How do I keep everything straight and level

[dazzystar]

Hi All,

I need to create a 2.4m x 2.4m perimeter inside my block paved patio for a concrete slab to be poured to support a hot tub. I'll be removing the patio blocks along with the sand and using 600mm x 150mm x 50mm concrete edging around the perimeter and getting these level in readiness for the concrete pour. I'll be bedding in these concrete edgings. This is something I've never done before and before I start I wanted to make sure I get everything I need in advance.

What I'd like to know is how I create straight and true lines for my edging to sit in. A spirit level on a vertical surface is one thing but not on the patio! Could someone tell me how I can string a line or use a laser level or whatever I need to do please? I've added a pic of the area with a rough outline in red of the square I need to create.

Cheers
Daz

 

[dazzystar]

 

[scbk]

I know hot tubs are heavy when full of water, but as the weight is spread out, would the block paving not be strong enough as it is?

 

[dazzystar]

No as there's too much of a slope on the blocks as some have also sunk a little too much.

 

[Mike13]

Use a clear tube/hosepipe as your spirit level, each end will be at the same height, and spare tube can wiggle across the middle of the area. Adjust each end alongside whatever point you decide things must be set to.

 

[robinbanks]

What I'd like to know is how I create straight and true lines for my edging to sit in

Pythagoras

Decide one edge by eye, depending on where you want your hot tub to be and how you want it to be rotated

Use a straight edge, such as a long spirit level, piece of wood (look down it to assess its straightness) or sheet of ply with factory cut edge, and a can of line marking paint; put the straight edge so that it covers the blocks you want to keep (put it on the outside of the square) and spray the floor so that the straight edge works like a stencil (you might want to put masking tape on your spirit level to keep it clean) giving you a clean line when the straight edge is lifted. If your eyesight is great you could do this with a sharpie, but it's hard to see when cutting. Mark your 2.4m line. If using a piece of ply as a measure as well as a straight edge, remember to check if it's 2400 (metric) or 2440 (imperial 8ft)

Now you have your straight edge marked, create a 3,4,5 triangle: for any triangle with two shorter sides of 3 and 4, the long side is 5 and the angle opposite the 5 side is 90 degrees. Use multiples to make the triangle larger for more accuracy

For example if you take the 2.4m line you just made as the 4 side, that's a multiplier of 6. If you were to attach two tape measures to the ends of the line then pull the tapes out so that one measures 1.8m and the other measures 3m, and adjust their angles so that when the tapes cross, the 1.8m is touching the 3m, then the angle at the other end of the 1.8m tape is 90. Mark the floor (with a sharpie) and then, keeping the two tape ends where they are, go to the other corner and do the same. Line through these points (which are 1.8m away from the sprayed line) to 2.4m. As a check, measure the distance between the two corner points furthest from the sprayed line; they should also be 2.4m apart, and the diagonals should measure the same (3.394)

Once marked with a sharpie and you're happy all measurements are good, you can put your straight edge down and spray your lines, then get your wet-cut stihl saw out and cut the lines