Practical Boat Owner – June 2019

PRACTICAL

My policy for painting GRP is guided by
two principles. First, the only bit that
anyone sees is the top layer of molecules
in the final coat. Primers and undercoats
may be useful for improving adhesion or
obliterating backgrounds and fairing the
substrate, but they are not always
essential. They may even make the finish
more vulnerable to impact damage,
because a thick layer of multiple coats is
more likely to spall deeply, producing a
prominent blemish that will be difficult to
smooth and touch-up successfully.
Secondly, most people will view the boat

from a distance of a few metres, when

minor imperfections will be invisible,

especially when the hull is afloat and light

patterns reflect from ripples on the water.

An ultra-perfect finish is impressive in

close-up but the effect is lost as soon as a

few lines of scum settle on it.

My own boat, London Apprentice, had a

double gel coat, but surface defects after 26

years of use demanded a paint covering. In

anticipation of this work, I’d eschewed any

polishes and I also degreased very

thoroughly before applying just two coats

of two-part polyurethane gloss. It was put

on and tipped off with a brush. As there

was a contrasting blue stripe below the

gunwale, I could use masking tape on that

stripe and brush straight over its edge,

rather than having to ‘cut in’ with the brush

under the gunwale, which would have

encouraged brush marks and runnels.

That double coat was rock-solid and

generally admired for 19 years, but at a

molecular level the gloss must have been

slowly fading because the white hull

displayed increasing amounts of yellow

staining from marine organic compounds

that required cleaning with citric or oxalic

acid. I therefore decided to renew those

upper molecules while doing the absolute

minimum of extra work. That meant

degreasing and power sanding, followed

by a single coat of two-part polyurethane,

cost about £40. Five years later people still

admire the quality of the ‘gelcoat’! Brush

marks are visible when sunlight slants

along the surface and when it is inspected

closely, but I can live with that, although the

yellow staining is now beginning to

reappear and I may be tempted to treat the

old girl to some more make-up.

Five more top tips

General excellence

“It’s amazing how many customers will

apply a gloss enamel on a damp day of

just 5°C, and wonder why the finish goes

matt,” a paint supplier told me.

And it’s no longer a case of merely

following the instructions on the tin and

hoping for the best. Paint manufacturers

have found that producing data sheets

helps applicators – both professional and

DIY – to get the paint on in the right

thickness and in the right conditions.

“We have found that social media has a

big role to play,” said Robbert van der

Eijk of Dutch-based De Ijssel Coatings.

“Boaters can now watch an instructional

video on YouTube that helps to build their

confidence, and also points out the best

practice for using each type of product.”

Some manufacturers also run paint

courses for instruction in best practice.

Delegates on paint courses learn the

importance of getting the mix ratios

between hardener and pigment exact

6: Always follow the instructions

7: Use the best materials you can afford

Professionals use the best products

available, even when it comes to

something as simple as masking

tape. Cheaper products could lead to

expensive failures

“Professional paints are expensive to

make,” said Jotun’s Marcus Reynolds.

“They are formulated to be highly

resistant to UV and to knocks and bangs,

but easily applied by brush, roller or spray

gun. It’s a big initial investment for the

customer, but if the coating lasts 10-15

years (and often longer) then it becomes

very cost effective, not just in materials

but also in time and effort saved each

season.”

The same applies to the sundries.

Cheap rollers, brushes and tapes that

break up after just a few minutes are a

false economy and can mess up the entire

topcoat. The professionals use top quality

products because they save so much time

by not having to go back over their work

to remove lost hairs, pick out bits of

broken foam roller, or touch in paint that

has leaked though inferior masking tape.

Time is money, so invest in quality.

Hull-painting for effect

by Ken Endean

Ken Endean's Sabre 27, London Apprentice

first had her topsides painted 24 years ago.

A second coat was added five years ago