There is a lot to review prior to your project….I would like to try and synthesize the past week into a pithy post that will touch all the bases, but it will take more than one post – how many?….let’s see how this goes.
A disclaimer: you will have to have seen and participated in this project to understand the intricacies. This post is really only going to help the active student…the rest may be more confused than before….this is because it is a complex structure…..let’s see this post as a form of notes to aid in your understanding and not a replacement for being in class and participating!
As usual, the first step in this process is the lay out. Let’s say we have to construct a form for column that will be the height of an existing wall and a form for a beam that will connect the column to the wall that will be a given length. Of course we have to get the elevation of the column using the laser level. I won’t go through this step in the blog because we have gone over it many time in the shop….if you are still confused, come and see me and we’ll do a tutorial together.
The layout on the ground has to be at the correct distance from the wall and the correct size. The beam will be, say, 2950 mm from concrete to concrete. Given that the wall has a plywood form on it that is 20mm, and that the plumb bob has an offset from the wall of 30mm, we subtract 50mm(20 + 30) from the distance and measure from the vertical line defined by the plumb bob….this means that we measure 2900 from the line to the front of the concrete that we will be pouring. Since we have already found the centre of this column using Pythagoras theory, it is a simple matter of drawing on the floor the dimensions of the 400mm x 400mm column footprint from this measure. Then attach the front and back template 20mm from the front and rear lines.
Ok, that’s done. Now we will build the forms for the beam sides. A little math is required: If the beam is going to be 2950 mm concrete to concrete, the forms for the beam sides will fit into the forms for the column and the wall, which means that the plywood for the forms will be 40mm shorter (20 + 20) or 2910.
The plywood is going to be supported on a little “ladder” wall (a short stud wall) that will be 50 mm shorter than the plywood, or 2860. We will therefor cut two 2 x 4 upper plates and two lower plates for the two sides of the beam this length and nail them together with studs cut to the length of the beam side.
We nail the sheathing to these ladders remembering that they have to be mirror images to each other:
The beam bottom is constructed with the same dimensions of ply and with a structural beam cut to 20mm shorter than that length to allow for support. This is all nailed together:
While this is on the ground, we nail 3-1/2″ nails into the bottom of this component to act as registration points for the shores. There should be 4 nails in total, the first two 9 inches in from each end and the others equally spaced in between.
So that is the layout and the beam. Next post: the construction of the column form!