AL CARON, Marion

A.Those stains have penetrated the finish and are deep in the wood. No guarantees, but sand to the bare wood with a floor sander, bleach the stain with household bleach or oxalic acid (use plenty of ventilation), and if most of the stain is gone, refinish. If a lot of the stain remains, then try staining the whole floor with a dark stain, then finish with polyurethane varnish.

As for the sill of the garden window, which is a little greenhouse that extends outside, the same thing happened, except by water. The cure is the same, but instead of all that work, why not apply a layer of Formica laminated plastic. Cut it to fit the space and apply it with contact cement. Or, apply ceramic tile.

Q. My stone retaining wall is skimcoated on the sides and top, and is beginning to crack. A mason suggested removing all paint, filling cracks in the skimcoat, adding a bonding agent and new skimcoat. Would this work? I’d like to add a tint to change the color of the skimcoat.

MARY YOUNG, Medford

A. Yes, that would work well, and the addition of a bonding agent will make doubly sure the skimcoat will stick. Frankly, I would avoid adding a tint. Some day you could remove the skimcoat to reveal the stone. Keep the skimcoat on the top; it keeps the top from succumbing to wear and tear and other weather.

Q. I have two skylights that leak which makes the plaster in the ceiling puffy and causes flaking. Roofers confirmed that the flashing is correct. I asked the manufacturer for a replacement window and they no longer make that size window (20-plus years old). Anything I can do other than ripping the whole thing out?

BUDDY, in Hotton’s chat room

A. If it is not the flashing it is the glazing (putty or a rubber or plastic gasket). If you can keep the basic frame (the one that is properly flashed), then try for a new unit. If it is a flat window (roof window) and not a skylight, try for a Velux.

Q. Just Curious. Why don’t kitchen sinks have overflow drains, whereas the bathroom sink and tub do?

JEFF, in Hotton’s chat room

A. Another great question, and another “stump the Handyman’’ triumph. Beats me. Perhaps it is because in this era of dishwashers and disposals, most sinks don’t have stoppers, but rather strainers that do not close or don’t close well. Anyone else have any brilliant ideas?

Another one that stumped the Handyman was this one: Why is a carpenter’s pencil very plump but flat? Because it will not roll away when placed on a roof or sloped surface.

Q. What is the best adhesive for ceramic tile on a concrete cellar floor? Some of the floor has been painted with a waterproof paint, and the floor is subject to moisture and water.

STEPHEN DOWNS, Kingston

A. Thin-set mortar. The best stuff you can buy; it has an additive that makes it grip like nothing else, and sometimes you can add something that makes it grip better. Use it on any surface: concrete, wood, plasterboard, any hard surface, indoors and out. It will work on paint as long as the paint is intact. I am not sure if it will work on metal. You will have to destroy it to remove it. I think it also works on granite, marble, and other stone.

Q. Energy-efficiency steps recommended to us include cutting a linear opening (5-plus feet) in the roof and blowing in 8 inches of cellulose insulation (and reinstalling the roof afterward ). We live in a Cape with a finished second floor and shed dormer. The energy firm sent out by Cape Light Compact said this would be preferable to an earlier recommendation that involved installing an attic access hatch. I believe the reasoning has to do with ease of access. What are your thoughts on cutting into the roof ? Is there any reason not to follow this advice? Most of the costs will be subsidized, so price is not a factor in our decision.

MARILEE, Brewster

A. If the intent is to blow insulation in the attic floor, cutting a hole in the roof is not a good idea for two reasons. One, the insulation would be blown in blind, and it could fill the eaves, a thing you do not want to do. Putting in any other kind of insulation (batts, rigid, etc.) is equally iffy. The second reason is that insulators are not carpenters and roofers, and it would be difficult for even a professional to reinstall the roof and new shingles without causing leaks. So, I think it is best to cut a trap door in the attic floor so an insulator could get up there and do it right.

Globe Handyman on Call Peter Hotton is also in the g section on Thursdays. He is available 1-6 p.m. Tuesdays to answer questions on house repair. Call 617-929-2930. Hotton (photton@globe.com) also chats online about house matters 2-3 p.m. Thursdays. To participate, go to www.Boston.com.