Green mildew on vinyl siding

Mildew on Vinyl Siding
Mildew on Vinyl Siding

Q.  I have green mildew on my vinyl siding. I used a 2200 PSI power-washer and was not able to remove all of the mildew. Is there a solution I can use to get the rest off without damaging the vinyl siding or do you have any other suggestions?

A.  I assume that you used a weak mixture or didn’t use bleach at all in your power-washer. Power-washing any mildewed surface without a strong bleach solution may remove some surface pollutants but it will not remove the mildew. If the mildew is found on small and easily accessible areas, you will have more success if you do it by hand because it is not easy to have the right concentration of bleach mixed with the water going through a pressure washer.

Wear heavy rubber gloves, mix fresh Clorox bleach and water in equal quantities in a 5-gallon plastic pail, and apply the solution with a soft bristle brush so as not to scratch the siding. If you add a cup of TSP or TSPPF detergent (buy in hardware stores) per gallon of the solution, you will also remove any other stubborn stains that plain water from the pressure washer didn’t get. If you only use a bleach solution, do not rinse it. But if you use detergent, you will need to rinse the treated areas.

Be sure that you cover vegetation with plastic after soaking it before and after the washing.

Cleaning and renewing a redwood deck

Q.    What is your recommendation for cleaning and removing mold from a redwood deck? Some of the deck boards have been down since 1963 when people were still using redwood, then picked up and relayed along with additional redwood deck boards in 1976 when the deck was enlarged in 1976. Environmental issues are of particular concern due to proximity to the lake.

A.    Redwood as well as other softwoods should not be pressure washed, as this would damage the wood.

The best way to clean any decking material of mildew and any other pollutants is to scrub it with a mixture of equal parts Oxy-Boost and Deck & Patio Cleaner from ecoGeeks, Follow directions on the containers. EcoGeeks products do not contain chlorine and are environmentally safe.

Moss between pavers in driveway

Q.  I have a driveway made out of paving stones. Moss has overtaken the spaces between the pavers. The driveway is in sun most of the day but a section of the driveway is sprayed with water during the summer by the sprinkler system. I think the moss started on that side and  spread.

My question to you is what can I use to rid the driveway of the moss. I tried Roundup with no luck.

A.    Try removing most of it with a long-handled scraper, and douse the joints between the pavers with a solution of three parts white vinegar to one part water.

Removing mildew from cedar siding

Q.    We have been using an Olympic stain on our cedar siding for about 15 years but not in the last few years. A significant mold has developed on the north-facing side of the house and garage. We need advice as to how to get rid of the mold without killing the extensive foundation plantings we have.

A.    The way to remove mildew is by means of washing the siding with a solution made of one quart fresh Clorox bleach and three quarts water (if you need more than a gallon, respect these proportions).

If the siding is also compromised by other pollutants, add a cup of TSPPF to the solution. The application of the solution is best done with a pressure-washer, but it is obvious that this is not possible in your case.

The alternative is to soak the plantings and cover them with plastic sheeting, and to wash the siding by hand, using a stiff-bristle brush, and wearing heavy rubber gloves and expendable old clothing (or buy a Tyvek suit). Avoid splashing as much as you can. Do not rinse the siding unless you have added TSPPF to the mix (in that case, rinse the siding with your garden hose and flood the plantings and the soil to dilute the solution – TSPPF is injurious to plants).

Insurance company says to remove moss from shed roof

Q.    The insurance company said we have to get the moss off our shed roof by this coming October. She said to use a power washer. I remember you said not to use a power wash on shingles. We removed a lot of trees from around the shed. Could you please tell me an easy do-it-yourself method? It looks black and light green to me.

A.    I wonder why the insurance representative told you to remove the moss from your shed roof. I can’t see any reason for doing so. Power-washing roof shingles is not advisable; the pressure is very likely to damage the shingles. It will certainly take off the mineral granules, which protect the shingles from UV rays.

When you say black and green, are you seeing a discoloration of the shingles such as is caused by algae? That’s a different story. Moss shows as a soft growth that can easily be picked off by hand or brushed off with a floor-sweeping broom, so it would seem that if its removal is required, it should be simple enough to do so without having to walk on the roof (unless the shed is very large).

Removing mildew from vinyl siding

Q.    I need to know if I can get mildew off of my white vinyl siding. We are pressure-washing it using a solution of mild soap and Clorox, then rinsing it with more water. I realize the Clorox is not good for the siding but the mild soap does not work. We are doing it sections at a time as the house is large. It is not that successful and I was hoping that you have a better solution. It is time consuming as well.

A.    The best way to remove mildew — and other pollutants that are sure to be present as well — from your siding is to wash the siding with a solution of 1-cup TSPPF, 1-quart fresh Clorox bleach and 3-quarts water. Keep the proportions the same if you need more than a gallon of the mix. Be sure to cover all vegetation with plastic after soaking it thoroughly. Rinse the siding and soak the vegetation again when you are done. Instead of pressure-washing the siding, try using a car-washing brush that is screwed onto a garden hose; its soft bristles are ideal for cleaning vinyl siding.

Deck is coated with mold, and stain is peeling

Q.    My pressure-treated deck and outdoor stairwells are coated with mold. They are located in an eastern exposure facing open fields. They had been stained about eight years ago and are now peeling too. How should this problem be solved?

A.    Were your deck and stairs coated with a solid color stain containing linseed oil? At this point, I suggest you have all the remaining stain removed. Try pressure-washing to make the job easier, but if this is not completely successful, you may have to use a paint-and-stain remover.

A paint store can advise you as to the best to use for these surfaces — probably a liquid remover, as they are less expensive than the gel or semi-solid types. Once the wood is clean, coat it with a product specially made for pressure-treated wood, such as the Wolman line that penetrates the wood and will not peel.

Metal strips to control algae on roof

Q.    Somewhere on TV, probably in “This Old House”, was a gadget to inhibit the growth of lichens on roofs. I have a lot and would like to get rid of them without the problems with Clorox all over. This gadget was a strip of metal with one of the metals, possibly one of the rare earths, an inhibitor for these plants. It goes in on the ridge pole and the needed metal leaches out, runs down over the lichen colonies and does them in. Very neat, tidy and easy.

I am reminded: if it is too good to be true, it probably is. Have you heard anything about this?

A.    The control of algae, moss and lichen on roofs is well-known in the northwest where the roofers use copper strips set just under the cap shingles on each side of the roof. In the northeast, we can see how these problems are controlled by looking at old barn roofs. Wherever there are galvanized metal roof vents, we see that the shingles below vents are as clear as the day they were installed. This is not the case on the other areas of the same roofs where algae grows unchallenged. The same thing is visible on any roof below copper or galvanized vents and flashings.

You have several choices. You can have a building or roofing contractor install a copper or galvanized metal strip snug against the bottom of the cap shingles or you can buy Shingle Shield zinc strips from The RainHandler and have them installed underneath the first course of shingles below the cap shingles, as per instructions. Home Depot and some hardware stores sell rolls of copper for the same purpose.

Copper is quite expensive; galvanized metal a lot less. You can order Shingle Shield on-line at Although Shingle Shield strongly recommends cleaning the roof of all growth before installing their strips, this is not necessary unless you are impatient and can’t wait for nature to take its course over several seasons. Having the roof cleaned with their solution is quite expensive.

If you have a ridge vent, you can have it replaced with Air-Vent, Inc’s zinc- coated ridge vent that, when it rains, leaches ions that poison algae and other growth. Any building supply store can special-order this ridge vent. But that’s more drastic than installing metal strips.

Be aware of the fact that these metal strips are most effective on algae — the unattractive black discoloration found on asphalt shingles throughout the country; they are not always as effective in the control of lichen and moss.