How to Sand a Parquet floor
Today we are going to discuss the right and wrong procedures when it comes to parquet restoration. I have had people within the floor sanding industry with 15+ years experience tell me that the correct way to sand a parquet floor is to go diagonally across the floor. I believe this is incorrect for the most part and here is why:
Wood is essentially long fibres densely packed together. All the strength travels in one direction and not the other. By sanding with the grain you are sanding with the fibres of the wood and not displacing them. This means theres less abrassive scratching. By sanding against the grain of the wood you are tearing these fibres and stripping away the wood much faster, this makes for a much faster and aggressive sanding process.
Ideally you would sand with the grain all the time and this is possible with floor boards or strip floors. Sanding with the grain is best because its less aggressive and you have less scratching making for a smoother, better looking finish. When sanding parquet diagonally you are sanding with the grain on half the blocks and against the grain on the other half. This means that the blocks which are perpendicular to your sanding machine are going to be sanded down deeper than the blocks on which you are sanding with the grain. This alone can lead to a lumpy uneven parquet floor.
To add to this, sanding diagonally will inevitably mean that, for small periods of time, the drum will sit entirely on 1 block again all over the floor. Each individual block in a parquet floor varies in density from one block to the next and even varies within the block from one side to the other. So when the sander passes over a block that is much less dense than the rest of the floor and the drum is touching that one alone, it will get sanded much deeper than the rest of the floor. (When I say much, im talking millimetres, but it all adds to the effect)
By sanding straight and across a parquet floor it deals with both of these problems. First of all it means that all blocks are being sanded with an equal degree of aggressiveness. But the main benefit of this method is that the drum will never be sat on one block alone. It uses the varying densities of all the blocks to regulate the pressure on eachother. With this being said, there is going to be pits and lumps from varying wood densities, our goal is to minimize this to fractions of a millimetre rather than 1mm or even 2.
Next you should switch direction from straight to across. This helps to eliminate any imperfections caused by the sander. This is especially true of people doing DIY with hire tools as they tend to leave chatter marks across the floor and even cut in on one side leaving a ridge in the wood. So your process should be straight on 36grit, across on 50g, straight on 80g, across on 100g and finally straight on 120g.
There are occasions when the rules need to be broken. Sometimes it is not possible to change the direction by 90 degrees, purely because of space restraints. For example, when sanding parquet in a narrow hallway, you must find another way. There are many different solutions (and infact you can tailor your floor sanding method to any floor depending on the wood, pattern, size, damage and time restraint). A good general idea is to just do the alternate sanding 22.5 degrees off the straight sanding (you dont need a protractor just judge it, half way between diagonal and straight :), this way you are not going directly with or against any grain and you wont be going in the same direction you previously sanded. Its not perfect because there will be variation in aggressiveness but we are trying to make the best of a bad spacial situation.
Another time you may want to consider breaking the rules is if you anticipate that the linear sanding scratches from the belt/drum sander will not come out with the buffing process, or that there will be no buffing process, which is most often the case with DIY. and example of this is sanding pitch pine parquet. The sap content of the floor makes it incredibly difficult to get the scratches out because the abbrasives get clogged up. If this is the case, you should have noticed it early on. In this case I would definately recommend doing the final sand diagonally so that if the scratches dont come out after buffing (or you dont buff at all, DIYers ;), they’ll be relatively unnoticable.
The above also applies to fingerblock mosaic parquet. The difference being that in general the blocks run straight and across, so you want to sand diagonally to regulate the flatness of the floor.
I hope this helps. We will be posting more floor sanding tips and tricks in the blog soon.
Also check out the parquet sanding project in Hitchin we completed recently here: Floor Sanding Hitchin
If this has helped and would like to let us know or if you have any questions, you can post them in the comments section below