Tips for setting gradient out

[Tomtomtom]

Hi, all,

DIY patio job of about 6.6 across back of the house and 3 metres out. Planning a 1:80 gradient across the 3 m and building that into my sub base (mot 1).

What im trying to work out js the best way to run my string so with the correct gradient to aid laying of the slabs. I'm using metal rods and string. But how do I ensure I have the correct gradient in the string? I could work something out, I.e graded measures on the rod but surely there must be a more accurate way to get it? I checked the site (EXCELLENT BTW) but didn't gather this part from what I read.

Any tips?

Edit: does anyone use those digital angle finders? The inclination will be between 0.7 and 0.8 degrees and they only have na accuracy plus minus 0.2 but perhaps this would be useful for laying the first slab and using that as a guide for the rest?

[Tony McC]

It's simply a matter of establishing a level (no fall) taut string line across the 3m span, and then applying the 1:80 gradient...

1:80 = 1÷80 = 0.0125 - so that's 0.0125m or 12.5mm per m. Multiply that by 3 for the width gives you 37.5mm, so the lower side of the patio wants to be 37.5mm (call it 40mm) lower than the high side.

Set up the level line - measure down 40mm - make a mark - reset the line, Voila!

[Dave_L]

I must admit I struggle with maths and gradients; to be honest I don't do them enough to remember how to calculate them!

[Tony McC]

There's a suite of calculators on the website that do it all for you.....

To convert between ratios and percentages - https://www.pavingexpert.com/gradient_01#gradient-convert

To determine amount of fall over a given distance - https://www.pavingexpert.com/gradient_01#findfall

[Tomtomtom]

Just worked out my issue.... I was assuming by line level you meant the line was level. Didn't twig that a line level was the type of spirit level. I was bobbling around with my 1.2m Tring to hold it steady. I think I have one too - result.

Thanks, chaps.

[Tony McC]

Not a 'line level' but a "level line" - a taut string line that is set to be level, flat, no fall in either direction. This is usually established with the aid of a straightedge.

The line levels, the little, finicky bubble levels that you dangle from a taut string line, are notoriously unreliable for anything other than absolutely basic setting-up. They are slightly more accurate than "rack of the eye" but not by much! We only ever use them as rough guides for, say, excavation, and then use a longer spirit level of at least 1.2m length for the setting-out, often extending its reach by combining it with a straightedge.... https://www.pavingexpert.com/setout02

[Tomtomtom]

Thanks, Tony.

Base done and all slabs laid. Bit of jointing to touch up (using easy joint) as on the edges of the patio there is nothing to hold it in place so it isn't tight to the edge.

[Tony McC]

Stop-up the open ends of joints with clay or duct tape and that will hold the jointing material in place until it cures.

[Bob_A]

Correct me if I'm wrong but didn't LLL came up with the idea of using
THIS