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.

Some useful bits here;

https://www.wrekinconcreteproducts.co.uk/products/

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 4×4 resource treated timber vertically sunk in the ground then fixed in with postcrete
Fix the beams to these uprights

https://www.google.co.uk/url?sa=i&url=https%3A%2F%2Fwww.wickes.co.uk%2Fhow-to-guides%2Fgarden-landscaping%2Fplan-build-a-raised-deck&psig=AOvVaw0C36YiMqCvbRiUzPayYaAd&ust=1589214969589000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCIDo6J_dqekCFQAAAAAdAAAAABAD

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 4×2
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!

Yeah +1 to make sure you don’t need planning permission.

This has a guide:

linky

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 4×4 posts and 6×2 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 6×2 for the joists. I would not use 4×2. max 400mm gaps between the joists.

4×2 joists will be fine if they are adequately supported. The floor joists in your 1930’s house are the same arrangement, 4×2 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.

https://i.ibb.co/1mZvGdF/A9-F1-D654-3838-4-F2-F-943-D-3115248-BDE57.jpg

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?