Sikaflex 291 won't stick to HDPE!!! Ideas?

[isuzurover]

Sealed up some butt and lap joints between wood, alum. and HDPE (all combinations of above) on the boat. After a few trips out, the Sika 291 is peeling back from the HDPE (or can be peeled away easily). All other joints are fine.

I did not use any primer.

I called Sika (WA) - who said that HDPE has a high surface energy (whichis correct), and they couldn't recommend any of their products (or primers) for the application. They called Sika head office (NSW) to double check, ... same answer...

Apart from ripping out all the HDPE and replacing it with ply, has anyone managed to either:
(a) get Sika 291 to adhere well to HDPE? (I thought of roughening the surface somehow?)
(b) used another sealant that adheres to HDPE? Sika said Dow "may" have something, but it would likely be prohibitively expensive.

[uninformed]

what is Sika 291?
what is HDPE? (high density poly????)

I know the guys that do the bathroom waterproofing need to prime any pvc for their PU's.. maybe something along these lines will do the job?

I have heard that Aluminium is very hard to get a good bond to...

[isuzurover]

what is Sika 291?
what is HDPE? (high density poly????)

I know the guys that do the bathroom waterproofing need to prime any pvc for their PU's.. maybe something along these lines will do the job?

I have heard that Aluminium is very hard to get a good bond to...

Sika 291 = Quick drying marine grade 1K Polyurethane Sealant

HDPE = High Density Poly-Ethylene.

Sika 291 sticks VERY well to ally. Most buses are held together purely with sika (aluminium panels on aluminium frames).

[uninformed]

ok, well if it were me, and having less tech knowledge than you, I would be going the waterproofing guy route, getting some primmer and doing a test piece...

but thats all I would be able to do in my shoes.

[isuzurover]

Thanks Serg - will go to bunnings and have a look.

Wish I had seen this before I bought the HDPE!
Poly Ethylene - what sticks..... [Archive] - Ausfish Australian Angling Forums

[uninformed]

not sure how good bunnings will be, they generally have a limited diy range. 99% of waterproofer's get their gear from specific suppliers.

I had a quick read of that link, a few things I have found:

roughing up the surface of PVC has no effect to help bonding of PU sika
aluminium and epoxy resin does not bond well.

[bee utey]

[ame="http://www.youtube.com/watch?v=h-9yhanz5DE"]How to repair and glue Polyethylene and Seaboard - YouTube[/ame]

[Gidget]

We use a hdpe pipe for trade waste drainage. Nothing in a plumbers tool kit will stick to it
It's not stick properties are one of the reasons we use it in trade waste drains. Grease & fat (with in reason) doesn't stick to the inside & build up.

Good luck

[Fluids]

25yrs in the pump & irrigation trade has taught me one thing .... hdpe (pipe, tanks, etc) cannot be adhered to by anything for the purposes of sealing, bonding, joining, etc ...

I've had limited short term sucess using sika type products by keying the surface quite heavily with a bastard file, coarse grit paper, etc, however the life span is quite short. The sealant eventually just peels off (like you discovered).

The only sucessful method I know of for joing hdpe is electrofusion welding ... but that is for joing hdpe to hdpe ...

[SimonM]

My mate has had good success with 3M Scotchweld DP8005 in his kayak. He says it is expensive though.