Comastic hull paint.

[casper ghost]

Hi..

I've always painted my hull with Comastic paint, when I first did it the price difference was very little over normal tar paint.now it's much dearer. I was told originally that once i'd used comastic I could only ever use the same over the top, but a chap recently told me that I can paint any tar paint over it.

Anyone know for sure which is right?

Thanks..

[soldthehouse]

Hi..

I've always painted my hull with Comastic paint, when I first did it the price difference was very little over normal tar paint.now it's much dearer. I was told originally that once i'd used comastic I could only ever use the same over the top, but a chap recently told me that I can paint any tar paint over it.

Anyone know for sure which is right?

Thanks..

Yes

Edited November 2, 2009 by soldthehouse

[casper ghost]

Tar over bitumen infact tar over most things

 

Can you clarify, is that a yes I can paint the cheaper tar over my comastic?

[soldthehouse]

Can you clarify, is that a yes I can paint the cheaper tar over my comastic?

I would say so but there will be others who will argue round and round about the technicalities

[Mac of Cygnet]

What's the difference between tar and bitumen? I thought they were the same.

[Big COL]

What's the difference between tar and bitumen? I thought they were the same.

 

 

Bitumen is a byproduct from the distillation of crude oil,

 

Tar is a byproduct from coal, plentiful and at giveaway prices when we were producing coal gas.

 

Next question will be what's coal gas

 

Big Col

[Mac of Cygnet]

Bitumen is a byproduct from the distillation of crude oil,

 

Tar is a byproduct from coal, plentiful and at giveaway prices when we were producing coal gas.

 

Next question will be what's coal gas

 

Big Col

 

Fair enough, but what I really meant was difference in physical and chemical properties, use, etc. After all, 'bitumen' and 'tar' are both used for what is put on roads (to say nothing of asphalt, which has a different origin altogether).

 

Yes, I remember coal gas. A convenient suicide method now lost to us.

 

Mac

[n.b.Goldie]

Hi..

I've always painted my hull with Comastic paint, when I first did it the price difference was very little over normal tar paint.now it's much dearer. I was told originally that once i'd used comastic I could only ever use the same over the top, but a chap recently told me that I can paint any tar paint over it.

Anyone know for sure which is right?

Thanks..

It is fine to put 'ordinary' bitumen over Comastic (vinyl tar) but it will not work the other way. This is because Comastic when applied over bitumen will melt the bitumen below and the whole lot will crinkle and split. Dry Comastic will not be attacked by wet bitumen and therefore will be stable when overcoated with bitumen.

 

If you go down the bitumen over comastic route the only way back if you decide to return to comastic is to scrape or sandblast the hull back to bare metal and start again.

 

Others might disagree but the above was my experience.....

[Timleech]

Fair enough, but what I really meant was difference in physical and chemical properties, use, etc. After all, 'bitumen' and 'tar' are both used for what is put on roads (to say nothing of asphalt, which has a different origin altogether).

 

Yes, I remember coal gas. A convenient suicide method now lost to us.

 

Mac

 

I'm not a chemist, know nothing of the technicalities, but the basic general rule is that different tar paints can be used with one another, different bitumen paints can be used with one another, but the two don't go well together.

 

Tim

 

It is fine to put 'ordinary' bitumen over Comastic (vinyl tar) but it will not work the other way. This is because Comastic when applied over bitumen will melt the bitumen below and the whole lot will crinkle and split. Dry Comastic will not be attacked by wet bitumen and therefore will be stable when overcoated with bitumen.

 

Bitumen over recent tar paint doens't key very well, it's liable to fall off. If you want to move from tar to bitumen coatings, use Rytex as your first coat over well-weathered tar paint.

 

Tim

[davidk65]

Hi..

I've always painted my hull with Comastic paint, when I first did it the price difference was very little over normal tar paint.now it's much dearer. I was told originally that once i'd used comastic I could only ever use the same over the top, but a chap recently told me that I can paint any tar paint over it.

Anyone know for sure which is right?

Thanks..

Can't really contribute to what paint can be used over what paint, but a word of caution about Comastic.

We had shares in a new boat and being one of the first "owners" to take the boat out after a weeks cruising I decided to touch up the black paint above the water line. It was Easter time, we were at Anderton, the sun was shinning. I found some black paint in the locker and so I started to roller the paint on. As usuall passerby gave me some stick, all very good humored and I was enjoying myself. I did not think for one moment I could be in any danger as I was out in the fresh air and was only at it for about an hour.

About 3 am in the morning, I thought I was dying. In fact, according to the doctor, that could easily have happened. I was ill for over a week with suspect liver and kidney problems all because of my use of Comastic. Much later, contacting the manufacturer, they said their product should only be applied when using some kind of air pressure mask.

 

Do be careful. It might do what it says on the tin, but it could also give you an unwanted bonus.

 

Davidk

[Chertsey]

It is quite nasty stuff, although I would and have used it again. My experience of using it in a hot summer when we first blacked Warrior three years ago included a sore face at the end of the day, and numerous small burns where drips had got on my arms - these have actually left (very light) scars.

 

Doing it for the second time last week in cooler weather produced none of these effects.

 

Having said that, I would use it again, because it's bloody good. The five coats we put on in 2006 (onto shotblasted bare metal) had left a very sound covering, no flaking and very little scraping below the waterline. We just scrubbed the greenery off and put on another two coats. Don't plan to do it again for another four years now.

 

But given the choice I wouldn't do it in high summer again.

[timboharticus]

What about chlorinated rubber paint ?

[the barnacle]

https://www.boatpaint.co.uk/acatalog/Spencer-Coatings-Comastic.html

 

its highlighted that Comastic should not be used over Bitumen?

[matty40s]

https://www.boatpaint.co.uk/acatalog/Spencer-Coatings-Comastic.html

 

its highlighted that Comastic should not be used over Bitumen?

well, we knew that in 2009, it hasn't changed much since then.

[the barnacle]

well, we knew that in 2009, it hasn't changed much since then.

 

oops - a trigger moment