Deck/hull seal: mildew issues

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   Hello,
The deck/hull and hull/transom seals are all heavily affected by mildew. (see pic below). 
It's pure a cosmetic matter, but I simply don't like the looks of it.  

According to Hanse this is a very rare complaint and might be caused by a bad batch from Sika. 

I have seen many Hanse yachts with the same issue and simply cannot believe that this a rare problem. 

This winter we'll remove the old deck/hull kit joint (also hull/transom joint and around life raft stowage area) and replace it with a new fresh seal. 

Does anybody know the best product to be used? 
One of my friends recommended Simson CA kit from Bostik. 

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JPB Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 22 November 2019 Location: nederland Status: Offline Points: 17	Post Options Post Reply Quote JPB Report Post Thanks(0) Quote Reply Topic: Deck/hull seal: mildew issues Posted: 28 December 2021 at 14:35
	Hello, The deck/hull and hull/transom seals are all heavily affected by mildew. (see pic below). It's pure a cosmetic matter, but I simply don't like the looks of it. According to Hanse this is a very rare complaint and might be caused by a bad batch from Sika. I have seen many Hanse yachts with the same issue and simply cannot believe that this a rare problem. This winter we'll remove the old deck/hull kit joint (also hull/transom joint and around life raft stowage area) and replace it with a new fresh seal. Does anybody know the best product to be used? One of my friends recommended Simson CA kit from Bostik.

AndyS Members Profile Send Private Message Find Members Posts Add to Buddy List Captain Joined: 14 June 2016 Location: River Dunes, NC Status: Offline Points: 206	Post Options Post Reply Quote AndyS Report Post Thanks(1) Quote Reply Posted: 28 December 2021 at 16:28
	It is certainly not rare! On our 385 we have had very good luck with a product called Wet & Forget. It is designed to kill mildew on patios, etc. I keep it on the boat - mixed as directed - in a spray bottle. All you do is spray it on the areas and let it dry. It keeps the hull joints pretty white. It is very safe and works great on other areas that want to get mildewed. Don't know if it will be availabe near you but, since the mildew is only a cosmetic concern, I like using this product rather than re-doing the entire joint.
	Andy Moonraker River Dunes, NC

Butcherboy Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 06 July 2021 Location: Devon Status: Offline Points: 4	Post Options Post Reply Quote Butcherboy Report Post Thanks(0) Quote Reply Posted: 28 December 2021 at 21:54
	Hi, Our 385 also has degraded mildew in areas of the caulking, it’s very much a common cosmetic problem our boat was quite bad when we got her at 4yrs old.Used spray bleach and a “Magic Pad” which removed much of the ingrained dirt and mildew. Plan to replace the caulking with a product called BT1 which has a built in anti mould additive, it has similar properties to silkaflex and I’ve had good results on my last boat but I don’t know if it is available in the Netherlands. Regards and a Happy New Year 🥳 Andy!
	Andy 385

JPB Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 22 November 2019 Location: nederland Status: Offline Points: 17	Post Options Post Reply Quote JPB Report Post Thanks(0) Quote Reply Posted: 24 January 2022 at 09:22
	Thank you, Andy!

iemand Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 13 February 2004 Location: Germany Status: Offline Points: 1099	Post Options Post Reply Quote iemand Report Post Thanks(0) Quote Reply Posted: 24 January 2022 at 19:28
	Be careful: BT1 is Silicone based which you normally don't want to see on boats!
	Hanse 312 MJ 2004 - Hanse 370e MJ 2007

JPB Members Profile Send Private Message Find Members Posts Add to Buddy List Sub Lieutenant Joined: 22 November 2019 Location: nederland Status: Offline Points: 17	Post Options Post Reply Quote JPB Report Post Thanks(0) Quote Reply Posted: 25 January 2022 at 10:57
	You are right! It's not recommendable to use Silicone based sealants. Thanks!

Rock Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 19 September 2014 Location: Netherlands Status: Offline Points: 404	Post Options Post Reply Quote Rock Report Post Thanks(0) Quote Reply Posted: 14 March 2025 at 15:08
	After I’m not sure how many years, my hull-deck joint is due for a touch up again. It looks decrepit once again. I have used various sika products in the past, various MS-55 polymer sealants and what have you. But all these don’t really provide a long term satisfactory solution. The sealant becomes wrinkly en mildewy over time. I know silicone is always said to be a no-no on yachts. Because of issues when paint/coating needs to be applies later on, fish-eyes etc. My boat is white, and as far as I’m concerned it will stay white, I can’t think of a reason why I would want to apply paint on the outside. It does seem to me (from researching) that silicone may actually the sealant with best resistance against UV and Mildew, it will stay nice, white and smooth. As the hull-deck joint sealant is purely cosmetic, no adhesion required whatsoever, except to the substrate, what would be a hard argument not to use silicone? has anybody used silicone ? BR, peter
	Hanse 400e "M-square2" #0241

Fendant Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 03 November 2012 Location: Switzerland Status: Offline Points: 1671	Post Options Post Reply Quote Fendant Report Post Thanks(0) Quote Reply Posted: 15 March 2025 at 06:48
	Peter, there are numerous postings about the mildew issues from the years 2012 - 2016. It is not rare, Hanse claims that it was a bad batch out of the Sika automotive sealant plant, which is a false claim. Purchasing apparently bought from another cheaper vendor.
	Frank

Schjell Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Joined: 24 April 2023 Location: Norway Status: Offline Points: 44	Post Options Post Reply Quote Schjell Report Post Thanks(0) Quote Reply Posted: 16 March 2025 at 08:58
	Hi, see the earlier post about this as well. https://www.myhanse.com/regarding-sikaflex-caulking-along-hull_topic14825.html
	2012 Hanse 385 - Second owner

Rock Members Profile Send Private Message Find Members Posts Add to Buddy List Commadore Joined: 19 September 2014 Location: Netherlands Status: Offline Points: 404	Post Options Post Reply Quote Rock Report Post Thanks(0) Quote Reply Posted: 16 March 2025 at 15:14
	Thanks for the replies, Yeah, I know about the bad sika batches. And applied new sika, some 8 years ago, and it looks like s#€%t again. I just don’t think these sealants are as resistant to uv and mildew as their producers claim them to be. And wondered if silicone could be the better solution for longer term cosmetic purpose. I know it’s a luxury problem, but can’t believe the solution is to re-apply new sealant every so many years …
	Hanse 400e "M-square2" #0241



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