Epoxy; my last question!!

[pcatterall]

I thought we had done it to death but please bear with me. I have searched back but can't find the answer.
I thought that the recommended thickness was around 1mm being 4 or five coats at around 150 micron. I have just returned to the West application advice thinking that their product was thicker and may require fewer coats. They recommend 6 coats giving 2mm of cover. ( and 300 micrn per coat!)
I realise that more coats will give a more water resistant barrier but this seems excessive,
any advice please?
I had been considering epoxy from 'resin-supplies' ( on price grounds) their advice was to expect around 100 micron cover per coat indicating around 20 coats and around 50 kg of epoxy.
Question is...... target for final thickness of epoxy on hull below waterline!

 

[VicS]

Consult the product data sheets for the materials you are considering.

I think you will find it may vary with product and the total thickness will depend upon whether you are restoring a hull that has suffered from osmosis or whether you are merely applying to a sound gel coat as a precautionary measure.

 

[GrahamM376]

As said above, follow the manufacturer's advice, not the retailers. Thickness of coats may vary a bit depending on temperature but, whoever quoted 20 coats is crazy.

 

[Elessar]

I thought we had done it to death but please bear with me. I have searched back but can't find the answer.
I thought that the recommended thickness was around 1mm being 4 or five coats at around 150 micron. I have just returned to the West application advice thinking that their product was thicker and may require fewer coats. They recommend 6 coats giving 2mm of cover. ( and 300 micrn per coat!)
I realise that more coats will give a more water resistant barrier but this seems excessive,
any advice please?
I had been considering epoxy from 'resin-supplies' ( on price grounds) their advice was to expect around 100 micron cover per coat indicating around 20 coats and around 50 kg of epoxy.
Question is...... target for final thickness of epoxy on hull below waterline!

If the epoxy is solvent free, it is easy to work out what thickness you will get for a given amount of epoxy. 1 litre will give a cube of epoxy 100mm x 100mm x 100mm which you can easily see will be 1mm x 1000mm x 1000mm. So a litre gives 1000 microns (1mm) per square metre. 400 microns is a good thickness for a protective layer, so you can see you need 2.5 litres per square metre.

What I'm saying is forget the number of coats, because coat thickness can vary with so many factors. Get a litre per 2.5 square metres and keep putting it on till you've used it up, then you will have the correct thickness (if you decide to go for 400 microns)

For solvented epoxy like gel shield, remember it is only 45% solids so will shrink back to 450 microns dry from 1000 when wet, so multiply the amount you need by 2.2.

 

[GrahamM376]

If the epoxy is solvent free, it is easy to work out what thickness you will get for a given amount of epoxy. 1 litre will give a cube of epoxy 100mm x 100mm x 100mm which you can easily see will be 1mm x 1000mm x 1000mm. So a litre gives 1000 microns (1mm) per square metre. 400 microns is a good thickness for a protective layer, so you can see you need 2.5 litres per square metre.

What I'm saying is forget the number of coats, because coat thickness can vary with so many factors. Get 2.5 litres per square metre and keep putting it on till you've used it up, then you will have the correct thickness.

For solvented epoxy like gel shield, remember it is only 45% solids so will shrink back to 450 microns dry from 1000 when wet, so multiply the amount you need by 2.2.

Perhaps you sell epoxy? Your quote of 2.5L/m is way out according to the manufacturers and my limited experience. Gelshield 200 for instance, info copied and pasted from the datasheet: -

Number of Coats 5 minimum by brush (min. 250 μm DFT)
Coverage (Theoretical) - 9.10 (m²/lt) by brush
(Practical) - 8.10 (m²/lt) by brush

In practical terms, I've used 2 litres of Gelshield 200 per coat on a 38ft boat, applied by roller.

 

[macd]

Perhaps you sell epoxy? Your quote of 2.5L/m is way out according to the manufacturers and my limited experience.

All but the final sentence of the first part of Elessar's volume explanation was correct. As he said, 1 litre over 1 square metre gives a film thickness of 1mm/1000 microns (assuming solvent-free resin). A 400 micron film would require 400cc per square metre, not 2.5 litres. The typical advice I've seen recommends a final film thickness of 500 microns or more.

I'll be back in a couple of weeks when I've worked that out in fluid ounces per square foot. God, I hate the metric system.

 

[Elessar]

Perhaps you sell epoxy? Your quote of 2.5L/m is way out according to the manufacturers and my limited experience. Gelshield 200 for instance, info copied and pasted from the datasheet: -

Number of Coats 5 minimum by brush (min. 250 μm DFT)
Coverage (Theoretical) - 9.10 (m²/lt) by brush
(Practical) - 8.10 (m²/lt) by brush

In practical terms, I've used 2 litres of Gelshield 200 per coat on a 38ft boat, applied by roller.

Yes quite right sorry 2.5 square metres per litre not 2.5 litres per square metre my silly typo now edited.

 

[pcatterall]

Thanks guys, 1 had the maths sorted it was the final recommended total, I will aim for 1mm or a bit under that!

 

[oldsaltoz]

If you apply with a roller and tip off with a brush you will get a very smooth finish.

 

[Pasarell]

Epoxy film thickness to be effective

The amount of epoxy needed to be effective is very much down to personal judgement. When epoxies were first introduced as osmosis protection / treatment every company recommended a different dry film thickness. IIRC the recommendations varied from 250 - 600 microns in the early 80's. What is important to remember is that ALL epoxies are permeable by water. Greater film thickness will reduce the rate of that permeability. If you take the boat our of the water every winter and only keep it in cool sea water during the summer the amount of water getting through will be less than if you keep the boat in all year and sail it in warm fresh water.
Also, as Elessar pointed out, the dry film thickness of a solvent based material will be much less than the wet film. It is the total dry film thickness that counts, not the wet film.
Graham M376, you say you have used 2L of Gelshield 200 per coat on a 38ft boat. At a guess the underwater area is about 35 sq m for a typical fin keeled monohull so you have covered 17.5 sq m / L giving a wet film of about 65 microns. Gelshield 200 is about 50% volume solids I think so you will have applied a dry film of about 30 microns per coat. Easy then to work out how many coats you need - once you have decided what the right dry film thickness is for your needs.