Sanding before or after acid?

[plainpainter 217]

Other than the deck I posted about the befores and 16 month afters - I usually end up sanding my decks down. I like it better that way - perhaps it's a better job - and perhaps folks in New England neglect their decks much much more than the rest of the nation - and we have really harsh elements here. Anyways - I got to thinking - if I put on an alkaline stripper followed by an acid bath - then sand. Then potentially aren't I sanding off the top layer of 'conditioned' wood? I mean - if you sand wood enough it becomes 'clean' but wood has 'stuff' in it that may or may not interact with stains. And a brightener seems a good way of sequestering that stuff out of the top layer.

So what I want to know - has anyone experimented with sanding after the stripping stage but before the acid/brightening stage? And did you notice any different results? The more I think about it - it introduces more days on the job and less profitability - but It seemed to me that it may be a superior job - who knows?

[MMI Enterprises 289]

Matt, btw another thought on yer sanding issue...

You know besides the stain makeup being suspect of causing the tannin reaction you could also look to what you sanded with as possable cause of the darkening. Metalic varieties of paper can impregnate wood fibers with enough metal to where tannins do their thing once moisture arrives. Is just like the tea bagging/ebonizing wood process or any tannin type staining really.

When I use nylon pads on the big floor machine I have no chance of such problem.

Edited December 10, 2008 by MMI Enterprises

[Beth n Rod 1,279]

I think the point we are missing here is removing the finish. Sometimes we are doing multi- applications of a strong Alki. Deciding when to stop the alki action is another matter. Has the Finish been removed? Do we need to to do it again? Do we want to stop the action of the Alki? Do we already know we have to sand? Is there allot of organic Stains, Rust stains ect..? Is there a need to Bleach the wood after stripping?

Stopping the action of the Stripper and Removing Tannin Stains and Brightening the wood are different actions although many or most times a simple neutralization works after a clean or mild strip of the wood.I do know the less moisture that is in the wood the better the Acid works for removing Tannins and Stains.

When using OxAcid a problem happens when it doesn't totally dissolve and it leaves a Salty looking resydue on your woodfriendmembers deck. Or Rod has been on your DEck working out to the Oldy's

If I keep on writing do you think I'll give Kev a Headache because I have one ? LOL

Well put!!! :lgbow:

Beth

[RPetry 564]

Kevin,

Wood season is another 3 1/2 months away, I have too much time....

Would this be an interesting chemistry experiment?

In a clean plastic container, add 10 or so ml. of 6 oz./gal. NaOH and 6 oz./gal. of citric acid. Do the same for NaOH and oxalic acid in the same proportion.

Allow to evaporate at room temperatures, ie: inside the house, and see if any "salts" or "residue" remains.

Or, even better, dilute the NaOH with 50 or 100 ml. of water (as a substitute for using a PW) and add the 10 ml. of acids. What say you?

[PressurePros 248]

"Combining an acidic compound with an alkaline compound produces a salt.

pH Acid Alkaline balance

[Beth n Rod 1,279]

"Combining an acidic compound with an alkaline compound produces a salt.

pH Acid Alkaline balance

Exactly!

Beth

[RPetry 564]

Ken and Beth,

Instead of reading about it, do it. Any harm in that?

[Beth n Rod 1,279]

Rick,

I've seen it happen. I know it only happens in certain cases, but I'm not going out in the cold weather to play. ;) I like the warm indoors right now.

Beth

[RPetry 564]

Beth,

Room temp, indoors, like 65 to 70 F. Not outdoors in mid-Atlantic winter.

I have not idea what you and Rod have seen. I'd like to see it.

As Jim alluded, it may be over mix of oxalic, and you are seeing oxalic crystals instead of so called "salts". I do not know, but am curious.

This may be boring to the greater mix of members. Lets bring back "The Great Bleach Debate!" Hah, now that was fun...

[Beth n Rod 1,279]

Rick,

I love ya man, but it's cookie baking time, and shopping time, and decorating time. Not in wood geek mode right now. You do the test. ;)

Beth

[MMI Enterprises 289]

Thanx for posting that site Ken...there's parts in it that speak to salts basically equalling buffers hence confirming my point.

Rick, I guess it would be interesting enough experiment but I don't think it will work to its fullest ability of making salt unless you do titration. The concentrations will need to be different depending for sure on what acid or base is used in order to end at their equivelance point. Besides their obvious starting ph's there are likely other factors I know nothing much of figuring such as starting water ph or temp, how old the chems , etc.. So but the use of 'equivelance point' is not a equal parts/measuring thing nor does it mean a neutral ph. As my link points out the 'end point' where the colored titration indicator additive shows up may not be exactly the equivelance point in all case neither. Refer to that page link or maybe it's sublinks on the indicators..maybe there is info ya can use if doing with citric acid.

Other prehaps more valueable experiments I suggest we take on would be to do some titrating with various branded stuff like citralic or hd80 along with their counterparts in raw form. Between that and generic ph strips we could confirm if label recommendations are worth a darn or if we can save some money or not.

In the end it does all depend what ph you want to end at in order to accommodate your stain or how bright ya want to go so that's why I mention the strips. Such won't work right with bleach as you proably know but probably fine with our other main wood chems.

[Beth n Rod 1,279]

Here's some ref that points out speed of ph lowering/buffering and perhaps is something of confirmation of some the points I make:

pH curves (titration curves)

"Titration curves for weak acid v strong base

We'll take ethanoic acid and sodium hydroxide as typical of a weak acid and a strong base.

Running acid into the alkali

For the first part of the graph, you have an excess of sodium hydroxide. The curve will be exactly the same as when you add hydrochloric acid to sodium hydroxide. Once the acid is in excess, there will be a difference.

Past the equivalence point you have a buffer solution containing sodium ethanoate and ethanoic acid. This resists any large fall in pH."

edit: correction though- above acid is acetic rather than oxalic..spelling is similar so no they not specifically talking of our oxalic example but just the same ya probably can still see the points and it suitable example.

I would like to make a clarification on this one.

The example above while completely valid does not take into consideration the concentration differentiation after the first wash as we create it.

The wash process significantly reduces the amount of caustic left on the surface for an acid to neutralize. Since I do not take measurements the actual concentration present is not exact but based upon pH testing, the fact that the wood after a strip or wash with an alkaline is indeed alkaline at this point the amount of acid required to neutralize the remnants is less than what the Titration chart illustrates.

For example: Take HD-80 at 8 oz/gal and strip off a finish. By the time one has completed the washing process and is ready to neutralize, the amount of HD-80 that is left behind is;

1. diluted

2. diffused into the wood fibers

3. significantly reduced in concentration.

Our practice is to use double the concentration of acid to Alkaline ratio. 2:1

So for a strip using 8 oz/gal the concentration of acid would be at 16 oz/gal.

Why? you ask. If the concentration is so reduced then wouldn't less acid be just as effective? No.

Because the wood is also saturated with water containing the alkaline stripper, the acid needs to be able to penetrate deep enough to reach the deepest saturation levels. In addition, the wash water on the ground is alkaline as well, so the rinsing off of the acid solution applied needs to be able to react there as well.

Rinsing is the ultimate part of the job performed because you get to ensure that nothing is left behind. Many acid products have a surfactant in them so as rinsing is done, bubbles will develop as long as there is an residual left behind. (no, we are not talking major bubbles here, just bubbling that is associated with the agitation of the rinse process but in this case the bubbles do not linger when the surface is free of chemical residues.

This post is just to clarify and expound on the points made by Kevin with the chart. I hope it provides some insight.

Rod!~

Edited December 13, 2008 by Beth n Rod
clarification, spelling

[plainpainter 217]

Rod - you use 16 ozs of acid gallon?!?!? Holy smokes! I tried Bob's oxalic at 9 ozs. per gallon once, and it made the wood look like dried out white bones!

[MMI Enterprises 289]

Rod,

This is not a one post thread and so claification about my belief on concentrations being key is not really needed. See here:

Not a chemist, so but the way I see it the main 'potential' to make problematic salts would be the starting concentrations of the metals (NaOH) and acid (which ever acid). In the course of cleaning or stripping we are already rinsing the main doses of metals with 5gpm+ before acidifying the wood.

The deeper point that perhaps could stand for some clarifying is that such graph/confirming info shows that if the concentrations were similar then the ability to go more acidic is hampered by the mandated buffering created. I used the info in a reverse deconstructing way. When I see it play out or proven that we are hampered is the point where I would say we dd not rid the deck of alkaline/metal. Your expounding is fine and all as we are all open but it is a tad different than what I expound so I wish to make that clear.

I say the acid does indeed find it's way in by nature of water being the common solvent. Hence the color flip. I am also saying I personally prefure to go more acidic and so is reason I keep the concentration higher than what the diluted/rinsed stripper concentration should need..

That said, Don't get me wrong folks, I do believe that a fair amount of alkalinity can not be rinsed entirely from the wood. Porosity or the fibrous lignin alike surely absorb and take away some the concentration from the main dose of chem that flows away while either applying or rinsing. I think it safe to say that what we start with in stripper concentration is not what we need to count on needing neutralized or overcome in order to head south towards acidic...no ability to go more acid equals a no to low salt/unbuffered situation. Just doesn't happen cause we rinse stripper sufficiently to prevent it.

Edited December 13, 2008 by MMI Enterprises

[plainpainter 217]

Rod,

Just doesn't happen cause we rinse stripper sufficiently to prevent it.

I agree 100%

[Beth n Rod 1,279]

Just doesn't happen cause we rinse stripper sufficiently to prevent it.

So do we.

And we do not use straight Oxalic.

Beth

[Beth n Rod 1,279]

Rod - you use 16 ozs of acid gallon?!?!? Holy smokes! I tried Bob's oxalic at 9 ozs. per gallon once, and it made the wood look like dried out white bones!

Did you pre-wet the wood before applying? Oxalic as very aggressive on bare wood. I use a 7:3 mix of oxalic:citric to knock it down a peg and make sure the wood is wet before applying. This helps to diffuse the solution and get better penetration and rinsability.

...

My apologies Kevin if you feel I stepped on your toes there bud. My intent was for the readers who are not as familiar with the processes as we are so as to avoid confusion.

Rod!~

Edited December 13, 2008 by Beth n Rod

[Beth n Rod 1,279]

Porosity or the fibrous lignin alike surely absorb and take away some the concentration from the main dose of chem that flows away while either applying or rinsing.

From Wikipedia, the free encyclopedia

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Not to be confused with Lignan.

Lignin or lignen is a complex chemical compound most commonly derived from wood and an integral part of the secondary cell walls of plants.[1] The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum,[2] meaning wood. It is one of the most abundant organic polymers on Earth, superseded only by cellulose, employing 30% of non-fossil organic carbon[3] and constituting from a quarter to a third of the dry mass of wood. As a biopolymer, lignin is unusual because of its heterogeneity and lack of a defined primary structure.

:confused: don't you mean cellulose?

[MMI Enterprises 289]

No appologies needed Rod..

On yer last statement about cellulose..Instead of defining what specific parts of the mass we call wood that can take on a ph or change in ph suffice it that I care not to guess. Perhaps we could suffice it to say that much of the structure would have to be able to be changed in order that we experience an alkaline or acidic situation. Our goal is changing it so it must be possable right? ..:)

The architecture, structure, or what have you is ordered in a fibrous way that can effect penetration of this or that and since lignin can be thought of as both the glue if you will or in some case as a seal that prevents things entering the rest of the ordered mass we have sorta no choice but to realize that it can be compromised, changed, or disolved (i.e-making pulp)....

As a mass, the terms fibrous lignin or fibrous cellulose werks well enough fer me...Whatever case, the ordered structure and/or absorbtion, etc. makes for whatever amounts of chem or ph we could claim the wood has left or displays...Rod do you by chance have any info on how the makeup of wood can mechanically perform concentrating duties to chems such as that of a filter? In case of a filter such takes place by way of the solvent travelling on through forcing a mechanical trapping. If the makeup of the mass is anywhere near as efficient as say compared to that of a reverse osmosis membrane then perhaps not much of what we term as our active chems can make it deeper then the next one. Weird, if not contradictory thought eh? Water might go bu not something else..haha. Maybe it does that on some micro cellular level but apparently, once again, doesn't show as such when brightening or flipping the color of an alkaline effected wood. Regardless, however strong the chemical concentrating could get by way of the solvent/water settling, pressure, absorbtion, etc. I would tend to think it can be still had at and diluted by the carrier/solvent that took it there in first place which is water. Hence rinse rinse rinse in case of at least the alkaline cleaners..

Hey besides all we have discussed I suppose we could discuss damage possable from leftover acids or alkalines. I imagine to tread there we would have to know something of a woods percentage of soluability or insoluability by specific acid or alkaline...anyways, I am rambling now..lol.

First paragraph here http://www.ipst.gatech.edu/faculty_new/faculty_bios/ragauskas/technical_reviews/Basics%20of%20Kraft%20Pulping.pdf explains something of lignin to where we can picture what it is and its duties.

[Beth n Rod 1,279]

Yeah, you are rambling hehehe.

As far as the question, no, I do not have any sources discussing the properties in that manner. I would have to say that we are likely to be dealing with adhesion/cohesion characteristics and these would be determined by the woods components in specific as well as the chemicals we use in relation to them and the interactivity or reactivity.

Suffice it to say that much can be determined with a simple litmus paper test.

I don't want to get any more off topic than I think we have in this thread as well.

Rod!~

[divine190 14]

You've been there, done that... agree with you totally.

The is a relative statement pertaining to whatever step is necessary on any particular job. No I don't strip then wash or vice versa. The one exception was a time that I washed a golf course type deck...algae had become moss! It was so thick I had to hit it with a bleach and sodium hydroxide mix first just to kill it off and wash it to remove the mess. Then I proceeded to strip the deck then neutralize afterwards. oh, I forgot about the foot deep layer of leaves I had to blow off first to even see the deck!

It wasn't one of my prouder deck jobs because the deck never sees the light of day due to the terrain and the tree coverage. The customer wasn't interested in having it sanded to help make the floor look any better which was severely neglected, had tons of planters and a cat that used it as a part time litter box.

Rod!~

[Beth n Rod 1,279]

Bump! And...ANOTHER classic thread.

Beth

[acegot 14]

Dont know how I managed to stay out of this thread.

[Beth n Rod 1,279]

Bump....