Wet 'n' Dry - or Random Orbital Sander

Robert Wilson

Robert Wilson

Well-Known Member
Joined
23 May 2012
Messages
8,053
Location
Second Coast, Ross-shire, overlooking Gruinard Bay
Visit site
Ready to sand-down epoxy filler before undercoating (GRP topsides). There are multiple "spots" of damage/chips now filled with "Watertite".

Would a R.O.Sander be ok, or must I use Wet 'n' Dry paper?

If must use it, what are the benefits of Wet 'n' Dry paper / drawbacks to a sander?

Any other tips, please?

Thanks, as usual.
 
The sand paper and the method of sanding are two seperate things. A RO sander will do more work for less effort with whatever sand paper you choose. Wet and dry sand paper is normally used when you want fine finish and is often used after RO sanding as part of the gradual reduction in abrasives size (increase in number in the paper).

If you are going to paint look at the grit size the paint manufacturer recommends
 
Last edited:
pmagowan said:
The sand paper and the method of sanding are two seperate things. A RO sander will do more work for less effort with whatever sand paper you choose. Wet and dry sand paper is normally used when you want fine finish and is often used after RO sanding as part of the gradual reduction in abrasives size (increase in number in the paper).

If you are going to paint look at the grit size the paint manufacturer recommends
Click to expand...

So, no drawbacks to the RO sander, obviously not to get carried-away.
I was a bit concerned that after "sanding off the highpoints" I might get too close in to the gel coat. But with great care I should be ok, yes?
Once down to a fairly smooth finish I can then take the last microns off with the wet n dry?

Thanks

And thank you Sarabande. I'll look into the longboard. Mind you, Khamsin hasn't a flat surface anywhere - she's all curves :)
 
You can fair curves with a 'torture board' as long as the board is slightly bendy in a uniform way. The two risks from a RO sander is that it is a power tool and can be aggressive if you are not careful and it can also create a swirling pattern if not careful. The main concern with any sanding is that it is hard with a small sanding surface to create fair curves. That is why the torture board is often used. The name is self explanatory!
 
Robert Wilson said:
So, no drawbacks to the RO sander, obviously not to get carried-away.
I was a bit concerned that after "sanding off the highpoints" I might get too close in to the gel coat. But with great care I should be ok, yes?
Once down to a fairly smooth finish I can then take the last microns off with the wet n dry?

Thanks

And thank you Sarabande. I'll look into the longboard. Mind you, Khamsin hasn't a flat surface anywhere - she's all curves :)
Click to expand...

Good article in this month's PBO on doing exactly what you are doing. Well worth a read.
 
Len Ingalls said:
Random Orbit sanders can be quite aggressive.
Quarter sheet sander less aggressive.

Assuming use of same grit paper.
Click to expand...

Good morning Len, long time no "speak"!
I take your point, as having learnt from experience while sanding down after stripping the paint I had caused some damage - hence the myriad of patches of epoxy now requiring sanding!
I shall turn-down the speed and proceed very carefully.
I don't have, or have access to, a sheet sander.

An update on the skeg. With needing to get the hull ready ASAP for the professional painter, the skeg task is on hold. The S/S insert is ready and all I have to do is pluck up courage to cut the vertical slot in the skeg to accept the insert. After that I have it clear in my mind what needs doing to re-fix the shoe.
Piece of cake.................. ;) All should be completed in time for the winter.
 
The dust from epoxy that is not totally cured can be nasty stuff.
Some people end up allergic to it.

Also it can tend to clog sandpaper badly.

Wet sanding may be better for these reasons.
Some really coarse paper to start with, or even a metalwork file can be good.
As it's topsides, which presumably you will want to paint to a high gloss, be aware that the epoxy may continue to shrink slightly making the repair visible.
 
Robert Wilson said:
Good morning Len, long time no "speak"!
I take your point, as having learnt from experience while sanding down after stripping the paint I had caused some damage - hence the myriad of patches of epoxy now requiring sanding!
I shall turn-down the speed and proceed very carefully.
I don't have, or have access to, a sheet sander.

An update on the skeg. With needing to get the hull ready ASAP for the professional painter, the skeg task is on hold. The S/S insert is ready and all I have to do is pluck up courage to cut the vertical slot in the skeg to accept the insert. After that I have it clear in my mind what needs doing to re-fix the shoe.
Piece of cake.................. ;) All should be completed in time for the winter.
Click to expand...

The joy of messing around with boats! / Len
 
lw395 said:
The dust from epoxy that is not totally cured can be nasty stuff.
Some people end up allergic to it.

Also it can tend to clog sandpaper badly.

Wet sanding may be better for these reasons.
Some really coarse paper to start with, or even a metalwork file can be good.
As it's topsides, which presumably you will want to paint to a high gloss, be aware that the epoxy may continue to shrink slightly making the repair visible.
Click to expand...

How long before the eopxy has fully stopped shrinking?
As nearly all the "fillings" are shallow, I presume they will stop shrinking sooner than deep/major repairs?
 
Not sure that is true of epoxy. Never noticed it using Watertite. The filler is very thin and doubt any shrinkage would be noticeable once it is flattened off.
 
Issue No 602 Summer 2016 Think PBO has 13 issues a year using their own idea on "months" that don't coincide with the calendar! Arrived with me last Monday.
 
RO sander with very fine paper. It's a boat, not a priceless piece of art. You can spend your summer sanding it to a superfine finish and then ding the harbor wall first time out and it was all a terrible wast of time.
Go sailing.
Capt. RoN
 
ronmarson said:
RO sander with very fine paper. It's a boat, not a priceless piece of art. You can spend your summer sanding it to a superfine finish and then ding the harbor wall first time out and it was all a terrible wast of time.
Go sailing.
Capt. RoN
Click to expand...

My thoughts entirely !
I am quite sure it won't be long after re-launch that the unthinkable happens - like when my new (to me) car picked up a dented door a week after it first arrived in my drive.
(SWMBO didn't see it parked there................................................:eek:)

My concern regarding sander v. Wet n Dry was whether the sander would "overheat" the gel coat or some other such damage.
Actually, I tried sanding a patch out of sight under the stern yesterday and all seems well.

I had to give up after ten minutes, I was frozen in the bitter north wind. For the last month we have had almost continuous calm and warm/hot weather. The heating went back on yesterday. brrrrrrrrrr

Thanks for your contribution to me knowledge bank :encouragement:
 
ronmarson said:
RO sander with very fine paper. It's a boat, not a priceless piece of art. You can spend your summer sanding it to a superfine finish and then ding the harbor wall first time out and it was all a terrible wast of time.
Go sailing.
Capt. RoN
Click to expand...

+1 for pure unadulterated common sense, pretty much the advice I was given and am sticking to.
 
You must log in or register to reply here.

Share this page

Top