Products and Tips to Stop Wood Rot

Wood has lot going for it. It is strong and stiff per unit weight, easy to work with, attractive, and economical. Teak decks provide classic good looks and superior non-skid. The downside is that without constant maintenance, wood rots, and even with maintenance it rots anyway, just slower.

Yes, a few special woods, such as teak, are highly resistant, but teak is neither light nor economical. Pressure-treated lumber might seem like an option, but it’s ugly, warps, does not take coatings well, and is not recommended for interior use. Cedar has long been used in canoes, and western red cedar fence posts have a long established reputation for durability.

What if it were possible to treat any wood we wanted to use, without making it ugly or degrading its properties? We researched mildew prevention and came up with a neat formula for surface cleaning and prevention (see Inside Practical Sailor blog post “Home Made Mildew Preventers that Really Work”).

In the course of that research, we came across borate-based formulas used by the U.S. National Park Service to preserve historic wooden structures, including totem poles, and historic boats including the USS Constellation. We’ve been using variations of this formula on our test boat and a back yard totem pole for 15 years (doesn’t everyone have one?). This chemistry is not new to yachting either; Halberg-Rassey recommends Boracol for wooden deck maintenance; it combines borate and benzalkonium chloride as anti-mildew agents, two chemicals that Practical Sailor has tested in many marine applications (see PS September 2015, “Fighting Mildew, Mold, and Lichen”).

What We Tested 

We did not test treatments that might present chronic health hazards or are not aesthetically pleasing. Copper napthinate, found in products like Copper Green and Termin-8, for example, has a horrible smell and is not recommended for indoor use. It also stains the wood green.

We tested Boracol, a product based on ethylene glycol (EG) borate ester. Bora-Care is very similar to Boracol, so it was not tested. The System Three EndRot system includes a borate-based anti-rot powder, Board Defense, as well as sealers and fillers to repair damage. We also tested home-brew versions. Finally, there are solid versions, installed in utility poles to provide additional rot protection. We tested Bor-8 rods and borax powder.

Our sample woods were western red cedar, which is very rot resistant, and fir and yellow pine, which are not. We did not test hardwoods, because they do not readily absorb treatments and because we were also more interested in woods that are lighter and more economical than teak.

Our DIY formulations can also be made using propylene glycol (PG). We found performance to be very similar, although some users believe the PG formulas are less effective than EG. Propylene glycol has lower toxicity to mammals and is thus a little safer to work with. Both ethylene glycol and propylene glycol are biodegradable and are classified as effectively non-toxic by the US Fish and Wildlife Service. Boracol comes in both EG and PG formulations. To confirm which formula you are buying, review the product safety data sheet (SDS), always a good habit.

How We Tested

Samples of fir, western red cedar, and pressure treated lumber were cut into roughly 11/16” x 1½” x 12” samples. One of each was set aside as a control (not exposed), and another was left untreated and exposed as an exposure control. We then treated samples with either borate solution, concentrated ethylene glycol (95 percent), or a glycol borate solution (see adjacent page, “DIY Wood Preserver and Teak Tips”). Some samples were coated with either Epifanes Clear High Gloss Varnish or West Systems 105/205 epoxy.

Beginning in October 2015, samples were placed in a compost pile, comprised of a combination of yard waste and kitchen waste, to ensure conditions were active. Four #8 brass wood screws were placed in each sample to make certain that the coating was breached and the sample would experience some moisture penetration, as though it was a part of a fabricated structure. 

Although the preservatives tested are water soluble, they absorbed into the wood and are not likely to wash out in any harmful concentrations simply by getting wet. There would need to be some flow of water through the wood, and a finish or sealant should prevent this, even on finished wood with screw holes or other minor penetrations. Thus, uncoated samples will more easily leach its preservative. Varnished or sealed samples will remain protected by an inhibiting borate or glycol solution even when they get wet.

We also had two “field” tests. In 2005, a backyard totem pole was carved from a dead yellow pine tree we felled and then re-erected. The in-ground portion was treated with the DIY glycol borate solution and coated with copper-based antifouling paint, roughly following National Park Service procedure.

In 2015, we fabricated a cockpit floor grating from treated red cedar. The boards were soaked in the DIY formulation for one month, dried for two months, and coated with Epifanes High Gloss Varnish.

DIY Wood Preserver & Treating Teak

The DIY borate solution was about 3 percent by weight, or about ½ cup of borax dissolved in a gallon of warm water. The borate concentration can be increased by adding an additional 5 percent boric acid. This variation is well proven in wood treatment, but we did not test it.

The DIY glycol borate solution was made by heating one gallon of ethylene glycol with one pound of borax, dissolving all solids. The solution was slowly heated (allow 20 minutes) to 260 F to remove all water from the glycol and the borax (borax is a decahydrate hydrate salt). We then maintained the solution at 260 F for an additional 20 minutes to complete the reaction. The resulting liquid contains both ethylene glycol and complex borate esters, is about as viscous as epoxy, and nearly odor-free.

Important Caution: heating glycol solutions involves both danger of fire (combustible liquid heated above its flash point) and potentially hazardous vapors (ethylene glycol vapors increase at high temperature). This project must be done with due caution and with active ventilation. The resulting liquid, after cooling, has roughly the same oral and dermal toxicity as ethylene glycol antifreeze and presents no inhalation hazard. For more information on toxicity, consult the Material Safety Data Sheet for Boracol, as it is very similar.

Teak treatment

Halberg-Rassey recommends Boracol, a glycol borate formulation, for maintenance of teak decks. To apply (DIY, Boracol or Bora-Care), clean and allow to dry for several days; the drier the wood, the more quickly and thoroughly it will be drawn in. Apply one moderate coat, covering about 350 square feet per gallon. This will soak in within a day or so, but will not dry on the surface for several days, so plan for fair weather. A light misting of water the second or third day can speed penetration, but no more than a light mist. Any excess will be rinsed off by the rain, or you can use a hose after about a week. Because the wood is not sealed, this will need to be repeated at least annually to prevent mold and mildew, perhaps twice a season in damp climates.

We did not test the effect of this treatment on sealant adhesion. If you are planning to recaulk the deck, either do that before treatment, or wait several months for the glycol borate solution to fully dry and rinse.

Observations

We coated the samples with three coats of each preservative, allowing drying time between applications. System 3 Wood Defense and the DIY borate solution dried within 24 hours, leaving a few crystals on the surface, which easily brush off. Moisture is thought to help the borate penetrate more deeply, so a light misting after drying should help.

Ethylene glycol absorbed within 24 hours, but required 3-4 days to fully dry. The glycol borate ester solution took 3-5 days to fully absorb and about one month to dry sufficiently to apply coatings. When we did not let a full month pass after treating wood with our homemade glycol borate solution, it did not accept varnish well.

According to Swedish builder Halberg-Rassey, who recommends glycol borate for treating teak, a light misting of water helps glycol soak in, but not until the second or third day (see “DIY Wood Preserver & Treating Teak,” page 15). Clearly, borate-only products are much easier to use when time matters.

Coating integrity. Epoxy adhesion seemed slightly impaired by the glycol-only formulation, even after long drying, judging from minor cracking noticed when screws were inserted. Varnish adhesion seemed unaffected.

Totem pole. After 13 years, the stump of the tree we cut down is badly rotted. However, when we excavated down 12 inches below grade to investigate, the post in the ground remains as resistant to a knife blade as it ever was. The rot protection seems nearly complete.

After ten years we drilled downward sloping, 8-inch holes into the pole. One hole we filled one borax powder and into the other side we inserted Wood Care Systems Bor-8 Rods, finger size rods coated with borax that slowly dissolve when wet. Solid treatments like these are excellent for providing time-release protection in chronically wet areas, such as timber engine mounts.

For comparison we observed a circle of pine totems carved by Korean artisans at a local county garden park, installed without treatment; they’ve only been there for five years and the wood below ground is already critically soft.

Cockpit Grating. After the failure of our modular wooden tile cockpit grating, we decided to build something more permanent. We started with western red cedar, which is light, rot resistant, and matched the light wood interior.

To ensure lasting protection, we applied five heavy coats of the DIY glycol borate formula during a one month period. We wrapped boards in a tarp so that they were constantly wet with the solution.

The treatment soaked in very deeply; when the boards were trimmed to size, glycol had soaked nearly to the core. The treated boards were then dried for two months on a rack that allowed air movement but prevented warping.

The finished boards were coated with four coats Epifanes High Gloss Varnish, with salt sprinkled onto the last coat to provide non-slip texture (see PS January 2016, “Do-it-Yourself Salted Surfaces,” and PS January 2012, “Traction in Action: PS Tests DIY Non-skid”).

The boards were then screwed to a flexible polyethylene backing, which conformed to the curve of the sole and permits removal for cleaning. After five years in use on the boat, we have seen no evidence of adhesion problems with the varnish.

Wood Rot Preventatives

Three Year Progress Report

Dimensional stability. One reason pressure treated lumber is not very useful in boats is warpage. As anyone who has been to the lumber section at a big box home improvement store can attest, firring strips and plywood sheets seem more prone to warpage if they’ve been pressure treated.

Glycol borate treatment, in comparison, appears to be less harmful. There was never any warpage in the 6-foot square cockpit grating we made from cedar that had been treated with glycol borate.

Often woodworkers will treat large, thick wooden table tops with glycol to prevent warping and cracking in dry houses in the winter. However, we don’t think this treatment is needed for wood on boats. Generally, the marine environment is not as dry as a house in winter, and the lumber we use is relatively thin. The exception might be heavy wooden bowsprits, where cracking can be a problem. In that case, we recommend glycol borate rather than just glycol.

Coating integrity. Epoxy must always be protected from UV with several coats of paint or varnish; we know from experiences that when left exposed to the sun, epoxy will begin to fail sun within one year.

Epoxy coatings peeled from several samples coated with glycol borate, but the varnish coated samples did not peel. Perhaps if we’d allowed longer drying times before coating the result would be different. The epoxy did not peel on samples treated with borax or glycol alone.

Varnish is not as hard as epoxy, and the wood had darkened under some of the varnish, evidence that more moisture had probably absorbed through the varnish than the epoxy. (We did not see this effect in our field-tested samples on the boat.)

Gluing treated wood. If you intend to bond treated wood with epoxy, read the West Systems reports on this before doing so. In general, the effects of treatment on bonding are minor if the drying time is sufficient, but the drying time can stretch for weeks when treating with glycol borate.

The so-called rot resistant wood used in the eBay patio tiles we previously installed as a cockpit grating are so badly damaged that we doubt we’ll be able to find them at the 6-year review. Small wonder a matching set also failed in the cockpit, although it took much longer.

Fortunately, our experience allowed us to approximate the rate at which the compost heap test accelerated rot. Three years in the heap seems equivalent to about 5-10 years in the wettest, most shaded corner of a chronically flooded  cockpit. We don’t recommend buying mystery woods, and wooden tiles, in general, seem to have some inherent problems.

Teak and holly flooring is popular for appearance, but the rot resistance of holly is very poor, less than pine or fir. As photo #3 (above) shows, the teak portions remain unaffected, but the holly turned into mulch.

Material loss and tensile strength. Both the untreated and treated, but not coated, fir samples lost some soft material between the grain and about 30 percent of their tensile strength. Without a coating, the rot-preventative treatments just leached out.

The coated samples lost less than 10 percent of their tensile strength, mostly due to moisture gain (wet wood is not as strong as dry wood). The test has not progressed long enough to determine if there is any difference between glycol borate and borate only. We saw no measurable difference between Boracol and our DIY formulation, but that is because neither deteriorated measurably when sealed.

Sealers and fillers. We tested the sealers and fillers in the System Three EndRot Kit to repair some damage around windowsills and on-deck spacers. They performed exactly as we would expect from any high-quality epoxy. The handy kit is targeted more at home owners and people with small rot problems. If you have larger projects, it will be more cost effective to buy the volume of epoxy, treatments, and fillers you need separately.

Red cedar. The red cedar proved quite rot resistant, even without treatment. It greatly outperformed pressure treated pine in many areas, especially in strength when wet. The pressure treated pine warped and became so flexible it was structurally useless, while the cedar retained its initial properties.

Liquids

Success with any liquid treatment hinges on drying time. If you are coating, you’ll have to wait until the timber is fully dry. Storing liquids on board can  be more challenging than it is with solids. This is the same reason we prefer individually sealed tablets to treat our water rather than liquids (see the eBook “Onboard Water Treatment, Storage, and Production.

Glycol Only

Drying is slow, as you would expect. There is limited evidence of rot protection. It is most often used for prevention of dry wood cracking.

Bottom Line: There are better approaches.

Borax Only

A borax solution is easy to whip up and easy to apply. We’ve taken to using this on aging pressure treated decks, carpets, and most anywhere we have mildew problems. Patio decks that have previously shown mold under flower pots and signs of beginning rot have been restored. For best results, seal with paint, varnish, or water-based exterior stain.

Bottom Line: This is the Budget Buy for general rot and mildew prevention and treatment.

System Three Board Defense

This treatment dries fast and we experienced no adhesion problems when trying to bond.

Bottom Line: Recommended. If we didn’t prefer making and using our own concoction, we’d use it.

DIY formula Ethylene Glycol Borate Ester

Used on the totem pole, described above, it is a solid top performer and the most time-consuming to work with. The main advantages over borate-only treatment are that the wood is stabilized against splitting, since the ester will stabilize the cell structure, preventing complete drying, and that the borate concentration is several times higher. Winter is a good time for this drawn out project. Just treat the wood early in the winter and wait.

Bottom line: The Budget Buy for long term preservation of soft woods. It’s a smart treatment for teak decks and swim platforms, and our Best Choice for woods that will be varnished. Just remember it can be a long wait until treated timbers are fully dry and are ready for coating.

Boracol 10RH

The only difference between this and the DIY borate ester seems to be the inclusion of benzalkonium chloride, which probably helps, though but we could not detect a difference. Like the DIY formulation, drying is very slow. Bora-Care is roughly equivalent, if this is more readily available.

Bottom line: This ready-to-use product has a proven history of protecting teak. Recommended.

Boracare

Very similar to Boracol, but without the benzalkonium chloride. When used in new home construction, contractors often dye it blue so that they can see what they have treated, but the plain material is clear.

Bottom Line: We did not test this product, but it has a long, successful history.

Solids

If you have a wooden boat, or your boat incorporates some big wooden timbers (engine-mount timbers, a timber mast step, a bow sprit, etc.), the drill-and-treat approach is worth investigating.

Bor-8 Rods

We have no quantitative data on Wood Care Systems Bor-8 Rods, but the chemistry makes sense and the approach has been accepted by power companies for the treatment of wooden utility poles; look near the base for tell tale plugs.

Bottom line: Recommended for chronically damp areas.

Borax

The bargain alternative is to drill 3/8- to ½-inch holes at least 4 inches deep, fill them with Borax, and seal with either caulk or plugs.

Bottom Line: This is our Budget Buy for damp wood protection.

Conclusions

Boating wouldn’t be the same without fiberglass, stainless steel, and aluminum, but wood serves vital structural purposes and we like the way it looks. Sailing is fundamentally an anachronism, and we like it that way.

Have a low-value project you want done in the cheapest way possible? Pressure treated wood works for fender boards and planks for storing jerry cans along the rail, but it’s not pretty and it warps. We don’t like it for anything structural, because it warps and softens. A boat is different from a patio deck. Western red cedar is a good alternative.

Borate solutions, including plain borax, borax plus boric acid, and Wood Defense from System Three, add considerable resistance. However, they need to be sealed in or they just leach out. Glycol ester formulations, including Boracol, Bora-Care, and our DIY version, prevent rot and also reduce splitting, but they are time consuming to work with.

We think their best application is teak deck treatment, because it is more resistant to wash-out than plain borate and long drying times are not a problem. If we were building a wooden bowsprit we’d soak it for weeks in glycol borate ester, let it dry for two months, and feel confident that we’d built something permanent that would neither split nor rot.

We’re not done. The samples are going back in the compost for another 3 years.

Between the natural resistance of cedar and the extra treatment, we’re hoping to enjoy our new cockpit grating for decades to come. The totem pole should stand guard over the backyard for at least a generation.