement to 3 parts sand, how much lime or plasticiser should I use in the mix? Sunday forecast is clear but only 12c during the day and 7c at night up here if that makes any difference

2) Which is the best type of sand for this aplication

3) How many 25kg bags of cement, sand and lime (or ml plasticiser would I need) I have had trouble with this as the online calculators seem to be mainly for m2 of blockwork.

Many thanks

Pippo

 

[stuart45]

You could use some old slates along the bottom where its really low. Use good quality building sand. Those temperatures are no problem.
NHBC guidlines for below DPC are 3/1 sand/masonry cement.
4.5/1/0.5 sand/OPC/lime. or 3.5/1 sand/OPC/Plaz.
If you saw what went on in the footings in some sites you would realize you don't need to worry.

 

[Deluks]

For 70mm I would be using brick to fill that and not a bed of mortar.

If you've a grinder then think about cutting bricks on a slope to fill the deeper sections. When they start to taper off less than half a brick thickness, you can use the mortar.

Also think about investing in a new spirit level

 

[pippo]

Thanks or the quick reply Stuart45,

I will go with 4.5/1/0.5 sand/opc/lime then.

Shall I place slates in the mortar where the mortar will be more than say 1" deep ?

Any idea how many 25kg bags of sand/opc/lime I need for 0.27m3 (rough will do as I can use leftovers for the blockwork later)

Pippo

 

[pippo]

Deluks

I have indeed invested in a new level since. My old cheap plastic banana one is now in the bin.

Its only as bad as 70mm in a small area but I am considering doing the first course at 1/2 bock height from the highest point and cut each block accordingly as I go around. I was going to use high density 4" thick concrete blocks as It will be timber frame above dpc and i thought that high density would be better for fixing the timber frame to. What are high density blocks like for cutting ? Would the lighter ones be good enough below dpc and take fixings from the tmber frame ?

Pippo

 

[hotrod]

Any idea how many 25kg bags of sand/opc/lime I need for 0.27m3 (rough will do as I can use leftovers for the blockwork later)

Get yourself 10bags sand, 3 OPC and 1-2 lime and you won't be far wrong. I personally wouldn't bother with the lime for what you're doing, I would just use a splash of Feb.

 

[stuart45]

Don't leave yourself having to cut the bottoms off the concrete blocks. Make sure you have got a full block at least for the first course. Bed the slate on a reasonable sizes bed, you could use another bedded on top if needed. If using bricks, get some with deep frogs, and cut with a trowel or brick hammer. Use your judgement on the thickness of the beds. If they are struggling to stay up to the line bed some slate. If the blocks are wet, the joints must be thinner.

 

[pippo]

Ok thanks for all your replies so far I have food for thought now lol.

Something else that is on my mind, my plan is to use block up to dpc (single leaf) and fill the middle with at least 4" hardcore and then 6" concrete up to the top of the block, how long should I leave the blockwork before it is strong enough to take a vibrating plate and when the concrete is poured will the single leaf blocks support the sideways weight/force of the concrete on its own without support ? It will be around 3 m3

Pippo