Western Red Cedar Solvent Soluble Extractives??? - Paint Talk - Professional Painting Contractors Forum
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Old 10-27-2018, 08:25 AM   #1
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Default Western Red Cedar Solvent Soluble Extractives???

I’m having a bit of difficulty finishing exterior WRC The house is 4 years old and the cedar is being stripped and repainted for the third time now due to blistering paint. Having been the interior painting contractor, with another company having done the exterior, this is my first go with the exterior cedar on this project.

Exterior construction materials include mixed species, the vertical siding being clear vertical grain WRC, and the facia and soffits being clear vertical grain WRC as well. The window and doors are FEQ genuine Mahogany, and the balance of exterior trim/millwork is Sapele. Exposed rafter tails and rake boards are framing grade knotty Douglas Fir. All the above were painted according to architectural specifications which included an oil primer and two finish coats of B&M Aura exterior low luster paint. The color is Kendall Charcoal, being very dark, with a light reflectance value of 12. The surfaces get extremely hot in direct sunlight due to the dark color. The paint is fine on both the Sapele & Mahogany, but is blistering on the cedar, and only on the south elevations. The Fir is another story, and is oozing pitch by the bucket full. The client has accepted that the Fir was probably not the best choice, and nothing can be done to remedy aside from pitch bleeding the wood with a blowtorch.

Getting back to the cedar:
The cedar was primed all sides as far as I can tell, as well as every end-grain cut being primed or glue-sized during assembly. I took numerous moisture content readings and all are less than 10% so I’ve ruled out moisture as the problem, KD cedar typically being 8%. The blistering is isolated to individual boards, and is occurring across the “entire” lengths and widths of boards. 10% -20% of the boards are experiencing finish failure. Being that the blistering is isolated to individual boards I’m ruling out solvent blisters as well. Where one board failed, the adjoining board is fine. The primer is releasing from the cedar only when top coated, or on locations where a second coat of primer is necessary. Both wet and dry film thickness are to manufacturer’s specs. There is no visible evidence of moisture or solvent within the blisters, however, what I did notice was a sticky pitch or sap-like residue beneath the blisters. This substance appears to be exuding through the oil based primer, actually causing the primer to darken and turn gummy. The exuding substance doesn’t have any dimension to it, and is more like a sticky film which is likely vaporizing due to the heat, causing the blisters. The color of the raw cedar was a bit odd, many of the boards having the appearance of being sapwood, but at 4” wide/vertical grain, I don’t think sapwood rarely exceeds 45mm. The cedar doesn’t appear to be new or quick growth based on the growth ring count on the boards, newer growth cedar being reported to experience problems with solvent soluble extractives, a condition which is considered rare. I can’t rule out that the cedar is new growth though. Finish failure is occurring randomly without any correlation to a particular board color whether it be from the heartwood, pith, or included sapwood portion of the tree. I’m just wondering if there are essential oils, sap, or pitch in cedar that could be volatizing due to the heat and solvent based primer? Cedar is typically devoid of pitch and resin, and pitch is typically only present in locations where the tree might have sustained injury. Non-excluded sapwood is typically culled out and discarded at the mill. There is very little information available on solvent soluble extractives in cedar.

The cedar was stripped mechanically and orbital sanded to #120 to provide plenty of tooth. It was then vacuumed and wiped down with acetone. No boards were left exposed to the elements and were primed within hours after initial stripping. I’m not priming in direct sunlight, but direct sunlight hitting the surface at some point before the primer sets is inevitable. There was no visible evidence of an extractive of sorts before priming. I’m hoping someone here might be able to share some knowledge as to the chemical properties of Western Red Cedar that might be causing this, and provide a possible solution rather that a tear-off/re-side and re-trim which the client is willing to do only as a “last resort”. A breathable finish such as an acrylic semi-solid stain is not an option due to the variegation in color of the boards.

The primers used on all three re-paints were B&M 100, 094, and 366. The 366 is the same as 094, yet comes in a deep base to allow it to be tinted to the finish color without compromising the performance of the primer. All primers were tinted to the finish color.

Another observation on the repaint:
Before making the decision to remove to existing finish, I did a couple of test sections where the existing finish was sound. I sanded the existing finish and primed it with 094, and the existing coating started blistering, the point of failure being at the wood’s surface.

The first failure occurred during construction. All the cedar siding was shop primed with what appears to be a high build acrylic primer. That started blistering immediately after being prepared and top coated by the original painter.

The B&M tech rep is at a loss too. His last suggestion was to try 024 Multipurpose primer or to replace the wood. The logic behind the 024 is that it has more binder yet is non-penetrating.

Another suggestion from a seasoned old school painter such as myself was to just prime it with deep base 100 tinted to the finish color, and let it go through the winter, with the hopes that whatever is exuding will dry down in the interim. Although the 100 should be top coated within 30 days, in new construction projects we’ve shop primed tens of thousands of linear feet of t&g cedar siding that was installed late fall, not being able to be top coated until the following summer without failure of any sorts.

The same boards that failed originally are repeatedly failing and develop blisters within hours after top coating. This is only happening on the south elevations. The original primer on the boards experiencing failure has deteriorated across the entire length and width of the board, with adjoining boards being fine. I’ve never seen this happen in my 32 years as a painting contractor and I’m really at a loss on this.

Any thoughts?
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Old 10-27-2018, 01:58 PM   #2
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I would do some destructive testing on the south side. Obviously the south side gets the most sun, as where most if not all moisture from inside the house will be drawn too. My guess is there is no moisture barrier nailed to the studs or sheathing.
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Old 10-27-2018, 11:58 PM   #3
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Thanks Mike. The problem turned out to be a condition called “slime flux” aka bacterial wetwood. Slime flux is a rancid fatty acid, an oil, which is produced through fermentation in Clostridium bacterium infested trees. The slime flux won’t dry down/fully crystallize during the kiln drying process and exudes from the wood after being reactivated by heat and solvents in oil primer. That would account for the blistering and goop. The bacteria produces an enzyme resulting in shake, separation of growth rings which is sometimes mistaken for checks. It also produces dark streaks running parallel to growth rings. I’ve been seeing a lot of this lately on white oak, the first time ever on cedar though. Not too common. Had a guy with a PhD in forestry identify the problem. No permanent fix aside from a tear off/ reinstall. Apparently the stuff will bleed completely through overlaid PVC trim. No way to hold it back.
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Old 10-28-2018, 01:09 AM   #4
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Sounds like something out of a horror movie - at least if the entire audience was all made up of painters.
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Old 10-28-2018, 12:16 PM   #5
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More like a dark comedy, with me being the lead star. Had the clients not been the two nicest people I’ve ever met, and paying for every hour spent, if it were any other client, I’d certainly be screwed.

It was more of a horror movie watching the exterior painters toiling over the blistering for months on end when the house was first built thinking thank god it’s not me. It was particularly scary watching them dish out the cedar with disc sanders when stripping it the first time. They absolutely murdered the wood. Looks like they sanded with rabid beavers, holding them by the tail while chomping away at the wood. I primarily am a wood finisher, finishing interior furniture grade millwork packages, window and door paks, and flooring, so I’m pretty surgical with the prep and was able to make their mess go away. The original painters lost their shirts, homes, and first born on the project, being on a fixed price working for the GC.
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Old 10-28-2018, 07:21 PM   #6
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Why would anybody want to paint Western Cedar? Why not just stain it or leave it? I was always under the impression that painting cedar was a no no..
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Old 10-29-2018, 07:15 PM   #7
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Quote:
Originally Posted by Alchemy Redux View Post
Thanks Mike. The problem turned out to be a condition called “slime flux” aka bacterial wetwood. Slime flux is a rancid fatty acid, an oil, which is produced through fermentation in Clostridium bacterium infested trees. The slime flux won’t dry down/fully crystallize during the kiln drying process and exudes from the wood after being reactivated by heat and solvents in oil primer. That would account for the blistering and goop. The bacteria produces an enzyme resulting in shake, separation of growth rings which is sometimes mistaken for checks. It also produces dark streaks running parallel to growth rings. I’ve been seeing a lot of this lately on white oak, the first time ever on cedar though. Not too common. Had a guy with a PhD in forestry identify the problem. No permanent fix aside from a tear off/ reinstall. Apparently the stuff will bleed completely through overlaid PVC trim. No way to hold it back.
After 40+ years in the coatings and lumber business this is the first I’ve heard of this. Very interesting. Thanks for the analysis
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Old 10-30-2018, 11:00 AM   #8
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Nace,

The USDA Forset Service has a pretty descriptive article on it,
“Wetwood in Trees:
A TimberResource Problem”

Not being a chemist, after further research, I misidentified fatty acids as oils, which they are not. They are partially soluble in organic solvents though. They do however plug up the water transport system in trees, making it nearly impossible to dry down in the kiln, with water being trapped in pockets under extreme pressure which are sometimes pencil thin and provide inconsistent moisture content readings, and likely wouldn’t register on a meter unless the probe was hitting the pockets. After further paint removal, all but one board exhibiting failure had visual evidence of wetwood, with streaks and discoloration in the wood similar in appearance to mineral streaks and/or spalting. The failure Is basically due to trapped moisture along isolated growth rings which no amount of air or kiln drying can remedy. The discoloration is typically yellow/orange in appearance in WRC as illustrated in the photo, or sometimes a brown to grey color. My first encounter as well on WRC. I work with white oak mostly and see flooring and veneers blow apart during the processing and finishing due to the degradation of the lignin on the earlywood as a result of pectinase formation, resulting in growth ring separation.
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Last edited by Alchemy Redux; 01-03-2019 at 10:47 PM..
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