In my last patio post I explained the labor intense task of bringing in base rock where the future patio would sit and compacting. Today I wanted to talk about the more tedious part of the project; using a string level to grade the slope of the patio.
Here's a shot of the patio base with some rock in place:
See all that yellow string? It's in place to help us make sure we're getting the grade right. It's important when creating a base that it is sloping away from the house (but not too much) and that it has a consistent level with no hills and valleys in the rock.
When creating our slope, we decided to go with 2 degrees. Some quick research told us that the slope (rise over run if you recall your high school geometry) is 1/4 inch per foot. We picked our centerpoint on the patio, which was the edge of the step from the deck (you can see it in the bottom right corner of the picture above) because we wanted to be sure the step from the deck to the patio was correct, and this was the easiest way we saw to do it.
From there we placed stakes around the yard and found level everywhere using a string level. We started with the level below, and quickly scrapped it.
This level worked much better for us. It was easy to snap on and off of the string, and the liquid was wide enough that we trusted the level more than the one above.
It's hard to believe that this little gadget, purchased at the hardware store for like $3, was one of the most valuable tools we had during the patio reno, and that it has been the way people have been finding level for thousands of years. We both read Ken Follet's Pillars of the Earth back in the day, a story about building a cathedral circa the year 1000, and there were lots of Tom Builder jokes made as we used string and a level in today's modern world of lasers and power tools.
Once we found level we had to do some more calculations. The picture below is of the stake we placed at that center point at the edge of the deck. The stone we are using is 1 1/4 inches high, and it will sit in 1 inch of sand, so we had to decide where we wanted the final patio height to be and level from there. Then we subtracted 2 1/4 inches to find the height that we need the top of the base rock.
In other areas of the patio things were a little more complicated, because we had to not only subtract that 2 1/4 inches for sand and stone, but also add or subtract an additional amount for the slope. Because our slope is 1/4 inch per foot, we measured the vertical distance between the center point and the stake and multiplied by .25.
For example, we planned our walkway below the deck to be 4 feet wide. 4 x .25 = 1, so we subtracted 1 inch from level, then that 2 1/4 inches for sand and stone, leaving us with our new height for the base rock.
Simple, right? You'd think so, but there was a lot of trial and error for us before we made it to that point. It's important to note that we only measured the vertical distance between the posts. Take a look at the picture again from above, when measuring for grading, it's important to measure perpendicular to the posts, not the string length, to do your calculations. The string could be 20 ft long, but the rise of the patio could be only 2 ft (so you would raise or lower the string only 1/2 inch).
Once we got our slope down we added string between the posts so we could see if there were any high or low spots in the patio that needed to have more rock added in, or removed to make it level.
This was definitely an arduous process, and took a long time to get right. It was great though to see the finished result: a patio base ready for sand and stone!