Smooth finish

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Dave Still
Posts: 3
Joined: 03 Apr 2015, 08:52
Design: Goth

Smooth finish

Post by Dave Still » 03 Apr 2015, 11:19

Hi I used to sail a watsit a few years ago before moving to devon all my model gear was sold to fund my wedding last year. I have recently found a local iom club so decided to build a boat and get sailing again.

I have just finished glassing a balsa Goth hull with 100g cloth I now have the textured finish how best do I get a smooth finish I am trying not to add weight but I think if I wet and dry it I will take to much cloth away. Shall I add a thin coat of resin and sand back a couple of coats may be required or will a clear varnish be a better option?

Dave

David L Alston
Posts: 72
Joined: 24 Jul 2012, 17:38
Sail number: 3011
Club: Leicestershire RYC UK
Design: Fatboy

Re: Smooth finish

Post by David L Alston » 03 Apr 2015, 22:30

I found that adding two or three 20- 25g cloths gets a smooth finish without adding a lot of weight. But as many will tell you the choice of resin is a key to low mass and high finish but most importantly an easy life.

Z Epoxy Finishing resin with 20 -25g cloth is a really good combination - easily obtained from a good Model Air shop. - It sands very easily. - The finer the cloth the less texture you will have and the higher the cloth to resin ratio.

You have however got 100g cloth on now so geeeeeeeeeeeently rub it down using a block and 1000 Wet Dry Paper - wet with a dash of soap in the water until it has matted but is still has some texture. Cover it again with 20-25g cloth but pull the cloth tight or card it out so cloth does not float up.

2 days later block sand it again.

Balsa has very little impact strength, it is the cloth and resin that provides this impact resistance.


But in all these cases you must give the glass a very thin coat of resin after sanding working it into the surface with your finger. This is to fill any pin holes. 20g - 40g of Z Epoxy should cover a IOM hull. Sand back with 1000 wet dry. - This should get rid of these tiresome pin holes which will only become evident when you paint - assuming you are using an air brush or a spray can.

Now you can paint - and this is where you will pick up weight like you will not believe so go easy. I generally put grey, white or black pigment into the resin so I don't need primer and simply apply paint to the hull or wing. It also helps with inspection - £5.00 for a small jar that will last years and years.



I use a small orbital sander, B&D palm sander, with a piece of 0.5 mm styrene (plastic) sheet glued to the sole plate. It is a bit messy because the water splashes about but it is really quick and in 15-20 min and you are done.

I would not suggest using varnish or sanding sealer because it dose not contribute to strength, adds weight and will most likely create a problem when you apply the top coat.

Dave Still
Posts: 3
Joined: 03 Apr 2015, 08:52
Design: Goth

Re: Smooth finish

Post by Dave Still » 04 Apr 2015, 08:05

Thank you that's very helpful I am endeavouring to keep weight down but as my first build I'll expect it could be improved on so any lessons learned can be implemented on the next.
This hull has only taken a week to knock out and I've really enjoyed it so far and can see when this boat is sailing I'll be building more.

Dave

David L Alston
Posts: 72
Joined: 24 Jul 2012, 17:38
Sail number: 3011
Club: Leicestershire RYC UK
Design: Fatboy

Re: Smooth finish

Post by David L Alston » 06 Apr 2015, 09:00

The problem with balsa boats, as a long term boat, is that you have to waterproof the inside as well as the outside. This is where you can end up plonking a tone of weight into the boat if you are not careful.

Every gram counts here so look at each former/bulkhead individually and decide if it is really contributing anything to the strength after the build and if not knock it out. Generally the hull should/will not need most of the bulkheads after the outside is glassed up and will hold its shape without any bulkheads.

Waterproof the inside of the hull before you put the deck on. Z-Epoxy Finishing resin without any glass cloth is ideal and will seal the wood well without too much weight pickup; expect to pickup about 40 to 60 g. It will also add some strength to the wood.

A boat I built became a pot plant bowl ,a worthy end to the boat. It was still perfect, apart from the hole, when I ditched it after some 5 years in the garden.

Dave Still
Posts: 3
Joined: 03 Apr 2015, 08:52
Design: Goth

Re: Smooth finish

Post by Dave Still » 06 Apr 2015, 16:41

So far with the outside glassed it weighs around 300g I remember my Wotsit was very flexible I'm hoping a balsa boat will be stiffer .

Dave

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