Fibreglassed Hull Sander/Grinder choice

[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.

[SVTatia]

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.

I would recommend the Makita 9031 belt sander. Expensive, but with a 40 grit belt, it removes a lot or material quickly but under full control and almost no dust. Great for small areas. I found one used for a fraction of the price, and I wish I knew it existed long ago.... I think there are Chinese knock-offs that you can get - good for one-offs.

https://www.makitatools.com/products/details/9031

[roverhi]

If you are talking sanding for fairing or removing bottom paint etc., you want an under 3,000 rpm 7" to 9" sander/polisher. Faster rpm heats up the surface and can melt the glass. If it's just small blisters, almost any 4" or so grinder will gouge them out but use the sander/polisher to dish out the grinding and fair them after filling. Use a foam pad on the sander/polisher to keep from creating divots.

[Northbound44]

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.

Gel peel and Gelplane seems to be the most effective tool used to remove defective gelcoat.

http://www.gelplane.co.uk

https://paintshaver.com/gelpeel-pro/

[coopec43]

Originally Posted by roverhi

If you are talking sanding for fairing or removing bottom paint etc., you want an under 3,000 rpm 7" to 9" sander/polisher. Faster rpm heats up the surface and can melt the glass. If it's just small blisters, almost any 4" or so grinder will gouge them out but use the sander/polisher to dish out the grinding and fair them after filling. Use a foam pad on the sander/polisher to keep from creating divots.

I agree 100%. Don't use a belt sander as you will gouge the surfase. Best tool is a random orbital air sander with a foam pad. I also used a Line sander (air)

[slug]

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.

This is a mid price professional grade sander

60 and 80 grit are common grades. Of paper

[Rucksta]

Address the small blisters with a countersink bit on a variable speed drill.
Grind off the tip to reduce cur depth if needed.
Then determine how much sanding / grinding is required.

[Chotu]

These are the absolute BEST! Built an entire boat using just 2 of them. One still going strong! Hundreds and hundreds of hours of continuous use. You can create works of art with them.

30 grit paper, cut out the sandpaper circle by tracing the pad, use 3M spray adhesive to keep the sandpaper on and easily remove when you need to change it.

Best ever. My favorite tool.
Use a foam backing pad.

https://www.amazon.com/Hitachi-SP18V.../dp/B000CPMF92

[billknny]

Originally Posted by SVTatia

I would recommend the Makita 9031 belt sander. Expensive, but with a 40 grit belt, it removes a lot or material quickly but under full control and almost no dust. Great for small areas. I found one used for a fraction of the price, and I wish I knew it existed long ago.... I think there are Chinese knock-offs that you can get - good for one-offs.

https://www.makitatools.com/products/details/9031

NO! NO!! NO!!!!!

And NOOOO!!!

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

[Reefmagnet]

I'd go with 4" disk grinder with either a course flap disk or "concrete grinding disc" for small blisters.

[s/v Jedi]

So if you’re doing spot repairs then I recommend a stripper disc in an angle grinder. The edge of the disc quickly wears away after which you get the ideal shape for grinding out small to medium blisters.

Also, I recommend a small, light but powerful enough grinder or your arms will fall off. The small Makita is everyone’s favorite for the reasons given. Below some links.

https://www.amazon.com/Pack-Black-St...93&s=hi&sr=1-4

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

[scherzoja]

If you're gonna grind out individual blisters, use a Dremel with sanding drum or a die grinder with carbide burr bits. Even normal drill motor (corded or cordless) with a carbide burr bit will work, but a die grinder is much better.

Dremel has advantage of extension "cable" that puts the bit at end of a 3' cable. You can hang dremel on belt and not wear out your shoulders holding the motor.

Disadvantage of dremel is that the on/off switch is a plastic sliding mechanism that fails to turn the motor on because the plastic gets flexible with age. Really a crappy design. If I can find an alternative to Dremel that has an extended cord, variable speed, and is small like a Dremel, but with at better on/off switch, I'd toss the Dremel in a heart beat.

Sanding sleeves on a dremel will wear out and clog quickly, but carbide bits last a long time.

I have the GD0601 (one speed) and wish I had bought a variable speed, then I could use it with sanding drums, but usually the carbide burr bits work much better.

https://www.makitatools.com/products/details/GD0801C
https://www.makitatools.com/products/details/GD0800C
Difference between 801 and 800 is the on/off switch.

https://www.makitatools.com/products/details/GD0601

[Reefmagnet]

Originally Posted by scherzoja

If you're gonna grind out individual blisters, use a Dremel with sanding drum or a die grinder with carbide burr bits. Even normal drill motor (corded or cordless) with a carbide burr bit will work, but a die grinder is much better.

Dremel has advantage of extension "cable" that puts the bit at end of a 3' cable. You can hang dremel on belt and not wear out your shoulders holding the motor.

Disadvantage of dremel is that the on/off switch is a plastic sliding mechanism that fails to turn the motor on because the plastic gets flexible with age. Really a crappy design. If I can find an alternative to Dremel that has an extended cord, variable speed, and is small like a Dremel, but with at better on/off switch, I'd toss the Dremel in a heart beat.

Sanding sleeves on a dremel will wear out and clog quickly, but carbide bits last a long time.

I have the GD0601 (one speed) and wish I had bought a variable speed, then I could use it with sanding drums, but usually the carbide burr bits work much better.

https://www.makitatools.com/products/details/GD0801C
https://www.makitatools.com/products/details/GD0800C
Difference between 801 and 800 is the on/off switch.

https://www.makitatools.com/products/details/GD0601

I have the below gadget and am not afraid to use it!


https://www.bosch-pt.com.au/au/en/pr...-35-06019C5040

[coopec43]

Originally Posted by Reefmagnet

I'd go with 4" disk grinder with either a course flap disk or "concrete grinding disc" for small blisters.

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.

[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.