The Art of Floor Sanding (part 3)
Good day!
Floor bore here again.
Before we go into more detail about sanding techniques a quick summary of the basic machines you will need to do the job properly .
A good belt sanding machine .
This is used for heavy sanding and flattening of the floors.A Rotary finishing machine .
This is for lighter sanding, finishing and some can also be used for oil application.An edger machine for sanding the edges no less !
Various machines to do corners ( there are a few different methods )
I have deliberately not talked about the different makes of sanding machines and tools at this point -
Safe to say that whatever machine you use should be set up properly and adapted to these processes as seems fit . Some machines sand harder than others !
So let’s start with some basic sanding theory .
Unlike most other contractors we say NEVER SAND WITH THE GRAIN !
This of course seems counter intuitive .
So let me explain .
Let’s take for instance a typical Victorian pine floor.
Presuming the floors have been repaired, all nails punched down and the boards are secure.
We prepare for our first sand .
Depending on the state of the floor and your machine ,we select our abrasives .
We may choose for example 36 grit abrasives on a fairly rough uneven floor .
We now make our first cut at approx 15 degrees to the line of the grain .
In fact we can vary the angle depending on how aggressively the floors need to be sanded but try to keep the cut fairly close to the grain and definitely never straight across the grain .
So why the angle and why not follow the grain.
There are two reasons for this .
Firstly we want to properly SEE the scratches that the 36 grit is making .
Sanding slightly across the grain helps identify these marks clearly,.
As well as this if we sand along the grain the scratches can also cut deeper especially with certain types of wood .
The idea is that we can now be sure when we sand with our finishing machines that these scratches are removed .
Remember to use the light shining across the floor which will magnify exactly where you are in the process.
The other principle to bear in mind is that we want the belt machine to do as little as possible.
By this i mean we need the belt machine to sand the floors just enough so that the rotary machine can take over . Belt machines are amazing but extremely powerful and if we go through lighter grit abrasives will cause their own problems so we want to change over to a lighter finishing machine at the earliest possible point .
In our work we never go beyond 60 grit abrasives when using our belt machine and normally finish on 36/40 grit.
How do we therefore prepare the floor well enough for the rotary machine to take over sanding duties.
Lets go back to our Victorian pine .
We sand the whole floor to an angle approx 15 degrees from the straight line lets say with a 36 grit abrasive .
With the light we can see exactly how the floor looks after the first pass . We may now need to go over the floor again in the same direction if further flattening is required.
If not we can now concentrate on reducing the depth of the scratches caused by our first pass
All good belt machines will have a drum weight selector. Heavy, medium or light .
Our first pass will have been on the heavy setting .
Now change this to medium and run over the floor in the same direction .
One can also slightly increase the walking speed on this pass. The faster the walking speed the finer the sand . Depending on the size of the room and make of abrasive we can also use the same slightly worn abrasive on this pass to further reduce the depth of the scratches.
We are now ready for edging.
Our belt sanders job is already done