Hey Guys just wanted to try and see if i'm being a little overboard with how flat this new floor has to be. As i posted before its a thermally modified birch floor. the milling was very good and there were only about a dozen or so spots where there was a low board that needed to be hit with the edger in the whole job. Here is what i did i started with a 36" drum sander and had at it. When using the drum it would at times strip 2 of the boards it was sanding evenly and sometimes it would do one and about half of the other, when i moved it over to that board it came right down. what was nice was the floor had darkened from wear so when it was stripped you could easily see what was sanded and not. Very rarely did i have to go over a board more than once to get it sanded down. This wood although a hardwood is softer now due to the low water content 2.5% and i was afraid of going across the boards at an angel for fear scratching it to deep, this was confrimed where the the floor had to be turned due the floor trusses underneath turning perpendicular to the others. when the sander went over it left very deep scratch marks in the boards running the other way. i fixed this by running a DA sander over it with the same 36 grit. so my plan was that since the whole floor is sanded once with the 36 grit i was going to work up my grits to probably 120 with the 12x18 DA sander. so my question is how flat should this floor be or get? when you walk on it you cant feel any bumps or unevenness and i think it looks great, where im questioning myself is when i shop vac going across the grain i can feel little humps through the brushes on the handle. is this normal is it supposed to be pool table flat. check out the pics

thanks

sean
FYI if you click on the pics it gets larger


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Sean,

You will only see the final result (being flat) when the finish is applied, that means it will be too late in the process.

Flat is flat, run your hand (flat with fingers spread) lightly across the floor and you will feel the difference. A long straightedge will show uneveness also.

Sanding a floor flat takes skills, somebody without this can absolutely ruin a hardwood floor.

A skilled craftsman ussually sands a new install first under a slight angle to flatten it better, then sanding is continued along the boards overlapping only about a third of the drum witdth.

Starting with 36 grit is absolutely not the smartest thing to do, scratches you put in will need to be sanded out, starting with 60 grit is ussually all it needs on a newly installed floor.

Continue sanding up to 100-120 grit not skipping more than 1 grit size at the time (in your case 36 - 50, 80 than 100 and 120). Finish with a screen (120 grit for an oilbased finish or when you choose a stain and up to 150 grit when you finish with a waterborne finish).

If you are not experienced running a drum sander rent the square buff type sander and take your time (overlap not more than 1/2 the width). Vacuum well between grit changes.

ps. the thermal treatment causes the darkening, the first sanded wood will always look lighter even if the wood would not be treated.

Johannes.