Another Decking recoat question

[zendo]

Is it enough to clean a deck with some sort of deck cleaner before recoating or do you have to sand or use a pant striper to remove previous coats of oil .I was thinking Spa n Deck which has been discussed in other threads .Previously i used Cabots natrual decking oil.

[Spelunx]

If you wanted to recoat with an oil finish, then a good clean is all that is needed, which is the reason a lot of people use them. Other finishes have to be sanded down before recoating.

Water based finishes are fairly new on the market, and have the advantage of not needing sanding to recoat, much like oil finishes.

My understanding is that you can use the water-based finish over the oil finish, there are a number of people around here that have used the products and swear by them, so soemone wil come along shortly and give you a definitive answer.

[jimj]

Dear Zendo,

There are several things to consider. In a nutshell if the wood feels smooth when you run your finger across the grain then it would probably not need sanding and any remnants of Cabot's decking oil will come out with the use of a sodium percabonate based product. This could either be using Flood Powerlift or 200 grams of a Napisan (or no name brand) mixed with 4 litres of warm water. Either way apply this mixture to wet timber and allow it to stand for 20-30 minutes. Keep it lightly misted if it looks like drying out. You may need to scrub and then rinse off thoroughly. You havn't stated how old the wood or it's exposure to sun or rain. If after you have cleaned with this method and if it looks stunning with just fresh water only on it then it will come up. After this step I apply a mixture of 50% oxalic acid-50% water and repeat the same process. After this I am ready for coating. I use Flood spa&deck with my business but the choice is yours to select what you feel you will be happy with. If you look at my portfolio in my website all of the after shots are spa&deck. The critical thing is that the wood needs to look stunning when cleaned back and wet and be smooth to touch across the grain with no old wood fibers on the surface. Hope this reply might be of some help.

Jim J www.restore-a-deck.com.au

[zendo]

Thanks jimj.
The deck is around a spa which is not covered so it cops all the weather its in good condition just starting get a bit dark the boards that are near the house still have good colour but further out from the house thay are starting to weather up. I justed wanted to get on top of it before to much damage is done. PS what is oxalic acid.
Kev

[jimj]

Sorry for the delay in getting back. Oxalic acid is the active ingredient in most of the commercial timber cleaner-brighteners that are currenntly on the shelves at the various stores. Without going too deep into Chemistry I use sodiun percarbonte ph 13 which is highly alkaline which is what detergent is to lift both oil and dirt from timber. A timber is roughly ph7 or neutral and most decking coatings are designed to bond to a ph neutral surface. By using a oxalic acid product Ph1 to follow after the sodium percarbonate it allows the timber to return to a more ph 7 neutral state. You will see a big difference with your eyes after using the sodium percarbonate and a much less difference after you have followed up with oxalic acid. It will be more effective in lifting black stains from metal objects and will definitely leave the wood a little brighter once it dries. Please be sure to thoroughly rinse both the the sodium percarbonate and the oxalic acid off. I use Floods spa&deck prep which is 10% oxalic acid. There are another 6 or so products available on the shelves just look for the active ingredient on the container. Hope this makes some sense.

[strangerep]

Oxalic acid is the active ingredient in most of the commercial timber cleaner-brighteners that are currently on the shelves at the various stores. Without going too deep into Chemistry ...

I took 1st-year Chemistry at Uni and I'd like to understand the
technical details of this a bit more deeply...

I use sodium percarbonate ph 13 which is highly alkaline which is what detergent is to lift both oil and dirt from timber. A timber is roughly ph7 or neutral

Does this depend on the timber species? I vaguely recall reading that
many hardwoods are more acidic than this, down around ph3 or ph4.
What's the correct story?

and most decking coatings are designed to bond to a ph neutral
surface. By using a oxalic acid product Ph1 to follow after the sodium
percarbonate it allows the timber to return to a more ph 7 neutral state.

That's interesting. What happens if the timber is too acidic? Does the
coating still have trouble bonding? Does the answer depend on the type of
coating (oil or acryllic)?

Please be sure to thoroughly rinse [...off...] the sodium
percarbonate [...].

Given that rainwater is slightly acidic, can one rely on several downpours
(as Sydney has experienced recently) to both remove any remaining sodium
percarbonate and also restore the ph back towards neutral, or is an oxalic
wash still essential?

I use Floods spa&deck prep which is 10% oxalic acid. There are
another 6 or so products available on the shelves just look for the active
ingredient on the container.

If I have solid oxalic acid crystals, what dilution proportions are optimum
when dissolving it water?

TIA.

- strangerep.

[jimj]

Dear Strange rep,

Thanks for your reply. It would take too long to sit at the computer and try to type all of the answers to your many questions. The steps that I outlined are the ones that I undertake on the restoration of outdoor timber decks. I answered the request in the hope that I might be able to help out Zendo. All I can offer is what I have found works for me and to put my website up for all to examine and see my daily work.

jimj www.restore-a-deck.com.au

[nickwithaz]

Dear Zendo,

There are several things to consider.... any remnants of Cabot's decking oil will come out with the use of a sodium percabonate based product. This could either be using Flood Powerlift or 200 grams of a Napisan (or no name brand) mixed with 4 litres of warm water. Either way apply this mixture to wet timber and allow it to stand for 20-30 minutes. Keep it lightly misted if it looks like drying out. You may need to scrub and then rinse off thoroughly.... After this step I apply a mixture of 50% oxalic acid-50% water and repeat the same process. After this I am ready for coating. I use Flood spa&deck...

Thanks for this info Jim - based on Strangerep's advice I used the Spa & Deck coating - and followed your recipe above to "unfinish" some boards I had previously oiled... went very smoothly - thanks!

Cheers,

Nick

[jimj]

Dear Nickwithaz,

Great to hear that you had a sucessfull outcome with your deck restoration. I too use Flood Spa&deck on all of the decks that I restore.

Jim J www.restore-a-deck.com.au