Preparing deck for stain

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WorBry

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Nov 19, 2011
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Hi,

I'm planning on staining the deck that I built from pressure treated wood about a year ago. I'll be using Cabot Wood Toned Deck Stain, a translucent oil stain, that was recommended to me as a good alternative to the more expensive Sikkens stains.

I'm aware that success, in terms of longevity of the stain, depends very much in preparing the wood. It's now had a year to weather and most surfaces have now turned greyish-pale indicating that the water seal (glaze), introduced by the original pressure chemical treatment, has broken down; some areas less exposed to the sun however are less faded.

I've read that it now necessary to abrade the surface to open up the pores that this is best done by first treating with a suitable 'cleaning solution', that additionally kills any mildew, and then using a high-pressure water jet to clean it all out and rough up the surface. The trouble I have with that is that my deck overhangs the pool edge and I'm worried what the chemicals in these proprietary 'cleaning solutions' might do to the pool liner and equipment as they are washed into the pool.

I've read that bleach solution can also be used, which would be safer for the pool (and undoubtedly shock it in the process) but I suspect that would probably kill all the grass and vegetation around it. An alternative would be to use non-chlorine 'oxy' bleach (the peroxide based stuff), which, although less effective as a 'cleaning agent', is supposed to be safer than chlorine bleach and less harmful to flora and fauna. I'm just wondering again though whether there would be damage to the pool itself.

Anyone have experience with this?
 
As long as you are using a strong enough pressure washer (gas powered) and the proper tip, I don't think that you will need any chemicals. If you do use potassium monopersulfate though, be aware that it will show up as CC on your chlorine test.
 
Thanks for your replies.

Yes, I'm inclined to wonder whether the 'chemical' preparation is really necessary. I don't see any obvious signs of mildew staining and the last think I want is corrosion of the deck bolts and fasteners. So, I'll maybe see how I get on with just the pressure washing alone. Never done it before so I'm not sure however aggressive it is. Like I said, there are some areas receiving less sun that are not as faded and possibly still have some residual 'treatment glaze' at the surface. Might pay to sand those sections a bit if the pressure washer doesn't take it off.

Cheers.

Edit: Just spoke to a decking contractor about it. He advised also that the pressure washing should be enough. He also said not to go above 500 psi with pressure treated wood (that has not been sealed/stained before) as higher pressures will force water deeper into the wood which then becomes trapped after sealing.
 
Actually, the more I read up on the subject, the more I'm coming to the conclusion that pressure-cleaning is not necessarily the best way to go and has the potential for damaging softer ACQ treated lumber (pine, in my case).

More important is to test that wood is sufficiently weathered and dry to receive the stain (i.e. the pores have opened up) and that the stain itself is specifically formulated to penetrate this type of wood, which the Cabot stain I have selected is. Other than that it should only be necessary to clean the surface by scrubbing with a stiff brush.

However, if the wood has been allowed to weather too much/long, and has 'greyed-out' from sunlight UV, the dried up surface fibers are less able to bind the stain, and in this case it is recommended to sand-off the top layer with 80-100 grit paper. Sanding is also recommended to promote penetration of the factory cut surfaces that were burnished by the cutter blades.

So much for the mistaken notion that the longer the wood is allowed to weather the better the result. Sure, the stain penetrates better, but then it fails because the stain doesn't bind as well. Wish I'd done this at the end of the last season now. 2-3 months would seem to be about the optimum time for drying out and weathering under fairly dry conditions.

The risk with pressure-washing is that in applying sufficient pressure to strip the top layer the softer underlying wood fibers get damaged and the pores, rather than being opened up, get closed up, so actually worsening matters. Plus, where cracks have developed there is a tendency for water to be forced deeper into the wood. That water then gets sealed in increasing the risk of further freeze-thaw crack damage over the winter months.

This said, I can't say I really relish the prospect of sanding down the entire deck. No problem with an orbital sander on the larger surfaces, but all those spindles, nooks and crannies - tedious. Not to mention the dust. So I can see the appeal of pressure-washing. Question is whether I could do it right. Maybe sand the accessible surfaces first, wash that off and then use a pressure washer to get into the difficult areas? Or maybe, pressure wash those areas first and then sand so that the wood dust is not forced into the exposed wood?
 
Well I spoke to a Sikkens dealer today who assured me that pressure-washing is fine. Pretty much confirmed the contractors advice. Keep below 500 psi, use a wide nozzle at around 12" from the wood. Work with the grain not across it. Be careful around knots. Sure water is forced into the cracks, but that's good because it flushes any dirt and loose dead fibers out. Sanding obviously won't do that and is liable to deposit wood dust in the cracks after hosing down. The important thing is to ensure that it is allowed to thoroughly dry out for at least 2 days.

So, I'm back on the power wash track.
 
Well, renting a power washer with an adjustable pressure control is proving more difficult than I thought. All of the washers for hire in my locale are fixed pressure and at least 1800 psi. I'm planning on staining at the end of August, but if I've turned up nothing by then, I'm thinking to resort to scrubbing with an oxy-bleach (sodium percarbonate) based cleaner and depending on the results, maybe some sanding.

By all accounts, the percarbonate cleaners do help to soften and remove grayed wood (opening the pores), as well as treating mildew (although less effectively than chlorine bleach); on closer inspection, I do have some mildew on the underside of the deck and supports, so it would probably best to address that in the process.

Looking at the MSDS sheets, a number of the commercial percarbonate deck cleaners do contain other ingredients that it might be best to avoid (sodium hydroxide included), so I'm thinking to try just Clorox Oxy-Magic which, as far as I can tell, contains only Sodium Percarbonate and Sodium Carbonate. If some does drain into the pool, what's the worst that can happen - some chlorine depletion and rise in alkalinity - nothing that can't be easily resolved.

From what I've read neutralization with an oxalic acid "brightener" or citric acid wash is not really necessary (as it would be with a hyroxide containing cleaner/stripper), provided the deck is thoroughly washed down afterwards.

Anyone else had success with this approach?
 
I used oxy clean powder on a deck in a house we rented while in college. Stuff works magic. Like $11 for a big tub at lowes if i remember correctly. This deck was gray and green and probably had not been treated in 10 years. It made it look not brand new but darn close. It was a pain because you had to scrub it pretty hard but it works well. As far as it affecting your pool I have no knowledge there. GL


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Thanks. Yes, I've read that it can take several applications and a fair amount of elbow grease to get through grimed and well weathered decks - I guess that's where a power washer comes in useful. Mine is just beginning to gray in the more exposed areas, but is otherwise fairly clean, at least on the top-side, so I'm hoping that it won't take that much. We'll see.
 
Also i used a regular water hose and nozzle that had a good jet option. I wetted the wood put oxy clean on and scrubbed, then let it sit for a few minutes and sprayed it off. Some spots required multiple applications mainly where water came off the roof and mildewed.


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Couldn't find any Oxy Magic in the local stores. Oxy Clean powder has some other minor components (ethoxylated ethanol, sodium metasilicate, sodium polycarboxylate), which no doubt improve it's efficiency as a laundry stain remover, but I thought it might be best to avoid getting into the pool. Found this alternative - Bio-Vert Stain Remover, which like Oxy Magic, contains only Sodium percarbonate and Sodium carbonate.

http://www.bio-vert.com/en/lessive-detachant-poudre.php

Thought it might be a good idea to test the treatment on some ACQ wood off-cuts that had weathered outside as long as the deck.

Without doubt, removing the 'gray' layer by straight sanding is an absolute pain and requires taking off a fair amount of wood, especially on uneven sections.

For the 'percarbonate wash' test, I dissolved about a 1/4 cup of the Bio-Vert in a litre of water. From the moment of application to the wood I could see it working to slough off the 'gray'. Left it to act for about 10 minutes before scrubbing (quite gently) with a nylon brush and then rinsing off. For sure, all the 'gray' was gone and the wood was noticeably brightened. However, it was clear that the treatment had gone on to soften the underlying fibres (more so than with just water) and there was a fair deal of etching and break-up of the raised grain edges. And this could only be resolved by sanding.

Tried again, this time leaving the wash to act for just 5 minutes and wiping the slough off with a wet/rinsed rag, instead of scrubbing. Again, after washing down with a hose, all the 'gray' was gone, but there was much less etching.

Probably, for harder woods that are well weathered and grimy, scrubbing (or power washing) is a must, and most of the peroxide gets used up in getting through those layers. For softer wood (like ACQ pine) that is only moderately weathered and relatively clean (like mine) however, I think care needs to be taken not to over do it, otherwise the results can be counter-productive. Might be best to do a section at a time. I'll maybe test the peroxide wash at different strengths also.

Although I've yet to try power-washing, I suspect that, in combination with percarbonate washing, the result would be pretty much the same as with scrubbing and require a fair amount of sanding.

When stained, the stain on the percarbonate-washed wood was definitely brighter and more uniform than that on the sanded wood, especially where sanding had not completely removed the 'grayed' fibres, which stained noticeably darker.

Of course, it's impossible to judge at this point which is the better preparation for long term stain durability.
 
Well, after more testing with the (BioVert) oxy-bleach I've pretty much come to the conclusion that:

1. It is very effective for loosening the 'grayed' wood surfaces resulting from physical wear and/or UV sunlight damage. The optimum solution (for my wood at least) is around 1/2 cup per 4 liters of tepid water; it doesn't dissolve instantly and needs a good mix. Best to avoid getting undissolved granules on the wood, otherwise it will etch. Use within one hour of preparation. For less severely weathered surfaces, I'd say keep exposure down to around 5 minutes before thoroughly rinsing off (strongest jet you can get from a regular garden hose), with repeat applications if necessary. Avoid scouring with circular motion and too hard; keep in the direction of the grain to minimize damaging the underlying wood fibres.

2. It is quite ineffective on surfaces with intact factory 'mill-glaze', particularly the larger pieces of lumber (posts, beams etc) where the glaze tends to be thicker (and darker), presumably due to the higher degree of pressure/heat searing caused by the larger cutting blades. The notion that oxy-bleach removes mill-glaze and opens the pores, I think is rather exaggerated. My observation is that, when left to work on it's own, it only etches and mottles the surface and repeat applications just make that worse.

I don't know (yet) how effective power washing (with or without cleaner) is at removing that glaze, but sanding (as tedious as it is) does do it well and without residual damage. Most articles on sanding decks say to use 80-100 grit. I would say (with an orbital sander at least) use only good quality 80 grit pads and change them often, and resort to hand sanding for any stubborn patches rather taking off too much with the orbital. Then after sanding a light oxy-bleach wash to brighten the wood uniformly.

The bad news is that the local council have just done a round of inspections and decreed that my pool deck fence at 41" high doesn't meet the new code requiring a minimum height of 48". Unfortunately mine was built just after the code was enforced. Annoying thing is that I had just lopped off the excess on the 4x4" deck posts and now have precious little to attach to. Plus, do I do the modifications now, and hope that the newly added wood has dried enough for staining in a months time or stain just the existing weathered wood and leave the new until next spring, which will look silly. :(
 
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