Painting over darker areas

[blackrose]

My neighbour is painting his boat - as have a few of us here during lockdown. He sanded back the original red paint and went through to the paint below in some places including where it was signwritten to reveal blue patches underneath. He's applied a couple of coats of red Toplac enamel but the colour saturation of the Toplac is very weak and the blue patches are showing through. Rather than paint 5 more coats of Toplac he's wondering what he can do to get rid of the patches before applying a couple of final topcoats?

 

I suggested just going over the patches with a couple of coats of Toplac, keying back and then applying two full topcoats but he thinks it will leave the surface uneven. Someone else has suggested using a lighter colour spray undercoat over the patches as it will only leave a thin layer and then go over with full topcoats of the red Toplac, but isn't car body spray paint cellulose-based and will that be compatible with the Toplac (both underneath and over the top)? If it is compatible will he have to wait for a certain period after applying the spray undercoat before applying Toplac? #

 

Edit: He's found that Halfords do a white enamel spray primer. Would that work as an undercoat on the patches?

 

 

Edited July 3, 2020 by blackrose

[Tony Brooks]

Well - if he must cut corners. Key with (say - non-professional guess) 400 grit wet & dry the whole panel. Two coats of self or close coloured undercoat followed by two or three of top coat.  One job of undercoat is to provide an all over even colour that when top coated will give the correct colour. May be just one cat of suitable undercoat would do but he would have to see if the colour showed through. He may still be able to see shadows of the signwriting in certain lights.

[David Mack]

Looks like he has just put top coat on . Undercoat is pretty essential with 'thin' colour topcoats. I would be minded to sand the lot, apply undercoat, ensuring there is no trace of the previous colour showing through, then two topcoats.

And take that masking tape off ASAP or it will go hard and unremovable.

[Tracy D'arth]

Red paints are notorious for having very little pigment and hence poor obliterating properties. That's why they fade easily.

Undercoat is the answer, its what it is designed for.

We used to have to paint red vans white occasionally. If the van was not painted black first, the white used to go pink in patches after a while.

TD'

[twbm]

Opinions vary,  but a coat or two of red oxide before you start covers everything and gives a good base for most colours.  

 

I think he may be in grit-yer-teeth-and-start-again territory. 

[markaitch]

hi folks, it's my boat. I though toplac straight over toplac would be fine...well it is, I've done that with the blue, BUT, I wasn't to know that red wouldn't cover the blue!...... Perhaps if I had attended a different painting school who knows,

anyway! Start again then. What are your recommendations for a suitable undercoat? Pre-Kote? white or grey? thanks in advance.

 

[Tony Brooks]

Do Toplac supply the undercoat in the same colour as the top coat? I would always choose the same colour undercoat if it was available, especially with red, and use a paint supplier that does it. Toplac should tell you their recommended under coat colour. I suspect the answer will be grey from the choice you give as long a sits a lightish grey. A proper painter will be along soon to advise I hope.

 

Is Pre-cote the recommended Toplac undercoat? If not do you want to risk  an incomparability between coats?

[blackrose]

1 hour ago, Tracy D'arth said:

Red paints are notorious for having very little pigment and hence poor obliterating properties. That's why they fade easily.

 

 

Thanks, I didn't know that less pigment was used in red paint and was surprised at how thin the red Toplac was compared to the blue Toplac that markaitch had used. 

 

I learned in a college physics lesson on a printing course many years ago that red colours fade easily because red wavelengths of light are the lowest energy in the visible spectrum, so red colours have to absorb far more light energy to appear red and this degrades the paint's molecular bonds. It makes me wonder why they don't use more pigment in red paint to counteract this phenomenon ? Perhaps Dr Bob of this forum knows?

6 minutes ago, Tony Brooks said:

Do Toplac supply the undercoat in the same colour as the top coat? I would always choose the same colour undercoat if it was available, especially with red, and use a paint supplier that does it. Toplac should tell you their recommended under coat colour. I suspect the answer will be grey from the choice you give as long a sits a lightish grey. A proper painter will be along soon to advise I hope.

 

Is Pre-cote the recommended Toplac undercoat? If not do you want to risk  an incomparability between coats?

 

I think it is but it looks like it only comes in white?

 

https://www.international-yachtpaint.com/en/au/boat-paint-products/undercoating/pre-kote

 

This is my undercoat of choice but it only comes in grey, blue and white.

 

https://www.hempelyacht.com/en-GB/products/hempels-primer-undercoat-13201

 

Undercoat colours do seem very limited. I don't think red exists - at least not in marine paints.

Edited July 3, 2020 by blackrose

[jacko264]

Why  don't people use primer , undercoat and top colour ? 

Where I work we still paint buses by hand using the same makes of paint as used on narrow boats 

and would never miss using primer  

Graham

[markaitch]

I'm aware of primer, undercoat topcoat..... for bare steel. What I'm doing is overcoating topcoat, all the previous coats are already there 

 

[Tony Brooks]

13 minutes ago, markaitch said:

I'm aware of primer, undercoat topcoat..... for bare steel. What I'm doing is overcoating topcoat, all the previous coats are already there 

 

Except they are not, but at least it looks as if the primer and/or undercoat were still intact (the dark patches).

[markaitch]

Except they are geeza!

The dark patches are Oxford blue toplac (over primer and undercoat), that was over-painted with fire red toplac topcoat. I've just sanded off the fire red back to the blue in places, and am overpainting the fire red toplac with fresh fire red toplac , So primer undercoat topcoat is all there

 

Edited July 3, 2020 by markaitch

[Bod]

Undercoat paint has higher amount of pigment than top coat. 

Thus is good for creating an even colour base for the gloss top coat. 

At present you have an uneven colour base.  One or two undercoats will leave a constant colour base for the top coats to provide the colour and gloss. 

 

Bod

[markaitch]

Thanks bod, I'm going to key it all and use international white pre-kote undercoat on the whole panel. Everyday's a school day! 

[dmr]

Ive just been restoring our castle panels, mostly the red surrounds. I used a dark blue undercoat because I was too mean to buy a red one (and it would be yet another paint pot in the paint store) and I needed three thick coats of red to cover the blue undercoat, and this was applied thicker than would be possible on a cabin side, so I suspect four good coats of a good red paint will be needed. But surely this is what undercoat is for?, get a red undercoat reasonably close to the Toplac colour and do two coats of it, then probably two coats of the Toplac.  If you are doing a big colour change then 4 coats is likely what is required.

 

................Dave

[Ryeland]

6 minutes ago, markaitch said:

Thanks bod, I'm going to key it all and use international white pre-kote undercoat on the whole panel. Everyday's a school day! 

I really would't use white undercoat. I think it won't give any depth to the red. Grey is usual undercoat colour for red, though I have been able to buy red undercoat before. Sorry can't remember what brand.

 

Richard

[WotEver]

4 minutes ago, Ryeland said:

I really would't use white undercoat. I think it won't give any depth to the red. Grey is usual undercoat colour for red, though I have been able to buy red undercoat before. Sorry can't remember what brand.

You can't beat Craftmaster...

https://craftmaster.myshopify.com/collections/paints-high-build-undercoat/products/dark-red

4 hours ago, blackrose said:

Undercoat colours do seem very limited. I don't think red exists - at least not in marine paints.

It certainly does.

https://craftmaster.myshopify.com/collections/paints-high-build-undercoat

[dmr]

2 minutes ago, WotEver said:

You can't beat Craftmaster...

https://craftmaster.myshopify.com/collections/paints-high-build-undercoat/products/dark-red

Craftmaster high build undercoat is lovely stuff. If cost is a big issue then Ive just found this stuff for £8 per litre....

 

https://www.smithandallan.com/brand/tekaloid/

 

I might get some and investigate but initially only for non critical jobs. Note that the £8 is before VAT and postage. Dunno if they do red.

Also note that it might use Xylene as its solvent so might just react with other stuff?   Probably best to get the Craftmaster.

 

...............Dave

[WotEver]

4 minutes ago, dmr said:

Also note that it might use Xylene as its solvent so might just react with other stuff?  

It does, so it probably would.  Tekaloid is lovely stuff to use, but I doubt it would play well with enamel.

[Ouse on Board?]

Ive just done ours, It was green, rubbed back, primed it with toplac primer (silver), 2 coats of toplac undercoat (white) and then toplac topcoat which in this case is blue. The attached photo has only one coat and was taken when it was wet. It needs a rub back and second putting on but covered nice and evenly over the undercoat. definitely worth the prep work. 

[beerbeerbeerbeerbeer]

47 minutes ago, Ryeland said:

I really would't use white undercoat. I think it won't give any depth to the red. Grey is usual undercoat colour for red, though I have been able to buy red undercoat before. Sorry can't remember what brand.

 

Richard

I’ll agree with that.  For what it’s worth. 

I painted red on top of white primer earlier this year. 
I think a red or grey primer would have been much better, as Ryeland says, it would have given more depth to the red. 
 

I was using up old paints. 
 

When better weather returns I’ll be slapping on a couple more layers of red top coat to see if it’ll improve. 

 

 

[blackrose]

1 hour ago, Ryeland said:

I really would't use white undercoat. I think it won't give any depth to the red. Grey is usual undercoat colour for red, though I have been able to buy red undercoat before. Sorry can't remember what brand.

 

Richard

 

I spoke to International Yachtpaint Technical a couple of hours ago on an unrelated issue so also asked them about markaitch's undercoat colour.

 

The answer was white Prekote mixed 50/50 with red Toplac.

1 hour ago, WotEver said:

 

It certainly does.

https://craftmaster.myshopify.com/collections/paints-high-build-undercoat

 

Yes, but it's probably best that someone using an International marine top coat sticks to the recommended International undercoat.

[jacko264]

4 hours ago, markaitch said:

I'm aware of primer, undercoat topcoat..... for bare steel. What I'm doing is overcoating topcoat, all the previous coats are already there 

 

We at work are painting buses that have been painted before  not just new panels  but it's always  primed first befor under coat and top colour 

Graham

[blackrose]

1 minute ago, jacko264 said:

We at work are painting buses that have been painted before  not just new panels  but it's always  primed first befor under coat and top colour 

Graham

 

You put primer over previous sound topcoats? 

 

I used to work in a boat yard and we repainted the passenger boats every year. We never put primer over previous layers of sound paint. It's not necessary and quite unorthodox. You only need to prime where you've hit bare steel.

[jacko264]

14 minutes ago, blackrose said:

 

You put primer over previous sound topcoats? 

 

I used to work in a boat yard and we repainted the passenger boats every year. We never put primer over previous layers of sound paint. It's not necessary and quite unorthodox. You only need to prime where you've hit bare steel.

Yes but we sand down the panels with 120 sanding discs first then the bus is washed and degreaser  is used  before primer  etc 

by the was its how  it's been done for the 30years I've worked there and a long time before I started there ??

Graham

Edited July 3, 2020 by jacko264