Plastic through hull fitting which sealant

tillergirl said:
Extracts from the Sikaflex blurb:

Sikaflex®-291i
Multifunctional adhesive sealant for marine application

Areas of Application: Sikaflex®-291i must not be used to seal plastics that are prone to stress cracking (e.g. PMMA, PC, etc.).

Removal: Uncured Sikaflex®-291i can be removed from tools and equipment with Sika® Remover-208 or another suitable solvent. Once cured, the material can only be removed mechanically.
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Mechanical removal does not mean grinding. Their words mean you have to cut it off as it is impervious to solvents.
 
Agreed, there are alternatives to grinding, but given how 'easily' you managed to remove the adhesive, it doesn't strike me as a partiuclarly effective: viz: "not the slightest difficulty in releasing the sealant". It is an adhesive! I regret I am mystified: why not use polysulphide?
 
tillergirl said:
Agreed, there are alternatives to grinding, but given how 'easily' you managed to remove the adhesive, it doesn't strike me as a partiuclarly effective: viz: "not the slightest difficulty in releasing the sealant". It is an adhesive! I regret I am mystified: why not use polysulphide?
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Absolutely no question about its effectiveness. No failures in 30 years

Polyurethane is far more versatile than polysulphide and half the price. I have little stowage for dozens of compounds and select for optimum value.
 
vyv_cox said:
I changed out my Airmar transducers a few years ago. Again, no problem removing the old one. As for skin fittings there is not the slightest difficulty in releasing the sealant. Grinding? Absolutely not.
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This is a job I have to do. How do I remove skin fittings / transducers which are sikaflexed in, please?
 
ddodg said:
I am refitting my old B and G depth sounder and need to reseal the plastic through hull fitting. I am aware that some sealants Sika 291 and CT1 both say they are not suitable for some types of plastic. Unfortunately I have no idea what type of plastic my through hull fitting is. Is there a good sealant for underwater use that does not affect plastics .
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We just changed 20+ thru-hulls including a few plastic fittings. We used 3M 5200. They are going to be there hopefully 20 years or more and we don’t care that it will be horrid to remove. 5200 is really tough and quite expensive, but reassuringly so. We tried Puraflex 40, but found it too weak. Fine as a sealant, but not as an adhesive sealant. The bigger valves could be rotated after a week. Not good enough, so we pulled them out and re-did them.
 
Zing said:
. . . We tried Puraflex 40, but found it too weak. Fine as a sealant, but not as an adhesive sealant. The bigger valves could be rotated after a week. Not good enough, so we pulled them out and re-did them.
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Must have been operator error. Whilst I've spent a lifetime using 3M 5200, on my own boat in the UK I've used PU40 as an alternative and have found no discernable difference. It's made by SIka and sold as an adhesive sealant for marine use amongst others. They publish data for the mechanical properties and I've no reason to believe they're fraudulently misrepresenting their product.

All through hulls should be mechanically fastened into the hull. It's quite acceptable to use butyl sealant if you so wish as you only need a sealant as the threaded fasteners are holding it in place. But I too like the back up of a adhesive sealant as I never plan to remove them until the end of their life. PU40 is perfect for this application.
 
Zing said:
We tried Puraflex 40, but found it too weak. Fine as a sealant, but not as an adhesive sealant. The bigger valves could be rotated after a week. Not good enough, so we pulled them out and re-did them.
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Failure to cure can often be caused by previous use of silicone sealants on the same fitting. Silicones inhibit the cure if many paints and sealants. I have used only PU40 for many years now and never found it to be soft or weak.
 
Motor_Sailor said:
Must have been operator error. Whilst I've spent a lifetime using 3M 5200, on my own boat in the UK I've used PU40 as an alternative and have found no discernable difference. It's made by SIka and sold as an adhesive sealant for marine use amongst others. They publish data for the mechanical properties and I've no reason to believe they're fraudulently misrepresenting their product.

All through hulls should be mechanically fastened into the hull. It's quite acceptable to use butyl sealant if you so wish as you only need a sealant as the threaded fasteners are holding it in place. But I too like the back up of an adhesive sealant as I never plan to remove them until the end of their life. PU40 is perfect for this application.
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I just looked up the tech specs. 5200 has a tensile of 2.5N/mm2 on fibreglass, but about 7N/mm2 in optimum conditions. PU40 is 1.5N/mm2 according to ISO37. So not as strong to no where near as strong as far as I can see.
 
vyv_cox said:
Failure to cure can often be caused by previous use of silicone sealants on the same fitting. Silicones inhibit the cure if many paints and sealants. I have used only PU40 for many years now and never found it to be soft or weak.
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We pulled out 20 yr old fittings. No sign of any silicone, but I can’t rule it out.
 
tillergirl said:
When did you ever say that? You talked about your windows using Sika. I assumed your pricing comparison was a typo. But is PU40 half the cost of polysulphide? Tool Station 300ml £7.19.
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Post #3. My use of Sika on my windows was many years ago. The last PU40 I bought was £4. But does it really matter?
 
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KompetentKrew said:
This is a job I have to do. How do I remove skin fittings / transducers which are sikaflexed in, please?
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You may be lucky and find you can just screw out skin fittings if they are the type that has a lug on the inside allowing a tool to grip it. Otherwise either grind the flange off or use a hole cutter after banging a piece of wood into the bore to take the pilot drill.
With transducers it depends if you want to keep or replace. To keep you need to get a blade between the flange and hull and then as far as possible around the thread from above. Keep pushing and it will loosen. Sometimes a very small drill can help if there is clearance.
 
vyv_cox said:
You may be lucky and find you can just screw out skin fittings if they are the type that has a lug on the inside allowing a tool to grip it. Otherwise either grind the flange off or use a hole cutter after banging a piece of wood into the bore to take the pilot drill.
With transducers it depends if you want to keep or replace. To keep you need to get a blade between the flange and hull and then as far as possible around the thread from above. Keep pushing and it will loosen. Sometimes a very small drill can help if there is clearance.
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I agree. With patience and perseverance I’ve always managed to remove fittings stuck down or sealed with Sika flex.
 
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