# Forum Home Renovation Decking  Black spots and marks on a new spotted gum deck

## Etinawi

Hi all. I have just had a 100 sqm spotted gum deck built. I have noticed many boards with black marks on them. They are very similar to what people have posted in other threads. I have attached some photos. 
I have decided to try and sand them off - especially after reading many replies from jimj in this forum. I will purchase a good quality random orbital sander using 60-80 grit sand paper. 
Considering the size of my deck, my question is: should I sand the whole deck or just the affected boards? I realise the areas that are sanded will become lighter in colour, but I'm hoping that after applying the decking oil, that it won't look too different to the unsanded boards. 
Any suggestions or advice will be most welcomed. 
Cheers

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## jimj

I would sand the entire deck. If it is 100m2 you do not need to sand the entire deck in one go. Sand from one end to another & do a section. I often will sand a zone & leave several of the boards sanded but not stained. Apply the coating to the sanded zone. Once that area is completed do the next zone. You may find by breaking this project into 3-4 zones. Sanding will remove the black stains, the pencil marks from the builder where the screws were placed and remove the small wooden burrs on the drill holes.  100m2 is a lot of $ invested by you. As an idea to guide you I could sand this deck out with my ROTEX orbital sander in around 
 5-7 hours or so.   
You can try 80 grit first. It may need to be dropped to 60. Good Luck 
jimj   restore-a-deck.com.au

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## Marc

Do you have a tree next to the deck?
What kind of oil was used?

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## sol381

id say its  from someone grinding metal on the deck..need to give it a good sand to get rid of it..

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## ringtail

Yep I reckon that's metal stain

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## Etinawi

> Do you have a tree next to the deck?
> What kind of oil was used?

  Hi Marc 
It's definitely metal shavings.  I had the builder who constructed the deck also install a metal top rail on the fence.  He had to cut the metal to size.  It's obvious he didn't cover the section of the deck where the metal was being cut before doing so.  He's a family friend, so I won't be taking it out on him.  Having said that however these black spots are in other areas that was nowhere near where the metal was being cut.  In in some cases, the black marks are bigger blotches rather than spots. 
The deck hasn't been oiled yet.  I'll be doing that once I've prepared the deck with a good sand and clean. 
I've opted to use Flood's Spa-N-Deck Wood Finish in Natural.   
My only other dilemma now is do I (after sanding the deck) go the whole hog with the Flood's Powerlift and WoodPrep or can I get away with a Napisan wash and high pressure rinse? 
I've read varying opinions in this forum about what the "right" thing to do is.

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## Etinawi

> I would sand the entire deck. If it is 100m2 you do not need to sand the entire deck in one go. Sand from one end to another & do a section. I often will sand a zone & leave several of the boards sanded but not stained. Apply the coating to the sanded zone. Once that area is completed do the next zone. You may find by breaking this project into 3-4 zones. Sanding will remove the black stains, the pencil marks from the builder where the screws were placed and remove the small wooden burrs on the drill holes.  100m2 is a lot of $ invested by you. As an idea to guide you I could sand this deck out with my ROTEX orbital sander in around 
>  5-7 hours or so.   
> You can try 80 grit first. It may need to be dropped to 60. Good Luck 
> jimj   restore-a-deck.com.au

  Hi Jimj 
I'd happily pay someone to sand it for me.  Pity you live in Qld  :Weeping:  :Weeping:  :Weeping:

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## Etinawi

> I would sand the entire deck. If it is 100m2 you do not need to sand the entire deck in one go. Sand from one end to another & do a section. I often will sand a zone & leave several of the boards sanded but not stained. Apply the coating to the sanded zone. Once that area is completed do the next zone. You may find by breaking this project into 3-4 zones. Sanding will remove the black stains, the pencil marks from the builder where the screws were placed and remove the small wooden burrs on the drill holes.  100m2 is a lot of $ invested by you. As an idea to guide you I could sand this deck out with my ROTEX orbital sander in around 
>  5-7 hours or so.   
> You can try 80 grit first. It may need to be dropped to 60. Good Luck 
> jimj   restore-a-deck.com.au

  Hi Jimj 
I've thought more about your suggestion and it makes perfect sense.  I will sand, prep and stain the deck in zones.  That will make this project less daunting and I will at least benefit from seeing the finished product in the zones I complete. 
As I mentioned in my reply to Marc, I'll be using Flood's Spa-N-Deck Wood Finish in Natural.  In your opinion, is it necessary to perform all steps they recommend?  i.e. Flood's Powerlift and Flood's WoodPrep before applying the Wood Finish? 
If not, then is a Napisan wash even necessary?  This is a newly laid deck.  I've given it a high pressure hose since it was laid and even that made it come out looking a light brighter than before.

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## jimj

You really can't make timber any brighter than it actually is. When I first started using the Flood powerlift, prep & then the coating I was trying to follow to the letter what they said. Over quite some time I discovered that a lot of what the manufacturer's said was a little iffy. OK wind the clock forward from 2003 until the present. 
  Today I just sand, then give the deck a very good hosing off with just a garden hose. This is to remove any dust left. I then let it dry or blow dry with an electric blower. I apply the first and Subsequent coats of Spa&Deck only to DRY timber.Even though Flood have this idea written on the can to apply it to timber that is saturated in water. SO no chemicals are needed as the sanding will instantly expose a new & brightest layer of timber that is possible.  
 The real issue to be addressed is the surface temperature of the wood. I always coat in bare feet . This allows me to feel the surface temp. The wood can only be from cool to warm. once it starts getting hot then  no coating ass it will just flash dry. Depending on where one lives will dictate the coating schedule. Here in summer I am finished coating by 8 am & can't start again until 4pm. 
You can always give me a call if you want.  no is on my website 
good luck 
jimj

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## Marc

Yes, probably right, metal grinding can do that and can travel a long way too.

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## gotwood

> ... once it starts getting hot then  no coating ass it will just flash dry ...

  They do things differently in Queensland.

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## jimj

Simply great reading gotwood. Can't blame my proofreader as there isn't one. Brought a great smile reading your reply. It will certainly help my spirits tomorrow when sanding my next deck.

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## METRIX

Jim, you want to be careful, flashing your ass to dry it could get you in trouble  :Biggrin:

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## jimj

Just enjoying the responses & funny how an extras S added to the word AS can bring such joy out of folks. It is what makes this forum great & fun. Sure beats the rants I generally throw out !!!

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## Etinawi

Thanks for the advice Jim.  I'll be rolling up the sleeves this weekend. 
Cheers

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## Etinawi

Hi Jim 
Considering the size of my deck that I need to sand, I'm trying to puchase large-sized packs of the orbital sanding sheets.  The "big green shed" stocks them for a brand (Diablo) in 80-grit and 40-grit sheets.  They don't stock (or Diable don't make) 60-grit sheets  I've sampled the 80-grit and while it works, it would be easier with 60-grit sheets.  My question then: would 40-grit be too harsh on the deck? 
Cheers

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## jimj

40 grit will be too harsh as a finished  surface IMO.  However, easily & quickly the 40 will take all of the top oxidised, black metal marks, pencils & burrs easily &quickly. After using the 40  you can go over with the 80. This will be very fast with not very much more effort. I often hand sand out decks with coatings with 40 & then again quickly with 80. 80 grit finish will give a better end result. Remember that after sanding & then hosing with water & applications of 3-4 coats of decking product the grain will "pop" or standup somewhat. It will still feel smooth to the barefoot regardless of the "SURFACE TEMPERATURE"

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## Etinawi

Thanks Jim 
I've purchased the 40 grit and intend to finish with 80 grit.  We have a nice sunny, dry weekend in Sydney.  Here's hoping I get most of the sanding done in the next 48 hours.

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## Bloss

If the screws are as shown in your pics you will need to drive them further in before you sand - they seem to be at the decking face level.

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## Etinawi

> If the screws are as shown in your pics you will need to drive them further in before you sand - they seem to be at the decking face level.

  Hi Bloss 
I agree. The screws were not drilled to a consistent depth.  But I managed to sand the entire deck 100+ sqm deck as is.  Not ideal, but I had my hands full with the sanding and oiling (2 coats).  Not owing a drill didn't help my cause either.  It's taken me two whole weekends and 7 hours in the week in between to get to this point.  I hope it's not too late to drill the screws later on.

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## Etinawi

After two full weekends and a day in between, my deck sanding and oiling project is now complete.  Thanks to all of you who contributed advice etc.  What I learned from this project is: 
1. 40 grit sandpaper was the absolute minimum required to get the tough black marks off the decking boards.  And even then, I didn't get it all off.
2. Relying on a random orbital sander alone won't cut it. I found using the good old cork block with 40-grit paper ideal for getting most of the dark marks off, and then going over it again with 40-grit, then 80-grit with the orbital sander.
3. I used Flood's Spa 'N Deck Exterior Wood Finish in Natural (on my spotted gum decking boards).  While I'm happy with the colour, it won't stop me from wondering what something like Cedar, Jarrah or Merbau would have been like.
4. What's with Flood's advice about applying the first coat on a wet surface?  I found when doing that (on only one section of the deck mind you), all it was doing was diluting everything and most of the solution was being lost in the space between the decking boards. 
Overall, I'm satisfied with everything achieved so far. The deck is north facing and a large portion of it is not under cover. It will be subjected to the hot, sunny summer days. So it will be interesting to see how long the current look lasts.  
I've attached some photos.  The first few show a section of the deck with the first three coats of the decking finish.

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## Bloss

Man ya gotta be happy with that! Great work! As Jimj says look to redcoat 15-18 mths and in highly exposed location maybe sooner - that way it'll be just a wash down and recoat not a re-sand. The trick is to look for any early signs of the coating failing - e.g.: water not from drops or running off as well and 'soak' patches which seem to stay wet a long time after the last rain.

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## Craigoss

Deck came up great, I had the same thing on my deck but i got all the black spots out by using an acid wash alone. Sanding 100m2 using an orbital sander is a tad crazy, I managed to get floor sander out on a weekend to give my deck a light skim when i was ready to coat the first time. He only charged me $50 and was done in about 10mins.

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## Etinawi

> Man ya gotta be happy with that! Great work! As Jimj says look to redcoat 15-18 mths and in highly exposed location maybe sooner - that way it'll be just a wash down and recoat not a re-sand. The trick is to look for any early signs of the coating failing - e.g.: water not from drops or running off as well and 'soak' patches which seem to stay wet a long time after the last rain.

  
Thanks for advice Bloss.  I'll be keeping a keen eye on it for sure.   One thing I have noticed however is that when wet, the water doesn't bead up.  I guess that's because the finish is not an oil.  Is that right?  I have another deck that I've used Integrain Ultradeck on and that beads right up.

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## Etinawi

I'd read many posts Craigoss about the pros and cons of an acid wash vs. sanding.  I'm sure the acid wash would have been a lot gentler on my ageing limbs, but I'm not disappointed I went with the sander.  Like I mentioned earlier, the black marks on my deck were quite deep in places.  So I'm not sure how well the acid wash would have handled that.

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## jimj

Well done and if it took a 40 grit paper then that's what it takes. Sounds as if a little more elbow grease was needed and that also come with the task. I have been using Spa&deck now for 13 years. For the past 8 I only put the first coating & subsequent coatings on a totally dry surface. I never apply the first coat on a wet deck. I only use Jarrah & sometimes Walnut tint . IMO the natural is too yellow, cedar & kwila too orange &redwood fire engine red. all of this info has been discussed by me in earlier postings. 
  You can put one colour over another so if you want to tone it down you could do a test on a sample board of natural first then a coating of walnut over the natural. just a thought! 
  jimj  PS for what its worth it took me 6 very hard  hours to complete on 14 m2 of many layers of sunburnt Sikkens cetol deck on a kwila timber deck yesterday. I used 50 sheets of a high quality 40 grit Klingspor abrasive attached to my Festool Rotex. Once in a while there are some hard days.  Its why you always keep the beer fridge full!!!

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## CeeBee

Hi guys, 
New to forum due to this exact situation. Don't want to hijack the thread but.........is this issue common with Spotted Gum? Or do you think it's caused by insufficient coating? 
We got our spotted gum decking constructed in Feb this year by a 'professional' company.  It was coated with Intergrain Ultradeck, but I don't think he applied as many coats as should...and reading reviews about this decking oil, I fear it also wasn't the greatest product choice. 
The deck is in full weather - no covering whatsoever, and we've had a buttload of rain. 
Went to coat it ourselves after the recommended 3-4 months (this is what the carpenter recommended we do), but it had already started with the black spotting, to the point where it's cracked/split on the surface.   
Based on your similar looking photos, I'd assume we'll have to sand it back. Currently, we are trying to strip the deck to try and get rid of the black bits, before we look to sand it. 
Frustrated is the nicest way to put how I feel right now.

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## frozensage

I have the same sort of issue but only with a bunch of board, maybe 5, that were left exposed when grinding a metal gate. If I were to sand them with a ROS on 40 then 80 only would that be fine? or would I have to sand the whole deck? 
I noticed alot of the board that were left outside to weather without being installed shows alot of cracking on the edges. The ones that are installed shows cracks where the screws head are.   Is this just what happens with spotted gum?

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## Craigoss

I have a spotted gum deck full exposed, I need to coat 3 times a year in order to keep it looking pristine.  You need to use oxalic acid to clean the black spots off. I got metal shavings in my deck after installation and it was covered in spots which all came out with an acid wash. I still need to spot acid clean some areas during re-coats if there has been any staining from leaves etc. Order of events for me is:
1) Napsan + pressure wash (multiple times if really dirty)
2) Oxalic acid wash if required
3) Sand if required
4) Oil deck 
Unfortunately it consumes a full weekend.

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## Etinawi

> Hi guys, 
> New to forum due to this exact situation. Don't want to hijack the thread but.........is this issue common with Spotted Gum? Or do you think it's caused by insufficient coating? 
> We got our spotted gum decking constructed in Feb this year by a 'professional' company.  It was coated with Intergrain Ultradeck, but I don't think he applied as many coats as should...and reading reviews about this decking oil, I fear it also wasn't the greatest product choice. 
> The deck is in full weather - no covering whatsoever, and we've had a buttload of rain. 
> Went to coat it ourselves after the recommended 3-4 months (this is what the carpenter recommended we do), but it had already started with the black spotting, to the point where it's cracked/split on the surface.   
> Based on your similar looking photos, I'd assume we'll have to sand it back. Currently, we are trying to strip the deck to try and get rid of the black bits, before we look to sand it. 
> Frustrated is the nicest way to put how I feel right now.

  Hi CeeBee. 
I used Integrain on another deck which had previously been coated with Cabots Aqua Deck. Have to say that after a year, the finish is beginning to flake off.  Now I'm not blaming the product per se.  Maybe I laid it on too thick or maybe I didn't prepare the surface well enough.  And this is why I chose Flood's Spa 'N Deck Exterior Wood Finish in Natural on my new deck.  Time will tell if that was the right choice.  I am glad I took the sander to my deck prior to coating it.  While it was hard work, it was definitely worth doing.

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## Etinawi

> I have the same sort of issue but only with a bunch of board, maybe 5, that were left exposed when grinding a metal gate. If I were to sand them with a ROS on 40 then 80 only would that be fine? or would I have to sand the whole deck? 
> I noticed alot of the board that were left outside to weather without being installed shows alot of cracking on the edges. The ones that are installed shows cracks where the screws head are.   Is this just what happens with spotted gum?

  Hi Frozensage 
I asked a similar question re: either sanding certain areas where the black spots were really bad or the whole deck.  It was suggested I sand the whole deck - which I did.  But I paid particular attention to those areas where the black spots were really bad. 
I haven't had any experience with my spotted gum boards splitting.

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## Etinawi

> Hi Frozensage 
> I asked a similar question re: either sanding certain areas where the black spots were really bad or the whole deck.  It was suggested I sand the whole deck - which I did.  But I paid particular attention to those areas where the black spots were really bad. 
> I haven't had any experience with my spotted gum boards splitting.

  Hi Frozensage 
I forgot to mention,  I too used 40 grit followed by 80 grit. Worked a treat.  Using 80 grit alone would have made getting rid of the black spots a lot harder.

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## Etinawi

> Well done and if it took a 40 grit paper then that's what it takes. Sounds as if a little more elbow grease was needed and that also come with the task. I have been using Spa&deck now for 13 years. For the past 8 I only put the first coating & subsequent coatings on a totally dry surface. I never apply the first coat on a wet deck. I only use Jarrah & sometimes Walnut tint . IMO the natural is too yellow, cedar & kwila too orange &redwood fire engine red. all of this info has been discussed by me in earlier postings. 
>   You can put one colour over another so if you want to tone it down you could do a test on a sample board of natural first then a coating of walnut over the natural. just a thought! 
>   jimj  PS for what its worth it took me 6 very hard  hours to complete on 14 m2 of many layers of sunburnt Sikkens cetol deck on a kwila timber deck yesterday. I used 50 sheets of a high quality 40 grit Klingspor abrasive attached to my Festool Rotex. Once in a while there are some hard days.  Its why you always keep the beer fridge full!!!

  Hi Jim.  Can you tell me where you source the Klingspor abrasive sheets?  I have another deck to sand and I'm after high quality sheets that will get the job done. In the off chance I can't source them, what other brands of abrasives have you had success with?

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## jimj

I have my local tool shop order them in. Not sure if you can find some on the net. You can use Festool 150mm abrasives. The brilliant series is for coatings & the rubin is for bare timber They will do an excellent job & wherever you find Festool being sold they should have a selection of Festool abrasives. I would think you would only need a box of Rubin 40 & 80 grit 
good luck

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