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Old 08-23-2012, 11:34 AM   #1
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Deck staining: percarbonate and power washing?


I have pool deck that I constructed from ACQ pressure treated wood (pine) about a year ago. By now there is a moderate degree of weathering (graying) on the deck floor and sections of the railing and frame that have received most sun exposure, not doubt hastened by regular soakings with chlorinated pool water.

I'm planning on staining the deck with Cabot Wood Toned Deck stain in September and am looking at the best method for preparing the wood.

When I bought the stain the dealer advised that the deck should be power washed, nothing else, just taking care to avoid damaging the wood by using a pressure not exceeding 500 psi and a wide jet nozzle. So I phone around all the tool hires in my locale and they all have power washers (gas and electric) but none that allow the pressure to be adjusted down to 500 psi. Seems that most people who hire these things to clean their decks are advised to take the electric models (1500 - 1800 psi range) not realizing that they are probably using too high a pressure.

This prompted me to research other preparation methods. I learn that power washing with water alone is not sufficient and that it is desirable to first apply a chemical deck cleaner. For weathered decks this should be one that degrades/loosens the dead (grayed) surface fibers so that the pores are opened and cleansed. Also important that the treatment is effective against mildew and fungi even if there are no visible signs, as spores may be lurking.

Cleaners utilizing sodium percarbonate and sodium carbonate as the active products appear to be well recommended in these respects, including home-brewed preparations made from domestic non-chlorine (oxy-bleach) stain removing powders (Oxi-Clean, Oxy-Magic etc).

I might add that my deck overhangs the pool and whilst I do intend to hang some plastic sheet to avoid stuff washing off into the pool, I know it's going to be messy with a lot of spray and so would prefer to avoid using a corrosive chemical that could damage the pool structure (steel walls & resin posts/coping) and liner. Peroxide-based (non-chlorine) oxidizers and sodium carbonate are widely used in pool water chemistry management and so I see no risk there.

I've come across several articles suggesting that, provided the percarbonate wash is allowed sufficient time to act (up to 20 minutes) and the surface is well scrubbed, it can be rinsed off with a garden hose without resorting to power washing.

I've done some tests on weathered off-cuts of the same wood using a percarbonate wash made from an oxy-bleach stain remover. I chose one (Bio-Vert Stain Remover) that (according to the MSDS) contains just Sodium percarbonate and Sodium carbonate: some other products (like Arm & Hammer Oxi-Clean) contain other components as well. Dissolved 1/4 cup in a liter of tepid water, for testing.

For sure, within minutes of applying the solution you can see it start to bubble and slough the dead surface fibers. Ten minutes seemed about the optimum time to act. Some scrubbing (medium stiff nylon bristle brush) was required to get out all of the grey on the rougher grained and uneven surfaces but I was careful to scrub in strokes with the grain.

After rinsing off with a garden hose however I noticed that no matter how gently I had scrubbed and wiped the surface, the exposed wood seemed to be very soft and frayed around the grain edges. After drying this left the surface with a pronounced mottled/pitted/etched appearance. I can only assume that the percarbonate, as well as removing the dead surface fibers, had gone on to affect the underlying wood - I dunno, maybe degrading the binding lignin.

I was anyway planning to lightly go over the cleaned wood with 80-100 grit sand paper as a final step before staining but removal of the pitting left by the percarbonate treatment would require far more aggressive sanding. I'm not too bothered about the aesthetics. My questions are more:

Is it desirable for a deck cleaner to leave the wood surface in this condition. I can see how it might promote initial stain penetration and initial adhesion but what does it do for stain retention in the longer term as these loosened fibers decay and are shed?

Is there another type of product that is better suited for preparing this type of wood for first-time staining? I tried just using laundry detergent. No etching but pretty ineffective in removing the grayed fibers. TSP - don't really want to get phosphates into the pool water (promotes algae). Oxalic Acid based cleaner/brightener - how does it compare ?

Would power-washing be of benefit or potentially make it worse? The percarbonate washing does leave the wet surface very prone to splintering. On the other hand, I wonder whether it would be more effective in flushing out residual peroxide that has penetrated deeper into the wood and continued to act on underlying fibers whilst the wood is drying out.

I've read that percarbonate is also effective for opening up 'mill glaze'. For sure, many of the larger sections of lumber in the deck (posts, joists etc) have retained the surface 'sheen' that is usually attributed to searing-pressure action of the factory planing blades. In my tests, percarbonate does etch these harder surfaces but it's no way near as effective at removing the 'glaze' as plain sanding. Would power washing be as effective?


Cheers.


Last edited by WorBry; 08-23-2012 at 03:28 PM.
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Old 08-24-2012, 11:48 AM   #2
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Deck staining: percarbonate and power washing?


Thanks for all your responses I guess my post was a little....well...verbose.

So, I'll be brief.

After more experimenting, what I found helps a great deal is - after first rinsing off the percarbonate wash, and while the wood is still wet - to go over the surface with wet/dry sanding pad (I had 100 grit to hand) and rinse again. This helps to slough off those raggedy fibers that are left over from the wash and definitely reduces the amount of mottling and the need for more aggressive sanding when the wood has dried. Need to be careful though not to splinter off the softened wood underneath - best just stroke the pad in the direction of the grain. Definitely makes a difference and I guess does what power washing aims to do.

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Old 08-24-2012, 01:27 PM   #3
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Deck staining: percarbonate and power washing?


Is that what people might call "furring" of the wood? If so I've seen lots of people describe that as an effect of deck cleaning and I believe they usually recommend sanding before staining to remedy that condition. Sorry I can't speak from experience as I've yet to undertake a similar project at my home. Have just been doing some preliminary research and deciding if I need to replace some boards before even attempting to clean. Previous homeowners had a hottub/spa on the deck and it was never stained that I can tell.
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Old 08-24-2012, 03:33 PM   #4
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Deck staining: percarbonate and power washing?


The chlorine from your pool has "eaten" away at the wood fibers over time.
I would use a power washer that has an unloader(the small red knob on the pump side) that will reduce the pressure. Most rental units have one but the rental company may not know how to really use a pw.
Another method we use is to clean with sudsy ammonia brushed cross grain to loosen up the fibers and rinse with water.
Any way you do it it has to be dry to 12% to apply sealer. I woud not apply a semi solid stain. I would use an oil product that can be reapplied yearly.
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Old 08-24-2012, 07:24 PM   #5
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Deck staining: percarbonate and power washing?


Thanks both of you.

Quote:
Originally Posted by MEE123 View Post
Is that what people might call "furring" of the wood?
Well I guess on the 'softer' wood where there is feathering of the grain contours, you could call it that, but on the thicker timber, where weathering has produced more of a dark, hardened glaze than graying, it appears more as pitting or etching of the lighter components of the grain.

Quote:
Originally Posted by CaptRandy View Post
The chlorine from your pool has "eaten" away at the wood fibers over time.
Most of my testing has been with off-cuts let I left weather (precisely for this purpose) but I'm sure you are right. The deck boards are well 'bleached' from the daily dousing with pool water, and I think the only time I've hosed it down with fresh water was when a flock of birds that had been feeding on berries or sumac graciously decided to drop their purple bombs in perfect synchrony whilst passing over the deck.

I did try out the percarbonate wash on several of the steps however, which are also quite bleached (more than 'grayed'), and yes it did leave them very pitted.

Quote:
Originally Posted by CaptRandy View Post
I would use a power washer that has an unloader(the small red knob on the pump side) that will reduce the pressure. Most rental units have one but the rental company may not know how to really use a pw.
Quite possible. My inquiries were over the phone, so I just took their word for it. Also in passing, just saw a neighbor using one to strip his deck, so I'll maybe have a word.

Quote:
Originally Posted by CaptRandy View Post
Another method we use is to clean with sudsy ammonia brushed cross grain to loosen up the fibers and rinse with water.
I'm not sure I'd want ammonia to get into the pool water (just thinking of the implications) but I'll look into that. Does it act to remove the grayed fibers also and do you need to neutralize after? Ammonia might also be difficult to find in my locale - recall looking for some when I had a skunk problem.

Quote:
Originally Posted by CaptRandy View Post
I would use an oil product that can be reapplied yearly.
Yes, I'm intending to use a Cabot Wood Toned Deck stain which is a translucent, oil-based product.

Thanks again.

Last edited by WorBry; 08-24-2012 at 07:28 PM.
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Old 08-24-2012, 07:46 PM   #6
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Deck staining: percarbonate and power washing?


Sodium percarbonate does not effect the linigins. Hypoclorit, which is in pool chlorine would affect the wood as described. We use percarbonate cleaners all of the time with no problems. I do agree, as you said low pressure is needed when power washing wood. A power washer that does not have a adjustable unloader can be adjusted by using larger orifice tips. I would not hire a company to power wash if they claim they can't adjust there pressure. They obviously don't have enough experience with power washing to know that certain tips and orifices adjust the pressure. I agree with Randy. It definitely sounds like the chlorine has began damaging the deck. After cleaning apply a brightener too, citralic works well. Sanding is usually recommended when you have furring, which is usually caused by improper power washing. Sodium percarbonate does not cause furring.
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Old 08-24-2012, 07:52 PM   #7
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Deck staining: percarbonate and power washing?


We use SUDSY AMMONIA, different than ammonia you usually buy. It is used to clean and brighten teak cockpits in large sportfisherman boats.
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Old 08-24-2012, 09:59 PM   #8
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Deck staining: percarbonate and power washing?


Quote:
Originally Posted by housepaintingny View Post
. I would not hire a company to power wash if they claim they can't adjust there pressure. They obviously don't have enough experience with power washing to know that certain tips and orifices adjust the pressure.
No, I definitely wasn't looking to hire a company to do it, just to rent a washer. One of those 'we have a pressure washer and will clean everything including your dog' outfits came knocking the other night. I asked them what pressure they would use to clean the deck, which was obviously taken as 'is your pressure washer powerful enough' as the response was 2000 psi mate, that'll get all the **** out. OK, no thank-you.

Quote:
Originally Posted by housepaintingny View Post
..... It definitely sounds like the chlorine has began damaging the deck.
When I tested the percarbonate wash on the deck steps I could see that it still left a fair amount of bleaching (I guess the chlorine damage had gone deeper) and that I was probably going to have to resort to power sanding (orbital) the deck boards and steps. Just weighing up what would be better - see what could be cleaned up first with a wash and then sand or the reverse?
I guess the thing that concerns me about the power washing is that if the chlorine damaged layer proves difficult to remove I could over do it and damage the deck.
The other thing that concerns me (in general) is that some of the 4x4 posts have developed quite large checks; fortunately none running the length of the post, but I'm keen to avoid any treatment that could make it worse.

I do of course wonder whether that could have been avoided by sealing the wood last September, but I was advised at the time that two months was too little time for the wood to weather and that it would be better to wait until the next year to ensure good stain penetration.

Quote:
Originally Posted by housepaintingny View Post
After cleaning apply a brightener too, citralic works well.
I have wondered about that. From what I've read, it's not necessary to neutralize after a percarbonate wash, as one would with a stronger alkaline treatment, provided the solution is thoroughly rinsed. Is there a particular benefit, other than brightening? Would it help with any residual chlorine bleaching?

Quote:
Originally Posted by CaptRandy View Post
We use SUDSY AMMONIA, different than ammonia you usually buy. It is used to clean and brighten teak cockpits in large sportfisherman boats.
Ah, OK. I don't think that type of product is available here in Canada, being ammonia based.

Last edited by WorBry; 08-24-2012 at 10:09 PM.
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Old 08-24-2012, 10:33 PM   #9
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Deck staining: percarbonate and power washing?


Instead of power washing get a pump sprayer from your local Ace hardware store, or home depot depending on how big your deck is get clorax bleach from costco or bj's they sell 1 1/2 gallon jugs 2or3 jugs in a case mix bleach and water 50/50 mix or 75/25 bleach to water spray plants or grass with water from your garden hose to prevent harming them spray deck with mixture from pump sprayer with fine mist gray disappears almost instantly scrub with a deck brush and hose off after about 10 minutes repeat if needed after that cabot makes a product called wood brightener 1 gallon mixed with water makes 5gallons of product pour into pump sprayer let it stay on deck for 10 minutes and hose off repeat if needed when deck dries in about 3days you should be ready for staining I'm not a big fan of Cabot stains I prefer Sikens they make a translucent stain called S R D for decks less than 2 ft. Off the ground I think they make 5 colors natural/ natural cedar , natural oak, mahogany,and butternut one coat applied with a lambs wool applicator if your deck is more than 3 feet above ground they make D E K applied same way except you apply 2 coats after first coat dries 24hrs. Depending the weather you can apply in direct sun second coat applied same way your deck will look like the oak floors inside of house product is excellent you will be very happy with the out come, I don't recommend power washing your your deck can damage wood and create more work
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Old 08-25-2012, 07:57 AM   #10
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Deck staining: percarbonate and power washing?


Well I've no lack of concentrated bleach (10%) for chlorinating the pool, but I'm not sure I'd want to go the chlorine route for cleaning the deck. Having read what it does to lignin and corroding galvanized fasteners, applying it to a deck that has already been affected by pool chlorine would seem to be adding insult to injury. Plus there is a fair amount of ornamental vegetation around the pool, not to mention grass that is still trying to recover from drought stress, and there is a big difference between splash over of pool water and sloshing around fairly concentrated chlorine; a 50:50 solution of domestic bleach would be typically around 2.5% hypochlorite.

I did consider Sikkens but found it rather (too) expensive for my budget and the Cabot stain was well recommended as an alternative. Otherwise I might have gone for TWP had it been available here.

The main problem with the power washing is that I have absolutely zero experience of it; I've never done it myself and have never had a deck washed by someone else. In fact never had a deck before this house. I was assured by the dealer who sold me the stain that as long as you don't exceed 500psi, use a wide nozzle at least 12" from the wood, and work with the grain it 'should be' OK. But I'd need to try it before committing.

I have seen advertized these gizmos that claim to convert a regular garden hose into a pressure washer - basically a constricted length of pipe ('wand') - but considering the physics, I can't see that they do anything other than create an illusion - the force of water is a function of flow rate and the only way to increase flow is by adding pressure to the line. The only benefit I can see is maybe in better control and localization of the jet.

Last edited by WorBry; 08-25-2012 at 08:30 AM.
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Old 08-25-2012, 08:33 AM   #11
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Deck staining: percarbonate and power washing?


I would not use chlorine based bleach on deck ever.
Don't be afraid of a pw with the unloader you can power down the pressure to an acceptable level. Use the green or white tip, practice on a scrap of wood to see how it works. Everyone starts somewhere. I did over 20 yrs ago and have done it for a living ever since.
If you decide to sand use no finer than 80 grit paper.
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Old 08-25-2012, 11:33 AM   #12
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Deck staining: percarbonate and power washing?


I'll maybe see what the neighbor who was pressure stripping his deck uses. Tell him his deck looks wonderful and express surprise if he offers to lend me it
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Old 08-25-2012, 11:56 AM   #13
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Deck staining: percarbonate and power washing?


Once you start using one you will be surprised how much you can do with it. We clean trucks, houses, pool surrounds, used cars, roofs, and of course decks and other wood structures. I have made a good living for over 20 years holding a wand daily.
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Old 08-26-2012, 11:09 PM   #14
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Deck staining: percarbonate and power washing?


I understand your concern about using bleach on your deck your not letting it dry on the deck your hosing it off after a few minutes wetting the surrounding plants,grass and anything else you don't want affected is a must the bleach is to remove the greying or the green stuff that's growing is alive and needs to be eliminated power washing. Doesn't exactly do that .sikens is more expensive than cabots but lasts a lot longer applied correctly you get what you pay for after all is said and done if it lasts twice or three times longer it's worth it you want to use the best product available on your own deck I've had to sand decks with a orbital floor sander after some power washing gone bad some wood looks like a tennis ball try staining that .I don't know how to send pictures to this site I have some before and after decks I've done on my IPad if you know how I can send them let me know I'll check this site daily I would never use a power washer on a wood deck or anything wood for that matter if you do plan on renting a floor sander as your next step to staining your deck.
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Old 08-28-2012, 09:09 PM   #15
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Deck staining: percarbonate and power washing?


Like I said, it's difficult to form an opinion on power washing without having tried it myself.

I've got a few weeks to go before I prepare and stain the deck (depends when the kids officially declare it too cold to use the pool). For now, and until I can can get my hands on a pressure washer to try out (on off-cuts that is) I'm persevering with the chemical cleaning tests.

Having run out of the Biovert percarbonate stain remover, I thought I'd try Oxi-Clean to see how it compared. Interestingly, I found it to be a little less potent than the Biovert cleaner. Whereas the Biovert seemed to slough the dead (grayed) surface fibers quite quickly, the Oxiclean took a bit more time and required more scrubbing to get it out of the rougher grain and knots. This said, there was much, much less etching and pitting of the underlying exposed wood, which seemed a good thing.

Whether this relates in some way to the percarbonate content, I'm not too sure. The MSDS for the Oxi-Clean powder states that it contains 30-50% sodium percarbonate and 55-75% sodium carbonate, but I cant find an MSDS for the Biovert powder, only that it's ingredients are these two chemicals.

I suspect however that it might have something to do with the other minor components in Oxiclean. In addition to ethoxylated alcohols (i.e. the non-ionic surfactant detergent) it contains two non-phosphate enhancers - sodium polycarboxylate and sodium metasilicate.

The latter is of particular interest, as I learn that it has several properties. First, it's a cleaning agent (primarily a degreaser) in it's own right. Secondly, it removes calcium and magnesium, allowing the surfactant to work more efficiently in hard water and preventing deposition/redeposition of mineral deposits (descaler). And thirdly, as a strong base, it serves to buffer the localized corrosive elements of the oxidative degradation processes (mediated by peroxide in this case) so minimizing damage to the fibers of the fabric that is being cleaned.

I have a hunch that the etching and pitting left after percarbonate cleaning represents such localized corrosion and that maybe the sodium metasilicate in Oxi-Clean helps to protect against it, albeit at the expense of some loss of potency in degrading the dead wood fibers. Seems reasonable to me.

So, for me, the main value of a power washer would be for getting into the nooks and crannies that can't be scrubbed and where a garden hose provides insufficient force to lift off and flush out the loosened dead fibers. I had a look at what happens when the wash solution was left to pool on a well weathered off-cut and it was not a pretty sight - the partially degraded dead layer just dried and re-hardened as a cracked, mangled crust - not something you'd want to leave on the wood for staining.


Last edited by WorBry; 08-31-2012 at 09:08 PM.
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