Sikaflex will not set!

[antaris]

We caulked a 10m long boat's hull-top seam with Sikaflex 291i... which does not seem to want to set...it is still sticky, 3 weeks later after some proper exposute to sun/dry weather....

Anyone else had this? Any cures? removing it all is a really messy job!

 

[coopec]

What temperatures do you have in the UK at this time of the year?

" On average in late March until April, expect daytime temperatures to range from 12 to 16 C (44 to 61 F). And expect temperatures to be around 5 to 7 C (41 to 45 F) at night. The record daytime temperature in March is "

Looking at the technical data sheet you should only apply it when the temp is 10C-40C

Does your wife/girlfriend have a hair dryer?

 

[prv]

What temperatures do you have in the UK at this time of the year?

Highly variable - I had my t-shirt off while sanding the binnacle a couple of weeks ago, now it's back to padded-overshirt territory.

That said, I've never experienced sikaflex not setting after such a long time, even in the depths of winter. I can only assume it's a faulty batch?

Pete

 

[antaris]

Cheers Coopec, we're in Greece!

The temperature is consistently above 10 degrees and the day applied it was at least 17-19...

you reckon that a bit of heat will do? Or will it go totally liquid?

 

[knuterikt]

We caulked a 10m long boat's hull-top seam with Sikaflex 291i... which does not seem to want to set...it is still sticky, 3 weeks later after some proper exposute to sun/dry weather....

Anyone else had this? Any cures? removing it all is a really messy job!

From http://www.uksealants.co.uk/downloads/Sika-291-Technical-Data-Sheet.pdf

Cure mechanism Humidity-curing
Application temperature product 40°F - 105°F (5°C - 40°C)
Tack free time 60 min

For cold-weather application, store units
at approximately 70F (20C); remove just prior to using.



Limitations
- Do not apply on frozen surface or through standing water

So dry weather is not a good thing.
What effect direct sunlight will have I don't know.

Maybe you should contact Sika for advice?

 

[coopec]

Cheers Coopec, we're in Greece!

The temperature is consistently above 10 degrees and the day applied it was at least 17-19...

you reckon that a bit of heat will do? Or will it go totally liquid?

Half your luck!!

Must be as prv says, a faulty batch. (Maybe I should read the post before I reply to it!!:apologetic

 

[prv]

I missed the Greece part. Sikaflex and similar goops are cured by absorbing moisture from the air. No problem in a UK winter, but how dry is it out in Greece?

Still, three weeks ought to be long enough to absorb enough water even from seriously dry air...

Pete

 

[knuterikt]

Cheers Coopec, we're in Greece!

The temperature is consistently above 10 degrees and the day applied it was at least 17-19...

you reckon that a bit of heat will do? Or will it go totally liquid?

Sikaflex 291i does cure by heat but by absorbing humidity from the air.
Is it exposed to direct sunlight?

 

[vyv_cox]

I have used Sikaflex 291 and PU40 many times in Greece, including at the height of summer with temperatures more than ten degrees higher than they are now. Never had any that failed to set, so I suspect the faulty batch theory to be correct.

 

[antaris]

Cheers guys... bummer!

will test water and haidryer and any combination of both (sounds dangerous). Otherwise, we'll have to spend 2 days cleaning the seam, aaargh!

 

[Bertramdriver]

It is generally believed that several years ago Sikaflex changed their formulation for 291. On the island there have been many, many instances of sikaflex being used and not setting, including a German boat which had all of its skin fittings replaced and then almost sinking as the sikaflex failed. I used it to seal a transducer three years ago and it has never cured. I check every time the boat comes out and it's always gooey and loose, but the seal has held. Now I never use it.
Sikaflex have never made any public statement (for fear of being sued, probably) but use with care and never below the waterline.

 

[coopec]

Now I never use it.
Sikaflex have never made any public statement (for fear of being sued, probably) but use with care and never below the waterline.

''

I'm reluctant to use Sikaflex as it is too permanent. I would NEVER use it above the water-line but what are a lot of people using below the waterline these days?

My B-I-L told me the other day there are different grades of Sikaflex these days.

 

[30boat]

I used white sikaflex around the inside perimeter of my forecabin hatch just to make it neater.It hasn't set in 10 years.I'm lucky I used good quality silicone sealant to bed the hatch in.It never leaked a drop.

 

[prv]

My B-I-L told me the other day there are different grades of Sikaflex these days.

There have always been different grades. The common one most of us use is 291 - a sealant with some adhesive properties. Usually on the shelf next to it is 292, an actual adhesive. There's one specifically for caulking decks. These three are the main standard ones, but I guess there may be more.

Pete

 

[prv]

It is generally believed that several years ago Sikaflex changed their formulation for 291.

They did, that's why it now has an "i" on the end.

Pete

 

[coopec]

There have always been different grades. The common one most of us use is 291 - a sealant with some adhesive properties. Usually on the shelf next to it is 292, an actual adhesive. There's one specifically for caulking decks. These three are the main standard ones, but I guess there may be more.

Pete

Pete

Thanks for that (made a note for future ref)
Cheers

 

[antaris]

oh ****, better get our scrapers out...

 

[GrahamHR]

Try spraying or painting a small section you've applied already, or on some of your batch on a solid surface, with an ammonia solution. The cure (X-linking) mechanism is normally free isocyanate + water ==> polyurea ( the "polyurethane" part of the final product is already pre polymerised in the material in the tube). The Isocyanate + water reaction in itself is pretty slow and needs catalyst to be present to have any decent rate.. The isocyanate + primary amine reaction is very fast indeed and does not need catalyst, ammonia is even more reactive with isocyanates than primary amines.

If ammonia does not result in any cure, there are no free isocyanates in there to react with water and the material will never "set"

If ammonia does result in cure, there are free isocyanates available and it will cure on reaction with absorbed water, albeit very slowly for this lot it seems. Probably due to low catalyst level, but increased acidity also retards the cure. One of the oldest used catalysts is "Dabco" ( TEDA, triethylene diamine) which used in a solution in ethylene glycol, propylene glycol or 1.4. butane diol. A GRP resin supplier might be able to supply it. Applying such a material to the surface will allow diffusion of the catalyst into the sealant and bring on cure if there is any isocyanate to react up.( catalyst levels do not need to be high and TEDA is very mobile in the polymer)

Sika probably erred on the side of caution with the catalyst level; the same catalysts catalyse the isocyanate+ isocyanate reaction, so reduce shelf life. Maybe to products for the Greek market have reduced catalyst levels, to minimise to the isocyanate+isocyanate reaction rate, as it's also temperature dependent.

 

[vyv_cox]

Sika probably erred on the side of caution with the catalyst level; the same catalysts catalyse the isocyanate+ isocyanate reaction, so reduce shelf life. Maybe to products for the Greek market have reduced catalyst levels, to minimise to the isocyanate+isocyanate reaction rate, as it's also temperature dependent.

I took mine out there from UK, not sure where it was bought. Also PU40, bought at Toolstation in Chester. Both worked perfectly. People have reported problems with the 291i version but mine were simple 291.

 

[prv]

Try spraying or painting a small section you've applied already, or on some of your batch on a solid surface, with an ammonia solution. The cure (X-linking) mechanism is normally free isocyanate + water ==> polyurea ( the "polyurethane" part of the final product is already pre polymerised in the material in the tube). The Isocyanate + water reaction in itself is pretty slow and needs catalyst to be present to have any decent rate.. The isocyanate + primary amine reaction is very fast indeed and does not need catalyst, ammonia is even more reactive with isocyanates than primary amines.

If ammonia does not result in any cure, there are no free isocyanates in there to react with water and the material will never "set"

If ammonia does result in cure, there are free isocyanates available and it will cure on reaction with absorbed water, albeit very slowly for this lot it seems. Probably due to low catalyst level, but increased acidity also retards the cure. One of the oldest used catalysts is "Dabco" ( TEDA, triethylene diamine) which used in a solution in ethylene glycol, propylene glycol or 1.4. butane diol. A GRP resin supplier might be able to supply it. Applying such a material to the surface will allow diffusion of the catalyst into the sealant and bring on cure if there is any isocyanate to react up.

Truly, the forum is an impressive fount of knowledge at times!

Pete