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I levelled mine at as much as possible by digging over and levelling up the topsoil then used some old paving slabs (from a pre-existing patio area I had dug up) as padstones and built up (as I wanted the decking to be raised up from garden level) using bricks on sand & cement dabs at 18'' centres before laying a 4x2 framework over and then laid the decking over.
I’d thought about the slab idea but then heard a few horror stories and was wondering how to level them?
Most of the ground is pretty firm, it’s just soft towards the back.
So my options are;?
-Dig 16 holes, 4*4 posts , postcrete and bolts
-dig 16 holes and make 16 300mm pads
- stick 16 breeze blocks down and er hope for the best
- use old slabs and figure a way to level them?
- spend a fortune on a 3.7m square concrete base (I imagine very expensive!)
I’ve found 46 * 17” slabs locally for £35
Wondering if something could be done with them, given my lack of budget time and skill 🤔
I’d thought about the slab idea but then heard a few horror stories and was wondering how to level them?
Most of the ground is pretty firm, it’s just soft towards the back.
So my options are;?
-Dig 16 holes, 4*4 posts , postcrete and bolts
-dig 16 holes and make 16 300mm pads
– stick 16 breeze blocks down and er hope for the best
– use old slabs and figure a way to level them?
– spend a fortune on a 3.7m square concrete base (I imagine very expensive!)
Why are you not just digging in 16 4x4 posts and postcreting them in. There is a lot of labour in digging but if you have the time that is not an issue (not sure what the ground is like - mine was awful digging through rubble by hand). If you have vertical posts then getting it level is a piece of piss. Getting it square is the challenge.
Looks good Jon - this would certainly be cheaper!
Might sound a stupid question but say I get the slabs I mentioned and use two layers or blocks on top -
if I add mortar / cement to first slab, a
add second slab/block and tap down until level - is the mortar going to be strong enough not to compress when I add the deck?
Why are you not just digging in 16 4×4 posts and postcreting them in.
Mostly because I don’t have a lot of time and the ground in some places is almost entirely hardcore (yet annoyingly soft at the back of the plot)
What we did for my son's deck was to make short posts out of 6x2 and whack them in with a rubber maul (a BIG rubber mallet) until they wouldn't go any further. From memory, on about a 0.4m x 0.5m grid. Then marked them off and sawed them level using a circular saw. The 6" dimension was across the joists so that we had some positioning tolerance if the post didn't go in quite square. That was 3 years ago and they haven't budged.
Mostly because I don’t have a lot of time and the ground in some places is almost entirely hardcore (yet annoyingly soft at the back of the plot)
I think you will still have to mess about in the dirt whatever solution. I'd just get out there and start digging.
PS. I started mine last August and it still is not totally finished. I took 2 weeks of work last summer I spent about 4 days digging and messing about with the posts. Another week on the frame the rest of that time lost just staring at it (and or watching youtube videos). Then got the deck down on weekends over autumn and this spring and did the hand rails about 2 weeks ago. I just need to face it with bricks now.
use old slabs and figure a way to level them?
You could set 4 posts in postcrete, one at each corner, at the height and level required.
Build frame from this, then slab under as many junctions of purlin and joist as you wish, with a slab dropped below, and wooden leg cut to length, then there's no eed to level all of them, just the 4 on the outside.
Similar really to what Jon has done, but you'll need a lot more joists, I always do 400 centres, especially with the weight you'll be putting on there.
Similar really to what Jon has done, but you’ll need a lot more joists
There were more joists by the time I had finished - it was WIP when I took that picture 😉
I thought that, was just to make sure he knew! 🙂
😃 yep, I’ve ordered timber for 400mm centres
Next idiot question ..
Assuming I did as John did, given the length (3.7m) could I just level (with a level and long timber) the corners with slabs and bricks/mortar or would it be better to level each support individually to each other in turn?
PS. I started mine last August and it still is not totally finished. I took 2 weeks of work last summer I spent about 4 days digging and messing about with the posts. Another week on the frame the rest of that time lost just staring at it (and or watching youtube videos). Then got the deck down on weekends over autumn and this spring and did the hand rails about 2 weeks ago. I just need to face it with bricks now.
I can see this being me almost exactly! I’m supposed to be studying full time rather than playing with wood in the garden 😐
I can see this being me almost exactly! I’m supposed to be studying full time rather than playing with wood in the garden 😐
Mine was built of the back of the house over an old outbuilding which had serious foundations which made it extra complex. it was also built about 4ft up and part of it over the old cellar access steps so over 2m drop in one bit. I fell through it twice during construction luckily not in the worst bit and no serious injury. Don't rush it just keep plodding along getting everything nice and square/level. Make sure you have a good saw set up as you will be doing a lot of cutting.
Top tip. If you find some of these they fit a 4x4 post in the centre square perfectly. Dig one of these in to each hole and use them to help line up the square. Support the post level and then postcrete. Once you have the 4 corners in everything else is fine.
Assuming I did as John did, given the length (3.7m) could I just level (with a level and long timber) the corners with slabs and bricks/mortar or would it be better to level each support individually to each other in turn?
If I am understanding you correctly, I levelled them approximately before laying the joists over and levelled in all directions - front to back, side to side and diagonally - and padded it out where necessary with extra shims. I was trying to do it as cheaply as possible so I asked at my local builder's merchants if they had any odds and sods of old paving sets etc that I could buy and they just directed me to a corner of the yard where I could fill up the car with whatever I wanted for free - just old bits n bobs that they could never use.
BTW, my effort is 3 years old now and it hasn't moved or shifted at all.
I'd be cautious about putting in substantial pad foundations. What you put in now you may want to take out in a few years. This isn't an extension, more like a garden shed in terms of mass and loads. Many Victorian houses are still standing with brick footings only and like a wooden deck can handle a little movement. Hammering it your posts until refusal would prob be enough.
I’ve just had my framing timber delivered.
Do you reckon this is ok with a split in the end, it’s going to be screwed into after all?🤔
If I am understanding you correctly, I levelled them approximately before laying the joists over and levelled in all directions – front to back, side to side and diagonally – and padded it out where necessary with extra shims. I was trying to do it as cheaply as possible so I asked at my local builder’s merchants if they had any odds and sods of old paving sets etc that I could buy and they just directed me to a corner of the yard where I could fill up the car with whatever I wanted for free – just old bits n bobs that they could never use.
BTW, my effort is 3 years old now and it hasn’t moved or shifted at all.
What did you use for shims john?
I was wondering if I should level from each post to the next with a spirit level and adjust the mortar between slab and brick accordingly or try to level from the far corners from each other using the spirit level on a straight edge for example ?
Do you reckon this is ok with a split in the end, it’s going to be screwed into after all?🤔
Aye, just shove a screw down from the top. Be fine.
So, the saga continues ..
I’ve now sourced 20 odd 40mm paving slabs that (it turns out) are the ridiculous 30kg ones that are horrible to lift..
I’ve also got some smaller bricks and off cuts I can hopefully use for levelling.
So... will pre mixed mortar be strong enough to dab between the slabs and bricks as per John’s decking above?
Is it better to level each support to each other with a 1.2m spirit level, or put the level on a joist and try to level across the full width of the frame?
Thanks 😊
*40kg slabs 😳
So, for anyone bored enough to feign an interest, I need some advice.
Having nearly destroyed my car by transporting what turned out to be 800kg of slabs in one go (yes, I know) I’ve now got my plot covered in weed membrane and the fence half heartedly re-preservative-ised.
However, because the slabs are big (600mm square) I’ve now got an issue trying to stop them rocking.
Is there any recommended way of stabilising them on membrane, or should I try to smash them into smaller bits?)
Thanks again
You need the 600m square area below each slab flat, that's all.
To stop them rocking, standard procedure would be to make up some cement. use a pile for each corner and another in the middle (covering what it will be supporting, and put the slab on top. - then tap it above the piles to level up using your spirit level.
If the ground is flat enough that a smaller piece will be stable then you could always try to use a smaller piece, but if it isn't flat then you will have a smaller contact with the wood sitting on top of it, and if you get any rot the deck will start to flex sooner. - However if you will already be putting a secondary masonry element above (brick etc) then of course the mortar layer between those can be used to give a level surface for your wood to sit on.
Thanks, can I put mortar onto weed membrane? I don’t really want to attempt to cut 20 * 600mm holes in it!
Yep, for info my plan was the huge slabs and then a breeze block on top (mortar between the two to get levels), then frame on top of that
I don't think mortar would react in any way to the membrane, so that's fine. It may bind as some mortar may seep into the weeve, but that shouldn't be an issue for you.
As long as the slab is in contact with the ground at the point the block will sit above, for weight transfer straight to earth it wont matter if part of the slab is floating as such. as long as it is stable in that position. If it is wobbly, and not in contact with the ground at the point of support, it is much more likely to crack and cease to be a functional support.
I guess the big question is how wobbly are the slabs when in the correct position. Even a bed of builders sand would help to stabilize, but at that point you may as well mix some cement in as then there is no way it will shift in the long term, could go for a weak mix just to hold it solid.
As per my picture, we didn't have an issue with rocking as the ground was flat and the product I used was also somewhat more robust than normal weed membrane - it's commercial-grade non-woven geotextile used under railway lines and roads etc so it really helped stabilise things. However I wouldn't expect individual slabs to rock when you have fixed everything together no matter what membrane you have used (and I didn't use dabs UNDER the slabs). BTW, I shimmed with all sorts of bits n bobs such as old bits of slate and tiles (my father in law, not only being a source of above-mentioned geotextile, is a habitual hoarder of stuff like that 'just in case' - in fact you can see some at the bottom of the first picture).
And I feel your pain re. the paving – I just used the last few I had to extend a walkway don the side of my house and I had forgotten just how heavy the bloody things are!
Another question - is it a bad idea to build the frame on a slope and then move it into position?
I can either build it on the lawn (on more of a slope) and try to move it onto the supports, or attempt to build it in situ but not aligned to the supports (ie build it and then lift and shift slightly)
Ta
Why are you not just digging in 16 4×4 posts and postcreting them in. There is a lot of labour in digging but if you have the time that is not an issue (not sure what the ground is like – mine was awful digging through rubble by hand). If you have vertical posts then getting it level is a piece of piss. Getting it square is the challenge.
I did the slabs method when I built mine in front of the patio doors and it was fine - lasted years.
However, the landscape gardener who built the current one did the above method 🙄 and LOTS of them, mainly due to me having two buildings on the decking.
Both have been a haven for rats though
I can confirm concrete under slabs onto a weed membrane works well. I bodged a load of 300mm slabs with a 50 mm gap between them 15 years ago, expected it all to break up and move within a year, still solid and not moved today.
Build the frame on the slabs, it'll be really heavy to move.
There's no way you're lifting a 3.7 x 3.7 frame.
Ok, so in this week’s instalment of How To Train A Cack Handed DIYer To Build A Decking...
I have my concrete slab/block supports in place and most of the frame, but have two questions:
- can standard wall tiles be used to level / fill gap between supports and joist? I don’t have much else but are they strong enough compression wise?
- I think I want to install noggins to beef it up as it’ll have a filth pond on it - what screws should I use, how about special fixings and should I pre-drill?
Many thanks
DIY Disaster-er of Derbyshire
Tiles probably ok if you're talking the odd one as a shim, they may crack, would have been better to get all the blocks level but that ship has sailed. Screw, wood screws (my go to screw is goldscrews from screwfix), twice as long as your joist is wide at least, probably 6mm size. Yes I'd pilot the holes through the joist but not into the end grain of the noggin, screws don't hold so well in end grain, go in easier and are less likely to cause splitting.
Don't forget to stagger your noggins to allow access for screwing, can't really do it any other way. If you really wanted the noggins to line up you could use joist hangers but that's a lot more work and expense for a less structural solution.
Thanks john,
Tbh I’m not quite sure what happened - I levelled each support to the ones immediately next them using a 1.2m level.
It could be that my joists are slightly warped but it some places there’s quite a gap.
I don’t have to add noggins but am a little worried about it’s rigidity given it’s quite a big area.
Any other suggestions for filling the gaps - I think I have some floor tiles somewhere, I assume they’re less likely to crack?
Another question..
Should I be checking the level between each joist or trying to ensure more that the “surface” of the joists is level in terms of being flat for the deck boards?
I think to your last question it's the overall level of the frame that's important. I think you're right to put noggins in, it will improve rigidity and stop the joists splaying and twisting.
It can be easy to get the block level wrong, joists may well be warped or even slightly different sizes. I think roofing slate is a builders packer of choice, if you get hold of a couple of them and cut them up.
As above, slate. It also acts as a son and many houses was used as the dpm
Thanks, I’ve got 5 slates from the builders merchant so that should help.
I had a quick look and it seems in some places the wood has bowed upwards - it’s level if force it down onto the support.
So in that case, should I just rely on the weight of the boards pushing it down?
Sorry for all the questions. I worked in IT for 12 years and my brain doesn’t like how non binary this sort of stuff is!
I would have thought the boards screwed down would deal with any bowing.