Blacking and resulting problem

[Alan de Enfield]

1 minute ago, Tacet said:

Well, its a little ambiguous but:

 

"after power washing the slime away it was clear that no blacking remained below the waterline, just the metal hull covered by a white powder.....r"

 

Unless there was no blacking below the waterline before the most recent was applied. Which would be odd and probably point towards Something Else other than the blacking process.

 

Yes - not clear.

A bit inconsistent, it makes no difference, but the OP may update or correct any misunderstanding.

[cuthound]

White powder is usually associated with aluminium oxidising.

 

The boat in question isn't a Sea Otter is it?

[GUMPY]

Mmmmmm white powder I remember those days

[Alan de Enfield]

1 minute ago, Loddon said:

Mmmmmm white powder I remember those days

If you do, then you were not there !!!

 

I once thought I remembered the 60's but I was wrong.

[rusty69]

8 minutes ago, Alan de Enfield said:

If you do, then you were not there !!!

 

I once thought I remembered the 60's but I was wrong.

I don't remember the 60's.I probably wasn't there!

[GUMPY]

49 minutes ago, Alan de Enfield said:

If you do, then you were not there !!!

 

I once thought I remembered the 60's but I was wrong.

Not 60's but 70's and 80's in the time the music industry was fun before the accountants got involved.

[Grassman]

I had a problem with blacking having 'fallen off', but mine was below the water line so I didn't find out about it until the next time it came out of the water to be blacked 2 years later. The blacking had been carried out in a dry dock next to another boat being blacked and I concluded that my blacking had been applied  just after they had power washed the boat next to mine and therefore part of my hull was damp when my blacking was applied.

 

It was on the side of my boat which had been next to the other one and was just a short section about 5 feet long. This next time I was doing the blacking myself so I prepared the surface, applied Vatcan rust treatment and then 3 coats of blacking. The next time I had the boat out the blacking was still intact thankfully.

[koukouvagia]

I've lost count the number of times I've had my boats blacked over the years.  I've never had a problem and often the blacking has been applied in less than ideal conditions.  I never take the old bitumen back to the bare metal, so later coats are just plonked on top of the old ones.  I wonder if this has been the reason why I've never had flaking bitumen?

[Bee]

1 minute ago, koukouvagia said:

I've lost count the number of times I've had my boats blacked over the years.  I've never had a problem and often the blacking has been applied in less than ideal conditions.  I never take the old bitumen back to the bare metal, so later coats are just plonked on top of the old ones.  I wonder if this has been the reason why I've never had flaking bitumen?

Quite possibly. Over the last few years there does seem to be a fashion for shotblasting hulls and even taking topsides back to bare metal. I would only ever consider doing that in pretty extreme circumstances and so long as the new paint is keyed to the old I reckon the new paint is adding another layer of protection.

[Dr Bob]

On 22/11/2018 at 21:43, WotEver said:

Agreed. But it doesn’t sound even remotely like MIC. That occurs in localised areas and manifests itself as shiny pits; it doesn’t cover a large area as a powder. 

 

I suspect the hull was cold and damp resulting in zero adhesion between the bitumen and the steel. 

 

Top marks for Snaygill’s handling of the matter and I would have no hesitation in using them myself. 

I think Wotever's response is spot on. There are a number of reasons why the blacking may fall off in sheet but cold/damp is highly probable. A number of posters have said that their coatings have been fine when applied to poor surfaces or in poor weather but likely the surface was not 'wet'. The worst conditions to paint is where  the temperature of the steel is at the dew point or perhaps one or two degrees above it so although the surface looks ok (and looks dry), it isnt. It will have tiny beads of condensation all over the surface and normal blacking just will not stick to that surface. Boat yards should not paint at these temperatures and it is very difficult to comply with this during November to Feb (or even March) in the UK without heated paint shops.

Top marks to the yard in this case for refunding the cost but it really shouldnt of happened in the first place. Did they have a wet & dry thermometer to measure the temp wrt dew point? I get the feeling a lot of these yards dont. I hope I am wrong. Many coatings are advertised as being ok to apply down to XX°C and it is wrong to assume you can do this. Buried in the application datasheet will be the instruction to not paint until the temp is 2-3°C above the dew point. This is often ignored and people wonder why coatings fall off.

 

[KenK]

Hopefully these attached photographs will show the state of the problem both above and below the waterline. One shows blacking fallen off above the waterline during the summer, you can see it is lifting even more on the left hand side. The second one shows the side of the boat after power washing above the waterline the blacking is still there below it has gone. The other a close up of the blacking at the waterline showing both types of damage                                                                                                       

 

Ken

[KenK]

Scraping the boat with the tools shown removed every trace of remaining blacking and the white deposit without any great effort, just as well as I did it myself.

 

Ken

[Dr Bob]

22 minutes ago, KenK said:

Hopefully these attached photographs will show the state of the problem both above and below the waterline. One shows blacking fallen off above the waterline during the summer, you can see it is lifting even more on the left hand side. The second one shows the side of the boat after power washing above the waterline the blacking is still there below it has gone. The other a close up of the blacking at the waterline showing both types of damage                                                                                                      

 

Ken

I find it very difficult to comment on paint problems from these type of shots. There is nothing like poking at it with a pen knife to see what the state of the coating is. Without details of how it was applied, it is impossible to know exactly what went wrong. If you want to try and guess what went wrong, then a start would be to identify the dates on which the boat was painted, if possible what time of day the painting of each coat was done and where was the location. You can then find the nearest weather station and look at the historic weather info for those days/times. In particular the dew point/hourly temp figures. Also, info on where the boat was, ie out in the open, in a shed, under a polytunnel etc. This may then give you info that points to the surface being too cold for application on that day. Even with all this info, at this late stage, the cause will only be a guess.

[MtB]

I've seen blacking coming off in a similar way to this on a boat that was blacked during warm sunny days last summer. No white power underneath, just plain adhesion failure.

 

Received wisdom at the time having asked around, was that the first coat of blacking should have been thinned (with white spirit?) prior to application. Subsequent coats don't need thinning. 

 

Might the first coat not have been thinned?

 

 

 

 

Edited November 24, 2018 by Mike the Boilerman
Amend a minor detail...

[Bee]

I've never thinned bitumastic. I've always thought it unnecessary on steel, I do thin varnish on wood so that it hopefully soaks in (Blasted stuff still falls off though) That looks like a very thick coating in one of the pics. Maybe the more recent coat reacted with the older stuff? Bitumastic always seems pretty forgiving stuff though.

[Dr Bob]

2 hours ago, Mike the Boilerman said:

I've seen blacking coming off in a similar way to this on a boat that was blacked during warm sunny days last summer. No white power underneath, just plain adhesion failure.

 

Received wisdom at the time having asked around, was that the first coat of blacking should have been thinned (with white spirit?) prior to application. Subsequent coats don't need thinning. 

 

Might the first coat not have been thinned?

 

 

 

 

When applying coatings to steel in hot weather, the danger is that the coating thickens very quickly as solvent evaporates on the hot steel so does not flow well enough and 'wet' the surface properly. This can result in poor adhesion of the coating to the steel. In these circumstances, adding thinner (ie more solvent) allows the paint to flow and give that good key that the first coat needs. Subsequent coats dont need that adjustment as intercoat adhesion should be good.

This will not have been the case in the OP's problem as the coating was applied in November - so it would not have been hot. As I said in a previous post, there are a number of possible causes of failure. In addition to cold/damp steel due to dew point, the paint could have been stored in a cold room so viscosity would be high hence a similar problem of flow. Adding more solvent isnt then a good idea as it could be too cold for the solvent to evaporate so you end up with a soft final coating.

[WotEver]

4 minutes ago, Dr Bob said:

When applying coatings to steel in hot weather, the danger is that the coating thickens very quickly as solvent evaporates on the hot steel so does not flow well enough and 'wet' the surface properly. This can result in poor adhesion of the coating to the steel.

I had that happen one hot summer with flashband primer applied to a hot, south facing brick wall. It was drying as I applied it. A few days later on another hot day the flashband just fell off. 

[MtB]

3 hours ago, WotEver said:

I had that happen one hot summer with flashband primer applied to a hot, south facing brick wall. It was drying as I applied it. A few days later on another hot day the flashband just fell off. 

 

Flashbanding? Bodgery of the highest order!!!

 

[WotEver]

21 minutes ago, Mike the Boilerman said:

 

Flashbanding? Bodgery of the highest order!!!

The preferred (and pre-supplied) method of sealing our conservatory roof to the house wall. A Wickes wooden conservatory some 20 years ago. Still standing, still waterproof, including the flashbanding. 

[MtB]

10 minutes ago, WotEver said:

The preferred (and pre-supplied) method of sealing our conservatory roof to the house wall. A Wickes wooden conservatory some 20 years ago. Still standing, still waterproof, including the flashbanding. 

 

Soooo lucky!!

 

Lead flashing is the Real Thing and typically lasts 100 years (before it gets nicked). 

[bizzard]

The old Black tar varnish being thinner adhered better.

[WotEver]

11 minutes ago, Mike the Boilerman said:

Lead flashing is the Real Thing and typically lasts 100 years (before it gets nicked). 

Yeah I know. When I fitted the supplied banding I figured I’d be replacing it in 12 months. 20 years on and it’s still good. 

 

Now I've said that it’ll probably start leaking next week!

[pearley]

Perhaps a Yorkshire thing, this customer service. Our first reblacking was done by Pennine Cruisers at Skipton (who have a very interesting dry dock set in a black hole) in March 2011. In the clear water at the head of the Lancaster a couple of months later it was obvious that rust was appearing. When I spoke to them they immediately offered to redo  it it, which they did in the summer.

 

The assumption was that insufficient time was given for the blacking to harden and/or the water was too cold. Whatever our blacking since have been in warmer months and I've ensured we stay in the dock for 7 days rather than in on Monday and out on Friday. 

Edited November 25, 2018 by pearley

[KenK]

I suspect we'll never really know what actually caused this problem, I tend to agree with my friend who works as an industrial chemist in the coating industry. The cold and damp conditions when the blacking was applied almost certainly prevented it from adhering correctly to the steel hull and possibly the hotter summer than normal also had an effect.

The one positive was the return of the cost of the work without a problem, if only all companies worked the same way.

 

Ken

[nb Innisfree]

After seeing some blacking coming away from the old stuff underneath I then started agitating the old coating with a rag soaked in white spirit, left to dry for a short time until it was sticky before applying new coating the problem never reappeared.