Wood – Can stained MDF be restored

Staining will highlight any imperfections in the wood. From the photo it looks like something has been wiped across the grain. That could be when you wiped the sawdust away or possibly if you wiped the stain across the grain.

Having a good surface to stain is pretty much essential as the stain will highlight even the smallest imperfections.

Applying thin coats as John suggests is the best way.

Also, don't forget that the wood will age - especially for something left outside - so any imperfections you see now will blend over time.

There's adhesives available from a company called Loctite‎, that come in different formulas. From temporary stick, all the way up to welded forever.

With black pipe, I would clean the threads really well to remove cutting-fluid used by the factory. I've gotten Loctite before at car parts stores, and the old farts there will give you a good recommendation on which flavor to use. Alternatively, you could use JB Weld, which again will require the surfaces to be cleaned thoroughly, but unlike most Loctite formulas will become effectively glued forever.. Good Luck!