wet and dry sanding

[bojangles]

hey guys,
I am new to fiberglassing, and was wondering when should you wet sand or dry sand? May be a stupid question, but I wouldn't have a clue.
cheers

[jimslade]

What are you trying to do?

[buckknekkid]

smooth things over with the wife?

[frosh]

Use wet and dry sanding (wet) anytime you want to smooth the job with medium or fine grade abrasive and you can get the surface very wet without causing any damage (which is almost always). Nicer to use wet than dry as avoids production of dangerous dust containing glass fibres, and usually gives smoother finish with less clogging of paper.

[bojangles]

yeah, I am fixing up an old Hartley 16, that I bought here in Christchurch. So is it kind of a choice between wet or dry? and wet usually produces a better finish, is that right? I am re-fiberglassing the hull but havent started yet, I was just curious about the whole wet/dry sanding thing.

cheers

[frosh]

It sounds like you are renovating a fibreglass sheathed wooden hull. Is this correct? If you are wanting to fine sand only, wet is OK but if the fibreglass is in poor condition you would be better off using a coarse disc on a power tool and removing all the glass coating. When you have almost removed all the fibreglass you will start exposing raw timber. Do not wet sand at this stage, as you do not want to wet the timber. After re-sheathing you can wet sand the cured fibreglass to get a smoother finish but it will dull the surface until you get to very fine grade of paper #600. No matter if you are painting over the top.

[tom kane]

When you are wet sanding there is no need to use a lot of water,just keep the area you are sanding lubricated,and keep a sponge at hand to stop water running everywhere,keep sponging the area with clean water,and keep the sponge and working area clean.A small addative of ammonia will help clear waxes and greases.

[bojangles]

yeah you are correct frosh, it is fiber over ply. I am probably going to sand down to timber as most of the fiberglass isn't flash, and some is rubbish as.

thanks for the tips guys

[yokebutt]

A dab of dishwashing soap in the water helps.

Yoke.

[jimslade]

Always dry sand unless you are using very fine paper for polishing later. The water will be absorbed into the substrate and give you problems with paint setup and later fade out. Moisture and topcoats dont mix well.