As the weather is currently on the damp side, I’ve taken the opportunity to step away from the work plan and finish prep the tank.
I’ve spent an industrious morning rubbing it down ready for the finishing coats.
In case you’ve never done a prep yourself here’s a run through.
First the tank was cleaned to bare metal and treated with an acid etch primer to kill off any rust remaining in the nooks and crannies, this left it with a red “base colour”.
Next a coat of grey primer filler was applied and allowed to dry, this was followed by a coat of beige primer filler, then another of grey and another of beige.
By this time the surface pitting had disappeared and it looked level so it got another coat of grey.
I now had 5 layers of primer of contrasting colours on top of the red base coat.
I had a spray can of black left from another job so I used this to apply a light coat, little more than a dusting on top of the whole, this is the “witness coat” and it does not matter what colour it is. The tank was then put to one side to “cure out” and let the paint solvents evaporate.
This was done a couple of weeks ago so this morning it was out with the “Wet and Dry” carborundum paper and set too.
I used two pieces of 400 grade wrapped over a stiff sponge block and started with that, using it wet.
First thing was to reduce the “new cut”of the paper so the two pieces were put face to face and given a quick rub against each other.
Toss one piece into a bucket of water with a shot of washing up liquid added and then start rubbing down with the other wrapped round the sponge, change the pieces frequently so they do not become clogged.
Idea is that you have one in use and one in soak and every now and then you wipe the job surface clean with another, softer, sponge
The aim is to rub off the “witness coat” without going through to the base coat.
As you go on you quickly see that what appeared a smooth surface was not as the witness coat is rubbed off the high spots but remains in the dips.
Here’s where the advantage of the alternate colours of primer shows itself since you can keep check of how near to the base coat you are getting as you rub the high spots away.
By the time you have removed all the witness coat you have a smooth surface, ready for the finishing coats, but not yet!.
You’ve rubbed the surface down wet, primer is porous, so the tank has now been put aside to dry out again before the top coats go on.
It’s a laborious, time-consuming job and is where the big money goes in a paint job, the final finish is dependant on the quality of the prepared surface as any blemishes will show through.