Silicone spray in bilge

[jenevers]

Has anyone ever sprayed their bilge with silicone instead of the usual Waxoyl etc? Seems an obvious anti moisture treatment to me, but I’ve never seen it mentioned.

[OldGoat]

14 minutes ago, jenevers said:

Has anyone ever sprayed their bilge with silicone instead of the usual Waxoyl etc? Seems an obvious anti moisture treatment to me, but I’ve never seen it mentioned.

Shock horror - duplicate post - a capital sin....

[jenevers]

27 minutes ago, OldGoat said:

Shock horror - duplicate post - a capital sin....

Triplicate actually.

[OldGoat]

I may be out of my depth - but the silicone sprays that I have used are lubricants only. Their water displacement feature is only to coat the substrate so that the lubricant can work (?). It also disappears quite quickly, so I don't think it's a solution

[Traveller]

I used Dynax and it is holding up well. Not sure I would trust a silicone spray.

 

[Sea Dog]

46 minutes ago, OldGoat said:

It also disappears quite quickly, so I don't think it's a solution

If it disappears due to mixing with the water, perhaps it is a solution? 

[jenevers]

I’ll try it on a piece of rusty metal and leave it half submerged in a bucket. I know if you spray silicone on paintwork, you can’t paint over it, so something must remain.

[Dr Bob]

19 hours ago, jenevers said:

Has anyone ever sprayed their bilge with silicone instead of the usual Waxoyl etc? Seems an obvious anti moisture treatment to me, but I’ve never seen it mentioned.

No, its not going to work.

You say 'anti moisture' treatment. Yes it may displace some water but if you mean anti corrosion, it wont be any use. To stop corrosion you either need a passivating material – like zinc powder etc – or a barrier coating.

Water permeates through barrier coatings via osmotic pressure. Nothing stops osmotic pressure. Barrier coatings have to reduce permeation and stick very well to the substrate to stop the water that does get through, wicking between the substrate and the coating. Epoxies are the best example with low permeation and excellent adhesion.

Spraying silicone on will displace water as you spray it on, but once on the surface, water will be driven onto the steel by osmotic pressure and displace the silicone and corrosion will take place. If you put silicone on, then you will have a very difficult job to put any coating on afterwards as it will be very difficult to get the surface clean enough to allow anything to adhere well. Dont do it.

[jenevers]

53 minutes ago, Dr Bob said:

No, its not going to work.

You say 'anti moisture' treatment. Yes it may displace some water but if you mean anti corrosion, it wont be any use. To stop corrosion you either need a passivating material – like zinc powder etc – or a barrier coating.

Water permeates through barrier coatings via osmotic pressure. Nothing stops osmotic pressure. Barrier coatings have to reduce permeation and stick very well to the substrate to stop the water that does get through, wicking between the substrate and the coating. Epoxies are the best example with low permeation and excellent adhesion.

Spraying silicone on will displace water as you spray it on, but once on the surface, water will be driven onto the steel by osmotic pressure and displace the silicone and corrosion will take place. If you put silicone on, then you will have a very difficult job to put any coating on afterwards as it will be very difficult to get the surface clean enough to allow anything to adhere well. Dont do it.

I bow to your superior technical knowledge. BUT how does green grease work (as used in the Netherlands)?

 I believe steel is still “as new”, decades later 

[Dr Bob]

22 minutes ago, jenevers said:

I bow to your superior technical knowledge. BUT how does green grease work (as used in the Netherlands)?

 I believe steel is still “as new”, decades later 

If it is put on thick enough then grease can create a barrier that does restrict water but it's not going to work if under water. Silicones are less likely to reject water as per hydrocarbon grease as they usually have siloxane groups which make them more hydrophilic. Maybe if you spread a couple of mm's all over then you would get some protection.

If it worked, then it would be the method of choice for bilges, but it isnt if you are after corrosion resistance. 

[rusty69]

11 minutes ago, Dr Bob said:

Silicones are less likely to reject water as per hydrocarbon grease as they usually have siloxane groups which make them more hydrophilic

I would have though hydrophobic Silicone would work,as it must have a fear of water and hence want to reject it

[Dr Bob]

7 minutes ago, rusty69 said:

I would have though hydrophobic Silicone would work,as it must have a fear of water and hence want to reject it

...but osmotic pressure will drive water through it. Easier to get through a grease than a fully crosslinked coating. Think of osmosis through a GRP hull. This is the mechanism that drives water through coating. A good thick coat of grease may protect on a vertical panel but not in immersion duty.

[rusty69]

2 minutes ago, Dr Bob said:

...but osmotic pressure will drive water through it. Easier to get through a grease than a fully crosslinked coating. Think of osmosis through a GRP hull. This is the mechanism that drives water through coating. A good thick coat of grease may protect on a vertical panel but not in immersion duty.

Oh.So its not scared then

[Dr Bob]

1 minute ago, rusty69 said:

Oh.So its not scared then

If you deionise it, the water will be even less scared.

[rusty69]

5 minutes ago, Dr Bob said:

If you deionise it, the water will be even less scared.

I would never attempt to Iron water (let alone deironise it), the waves would be impossible to remove.

[jddevel]

Reading this topic I wonder has anyone ever used the tank sealants as used on car/motor cycle fuel tanks?

[Dr Bob]

4 hours ago, jddevel said:

Reading this topic I wonder has anyone ever used the tank sealants as used on car/motor cycle fuel tanks?

Like I've said earlier, if you want to stop corrosion, you either passify it with a sacrificial material (ie zinc) or put a barrier coating on that stops water permeation and sticks very well. The coating can be a grease, a gel or a solid. The best barrier coating for anti corrosion is probably epoxy as it forms a dense 3 d matrix that restricts water permeation and sticks exceptionally well. Yes, sealants will work but ones used on fuel tanks will be designed to resist fuels rather than water.  The best coatings for use at the bottom of fuel tanks are 2 pack epoxies but that assume they will adhere well, which in turn means good surface preparation. In engine bilges, surface prep just cant happen so anything is a compromise. A rust converter such as vactan etc covered with a reasonable 'paint' has to be the best solution unless you can get it clean. 

You only have to look at current practice to work out the best way to do it.

In the 80's I lead a team that developed a modified epoxy coating that really did stick well to oily, rusty steel. It worked very well BUT it was too expensive for the coatings market and the resistance from the painting contractors (who make their money by charging for grit blasting) who would loose a lot of business. Unfortunately that product is not available today. It would have worked very well.

[rusty69]

3 minutes ago, Dr Bob said:

Like I've said earlier, if you want to stop corrosion, you either passify

How do you passify it? Take it for a pint

[Dr Bob]

1 minute ago, rusty69 said:

How do you passify it? Take it for a pint

No, our bilge is not 18 yet. I'd sit it down in front of the TV/video/I-player and stream Tellitubbies continuously.

[rusty69]

1 minute ago, Dr Bob said:

No, our bilge is not 18 yet. I'd sit it down in front of the TV/video/I-player and stream Tellitubbies continuously.

Might be cheaper to passify it rather than passivate it when it reaches 18.

[system 4-50]

The Romans perfected pacifying. You burn everything to the ground, spread salt on it to prevent stuff growing, and sell everybody around into slavery.  Didn't work on rust though.

[Dr Bob]

Didnt work north of Falkirk either - except for a brief excursion as far north as Perth for 20 years or so. Must have been the weather!

[jenevers]

So would a mixture of oil and diesel work for a few years? Diesel is great as a penetrating oil, so would get into the pores of old, rusty steel. On an old boat, with inaccessible parts in the bilge it’s just not feasible to reach, to treat with Vactan and then paint, but directing a jet of oily “ yackum”  should do the trick. 

[Peter Reed]

19 minutes ago, jenevers said:

So would a mixture of oil and diesel work for a few years? Diesel is great as a penetrating oil, so would get into the pores of old, rusty steel. On an old boat, with inaccessible parts in the bilge it’s just not feasible to reach, to treat with Vactan and then paint, but directing a jet of oily “ yackum”  should do the trick. 

Does diesel not float on water?

[roland elsdon]

We used to put the old engine oil under the shuts of our ( not to offend the offendables) purpose built for trading on the canals and waterways of the uk, but in later years retained in sympathetic condition, with a chimney only on the correct side craft , ( known as a narrowboat) , as well as waxoil. Given the bottom was sympatheticaly  replaced in 1982 it had to be re replaced in about 2009. I can confidently say it didnt work, but it did stink collect coal dust and emulsify, as well as being a pollution issue