Sandblasting antifouling

Originally Posted by souljour2000

On this topic...is there a reason anyone might not recommend pressure washing to get rid of really old and flaky bottom paint on a good condition sailboat hull from the mid-80's that has been on a trailer most of it's life?

No,

way safer than blasting (cheaper too), but you MUST use a rotating nozzle!

Regards
Richard

[souljour2000]

Thanks for your comment Apex... The cosmos has awarded me temporary access to 6.5 hp pressurewasher ...my 20-foot trailer-sailer has never had a bottom job and is over 25 years old...looks like it has had two different bottom coats over the original gelcoat..they obviously neglected to get rid of the original reddish stuff and the aqua-colored is peeling badly..the underlying first coating of red will be harder...I'll have to look and see if its a rotator nozzle...may be able to borrow one if not...

The 6,5 hp do´nt mean anything, the water presuure they can produce is what makes you happy. You need far more than the average 120 bar to have success. From 250 bar up you might succeed (professional equipment shoots at 500 bar upward). The rotating nozzle is a standard on all higher pressure units. It has two advantages. First you do´nt shoot through too easily, second you have much less backpressure. (250 bar straight nozzle shoots you straight off your scaffold, or lets a crane gondola swing so violently that the backswing causes a probably deadly impact.)
Notice! A 500 or 800 bar has still so much backpressure (rotating nozzle) that one needs a assistant to be held in position!

Shoot a simple pattern! straight forward, straight back the same lane ONCE!
then the next lane, offset (deeper) exactly the width of the nozzles effective area. Start and end each lane off the hull (shoot in the wind), otherwise your "turning points" get shot 4 times. That can be too much.
DO NOT play with patterns! Do not shoot "like the bull pees" .You loose control which area was treated, which not!
Do not try to remove single specks or areas of "wrong" colour! Just wash it down, one move forward, one backward, to have all angles of attack involved once. When you focus on a single "faulty point" you are through in no time!
You will not get a "even" finish! Some paint sits where it sits forever. Thats fine, do´nt bother, it will never come off, good for you.
Of course you can sand after washing it down, usually you must not. Just make sure it is REALLY dry before you apply your new paint.

Good luck and success!

Richard