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Hellos
In my continued quest to make pleasant the festering pit of mud and children’s toys that is our garden, I’m building a 3.7m * 3.7m deck that will support an inflatable hot tub.
I’m just wondering what to use for risers - I’d thought about breeze blocks but am not sure how you can add small increments to the height of them?
Are those plastic adjustable risers strong enough for a temporary hot tub? They say they can take 1 vertical ton each but the manufacturer website suggests not suitable for spas (but perhaps they mean big permanent ones?)
Ta
Can you put blobs of cement under the blocks so the tops are level?
I am neither a landscaper nor a builder.
Dig down a little and use 2 breeze blocks? They probably should be on a concrete pad anyway. If you're putting an inflatable on then use lots of joists and decent thickness decking boards.
Yeah I guess so 🤔
Stumpyjon - I’ve accounted for 4*2” timber for the frame and decent thickness decks. My local supplier (who also install) have been very helpful indeed in that respect.
The plastic things look very handy but I’ve no idea if they’re up to the job?
Anyone else?
I’ve quite a lot of timber being delivered soon :-S
You can get concrete posts for support. Think the top is shaped to allow a joist to sit on and it has a shoulder to bolt through.
Bits of slate is the accepted method of making up small level differences.
I would be inclined to use a paving slab on a concrete foundation to spread the load and something like the already mentioned breeze block. Space out with plastic spacers as they go from 1mm to 10mm. Any more then use some wood. Remember there is going to be a lot of weight there so get the base well sorted.
You could use 1/2 bag of fence post mix under the flags
Use lengths of 4x4 resource treated timber vertically sunk in the ground then fixed in with postcrete
Fix the beams to these uprights
The above is a very good guide on how to construct decking that will be taking some weight
I’ve just poked about the garden and it seems my plot is on more than a slope than I’d really thought it to be.
I know in theory I should probably use the posts in concrete , level then chop posts off method but I’d not accounted for that in my timber order and it’s also a fair size decking so would need extra supports?
Wondering whether I can just stuff the weed membrane down and hope I can get things level with breeze blocks?
You could do it that way, but the deck would settle in a very short time, especially with putting a jacuzzi on it
Do it once , do it right
Do it right the first time and it will last.
Dig some holes, concrete some posts in, you’ll need the same amount of posts as concrete pads anyway to support the span of the 4x2
I’d dig them every 1.2-1.5m apart
Level them up then bolt the joists to them.
Phone the timber supplier first thing in the morning, they may be able to add on some additional timber
Something to bear in mind is that (in England and Wales) you need planning permission for a deck if it's more than 30cm above the ground. If it's higher than that, and you have neighbours and 6 foot fences, they will see you walking about and realise you could see into their garden, and they'll complain. Guess how I know.
Thanks guys, so the deck is supposed to be at ground level really hence why I thought breeze blocks rather than posts.
So, 3.6m square would require at least 16 supports by my reckoning? Eek. That’s a lot of wood, concrete and skill I’d not considered!
Ok, so can somebody help me work out what I need? I iz confused.
I’ve ordered enough framing timber for 9 internal joists at 40mm centres.
As there’s an odd number of internal joists I can’t get supports at 1.2m intervals or 1.5m.
I could have corner support, 1.2m across then first support, then 1.6m until the next support then 1.2m until the final corner support. It feels like that that middle gap is too big?
Also, would I just use 2*4” for the supports?
What bolt size would I need? 🤔
This has suddenly got more complicated than I’d hoped it would!
Personally I'd go for 4x4 posts and 6x2 joists. I'd still use breeze blocks but wouldn't consider them straight on the ground, level them up with a spirit level, pad of concrete underneath, then you can just build on top. If you want posts, dig the holes, build the frame with posts attached, pack out under the posts with stones etc. Get it level then pour in concrete around the posts, allow to set then plank it out. That way the posts are upright, in exactly the right place and the right height.
Thanks stumpyjon - unfortunately I’ve already ordered the timber so am stuck with 2*4 for the frame.
The concrete pad idea sounds good though, especially as I wouldn’t need more timber/bolts.
Only issue is the slope - I guess I’d have to dig out the higher end of the ground so I can get all pads at the same level?
How deep should the pad be? Presumably something ready mixed like postcrete would be ok?
Thanks
I have just built a 4m x 4m deck in my garden.
As per easy Girl. I would use 100mm x 100mm (4inch) posts with postcrete, get them vertical, height not so important as you then attach the 4 sides of the box and cut anything that protrudes up.
Getting it square is the harder part, if its wooden posts getting it level is easy.
I used 6x2 for the joists. I would not use 4x2. max 400mm gaps between the joists.
4x2 joists will be fine if they are adequately supported. The floor joists in your 1930’s house are the same arrangement, 4x2 joists supported in brick sleeper walls approx 1.5m apart
Maybe put a step in it if it's on a slope? How steep is it? Don't forget if >30 cm higher than ground will need planning permission and that's very likely on the down slope end.
Our deck sits on a concrete pad which the builders did when we had the extension done.
It's supported by a ledger board and those adjustable plastic feet. It's probably 5 x 2.5 meters so not massive, but the plastic widgets (Wickes sell them) are sturdy and easy to use.
If I was building something without a pad, as above, set some blocks in concrete and use a combination of resting on the block / some plastic widgets to level the slope.
RRR, you don't have to dig too much out at the top end. I built my neighbours deck like this, up slope it was a single breeze block on a pad, downslope it was up to 4, depends how much of a slope it was. We took some care putting the pads in, Trying to get their relative heights to in increments of a breeze block laid flat. When we built the stacks up we used the motar joints to fine tune the final heights and a 2m spirit level. It was worth getting that right as buildingbthe deck was then relatively straight forward.
The slope I guess (haven’t yet got any long timber to offer up) is 6” over a 4 metre drop.
I wouldn’t say I’ve much experience in these things so am looking for the simplest solution really!
The other challenge I have is that the soil at the top of the slope is full of hardcore from a previous owners patio and then bit at the bottom is softer and has a few old rotten tree stumps , just to make life more interesting ...
So, does 16 concrete pads sound about right? I feel like there should be some clever way of getting the pads a similar height without using loads of breeze blocks on top!
if you've joists that are long enough then you could just do your 4 concrete pads in a row (or however many you want), put a breeze block on each one, lay the joist over all 4, pop a level on the joist, then wiggle them till the joist is level and resting on all 4 of them, the soft concrete at this point will allow the breeze block to move up and down a bit
Right, so without a proper spirit level (on shopping list) and long timber it’s hard to tell but I’ve revised the drop to about 6” from closest edge to just under the fence where the ground drops.
The issue I’d forgotten about is that along the line of the fence (so a right angle) is a series of rotten stumps - some are solid and some soft. The plot is 4M * 4.1M but not perfectly square, hence my intention to put a 3.6M square deck on it and fill the edges with a decorative slate or something / plants.
The ground closest is solid and full
Of gravel, soft and squishy next to the fence.
I’m really not sure I could get co concrete pads at the same level and indeed whether they’d subside?
So, the concrete pad idea is growing on me.
Any idea which of Wickes finest pre mixed concrete would be best?
I’d thought postcrete but that’s kind of meant to be lobbed in a hole and watered innit? Would it give a smooth enough top to put a block on or the joists themselves? Or would a quick drying concrete be better?!
Thanks all for the continued help and emotional support. I threatened to cancel the timber order and buy 2 bulk bags of plum slate earlier .... :-S
1 part cement, 2 parts sharp sand, 3 parts ballast for concrete, 2 parts cement to 3 parts builders sand for decent mortar. Don't buy the premised stuff it's all sand and no cement.
1 part cement, 2 parts sharp sand, 3 parts ballast for concrete, 2 parts cement to 3 parts builders sand for decent mortar. Don’t buy the premised stuff it’s all sand and no cement.
Postcrete is just cement + sand + other shit. If you buy seperatley you can mix yourself and lob it in a hole and then adding water. Old bits of bricks and the remains of your wife ect. Will set fine.
Cheapest, but more labour intensive, is to buy ballast and cement if your making concrete. Wickes sell it in 25kg bags so that makes it easy to gauge the ratio, 5 ballast bags to 1 cement bag
Depends on the size of your hole but that we’ll probably do 2 or 3 pads easily.
, 2 parts cement to 3 parts builders sand for decent mortar
Wtf are you mortaring with that? 5:1 is the most common mix, maybe 3:1 for pointing in exposed circumstances. 3:2 and you'll get loads of problem with shrinkage, not to mention it costing triple what it should
So, I was thinking of 150mm square pads * 16.
Do you think I need more concrete per pad?
I appreciate the ready mixed stuff is a lot more expensive but I’ve got no concept of how much concrete (ballast, sand, cement) I’d need for one pad?!
Ta
Postcrete will be fine, and way less work and mess.
Thanks, do you reckon one bag of postcrete would make one 6” cube pad?! I’ve really no idea
How deep are you making it? One bag makes about the same volume dry and wet
Well I was thinking 150mm wide and 150mm deep. I guess I might get a couple out of one bag?
I’m not an expert on concrete, but I wouldn’t be using postcrete to make pads.
It’s ok for what it is designed for , I.e to surround a post in a hole, which ground pressure / stitchion etc come into play, but if exposed then it’s not got a lot of strength and can blow out fairly easily.
Use the ready mix concrete or high strength concrete instead. It’s a couple more quid a bag, but it’s the old adage, buy shite buy twice 😉
Wtf are you mortaring with that? 5:1 is the most common mix, maybe 3:1 for pointing in exposed circumstances. 3:2 and you’ll get loads of problem with shrinkage, not to mention it costing triple what it should
Oops, should have been 5:2 ratio, from my father in law, ex victorian builder who still went to work in a suit jacket and tie. Proper old school. Worked well for me on the walls and garage I built.
Don’t use postcrete for a supportive structural pad, there’s good reasons why proper concrete mix is used in structural situations.
Either mix it up with ballast and cement yourself 5:1 or look into if you can pre mixed proper concrete (I’ve no idea if you can, we always mix our own,I’m a builder by the way)
Personally , a 6” cubed pad isn’t big enough. Your bearing all the weight of the deck and what ever you put on it on a 6” square.... it will most possibly subside over time, make it bigger, at least 300mm square and deep, deeper the better really, especially if there is a slope involved
1 bag of 25kg premixed concrete would do 1 300x300x300 hole I should think, but always best to budget for more as your holes are never going to be the exact size you want them to be.
Sounds reasonable! Thing is, 16 bags of pre mixed stuff is going to add at least £150 to the cost.
I’d hoped I’d be using some breeze blocks for a few quid!
The 150mm cube idea was based on a B and Q guide but yep it doesn’t sound a lot to put it on, especially with the inflatable hot tub going on it.
This is rapidly turning into a nightmare ish money pit of nightmares..
Plenty folk sit them on slabs, and there's always folk giving slabs away. Mine is sat on a full 6" concrete pad, I had a load of broken slabs and aggregate to get shot of, easiest way was to use it as a deck base, it'll never move! (and it never has)
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.