Jonny A
Active member
I'm stripping back and re-varnishing my tiller. What's the best way to get rid of black mold stains, without creating problems when I put varnish back over it?
Thanks
Thanks
How to remove black mold from wood
- Thread starter Jonny A
- Start date
pvb
Well-known member
Boracol 5RH will get rid of the mould. No problems varnishing over it.
VicS
Well-known member
Any benzalkonium chloride based mould killer ( eg Patio Magic, Polycell 3 in 1 Mould Killer) will kill the mould although not remove the black stains.
Boracol contains benzalkonium chloride and disodium octaborate. If, as pvb implies, it will remove the black spots then its the stuff to use otherwise Paito Magic or Polycell 3 in 1 will be cheaper but you may have to also use a wood cleanser.
Owatrol Net-Trol received favorable comments in a PBO teak cleaner test a couple of years ago
Sandy
Well-known member
Vinegar, the clear stuff not any fancy cider or wine type.
ashtead
Well-known member
If all else fails swimming pool liquid chlorine is effective at removing staining from slabs so might work on a tiller?
Spyro
Well-known member
Bleach
sailorman
Well-known member
as stated in post 5 :encouragement:
Humblebee
Well-known member
Oxalic Acid, the active ingredient in Y10 and other cleaners, should do the trick. Cheap and widely available on the Internet. Handle with care though and look into safety instructions before use.
VicS
Well-known member
Liquid chlorine.
I would rinse off any hypochlorite or bleach solution , perhaps also neutralise the alkalinity and the chlorine after use with vinegar.
Bleach was also included in the PBO test mentioned previously https://www.pbo.co.uk/gear/10-teak-cleaners-tested-27992
TQA
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Alternating applications of oxalic acid and strong bleach removed 90% of the black stains on the timber framework on my Morris 1000 Traveller.
Mind you that was ash.
Mind you that was ash.
biscuit
Active member
"Wet and Forget".
Soak using a spray. If it doesnt rain, wash off next day.
Repeat in 2 years.
Soak using a spray. If it doesnt rain, wash off next day.
Repeat in 2 years.
Mistroma
Well-known member
Sounds reasonable as it probably has the same (or closely related) active ingredient as Patio Magic. Use whichever one is cheaper on basis of % active ingredient vs. cost.
I don't think you usually need to wash off Patio Magic. It is worth rinsing off eventually before launch if it doesn't rain before that time. Just ensure it won't rain for 5-6 hours after application and then forget about it. Any small unbound excess will be washed away by rain or next time you wash the boat.
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thinwater
Well-known member
It does. But it won't remove the stain.
Oxalic acid for the staining, then Boracol (or better, home brew you own with glycol and borax--article in Good Old Boat magazine a few months ago). The Borcol will take a while to dry (days) completely. Then re-varnish.
The borax/glycol treatment, if soaked for a good while, is almost like pressure treating the wood, without the down sides. I've been doing some long-term testing, and the results have been impressive.
Jonny A
Active member
Thanks everyone for all the suggestions. I've spent the afternoon trying repeated applications of diluted bleach but it hasn't had much effect. The stains have been sitting underneath the old varnish for several years (I guess) and appear pretty ingrained.
I was going to try the white vinegar option next as the shop down the road has bottles for 59p. Any suggestions on application - do I need to dilute it, and how long should I leave it on for?
Thanks again.
I was going to try the white vinegar option next as the shop down the road has bottles for 59p. Any suggestions on application - do I need to dilute it, and how long should I leave it on for?
Thanks again.
VicS
Well-known member
No.
Its pretty dilute ( 5% ish ) as it is. It wont do any harm if you leave it on overnight or longer . I'll be surprised if it has any effect.
johnalison
Well-known member
I agree; it probably needs both methods, though I think that I would use them in the reverse order, with Boracol/Patio Magic to control the mould, followed by oxalic acid to brighten the wood.
PhillM
Well-known member
Sandpaper. Mould is usually on the surface only, if not it’s rot, which is different.
Sandy
Well-known member
Are you sure this is mold and not staining?
Mistroma
Well-known member
Sometimes I think things are just so obvious and have been said many times before that I just forget to mention them. Then I see people mixing up nitrites and sulfites plus many other things and remember it isn't so obvious to everyone.
As you say, it's worth mentioning, Quaternary ammonium salts won't remove stains, just surface mould.So better off using Patio Magic or Boracol if you want to pay more for the added Disodium Octaborate to keep termites at bay (or claimed synergistic effect in conjunction with Benzalkonium Chloride).
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Jonny A
Active member
This is what it looks like:
It's too deep in the grain to possibly sand out. I don't think it's rot though, the wood itself looks fine, it's just discoloured. And I'd really like to get it removed before I re-varnish.
I feel bad enough putting bleach onto the wood as I'm worried about leaching out the oils. And I don't want to use any sort of patio cleaner as I don't know what all the ingredients are - I don't want some sort of residue buggering up the varnish.
It's too deep in the grain to possibly sand out. I don't think it's rot though, the wood itself looks fine, it's just discoloured. And I'd really like to get it removed before I re-varnish.
I feel bad enough putting bleach onto the wood as I'm worried about leaching out the oils. And I don't want to use any sort of patio cleaner as I don't know what all the ingredients are - I don't want some sort of residue buggering up the varnish.