Timeliness key in treating ugly oil stains

Q. We have a very thick, ugly oil stain on our concrete garage floor, caused by a leaking old car. How can we clean it up?

A. The most important rule for dealing with oil stains on garage floors and driveways is to try and remove them as soon as possible after they appear. Second, immediately repair oil leaks caused by vehicles or lawn equipment or, if there is a delay in repairing, use a drip pan (metal drip pans are sold at auto-parts stores) or other collector to catch the drips.

Many times leaks are caused by a loose oil filter or loose oil drain plug. Thick deposits of grease should be scraped off, leaving just the surface stain.

Over the years I have received reader recommendations for a number of oil-stain cleaners, but none more often than Oil Eater, which is sold at some discount stores and on the Internet. It is available in liquid form, for spray application, and as absorbent pads. Several applications might be needed for old, deep stains.

I have also used absorbent materials to remove or improve fresh stains. Absorbents can include cat litter (not the clumping kind, which can cause stains of its own if it gets wet), sawdust, powdered detergent, and pads of paper towels.

Old stains can sometimes be reactivated, so an absorbent will work by spraying with paint thinner or kerosene. Let absorbents work for a couple of hours, then sweep up and apply new material if necessary. If pads are used, blot, don’t wipe.

Q. We recently found a patch of powdery white stuff on our basement floor. We applied a sealer and basement-floor paint. Will that solve the problem?

A. I doubt if you have solved the problem. The white stuff, called efflorescence, consists of minerals leached out of the concrete by moisture. The permanent cure is to find and repair the cause of the moisture, which can be very difficult.

In some cases, water seeps through basement floors and walls because of improperly working rain gutters or poor drainage that allows rain water to accumulate near the foundation. In other cases, water seeps through floors because a waterproofing membrane was not installed under the slab.

In short, it is probable that the white stuff will show up again despite the sealer and paint. It is normally harmless calcium carbonate and can often be cleaned up by dry brushing with a stiff broom or scrub brush. Scrubbing with water will also sometimes remove the deposits.

Powerful acids are sometimes used to remove difficult efflorescence, but I don’t recommend them for use by do-it-yourselfers.

Q. Our concrete porch has a number of hairline cracks that we fear will worsen because of poor drainage on the porch, which is not sloped properly. We were told at a hardware store that sealing the concrete would be “a waste of time.” Any ideas?

A. I’m not sure what your hardware-store adviser had in mind, but I certainly think you should patch the cracks. They will only get worse if they take on water, especially if the water freezes. You can patch the cracks easily with a concrete patch sold in caulking-gun cartridges at most home centers.

If the porch slab is in reasonably good condition, it might be possible to correct the slope by adding an overlay – a layer of new concrete several inches thick. You should consult an experienced masonry contractor to see if this is possible.