Tuesday, July 7, 2015

End of the first phase, now the next phase begins

The blasting begins!
We survived the sandblasting and painting. As Dough says: I have learnt so much from my mistakes, I plan to make some more. The steel boat gurus say you should not sandblast more than you can paint the same day. The painters and others say steel does not rust so fast. Well, it does. I had hoped to do the sandblasting and painting in May, the driest month in Pretoria, but one thing and the other delayed us till end of June, a period where fog and early morning frost or dew is a real possibility.

We decided to sandblast inside, and then spray it. Then we would sandblast the outside and spray that. Of course the blasting outside would damage some of the paint inside. As a sop to my paranoia about rust it was conceded to blast the loose parts like tanks and window frames on the last day of blasting, so the painting could begin immediately.

Hard, dirty work. There has to be a better way. 
I had decided to use Carboguard 550 epoxy primer in two colours: blue over the blasted steel so it is easier to see what areas were missed, then a second coat of gray to build up to the required thickness.

The first problem was that, once we had blasted the outside, rust spots appeared overnight, requiring a second brush blast. And the loose parts picked up damp from the floor they were laid on, showing rust within hours, again requiring a second blast. Secondly the blasting opened up pinholes and porous welds, at a time where re-welding was just not possible. Thirdly we did not realise how difficult it would be to remove the spent grit from inside. The contractor eventually gave in and rented an industrial vacuun cleaner, which did the job in minutes.

Rust spots on the rudder within hours. Damp floor is the cause
Luck was with us: the 5% chance of rain did not materialise. Then problems with the airless spray machine caused it to spray a thick first coat, in effect two coats at the same time. Which meant that the inside of the boat and most of the loose parts are now blue, the rest is gray.

Outside blasting did not cause much damage to the inside paint as far as we could see, but I will do a minute inspection once we are in full sunlight.

Next time I build a boat (Wife having hysterics in the background) I will decide on the paint system before beginning to build. All steel will be blasted at a proper sandblasting plant and coated with a  welding primer. Then, as the work proceeds, it will be wire-brushed and re-primed.

And I will not have freshly painted parts nearby when someone brushes grit off the hull....

Pinholes and porosity. 
The idea of building upside down so the grit from blasting inside would fall out has much to recommend it. So too Colvin's idea of leaving the keel plates off, so grit can be shovelled out there. Buckets of grit weigh a lot!

Now what remains is a few spots of remedial painting and cleaning up the site, then begins the woodwork. A lot of new mistakes to make...

And the primer goes on.