Hull sanding

[Yarrow]

I have sanded my mahogany hull with a belt sander using 60 grit belts. What grit do I need to go down to prior to varnishing. in order to get a decent finish?

 

[oldharry]

That sounds pretty brutal! You will have raised the grain and quite badly damaged the timber surface. You need to go over again quite thorughly with 120grit to to flatten the grain, then again with 240 and maybe finish off with 300 grit to get a decent finish. Make sure you dont polish the surface and harden it if you use the 300 grit or you may have difficulty getting the varnish to penetrate.

 

[Peterduck]

Firstly, put the belt sander away and save it for use on something that is less critical than a boat; say a fowl pen or something like that. A random orbital sander will be less harmful and yet faster than a rectangular pure orbital sander. If you want a fine finish, as is implied by the use of varnish, an orbital sander is definitely the way to go. Start with 80 grit until you have removed the the marks from the belt sander. Then 120 grit until you have removed the marks from the 80 grit. By now, you should be ready for the first coat of varnish. This will harden up the surface and begin to fill the pores. When the varnish has dried, sand lightly by hand with 240 wet-and-dry, used wet with a dash of detergent in the water to prevent clogging of the paper. Dry, varnish and repeat the last sanding for six coats. Now you can begin to get fussy about a good finish with the next four coats. There are, unfortunately, no short-cuts to a good finish.
Peter.

 

[ccscott49]

After you have used the orbital sander, before you varnish, go over the whole hull, with sandpaper and a flexible block by hand, this will take out all the little swirls you get with the random orbital, which will stick out like a dogs balls when the varnish goes on, too late afterwards.

 

[tidclacy]

Try the book in the Wooden Boat Series, Painting and Varnishing. It has a wealth of knowledge and will tell you everything you need to know about the subject plus more. Tells you how to use a disc sander properly but to late now for you. /forums/images/graemlins/smirk.gif

 

[Yarrow]

Thank you,gentlemen. I'm not sure that I had much choice with the coarse sanding. The hull is over a hundred years old, left derelict for thirty-five, and it was pretty rough. I'm never going to get a perfect finish, and I'm the wrong side of seventy, so I might have to accept a few defects to see it finished. The alternative is to paint it, and I don't want to do that.

 

[LittleShip]

"which will stick out like a dogs balls"

Colin........ you do have a way with words! /forums/images/graemlins/smile.gif

Tom

 

[Seagreen]

Over 100 years old - can you post up a picture, please? What was she built for?

 

[Yarrow]

She was built as a ferry on the River Severn at Worcester. Laid aside about fifty years ago, and gradually became derelict. The previous owner rescued her and replaced the keel and ribs, then ran out of time. I am continuing the restoration, and am going to fit steam plant.

 

[Keith 66]

For sanding Hulls belt sanders are lethal and i have seen boats that had half the heads of their fastenings sanded away.
A random orbital sander is best, rough fairing can be done with 40 grit then 80 grit i find only the 40 grit leaves swirls.
For varnishing rough sand with 80 then go straight to 240 grit change the disc regulaly
Most DIY random orbitals are fitted with velcro pads which are a con by the makers as the discs are so expensive.
When you buy a random orbital sander throw the standard backing pad away and fit a stick on disc foam feather edge pad.
The stick on discs are way cheaper and can be got from any car trade paint suppliers
I have had a Sealey ER150 random orbital sander for 15 years now and it is the best sander i have ever used.