Fibreglassed Hull Sander/Grinder choice

[Reefmagnet]

Originally Posted by coopec43

NO!


I did my boat using an air random orbital sander and an inline sander and while it is not perfect I am happy with it.

An ROS is an invaluable tool for boat work and everyone should own at least one of these but the OP's discussing blisters, usually found on this part of the boat, where a 4" grinder makes a very effective "rough shaping" tool.....

[slug]

Originally Posted by Ambler

Best sander by a country mile is a Festool gear driven random orbital 150 with a dust extraction system. Ask any professional fibreglass repairer.

Great tool. Costs a months salary

If you need the best and have deep pockets check out Mirka

https://www.mirka.com/

[coopec43]

Originally Posted by Reefmagnet

An ROS is an invaluable tool for boat work and everyone should own at least one of these but the OP's discussing blisters, usually found on this part of the boat, where a 4" grinder makes a very effective "rough shaping" tool.....

I certainly have a belt sander (and I'm on my second one) I have X4 angle grinders one set up with a "flapper wheel" and I use that a lot for preliminary sanding.

I always thought most blistering was above/below the waterline and that is why I suggested a Random orbital sander or line sander.

[jhulmer]

Originally Posted by slug

This is a mid price professional grade sander

60 and 80 grit are common grades. Of paper

+1! I bought one of these to redo my deck, hull and bottom. It is a controllable beast that reduces your sanding time. It has two modes RO and Grind for heavy removal.



It is a little on the heavy side but you get through quicker.
Jim

[GRIT]

We built our boat with this unit.
https://www.grainger.com/product/14F...g!439044756658!

Basically the same as what Chotu used, but in a slightly different form. It's really fantastic, how much meat you can take off with this thing. With a little practice, you'll be done in no time. I've used this unit for 10 years, it stripped several years of bottom paint from a Corbin 39 in less than 2 hours.

It has a 5/8 spindle, so you can attach whatever pad, or grinding disks you want. Worked great with a cutoff wheel too, but there's no guard for it, so use it at your own risk.
I used 8 inch pad and paper on this unit, it really works a treat.

Cheers, and good luck.
Paul.

[slug]

Originally Posted by jhulmer

+1! I bought one of these to redo my deck, hull and bottom. It is a controllable beast that reduces your sanding time. It has two modes RO and Grind for heavy removal.



It is a little on the heavy side but you get through quicker.
Jim

Yup a little heavy

It’s a commercial grade multipurpose sander

If you have have a big sanding project on the horizon pick up some abranet sandpaper

This sandpaper is a mesh

The advantage of mesh is dust removal and no clog

Sand paper clogs when it overheats

The mesh design attack’s this overheat problem

https://www.mirka.com/ABRANET-540/

[Cadence]

Originally Posted by SeaSloth

I have a lot of small blisters and prior-poorly done blister repairs I need to fix. Many of these will require removal of some hull material so I can properly patch them.

I don't know the best tool for the job. I sanded off the bottom paint and old epoxy coating with a Bosch 6 inch rotary sander and 20 grit paper. I could use it I suppose but it wasn't fast (which may be a good thing considering my inexperience with fiberglass).

What tool is best for this job?

Thank you.

JMHO 20 grit may be to aggressive.

[slug]

Originally Posted by Cadence

JMHO 20 grit may be to aggressive.

Yup

I use 36 grit occasionally

If 36 wont work I shift to a two handed , 1 grit tool

[Slainte1]

Have to agree with Chotu but in my case I used a Black & Decker Polisher with 3M foam pads 30 yrs still going strong. you need slow speed and v coarse discs,

[SVTatia]

Originally Posted by billknny

NO! NO!! NO!!!!!

And NOOOO!!!

You will NEVER see a professional doing this kind of work with a belt sander! For really good reasons.

YESSSS YESS and YESS !!!!

I guess you've never used this particular belt sander... I have, extensively, and some have others...

As per OP "Many of these will require removal of some hull material so I can properly patch them."
My recommendation was for the BLISTERS, not for peeling the entire bottom.

Please take a moment for some learning:

https://www.youtube.com/watch?v=czaoO6Y4bsM&t=558s

[JOHNMARDALL]

I'm not clear from your post if you've already sanded the bottom or are thinking about it, but no matter what kind of sander you use, this is a hard and time consuming job that will cover you in toxic bottom paint. Your yard may not even allow you to do it. I suggest having the bottom professionally peeled and faired, or blasted with glass beads. which will give you a finish you can fair yourself. Been there, done that, never again.
John Mardall
for
Vetus Maxwell Boat Equipment.

[Cadence]

Just my humble opinion! Blisters are cosmetic for the most part. If they go into the glass grind them out and fill after drying out any wicking. It's a case of a poor finish job gel-coat. Probably humidity related.

[SeaSloth]

Thank you all for the replies. Let me clarify a bit. I already have the Bosch orbital sander recommended. It is the same used by my yard for bottom sanding. I have full face respirator, Tyvek suit, vacuum...the works. I used 20 grit because 40 wasn't taking off the 5 layers of paint and 2 layers of epoxy. The epoxy was especially tough. The results were good. The yard I was at at the time has a great reputation and the yard manager told me that the surface was as good as his guys would do. I'm not at the yard anymore which is why I'm asking here.

I have 20 to 30 four to five inch diameter divots that appear to have been ground out and filled with fairing material rather than patched and/or the fiberglass patch material has developed voids. This caused large blisters of the paint as opposed to bliters of the gel coat.

I need to remove the old patches of fairing compound and glass and expand the diameter of the area so I can put a proper patch in place.

If the Bosch is the right tool I'm happy to use it. I just dont know if this is a job for sandpaper or something tougher. Using a grinding wheel seemed like overkill and it frightens me a bit to use something that strong but given how long it took to remove the paint I was afraid using sand paper was to weak.


Thanks again for your help. It is very appreciated.

[s/v Jedi]

You really need to use the angle grinder with stripper disc or flap-sanding disc. You can not use a sander to grind out blisters, not even a Festool.

[jimbunyard]

Originally Posted by SeaSloth

Thank you all for the replies. Let me clarify a bit. I already have the Bosch orbital sander recommended. It is the same used by my yard for bottom sanding. I have full face respirator, Tyvek suit, vacuum...the works. I used 20 grit because 40 wasn't taking off the 5 layers of paint and 2 layers of epoxy. The epoxy was especially tough. The results were good. The yard I was at at the time has a great reputation and the yard manager told me that the surface was as good as his guys would do. I'm not at the yard anymore which is why I'm asking here.

I have 20 to 30 four to five inch diameter divots that appear to have been ground out and filled with fairing material rather than patched and/or the fiberglass patch material has developed voids. This caused large blisters of the paint as opposed to bliters of the gel coat.

I need to remove the old patches of fairing compound and glass and expand the diameter of the area so I can put a proper patch in place.

If the Bosch is the right tool I'm happy to use it. I just dont know if this is a job for sandpaper or something tougher. Using a grinding wheel seemed like overkill and it frightens me a bit to use something that strong but given how long it took to remove the paint I was afraid using sand paper was to weak.


Thanks again for your help. It is very appreciated.

Well now that we know exactly what you're dealing with, we can better answer your question (or at least give an informed opinion)

Given the relatively small area you're grinding and the tool you already have, you should be fine using it. Although the maximum speed in direct drive is rather low (compared to an angle grinder), with extra coarse discs you should be fine, if a little slow.

The variable speed will aid you greatly when inexperienced, slow down until you get the hang of it to avoid digging too deeply into the glass.

As a reference, for maximum stock removal, I use a 15 amp, 6000 rpm grinder with 7" 16 grit resin discs, 'smoothing' with 6" 40 grit discs on a Fein DA with vacuum dust extraction. Neither have variable speed, but I recently broke down and made a variable speed control for them (and any other 120vAC brushed-motor tools) from a plastic duplex box, a rotary dimmer switch, a standard house receptacle, and a 6 foot 12/3 cord and plug. Really makes controlling aggressive tools a lot easier, and reduces finishing time...