Anybody know anything about building slipways?

Kelpie

Kelpie

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Not really boaty. I need to put a surface on my driveway due to the steep slope, and concrete seems much cheaper than the quotes I've had for tar. At first I thought maybe you can't use concrete on a slope, and then I wondered how they do slipways, which are exclusively done in concrete.
I don't suppose anybody here has been involved in making one at a club or some such?
 
I've built a few steepish farm drives and gate entrances in concrete. You need to ask the supplier about high and low slump ratios, and to cast in small sections. Beware of over-tamping.
 
Not sure quite how steep your driveway is going to be but on the couple of slopes I've cast I've found the reinforcing steel grid I used stopped anything moving. I didn't do it by laying out the grid and then pouring through because then it does need to be fairly sloppy, I did it by laying two or three inches of the concrete across the area, then putting the steel mesh on that, then covering over with another two or three inches of concrete before finally using a length of 4x2 across to tamp down, working both up and down the slope.
 
If you had posted this last week , I might have said "when are you planning on doing this, I will come and give you a hand." Too late though, I spent a day at the local scout camp putting in a concrete base for a gas tank this week, My contribution was £120 for a new mixer. I reckon the osteopath bills will only come to double that before I can walk again. Not quite that bad, but my brain writes cheques that my body can no longer cash.
Preparation is everything. Scrape the bottom of the road box flat (ish), erect the shuttering, 75mm of hardcore on that and wacker it in. 150mm of concrete on top will carry anything except HGV's. I don't know what you are putting on the concrete but rebar isn't really necessary unless its a big area and you wish to prevent cracking. For this type of job have used wire netting very succesfully . You will need an expansion joint every 4 to 5 metres.
Mix it slightly dry if you have any worries about it slumping down the slope but it would need to be a fairly steep slope for that. Bear (bare?) in mind its harder to rake when semi dry.
Have fun.
 
Kelpie said:
Not really boaty. I need to put a surface on my driveway due to the steep slope, and concrete seems much cheaper than the quotes I've had for tar. At first I thought maybe you can't use concrete on a slope, and then I wondered how they do slipways, which are exclusively done in concrete.
I don't suppose anybody here has been involved in making one at a club or some such?
Click to expand...

Been working with concrete all my life. The important thing to appreciate is that wet concrete is not a liquid it has shear strength. Generally there is no problem laying on slopes up to about 1:3 but you need to keep the mix relatively dry. As somebody has already said this "workability" is measured by the empirical "slump test". You could try asking for 50mm to 100mm slump but it should be enough to tell the readymix supplier that you are laying it on a steep slope.

We re-built a slipway at our club a few years ago placed all the reinforcement in advance of concreting. We poured through the bars with no difficulties. Start at the bottom. Place and compact the concrete slowly and screed it off roughly to level as you go. You don't want to end up with too much at the bottom and have to shovel it up the hill!

Don't forget to cover the wet concrete with polythene as soon as you can and keep it covered for 3 or 4 days. This is called curing and stops shrinkage due to rapid water loss until the cement paste has gained enough strength to resist cracking.
 
We did a slipway here, gradient of most of it 1-6 which is about as steep as it is comfortable to walk on. We had no trouble laying it working down from the top but we had an existing pier alongside which meant that we did not have to barrow it over the steel. Concrete shrinks on curing so to avoid random cracks it is better if you lay it in alternating bays. If you buy a 6 cubic m. load and you are laying it 150mm thick that is about 36 sq. m. say 9m by 4m wide, a straight joint about every 3 or 4 m. looks a lot better than random cracks which can grow moss, if you are laying continually place boards across at regular intervals to create a joint, take it out or loosen as soon as it sets, later you can fill with cement. An even better way is to use the galv. steel inverted tee shaped jointing laths which remain in place permanently. A dry mix as well as resisting flow allows the surface to be textured for grip with the tamping board.
Having said that, I used precast block pavers for our steep garage apron, 6m.x 6m. at 1 in 8, With good preparation they are much easier to lay than concrete and you can do the job easily single handed without the time pressure that ready mix imposes. The 50mm. thick ones are strong enough for domestic traffic, eight years and no cracks so far. The in situ conc. garage floor is also 6m. square, it has one contraction joint down the middle which is just visible, surface was polished using a big steel float like a snow board on an extendable shaft, I used a richer mix here to get a good smooth dust free finish. I employed a dumper with driver, and a concretor for the half day it took to lay the floor, would have been impossible single handed and the guys skill and know how was well worth the £100 I gave him.
 
Thanks for the replies.
I've done a fair bit of concrete work before so I know the basics, just everything I have done has been with the aim of a level surface, and involving lots of tamping and floating. So I was a bit unsure about how you go about getting the air out and getting the concrete worked down into the formers and around the rebar, if you can't whack it about a bit.
I've got a vibrating thingy (my google ad history went a bit funny for a few days after I bought that!) but that pretty much liquefies the concrete so I guess it'll be useless for pouring on a slope.

Has anybody used top shutters at all? It would mean buying a lot more timber.

Hadn't even thought about how to get the barrows down over the rebar... side access is not great, maybe planks laid on bits of timber to keep them clear of the rebar?
 
Kelpie said:
Hadn't even thought about how to get the barrows down over the rebar... side access is not great, maybe planks laid on bits of timber to keep them clear of the rebar?
Click to expand...

It sounds as if you have a decent slope, so purloin a few lengths of corrugated sheeting and make up a slide. Empty barrow at top, and jiggle the mix down the hill.
 
sarabande said:
It sounds as if you have a decent slope, so purloin a few lengths of corrugated sheeting and make up a slide. Empty barrow at top, and jiggle the mix down the hill.
Click to expand...

That's a sterling idea. The lorry might even be able to shoot into the top part of the area anyway.
 
Triassic said:
Not sure quite how steep your driveway is going to be but on the couple of slopes I've cast I've found the reinforcing steel grid I used stopped anything moving. I didn't do it by laying out the grid and then pouring through because then it does need to be fairly sloppy, I did it by laying two or three inches of the concrete across the area, then putting the steel mesh on that, then covering over with another two or three inches of concrete before finally using a length of 4x2 across to tamp down, working both up and down the slope.
Click to expand...

Great thread, answers nearly all my questions for a similar job,.
BUT

My drive is steep (1:3 in places?) and I need to get an eight-wheeler(16 tonne?) loaded with a 3.5tonne boat up and down it.

What sort of thickness of concrete would I need? Any ideas?

Thanks in anticipation
 
Rough guess.


Layer of Terram
Layer of rammed hardcore 150mm
Another layer of Terram
150mm high-test concrete with proper rebar and mesh. Possibly use fibre-reinforced concrete, making ure hte supplier knows it's for a steep slope.

I have not laid a long drive, so there will be optimum sizes for bays that need advice.
 
Thank you.
My drive is only about 25 - 30 metres long and the base is solid-Scotland so I wouldn't need the first layer of Terram.
And certainly not need passing bays!!

You think 150mm concrete would be ok for circa 19/20 tonnes? If so, that's nicely within funds.

I have a local ready-mix supplier (a friend) and I like the idea of corrugated sheets to slide the mix to the bottom.:)

:encouragement:
 
By 'bays' I think he means individual slabs between each expansion joint (usually about 5m at a time), not passing places!
 
Robert Wilson said:
Great thread, answers nearly all my questions for a similar job,.
BUT

My drive is steep (1:3 in places?) and I need to get an eight-wheeler(16 tonne?) loaded with a 3.5tonne boat up and down it.

What sort of thickness of concrete would I need? Any ideas?

Thanks in anticipation
Click to expand...

Are you sure about the 1-3 gradient? You know that is too steep to walk on normally. Getting a boat up it would be quite a challenge. There was an item on TV during the week about the worlds steepest street, in Dunedin NZ. It was 1 to 2.8 and looked very strange indeed, they had to keep a cop there to stop kids on bikes killing themselves. Building regs. require access ramping to dwellings to be max. 1-12 gradient but driveways are practical up to about 1-6 if there is an alternative route, it is quite difficult to get soil to stay in place at much more than 1-3.
But of course a permanently rigged rope and some carbineers and you could start a climbing school!

Thickness of reinforced concrete is traditionally 150mm. in paths and driveways, carefully laid, well reinforced, on a flattish surface with frequent movement joints 100mm. is possible but probably not at 1-3 gradient.
 
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Kelpie said:
By 'bays' I think he means individual slabs between each expansion joint (usually about 5m at a time), not passing places![/QUOTE]

Doh !!:o

Quandary said:
Are you sure about the 1-3 gradient? You know that is too steep to walk on normally. Getting a boat up it would be quite a challenge. There was an item on TV during the week about the worlds steepest street, in Dunedin NZ. It was 1 to 2.8 and looked very strange indeed, they had to keep a cop there to stop kids on bikes killing themselves. Building regs. require access ramping to dwellings to be max. 1-12 gradient but driveways are practical up to about 1-6 if there is an alternative route, it is quite difficult to get soil to stay in place at much more than 1-3.
But of course a permanently rigged rope and some carbineers and you could start a climbing school!

Thickness of reinforced concrete is traditionally 150mm. in paths and driveways, carefully laid, well reinforced, on a flattish surface with frequent movement joints 100mm. is possible but probably not at 1-3 gradient.
Click to expand...

I was guessing. I'll measure it more accurately tomorrow. I saw that Dunedin clip, and I'm sure mine is not that steep!
Click to expand...
 
Robert
If you have not done any concreting before I would recommend you ask your friend to recommend someone with experience to give you half a day when placing. It will not be wasted money as there are quite a few knacks and tricks in shuttering and tamping that will save you more than you have to pay him in wasted concrete. I had been an architect and my wife and I built our first house including placing all the concrete floors and screeds, but the labourer that helped me place the garage floor here knew how to make the job easier, better and more economical. The Terram or just polythene sheet is useful if you are attempting to lay to minimum thickness as it adds strength by ensuring that the bottom inch or so does not go crumbly and makes laying an easier job so worth balancing its cost against going thicker?

'Bays' is a term used by engineers, it has nothing to do with lay bys, it simply means a square or panel of defined size. Concrete is laid in bays, walls are constructed in bays etc.
 
I never knew laying concrete could be so interesting!
Really nice to see straightforward constructive comments from people with the experience, it make the forum worthwhile.
And a nice change after reading stuff from the likes of Nicolas321blast-off.

Robert
We need some pictures, before and after.
Peter
 
Yes I'm glad my question has led to useful information for other people as well!
And unlike mine, Robert's driveway will be a slipway, of sorts, given it is going to have a boat on it :)
 
Resolution said:
I never knew laying concrete could be so interesting!
Really nice to see straightforward constructive comments from people with the experience, it make the forum worthwhile.
And a nice change after reading stuff from the likes of Nicolas321blast-off.

Robert
We need some pictures, before and after.
Peter
Click to expand...

Sure thing, Peter - but don't hold your breath. I have an engine to sort out first !!!

Quandary.
Thanks for the advice. Much appreciated and I have taken note.
I have done concreting before, but not to this complexity.
I once laid a pad for a large greenhouse. Full load of Readymix dumped on the main road into Darlington, three of us with shovels and barrows. Took a bit longer than expected, hotter day than expected, concrete went off quicker than expected - hardening lump of concrete on main road.
Oooooops.
PANIC!!
 
i would set plywood “stairs” in the slope, to reduce slumping from potential big scale to a series of small ones. In fact, er that;s the right way to do it - then you just a a series of short slopes. I’d jet blast the existing surface, put a 2-4 inch mesh down, then ply shuttering either side at the level of the final slope, and ply at various heights, perhaps supported being with a bit of rebar. Do the stairs first, then bog around with the slope on final pass, and this means you CAN use the tamping machine and I win the Best Answer prize :-)
 
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