Paint Choice – where did I go wrong???

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17 October 2011 at 17:16 #32129
Rick Devonshire
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@rickdevonshire
I have just started on the the task of painting the hull of my RAF Crash Tender (built from the original Aerokits plan). The hull is constructed of ply and with an initial undercoat of Homebase Quick Drying Primer and Undercoat. I then purchased, also from Homebase a couple of 50 ml pots of red and black ‘Polyvine acrylic enamel paint’ as top coats. All these products are water soluble.

This afternoon I set about painting the bottom of the boat with the red paint and my trouble started! I found it impossible to lay down a cosistant paint layer. It needed a very thick layer in order to cover but if you slid the brush over the area recently painted the paint picked up again on the brush leaving the surface bare! It was such a mess I eventually decided to wipe off as much as I could.

Anyone else had trouble with this type of paint??

Rick.
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17 October 2011 at 17:16 #6741
Rick Devonshire
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@rickdevonshire
17 October 2011 at 18:27 #32132
Colin Bishop
Moderator
@colinbishop34627
Sounds like the top coat is not ‘keying’ to the undercoat. How long did you leave the undercoat to dry? These ‘quick dry’ paints are touch dry quite quickly but can can take a while to harden properly as they seem to ‘skin over’.

Water based paints are what you commonly find these days but they are inferior to the older oil based type. If I were you I would rub down the hull to get rid of any remaining red paint and then start again using something else. Better still get rid of the quick dry primer too although it may be OK once really hard.

The best idea is always to make up a test piece first. In your shoes, i would make up a test piece using the homebase primer, leave it for several days and then try overspraying that with one of the automotive primers. The Halfords grey or red primer seems to be pretty tolerant. If that works then you can continue with a car paint to the colour of your chioce but make sure it also from Halfords as the different makes of spray cans are frequently incompatible..

A one part yacht enamel is a good traditional paint but probably too expensive for use on a model.

Good luck,

Colin
17 October 2011 at 19:01 #32134
neil hp
Participant
@neilhp
even water based acrylics wont go on top of oil based house paints and it seams from the paint you discribe as an undercoat, it is an oil based paint.

sadly if this is the case, the only way from here is to strip ALL paint from the hull back to bare wood.

once back to bare wood use a cellulose based sanding sealer to prime and undercoat your model, rubbing back after every couple of layers with medium grade wire wool( about 8 – 10 layers of sanding sealer is what I give bare wood) and then you can apply your acrylic or car spray paint.

neil.
17 October 2011 at 19:23 #32136
ashley needham
Participant
@ashleyneedham69188
This household type water based paint I have found is totally useless…as described, it never seems to cover properly and woe betide if you go over it before its dry.

Stick to Dulux grey primer, or Halfords spray primer and then good old Humbrol (or whatever) oil paint.

Ashley actually having just covered a hull in Eze-cote acrylic resin/fibreglass cloth, and now wondering if Halfords spray acrylic will make it go all wrinkly??
17 October 2011 at 20:09 #32138
Colin Bishop
Moderator
@colinbishop34627
Ashley, no it should be OK. I used Eze-Cote to stick and impregnate paper plating on my liner model and the Halford’s primer went on over that with no problems.

Re my earlier note, I’d assumed that a water based primer/undercoat was used. It’s not altogether clear from Rick’s initial post.

Acrylics can be OK for painting fittings etc. but I agree it’s best to stick to oil/polyurethane or automotive sprays for hulls.

Above all, don’t mix different brands unless you are already quite sure they are compatible.

Colin
18 October 2011 at 11:02 #32143
Rick Devonshire
Participant
@rickdevonshire
I assumed both undercoat and top coat were water based since both containers expained that brushes could be cleaned with soap and water. Was I correct in this assumption?

Hence I expected them to be compatable.

Rick
18 October 2011 at 11:41 #32144
Colin Bishop
Moderator
@colinbishop34627
Not necessarily Rick. Although the paints may be water clean up the formulation may be very different. Household emulsion paints are water clean up too but you wouldn’t use them on your boat!

This is where people also get caught out with spray cans which are described as ‘acrylic’ and so they are, but the solvent used to carry the paint can vary tremendously and often does, sometimes with catastrophic results.

In your case it would seem that the undercoat you have selected does not provide either a mechanical or chemical key for the topcoat you are using which is why the brush just drags it off again. Yes, you can ladle it on in a thick coat which may eventually dry but it won’t adhere properly and any sort of impact is likely to cause it to peel off.

Paints are frequently described as systems with primers. undercoats and top coats being matched chemically. Mix manufacturers or paint types and you are on your own!

Many modern paints are poor quality compared with their predecessors because of the reduction in solvent emissions. I have a bathroom door which I painted five years ago with a water clean up paint intended for wood and it has never hardened properly like some of my other doors which have a traditional oil based eggshell finish which is much harder.

Colin
18 October 2011 at 16:28 #32148
Rick Devonshire
Participant
@rickdevonshire
Thank you for your explanation Colin, I must be aware of this when I purchase top and undercoats in future.

In the meantime it’s back to the sandpaper!

Rick.
18 October 2011 at 16:37 #32149
Colin Bishop
Moderator
@colinbishop34627
Don’t worry Rick, you’re hardly the first one – we’ve all been caught out at one time or another. You make what seems to be an entirely reasonable assumption and then it proves to be anything but! A bit of elbow grease should put things right.

Colin
18 October 2011 at 17:10 #32152
Ian Gardner
Participant
@iangardner62867
Painting never used to be this difficult! I have found that some paints are very difficult to apply nicely- notably the Plasticote range in jars. I was quite excited when I found this range as they had such a variety of shades.

I decided to go back to good old Humbrol but that seems to have deteriorated in quality.

Perhaps Colin is right, buy a couple of tins of proper marine enamel and paint all your boats the same colours!

Ian
18 October 2011 at 18:03 #32153
Colin Bishop
Moderator
@colinbishop34627
I agree, painting didn’t used to be so difficult as it is now, probably because most paints were oil based and generally compatible with each other. Humbrol isn’t what it was either, I still have a lot of the old tins and the paint is certainly easier to apply than the new ones. However Paul Freshney, who is something of an expert on painting, reckons that they are still OK when sprayed with an airbrush in thin coats.

At the moment I do find that Halfords spray cans are the most reliable, the primers are good and you can usually find a suitable top coat shade. Polyurethane varnish over the top will then give you a matt or satin finish if you don’t want the gloss. Another advantage of Halfords is that the red oxide primer is a good match for the underwater part of hulls and the grey primer for naval vessels. You then only need to add a coat of varnish over the top. Their matt black is also pretty good too with a slight sheen.

Other people have found Plasticote sprays OK as long as you do everything with Plasticote and don’t try to mix them with Halfords. Wilkinson also do a range of spray paints which are quite good.

I have had good results when painting white metal fittings by using a Halfords white or grey primer followed by either Humbrol enamel or Tamiya acrylics but it is always best to experiment first.

Colin

Edited By Colin Bishop, Website Editor on 19/10/2011 10:26:41
18 October 2011 at 22:44 #32156
Ian Gardner
Participant
@iangardner62867
A very comprehensive review of the situation I would say!

Having been a long time devotee of applying Humbrol with a brush, my latest model is being painted with Halfords acrylic sprays over their hi- build primer and white and grey primers and I have to say I am delighted.

I once had a ply model where the acrylic spray paint lifted after a while, but I think this must have been due to a poor substrate, where the wood was moving about. I now use two coats of Zpoxy rubbed down. What I have learnt is that there are no short cuts!

I have recently discovered Humbrol Gloss Cote and Satin Cote which seem to go on very well and dry quickly- how durable they are remains to be seen.

Ian
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