Questions: have you seen stained cedar turn black like this? Why? Was it holding moisture after its first cleaning? What can I change to get better results?
Looking for a little help on a cedar house that was Stained about 4 years ago but since has been taken over by mold. I went on an appointment to do a test on this clients cedar house. Usually they grey out after some time but this thing is nasty brown and black mold all over.
Being in the 40’s Degree, I wasn’t overly confident I’d get great results but I did a test of hydroxide and percarb in left and right corners in picture and about a foot out on left and right sodium metasilicate.
Only had a homeowner special pressure washer to rinse. Followed up with oxalic and rinsed.
Had some results but not to my satisfaction and deep staining apparent still along with some black on surface.
Is this a temperature based result? Do I need to increase 15 min dwell? Stiffen up the mix from 8 oz/ gallon to 12?
Also found a spot where sealer was intact by the ac unit. Looked great!
I can’t tell from your post… did YOU previously wash it and stain it, or did somebody else do all or part of that?
Is that white, yellow, or red cedar?
How was it previously washed?
What stain was applied, and what was the moisture content of the cedar at application?
I can’t tell if that stain was a semi- or a solid. In my experience, semi-transparent stains are uniformly a nightmare and I steer all homeowners away from it. Part of the problem is that the stain manufacturers have had to remove most of the effective ingredients for environmental regulations. For years we’ve seen semi-transparent stains which were basically mold food, and it didn’t matter whether they were applied at the factory or on-site (i.e. surface prep wasn’t the issue).
In regards to cleaning this mess, YES the surface temp at application will absolutely make a difference in SP’s effectiveness… as will sunny vrs cloudy (photoactivated).
When you say “hydroxide” do you refer to sodium h or potassium h?
I always compare cleaning cedar to cleaning laundry. Both are soft, porous, and fibrous. Like a load of laundry, you might have to first wash this house with an actual cleaning solution (as you are experimenting with), and then hit it with 1% SH to help hide the stains that remain. Unless you don’t care about it, do NOT try to clean cedar with just SH…
Thank you for the response. I like the details you mentioned. I’m all about the small stuff! The best of the best dwell in the details.
1: I did not clean or stain this house.
2: It is Red Cedar. I thought it’s supposed to grey not turn into that moldy?
3. Customer said clear so I guess semi transparent. I don’t do staining/ sealing but I don’t mind learning You can see the color through but it was a bit orange yellow.
Your comments on the moisture content and semi trans sealer are interesting. There is no way these guys tested moisture content and even if we could get a hold of them, they don’t know. They waited a week until sealing.
Customer has no clue on type used.
I used sodium hydroxide mixed with percarb. I assumed I was getting lower results based on temps and mix strength.
My questions:
Been told forever not to hit cedar with sh. Do you think I am never getting the residual stains out with traditional wood chems?
Also, some guys I spoke to just rinse off like a regular vinyl house wash. Do you do that?
I always go and pressure wash with grain, 8-10” away with 40 or 60 degree 500-750psi.
Do you think hitting it with a light sh around .75% just to knock out that deep stain would be ok?
So the metasilicate seemed to have slightly better results. You are saying hit it with that, rinse. Hit it with a house wash mix or light hw mix and then citric.
With every single cleaning option at my disposal, and all the years and tens out thousands of hours spent cleaning cedar, I won’t prep cedar siding on a job if I know that a semi-transparent stain is going to be applied. Today’s semis are just that bad, and unless we drop a neutron bomb and irradiate the house, nobody will ever remove every molecule or organic matter from a cedar shingle. We’re basically trying to clean a sponge. We can do it well, or poorly, but never perfectly. That being said:
I personally wouldn’t hesitate to treat red cedar siding with light SH if you still have stubborn staining remaining after cleaning with percarb, metasilicate, or sodium hydroxide. (Again, think in terms of laundry; SH alone won’t clean the porous & fibrous material, but it can help brighten things once cleaned). This isn’t just my 15 years of cleaning cedar; one of the cedar-cleaning methods advised by the Cedar Shake and Shingle Bureau uses SH.
Unlike vinyl or Hardi, the uniformity of SH application will be very important here. Apply very light mix onto wet wood; apply side to side from bottom to top; take are to avoid areas of great overlap. You’re looking for a very mild lightening over several minutes of dwell, then rinse. With cedar, you usually don’t know what you’ve really done until things are dry, so getting the knack to this is often a frustrating and long process.
But, look under the window sills to see the nail heads holding the shingles in place. If the nails are galvanized rather than stainless, be aware that the SH can lead to or exaggerate “rust stains” leading from the nail heads, in which case I wouldn’t use SH. Instead, you can offer to treat the cleaned, dry siding with an ABDAC product, such as this one which is my favorite by far. “Wet and Forget” is a more common variant, but one which I’ll never use if I have a choice. This product will dry like water and sloooooowly remove stubborn staining, but will also lighten the cedar a couple shades. Again, uniformity of application is critical, although this is even trickier to get right because it is water-clear and you won’t see results for at least many weeks if not months.
If you mean they “rinse off like a regular vinyl house wash” in terms of SH application, see my answer to #1 above.
Yep, pressure rinsing with the grain, fan tip, etc. It’s about the cleaning chems applied, not the pressure.
0.5-.75% is fine, along with some non-“bleach activating” cling/surfactant to help it dwell for many minutes. Again, don’t be that guy watching the siding brighten in 2 seconds.
Yes, I’m saying clean cedar however you need to with percarb, hydroxide, metasilicate, etc etc and then - if you’re not happy with the look or if stubborn organic staining exists, run it through a light brightening cycle with SH. I’m not personally convinced of the benefit of citric or oxalic after SH, but again… there isn’t one singular way to clean dirty laundry.
For anyone who has read this far: sodium hypo is a fine and appropriate tool for helping to remove organic growth from hard, non-porous surfaces. It is ineffective at cleaning the microscopic nooks and crannies of porous, fibrous materials such as bare cedar. Yes it WILL make everything bright, but bright and light isn’t the same as clean on a molecular level. As I’ve advised others on this forum: SH is a quick, cheap way to make cedar look better and if you’re just trying to put lipstick on a pig, go for it. But if you’re trying to prep cedar for a stain, or if you’re trying to get 30+ years out of cedar siding, carpet bombing dirty cedar with SH isn’t the way forward. Kudos to @Msm for having more than just SH in his chemical toolbox.
Nice write up. I agree with your assessment of SH on wood in general. I don’t like it, and I really don’t think people truly understand how it works. I much rather use percarbonate when I am just cleaning wood. I don’t do cedar, log homes are the only thing I do other than decks and the occasional fence. The forestry lab had a write up on doing the acid after application and their justification for it, but I am sure you read that.
Thank you for the response. I appreciate the wealth of knowledge. I just did an application of sodium per carbonate and hydroxide on my own house and then a light SH Followed by an oxalic to take out the nail stains I’ll post a picture of the results. I’d rather test this process on my own house and a customers. So far it appears like I have really nice results in most places.
