Q: My redwood house is 40 years old and was never stained. It is weathered gray. Can I stain it now and if so what prep work is needed and what stain should I use? – K.H.
A: If the underlying wood is still solid, You can certainly stain old redwood siding as long as you do the necessary prep work. As with any paint job, the prep work is the most important part of the job, and often the most time-consuming.
If you stain right over the weathered surface, I don’t think you’ll be very happy with the uneven appearance or with the longevity of the finish. Applying a finish to weathered wood is like painting over chalk on a blackboard. When the chalk falls off, so does the paint.
The same is true for applying paint or stain over dirt. The paint bonds to the dirt, not the underlying wood. For that reason, it’s best to thoroughly clean the surface before staining.
Pressure Washing
The quickest way is pressure washing, but this is also the most risky as you can gouge out soft areas of wood, leave a lot of raised grain, and force water into the wall system. If you do decide to try pressure washing, make sure that the contractor is experienced with soft wood sidings and uses an appropriate low pressure.
Also do it in dry weather, when the building will have time to dry out thoroughly before applying the new finish. Water can also penetrate to the back of the siding through joints and nail holes, so extra drying time is recommended.
Low-Pressure Sprayer or Sponge
A more sensible, but more labor-intensive, approach is to use a commercial cleaner or mix your own. You can apply the cleaner with a large sponge, but it is quicker with a low-pressure sprayer which you hand pump.
Low-pressure sprayers are commonly sold for gardening and applying deck cleaner and include a wand for spraying a wide band of cleaner with a sweeping motion. Spray on the cleaner, scrub it in with a large, stiff cleaning brush, let it set for several minutes, then rinse with a hose. DO NOT use a metal brush as this can leave metal particles that will stain the wood.
The type of cleaner you need will depend on the conditions. If the siding is a uniform gray, without dark spots from mildew or water stains, then you can use a mild detergent. If you need to lighten sections of the wood, then you will need to use a bleaching agent in those areas.
Choosing A Cleaner
Many commercial cleaners are sold for decking, which are equally suitable for siding. However, avoid strong bleaches and cleaners that can harm the wood and create a health hazard for the user. In particular, avoid products with chlorine bleach or strong alkali cleaners such as sodium hydroxide or potassium hydroxide.
Instead look for the active ingredients oxalic acid, sodium percarbonate, or soda carbonate (also called soda ash or washing soda). Oxalic acid and sodium percarbonate will both lighten the wood to some extent and are useful if the wood has darkened.
Sodium carbonate is more a straight cleaner found in many household cleaning products and detergents. A popular product called Oxyclean is mainly sodium percarbonate (an oxygen bleach) and sodium carbonate (a cleaner)
You can find these compounds in a number of commercial products, or just buy the basic chemicals for a lot less money and mix your own. While these are less harmful than the other cleaners, they can still be harmful to your skin and eyes in concentrated form, so be sure to use gloves and eye protection when mixing any applying.
Removing Stains
For troublesome stains, mix a paste of three parts oxalic acid to one part water, and apply the paste with a brush or spackle knife. Let it sit for at least 15 minutes, then rinse off.
For larger sections that need lightening, spray on oxalic acid, scrub it in with a non-metal scrub brush and let it sit for several minutes. Then rinse thoroughly.
Whatever product you use, test it on a small area before applying to a larger section or the whole house.
Sanding
Once the wood is clean and dry, it’s best to lightly sand the wood with 80 or 100 grit paper using a palm sander or orbital sander. This will remove any loose material and rough up the surface for an improved bond with the new finish. You’ll want to sand enough to expose solid wood to accept the new stain.
Choosing a Stain
If you want the redwood siding to retain the dark red color of freshly oiled redwood, then you should consider choosing a stain with that color pigment. A clear finish will give you that appearance when the first apply it, but it won’t last more than a couple of years. And oil finishes promote mildew growth unless they contain effect mildewcides.
To keep a “natural” reddish look, most people choose a stain that is roughly the color of freshly oiled redwood. Definitely try a sample before committing to the whole house. In essence, you are tinting the redwood the color of redwood. This will help it retain the original color rather than weather to gray again.
For most situations, I prefer semi-transparent oil-based stains. These have enough pigment to add some color, which retaining the natural look of the wood. You will need one with a mildewcide or you can add this to the stain yourself since oil promotes mildew growth in redwood. You may be able to find a finish formulated for use with redwood.
Oil vs. Water-based Stains
In many states, including California, it is increasingly difficult to find any 100% oil-based finishes due to environmental laws. There are water-based finishes and hybrids, often sold as “oil-based finishes that clean up with water.” Read the label carefully to find out what you are buying.
One-hundred percent acrylic (water-based) stains are generally available in semi-solid and solid formulations. These are somewhere between a stain and a paint, with a coating thickness between the two. On the plus side, solid and semi-solid stains show more of the wood texture than paint, tend not to peel like paint, and are easier to refinish. On the downside, they won’t last as long as paint.
There are too many products on the market, which constantly change their formulations, to make a specific recommendation. Also a product with the same name may have different ingredients in different states due to environmental laws. That said, some product lines that I have used with good results on wood siding are Cabot, Penofin, Sikkens, Flood, and Messmer’s. Just make sure you read the label! A professional paint store (not a home center) can usually provide a good recommendation.
If you need to renail areas, go with stainless-steel fasteners if you want to avoid black stains around the nails. — Steve Bliss, BuildingAdvisor.com
Read about Finishing Wood Decking
George says
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I’m in Southern California with original 1953 redwood siding. The siding does not look weathered. I was wondering if I am sanding the siding to expose raw wood, do I need to clean it first?
This is my plan: I read about using 30 to 50 grit sandpaper to open the pores to increase semi-transparent stain penetration. I’m using 60-grit sandpaper and cedar-color stain.
The siding has nail stains. Will try the oxalic crystals — had just let it be part of the character over the years.
My Big Question Is: assuming I am done and happy with results.. I am thinking about adding a clear coat to extend the overall life of the finish till need to refinish. What are the schools of thought if it worth doing.. will it extend life or defeat purpose by creating a clear layer that could crack, peel or chip off sooner, if it does not bond the the semi- transparent stain? Is this even a concern?
buildingadvisor says
If you are just using the sandpaper to rough up the surface of the wood, then cleaning it first makes sense. However, if you are sanding deep enough to expose new wood then you are correct that cleaning first wouldn’t accomplish much.
If you are using a semi-transparent penetrating stain, then the usual way to extend the life of the coating is to add a second coat — assuming the wood will accept a second coat (which is probably the case if it hasn’t been stained since 1953). If the wood won’t take a second coat right away, it probably will within a year. You can add additional coats as needed — often getting more years with each coat with traditional oil-based penetrating stains.
If you are worried about too much pigment, the you could use a clear finish for your second coat. I’d try to stick with the same manufacturer and the same finish if possible, but choose one with very little or no pigment. Beware that some “clear” exterior finishes are not clear at all. Always test first.
As for selecting a different type of top coat, mixing and matching finishes is risky and the results hard to predict. The variety of finish types now is vast. And using a film-forming top coat, such as exterior varnish, will likely lead to the sort of cracking and peeling you refer to.
If you still wish to use different finish types for the first and second coats, definitely test a small section of wall first. Also check with the manufacturer of the pigmented stain as to what they recommend to extend the life of the finish. Most likely they will tell you a second coat.
Olive Dorman says
How To Repair Redwood Siding Damaged by Power Wash?
My redwood house was stained last November and December. It was last stained 13 years ago so there was a lot of discoloration. The painter insisted on using a pressure washer after applying cleaner’ and ‘brightener’.’ which was not very effective. A scribe brush was not used. The result is gouged wood and a lot of black areas. In some places, the pressure washer was used to the extent that it was peeling off the wood it self .The same was done to the cedar trim, with the same results, yellow and black with the deep gouging. We had the occasional rain and the temperature was in the low sixties and below. The redwood and cedar were not allowed to dry. Subsequently the windows are clouded and streaked with what I’m guessing is stain. I am very unhappy with the results as you may guess. Another problem is just around the corner., Summer. It gets very hot here. I am guessing that the redwood will split and some of the knots will fall out. Is there any way to save the siding and trim? Is there anything that can be done to save the wood?
buildingadvisor says
I’m sorry to hear about your situation – sounds like a real mess. As the article states, pressure-washing is a risky approach when cleaning redwood, cedar, and other soft wood sidings. It sounds like they used far too much pressue and damaged the wood surface. Where the wood surface is gouged or damaged, you can try sanding with a random-orbital sander and may be able to salvage some of it. The worst areas may need replacment.
The staining can be improved, but usually not 100%. One question: Are the black stains new since the cleaning or were they already present. It would help if you could send a few photos.
Black stains on redwood and cedar can be caused by three main issues:
1) mildew
2) extractive bleeding of tannins
3) tannins contacting iron (such as nails) and water
With a low-pressure garden sprayer (or deck sprayer) available at the hardward strore, a stiff non-metallic brush, and some elblow grease, you should be able to remove most of the stains.
You can test for mildew with a few drops of household bleach. If that lightens the stain, it is mildew. At that point you can use a commercial mildew cleaner like Zinnser Jomax, or mix your own cleaner. A tried-and-true formula mixes one cup of TSP, one cup of household bleach, and one gallon of water. With bleach, ALWAYS WEAR EYE AND SKIN PROTECTION and NEVER MIX WITH AMMONIA. After treating the wood, rinse with water, let it dry, and retreat if needed. The deeper the mildew has reached below the surface of the wood, the more difficult it will be to remove.
For extractive bleeding, test with a small amount of oxalic acid crystals dissolved in water and wait ½ hour to see if the stain fades. To clean, use the same treatment as described above, and rinse well. Then apply with a soft brush a solution of 4 oz. of oxalic acid dissolved in water (in a non-metallic container). After the wood dries, rinse it well with clean water.
For metallic stains, you can use the oxalic solution descibed above. Stains around nails are difficult because of they run all the way though the wood. One apporach is to clean the surface around the nail as best you can, apply a sealer in the hole, and fill with a color-matched exterior wood filler.
Once the wood is sufficiently clean and dry, you will will need to apply a redwood-tinted stain if you want to retain the redwood appearance. There are many products on the market. The traditional solution of oil-based penetrating stain is no longer available in much of the US, but there are may alternatives. Check with a professional paint store (not a homecenter) for recommendations.
The photo in the article is from Colin Groth, a builder in Oakland who does a lot of work with redwood. He could be a good resource if you are in that area (I am on the East Coast). Also, the California Redwood Associate or a large redwood distributor like Big Creek Lumber migh be able to put in touch with a specialist who can help you out.