Need to build a new shed (sigh)

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Hi, today i took down a old garage i had in the garden, due to rot, bowing and leaning, it had stood for 55 years

The garage has a brick footing which is at least 3 courses deep (underground) and it had a concrete slab poured inside the garage about 10 years ago, the garage was built right against the boundary with my neighbour and id like to build the shed the same way but my neighbour has concrete slab on his side so theres essentially a 3" gap where the bottom plate of the garage sat.

Im gonna reuse most of the wood from the garage, new featheredge cladding and some fibre cement sheets for the roof

Where do i start?

 

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Pictures

 

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Can i fill the void with concrete to bring level with the slab abd then build on that ?

 

[Shultzy]

Yes, but you need to "key" the existing concrete so that the new concrete will adhere to it. Make sure you brush, vacuum and clean with concrete cleaner before adding the new concrete.

Make the shed sides flat on the floor and finished, then just stand them up and screw / bolt them together.

 

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Thanks for the reply, can you explain what you mean by key the existing concrete? I googled it but didnt come up with much

 

[John15]

To build your new shed to the same line on the boundary all you need do is clean out the groove down to the brickwork footings then fill with concrete.

John

 

[Nishing]

Cheers john

Another issue is the concrete slab has a rough uneven surface, can i fill the voids between slab and bottom plate with mortar or is there some other method ?

Thanks

 

[John15]

I think levelling up the slab was what Shultzy was explaining. It's not an easy job and depends how far out of level and the surface condition.
For low areas say up to 10mm you can use a Self Levelling Compound. Any more than that a mortar screed up to 50mm would be needed. Any localized high spots need to be reduced with a scabbler or small breaker then the surface made good with Self Levelling Compound.
Surfaces to be made good will need to be cleaned and roughened.
When preparing the remedial areas avoid a feather edge - vertical face should be cut 5 - 10mm deep.
If the slab has defects over most of the surface it would probably be better to apply a 50mm sand and cement screed over the whole area, having first prepared the surface as Shultzy has described, ie roughen and clean the surface then apply a coat of Unibond.
I hope this helps.

John

 

[RogerS]

Did that gully act as a drain to take away surface water from your neighbours concrete slab? If you then fill it, I wonder where all that water will now go?

Just a thought.

 

[Nishing]

Did that gully act as a drain to take away surface water from your neighbours concrete slab? If you then fill it, I wonder where all that water will now go?

Just a thought.

No the garage frame was in the slot before the concrete was poured on either side

 

[Nishing]

I think levelling up the slab was what Shultzy was explaining. It's not an easy job and depends how far out of level and the surface condition.
For low areas say up to 10mm you can use a Self Levelling Compound. Any more than that a mortar screed up to 50mm would be needed. Any localized high spots need to be reduced with a scabbler or small breaker then the surface made good with Self Levelling Compound.
Surfaces to be made good will need to be cleaned and roughened.
When preparing the remedial areas avoid a feather edge - vertical face should be cut 5 - 10mm deep.
If the slab has defects over most of the surface it would probably be better to apply a 50mm sand and cement screed over the whole area, having first prepared the surface as Shultzy has described, ie roughen and clean the surface then apply a coat of Unibond.
I hope this helps.

John

Thanks john

I havent actually checked how level it is yet, but i know its not the smooth finish you would want if you were pouring a concrete shed base.

The sand cement screed option sounds fairly straight forward, but will it be strong enough?

 

[John15]

A 50mm screed will be strong enough provided the preparation and laying operations are correct It needs to be done by someone who knows what they're doing. As I've said above the substrate (existing slab) must have a key (scabbling) and be clean (no dust etc) and a bonding agent applied. Check on the mortar mix and water content - probably 4:1 will be OK and a little on the dry side to minimize the risk of shrinkage cracking. Hopefully someone will come on with some additional info on screed laying.

John

 

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Ok ill probably stick to self leveling compound then or if the slab is to uneven i may just build the shed in another location and pour a new slab

 

[charlibalv]

You could try using 75mmx75mm wood posts as bearers, then shim to level. I did this on a shed I built 15 years ago. Its 6 meters long by 2.4 meters wide 3 meters high, double walled and its had a lot of kit in there the heaviest single piece was 500Kg and its still dead stable. Also as its off the ground there is no sign of rot anywhere.

 

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Im just gonna build it on the slab i think as it should be the cheapest option, i wont need to anchor the frame to the base will i?

Also i want a low sloped roof about 10 degree max, what is the process for building the roof? I dont really know were to start

Thanks

 

[Nishing]

I meant a lean-to type roof with the slope running side ways rather than lengthways if that makes sense

 

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Ok another question, how can i do say a 4m long wall frame with only 2.4m timbers?

Doesnt the bottom plate need to be one piece?

Thanks

 

[charlibalv]

Ok another question, how can i do say a 4m long wall frame with only 2.4m timbers?

Doesnt the bottom plate need to be one piece?

Thanks

The way I did mine was sheets if 2.4 x1.2 m USB with a 50mm x 75mm timbers screwed and glued to form sides and top and bottom plates for the walls These were reinforced at the corners then I bolted these together to form the 2 long walls (3 of them per wall). The bottom plates were then screwed into the flooring, (the floor was 75x75 mm fence posts, shimmed to level, then 12 mm ply, then jablite insulation then 2 layers of 12 mm ply off set, all framed round the edges to receive the wall plates). I filled the space between the timbers with insulation then skinned with 6mm ply. Outside I attached laths covered these with thick plastic sheet and then added the feather edge cladding. The roof was some simple trusses (100mm x 50mm timber cut to form a 22.5 deg slope) and they were covered in try wall polycarbonate. May be over the top but it is still in the same condition today as it was when I built it.

 

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Thanks but i dont have osb and dont plan on using any osb/ply in the construction as i have cladding and timbers abd dont want to spend hundreds of pounds on this, any other options

 

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Just measured the thickness of my slab, its only 1" so dont think building on that is a option