A threshold is a raised panel immediately below a door designed to prevent objects and water from coming under the door. Because of its location, a threshold is probably one of the most abused parts of your home. It gets kicked, bumped and, being the first part of the house people step on after coming inside, is regularly subject to mud, sand and anything else that shoes tread.
The Major Problem
Thresholds are small and the weight of people standing on them is concentrated in a very small area. A 140lb person standing on an area of one square inch is applying a grinding pressure of 140lb per sq in. This means that dirt gets deeply embedded and some grits can break through any varnish layer and allow water to penetrate.
A Contributing Factor
No matter how house-proud people are the threshold is generally hidden by the door and does not get included in the regular house cleaning routine. This is what leads to disrepair. Regular maintenance, even if it is only a scrub with a stiff dry brush, will help to keep a threshold clean.
Bringing a Threshold Back to Life
Once a threshold has become deeply engrained with dirt the cleaning becomes more complicated. Often the only way to restore the threshold is to use abrasives like sand paper or heavy duty floor cleaner. If there is grit in the surface, a scraper can often remove most, if not all, of it and then a brisk application of a medium sand paper can remove the surface discoloration.
For Really Bad Staining
Sometimes it is necessary to remove the threshold and clean it in a workshop or on a bench. This is not easily done if the threshold is glued to the floor and in such cases will be better not tried. If the threshold has to be cleaned in position, it is important that abrasives are not allowed to damage the surrounding floor. To prevent this you should use a flat piece of tin or a trowel to mask the floor. The tin can be held in place by your free hand or a knee and only needs to be wide enough to protect the area on which you are working.
If you have done all you can and the threshold still does not look clean enough, you must consider careful use of chemical cleaners or mechanical sanders. Whichever you use, do not get over enthusiastic. Stop as soon as it is clean. Examine the surface of the threshold and if it seems pitted because of the grit that has been scraped out of it, brush it lightly with water. The water will fill any small pits and should encourage the compressed timber to swell and erase them.
Bringing It Back to Life
After allowing the threshold to dry thoroughly you should rub it down with a very fine glass paper to create a good surface to apply the varnish or a stain. If there are still slight stains on the threshold a colored varnish would be the best choice. Use masking tape if the threshold is still in place on the floor. Apply the first coat and allow it to dry and then rub it down with very fine glass paper before applying a second coat. If two coats are not enough, repeat the process until you have a result you are pleased with.
Thresholds are rather neglected but cleaning them as a part of the normal house-keeping process can keep them looking good and save a lot of unnecessary hard work.