Hello, I bought a truck that already had hardwood put in bed it needs to be refinished but it has alot of black spots is there anything I can put on it to take them out sanding dosen't seem to do it. Thanks Michael

 

Its hard to say not knowing what the dark spots are. You said that they wont sand out so I will assume that you have sanded any finish off and you are down to bare wood.If they are dark spots from stain you can sometimes use bleach. I've never tried it, I just remember it from my high school wood shop class. You might be careful with this it may lighten the wood and leave the black marks alone.
If its oil spots on wood you may want to mix a couple tablespoons of apple cider vinegar with about 16oz of water. I have a spray bottle for this but you could mix in a container and just wipe it on. Let it sit for 15 mins give or take. Water alone will make the grain of the wood rise up, the vinegar just helps it rise a little more. This may bring up the dark spot and then you can sand it off.
Just a couple of thoughts on the matter

 

if your black spots are from water (especially on oak) they come from a reaction between iron in water and tannic acid in the wood. if you have sanded the wood or otherwise removed the finish, the black spots can be bleached with Oxalic Acid. oxalic acid is usually available in the paint section of a hardware or big box. my ace hardware carries it. you dissolve it in warm water and apply. it is best to use distilled water. if you use other water that has any iron in it, you will turn the whole board gray (don't ask me how i know that). if the spots are from iron in the water, the oxalic acid will make them magically disappear (may take a little while). i usually put some solution on the whole board so you don't get a light spot. when finished, rinse thoroughly and then rinse with a solution of water and baking soda to neutralize any remaining acid. it is very difficult to keep oak from getting black spots in an outdoor situation. many coats of marine spar varnish might do it. let us know if this works. i often use oxalic acid on oak furniture. dick r.

 

You may have natual dark spots, knottes and some grains show as dark spots... I would pick a test spot that isn't noticable and test it with bleach... use a q-tip to apply it if you want to try to whitten it... Some times you may have to darken the wood with stain and then either way you choose use a marine grade varnish....