Question - I built a picnic table of pine. What should be used to preserve it? Would any perservative be safe for children eating off the table?

- John Adams, Somerville, Mass.

Answer - You could treat it with a clear sealer, which must be reapplied every year or two, creating an unavoidable maintenance situation. Be sure to treat all surfaces, including the underside of the top and all legs and connectors.

But I think it'd be better to use a semitransparent stain; you can get the color of your choice, it will dry well enough so it will not rub off on clothing, and it will preserve the wood probably better than a sealer. And, good news, it will last three to five years. As for safety as an eating area, it will not be a problem as long as the kids don't chew it and as long as they use plates. Incidental picking up of food should not be a problem.

Question - The outside flap of my exhaust fan does not close when the fan goes off. The fan is housed in a hood, so it opens on a horizontal plane rather than a vertical plane as on a fan installed in a wall. My neighbors have similar ones that work well. It is a Nu-Tone.

- John Donnelly, Needham, Mass.

Answer - It sounds as if the spring or other device that closed the flap when the fan stops is broken or gone. I would contact Nu-Tone, which has a good name in ventilation and which should be happy to fix it to keep up its good name.

Question - I am replacing the spruce floorboards (they rotted out) with pressure-treated boards in a 10-by-40-foot deck. I think the joists and other parts of the frame are OK. Should I put the new boards lengthwise and parallel to the house, the way the original boards were, or should I put them at right angles to the house, so I can use 10-foot boards and don't have to butt any boards together, end to end.

- Theo Madden, Duxbury, Mass.

Answer - Put them the same way as the original boards were; keep a 3/8-inch gap where they butt end to end, over a joist. If you tried putting the boards at right angles to the house, you would have to rebuild the frame.

The only problem you might have is water staying in that joint where the boards butt end to end over a joist. In fact, that is where decay might have occurred in the frame. To get around that, I suggest you lay an extra joist an inch or so away from the original joist wherever boards butt end to end. That way you can have the gap between board ends, but the water will drip into the space under the deck, preventing further decay.

Question - My house was built 15 years ago with all cedar board siding. It was treated with Aquatrol preservative until it was discontinued. Now it is treated with CWF-UV. My problem is that sunny areas are bleached out and shaded areas are very dark.

I would like to paint the house a cedar color to reduce maintenance and have a more even color. Can I paint over the CWF-UV or must it be removed?

- R. Norton, Rainbow Springs, Fla.

Answer - One must assume that the cedar is still in good shape, other than bleaching out and darkening. For starters, check those black areas to see if they are mold or mildew. Put bleach on a small area of the black; if it turns to cedar color in five seconds or so, it is mold, and it must be removed. Kill it and remove it with a solution of one part bleach and three parts water, then rinse. Wear skin and eye protection when working with bleach. If the bleach test does not turn it light color, then it is weathering and nothing has to be done, although you might want to sand it to the bare cedar in order to keep the new treatment even.

I think you can prime and paint over the CWF, but I would not suggest paint or primer but rather semitransparent stain, which you can get in a cedar-look color. One coat is needed, and the stain will last three to five years. The stain might go over the CWF, particularly if the CWF has weathered for a year or more. So, treat a small area with the semitransparent stain; if the stain beads up, stop, because it is not penetrating the wood and you have to let the CWF wear off or sand thoroughly before trying the stain again. And the CWF may stay longer on protected areas such as under windows and eaves, so you might have to sand those areas anwyay.

If the cedar sucks up the stain without beading up, go ahead with the stain for an even, long-lasting finish.

Question - I am putting in a used radiator to replace a smaller one in my son's room. How can I clean out the used radiator? The boiler is only three years old, and I am getting a lot of rusty, sludgy water when I drain the boiler.

- Rob Warren, Newton, Mass.

Answer - Remove the steam valve of the used radiator and flush it with a hose or a pressure-washer. The rusty, sludgy water is probably not coming from the new boiler but from the other radiators in the system. In that case, you might try flushing all the other radiators.