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Painting over old Bitumen on hull


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Hi!

I've got an old narrowboat covered in old bitumen. Most of it has been replated but budget ran dry for the front and back, which is a decent thickness anyway.

The original plan was to paint a few layers of solvent based red oxide over all of it, then a few layers of bitumen.

I'm a bit concerned about painting over the old bitumen. It's really stubborn stuff! Tried to get as much off as possible, but as it's unlikely it will all be removed I'm wondering what the best way would be to go about reblacking it.

I've read a little about aluminium based primers, or bitumen sealers. Does anyone know anything about them? Any other suggestions also welcome! Unfortunately no funds for sandblasting or any such luxuries. Grinders just smear it about, and time is short!

Any help much appreciated with all the gratitude!

Thanks,

Sama

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IIRC - 'cos I never saw my boat out of the water before it was reblacked - but after reblacking it looked 'fine' (no lumps etc). OK I did use a vinyl tar, but I thinks a good dose of high pressure was removed most, if not all of the loose bits - which is what the OP wants??  

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If its an old boat it might be just as good to use bitumen all over it again. The stuff is a sod to get off and although an epoxy is probably the best stuff available now I would worry about the effort and expense if it all peeled off the bitumen. I would put 2 or 3 (or more) coats of bitumen on it, give it a good few days to dry right off and then promise myself to get it docked in 3 years time or whenever it looked like rust might be showing through. Don't forget to do the bottom.

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Wow, such quick response! Thank you all.. much relieved to know I can just paint more bitumen on the old bitumen. Was worried the bare metal had to be prepped. Will have another tap of the old to make sure it really wants to be there, then put on a few more layers.

Much gratitude! :)

Thanks,

Sama

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35 minutes ago, Bee said:

If its an old boat it might be just as good to use bitumen all over it again. The stuff is a sod to get off and although an epoxy is probably the best stuff available now I would worry about the effort and expense if it all peeled off the bitumen. I would put 2 or 3 (or more) coats of bitumen on it, give it a good few days to dry right off and then promise myself to get it docked in 3 years time or whenever it looked like rust might be showing through. Don't forget to do the bottom.

Just to clarify 2 pack epoxy has to be applied to squeaky clean bare steel initially, then you can clean it and apply more when the boat comes out of the water.

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13 minutes ago, abnormalsheep said:

Wow, such quick response! Thank you all.. much relieved to know I can just paint more bitumen on the old bitumen. Was worried the bare metal had to be prepped. Will have another tap of the old to make sure it really wants to be there, then put on a few more layers.

Much gratitude! :)

Thanks,

Sama

I thought you wanted a posh finish...

  • If possible hire a 'proper' power water jet machine - shouldn't be expensive
  • or wire brush loose and flaky bits off
  • or scrape loose etc

If you just slap on any coating over old, then you'll clog your brushes, waste paint and money.

If possible - and the old bitumen is well worn consider putting using Comastic type covering - twice as expensive but lasts much, much longer especially in waters where there's a lot of contamination.

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Not particularly looking for any kind of posh finish, in fact I quite like the bodgey look (got the boat with an osb covering which I've grown quite fond of)... just want it to be waterproofed really. Not entirely sure which kind of bitumen I have... it's quite an ominous tin that has nothing but a little sticker saying 'bitumen' on it.

If it'll be well enough to put a few coats on the old bitumen I'm more than content to do that. I'll give it all a good scrubbing and picking before painting and hope that'll be sufficient?

(I know epoxy has an adverse reaction when applied to old bitumen which is why I got more bitumen. Original intention had been to give a coat of red oxide first, but have since read stuff online that red oxide would also react with the bitumen.)

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16 hours ago, abnormalsheep said:

Wow, such quick response! Thank you all.. much relieved to know I can just paint more bitumen on the old bitumen. Was worried the bare metal had to be prepped. Will have another tap of the old to make sure it really wants to be there, then put on a few more layers.

Much gratitude! :)

Thanks,

Sama

You can use a primer if you want but not red oxide. It has to be a primer suitable for underwater applications such as International Primocon, which can be applied to bare metal and can also be used as a conversion coating on top of patches of unknown well-adhered (not flakey) paint.

Before I got my boat grit-blasted to get rid of all the bitumen and switched to two-part epoxy, I used to apply two coats of Primocon prior to blacking and I think it probably gives the hull an extra year before it needs reblacking (compared to just using bitumen direct to the bare steel). It dries in about 2 hours so you can get the blacking on fairly quickly.

http://www.yachtpaint.com/gbr/diy/products/primers/primocon.aspx 

 

 

P1000400.JPG

Edited by blackrose
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10 hours ago, abnormalsheep said:

 

(I know epoxy has an adverse reaction when applied to old bitumen which is why I got more bitumen. Original intention had been to give a coat of red oxide first, but have since read stuff online that red oxide would also react with the bitumen.)

It's not really that epoxy would react to being painted on top of bitumen, just that there's no point painting expensive epoxy on top of cheap bitumen which will eventually fall off. Likewise you wouldn't get an adverse reaction painting bitumen on top of red oxide, just that red oxide primers aren't intended for underwater applications. 

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3 hours ago, blackrose said:

Likewise you wouldn't get an adverse reaction painting bitumen on top of red oxide, just that red oxide primers aren't intended for underwater applications. 

Plus they're not 'proper' red oxide any more anyway. No lead. 

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  • 3 months later...

Thanks blackrose for the suggestion of the primer. Had no idea red oxide was no good underwater - it had been confidently recommended by a friend who had some experience doing his boats. 

So, International Primocon to go over remnants of bitumen. I'm guessing its only really suitable for bitumen blacking, as epoxy needs some metal to soak into?

Someone today also informed me about this 480 rubber stuff from arcrite... anyone know of this?

Been severely procrastinating, so the hull is still not painted. New steel rusting, but mill scale still holding on. Thinking to have a go with a flapper disc to get it off as its been rusting for a few months now and still there is the scale. 

Edit: just read through the older replies about Comastic... is it a type of bitumen?

Seems popular opinion is not to bother priming?

Thanks again for the information & advice

Edited by abnormalsheep
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2 hours ago, abnormalsheep said:

Thanks blackrose for the suggestion of the primer. Had no idea red oxide was no good underwater - it had been confidently recommended by a friend who had some experience doing his boats. 

So, International Primocon to go over remnants of bitumen. I'm guessing its only really suitable for bitumen blacking, as epoxy needs some metal to soak into?

Someone today also informed me about this 480 rubber stuff from arcrite... anyone know of this?

Been severely procrastinating, so the hull is still not painted. New steel rusting, but mill scale still holding on. Thinking to have a go with a flapper disc to get it off as its been rusting for a few months now and still there is the scale. 

Edit: just read through the older replies about Comastic... is it a type of bitumen?

Seems popular opinion is not to bother priming?

Thanks again for the information & advice

Epoxy does not soak into metal. It sticks to it. It doesnt stick well or cure well over bitumen.

If you have mill scale, remove it. If you dont, whatever you paint with over the mill scale will fall off. Temperature swings over winter will cause differential expansion and contraction causing the mill scale to detach from the steel so anything painted on the mill scale will fall off. In the old days, you left steel covered in mill scale over winter so it would fall off more easily. Are you sure it is mill scale? Mill scale is not rust. It is the 'left overs' after the manufacturing process.

 

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On ‎16‎/‎06‎/‎2017 at 15:41, abnormalsheep said:

I've got an old narrowboat covered in old bitumen

 

On ‎16‎/‎06‎/‎2017 at 22:34, abnormalsheep said:

I quite like the bodgey look (got the boat with an osb covering which I've grown quite fond of).

Are you thinking of 'waterproofing' the OSB board with the bitumen, or, just the steel hull ?

 

We did previously have a forum member who painted her entire boat in bitumen (including covering all of the vents)

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16 hours ago, abnormalsheep said:

Thanks blackrose for the suggestion of the primer. Had no idea red oxide was no good underwater - it had been confidently recommended by a friend who had some experience doing his boats. 

So, International Primocon to go over remnants of bitumen. I'm guessing its only really suitable for bitumen blacking, as epoxy needs some metal to soak into?

Someone today also informed me about this 480 rubber stuff from arcrite... anyone know of this?

Been severely procrastinating, so the hull is still not painted. New steel rusting, but mill scale still holding on. Thinking to have a go with a flapper disc to get it off as its been rusting for a few months now and still there is the scale. 

Edit: just read through the older replies about Comastic... is it a type of bitumen?

Seems popular opinion is not to bother priming?

Thanks again for the information & advice

I'm not sure why anyone is talking about epoxy? Forget about epoxy paints unless you can get the entire hull grit-blasted and back to metal.

Primocon underwater primer can go over bare steel or old paint but not over rust! If the bare steel is rusting you'll need to get the rust off with an angle grinder & wire wheel (not grinding or lapping discs as these will take off good steel). Make sure you have all the PPE - dust mask, gloves, ear defenders and especially eye protection.

I've you've hit the old bitumen with a decent pressure washer the bits that won't come off can be considered sound paint and can be painted over. Whether you want to prime the bare steel patches or not is up to you. In my experience I found it gave the boat an extra year in the water compared to not using it under the bitumen. 

13 hours ago, Dr Bob said:

Epoxy does not soak into metal. It sticks to it. It doesnt stick well or cure well over bitumen.

If you have mill scale, remove it. If you dont, whatever you paint with over the mill scale will fall off. Temperature swings over winter will cause differential expansion and contraction causing the mill scale to detach from the steel so anything painted on the mill scale will fall off. In the old days, you left steel covered in mill scale over winter so it would fall off more easily. Are you sure it is mill scale? Mill scale is not rust. It is the 'left overs' after the manufacturing process.

 

My hull was completely covered in mill scale. It didn't come off for 10 years until I had the hull gritblasted prior to painting with two-part epoxy.

3 hours ago, pearley said:

We put 3 coats of Joton Vinyguard over our old bitumen followed by 3 coats of SML Ballistic Black. Very impressed. On the waterline rubbing strake where the blacking has rubbed off you can see the silver primer is still there.

I used Vinyguard when I worked in the boatyard. It's very similar to International Primocon.

Edited by blackrose
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12 minutes ago, blackrose said:

I guess some people just don't know when (or where) to stop! :lol:

 

12 minutes ago, blackrose said:

I guess some people just don't know when (or where) to stop! :lol:

It was suggested that it was a bad idea to block / cover the vents, she took offence & she never posted again - maybe that proved the point ?

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Hehe, epoxy is now well behind me.

I think I will keep using the wire wheel (gently) until satisfied with bitumen removal, then use one of the recommended primers before the layers kf fresh bitumen.

The new steel definitely has millscale... a kind of weird shininess. I think I will use a really soft grade flapping disc to remove it? 

I have been removing the paint right the way up to the gunnel, and was thinking to bitumen the whole of the sides, unless it is the wiser consensus to use a different paint above the waterline?

The osb is a whole other kettle of fish....! Will probably be another floundering post written about that at some point ;) but no, no plans to bitumen it as of yet... might stop it leaking though!

Re: winter.... as I have procrastinated so long, the season is fast approaching. There are still plates to be welded at the front of the boat, so realistically wouldnt be able to paint until october/november... which is probably too late to do a decent job? Really do want the best for my boat!

Thanks again for all the experienced advice, really has put my mind at ease a bit more.

Sam

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