Bedding UHMW Keel Strip?

[Joel]

I have the bottom of my weekender painted. Before I flip it back over I am going to put a UHMW shoe on the keel. Is a bedding compound necessary between the keel and the UHMW? I was going to use 4200 but, now I am wondering if there is really any reason to do this. The strip will be mounted with countersunk #10 flat head screws into oversized holes filled with an epoxy/silica mix. The epoxy plugs were drilled and tapped to accept the machine screw threads. On the sample pieces I made up the screws hold very tightly.  There are some 1/8" gaps between the UHMW and the keel in a few places

Thanks,

joel

[Andrew_Butchart]

Even a hairline joint would allow water to get between the keel and your strip, possibly causing hidden rot or other problems so I would suggest some sort of bedding compound.

For me, (I'm cheap) I used roof patch compound to bed the steel strip I put on my keel.  After a year sitting in my garage I've had no problems 

When I paint the bottom (hopefully very soon), I'm just going to slather paint over everything.

[Joel]

For me, (I'm cheap) I used roof patch compound to bed the steel strip I put on my keel.  After a year sitting in my garage I've had no problems

Well Andrew, The very thing that raised this question was the price of the 4200.  The other bedding compound I was considering was Dolfinite. I dont know if it's appropriate for this application. 

I have a book "Buehlers Backyard Boatbuilding"  His methods also lean toward the cheap frugal side. He likes roofing tar as a bedding compound but warns it will bleed through anything you try to cover it with.

joel

[Hirilonde]

Nothing will stick to UHMW plastics well or for a prolonged period.  That is why they work well as bushing material.  That they are so resilient is why they work well as a chafe strip.  I'm not sure any bedding will keep water from getting between the strip and your keel.  It may work to use a material that will stick to the paint of your keel and solidify enough to create a gasket which will protect your keel from having its paint removed by your chafe strip.  I would think you would still get some algae growth behind the chafe strip if the boat stayed in the water for a prolonged period.  I would try 3M 101 or Sikaflex 291.  Both will stick well to paint and form an elastic gasket that will offer some protection.

[Charlie Jones]

an interesting question might now be- "what will STICK to UHMV?" 

[Joel]

From what I have read there are no adhesives or sealants that will stick to UHMW. As Hirilond

[Andrew_Butchart]

I have a book "Buehlers Backyard Boatbuilding"  His methods also lean toward the cheap frugal side. He likes roofing tar as a bedding compound but warns it will bleed through anything you try to cover it with.

joel

I'll have to get that book one of these days.  As far as the tar bleeding through the pain, it's on the "fish side" and I'm sure they won't care  ;D  Mind you, I've got the strip covering the entire keel ... I may have to consider painting that part of the keel brown.

[lewisboats]

Has anyone ever tried what they call "Pipe Dope" as a bedding compound? The stuff we use at work (a meat packing plant)...Rector Seal...seems to be able to withstand everything that Cleanup can throw at it (various acids, detergents, High pressure 140 degree water, even steam heated 190 degree water) each and every night. It stays flexible forever but doesn't rub or wash off. I've taken apart pipes that are 15 years old that still have the dope in the threads...and no rust on the protected threads.

Steve

[Joel]

Steve , We also used Rector Seal where I worked. It's basically a teflon pipe dope. You can use it on any kind of threads even PVC. The stuff I am familiar  with is kind of thin and is applied with a brush. I dont think it would work well for bedding. The same company also makes another product called Duct Seal. We used it to seal the ends of electrical conduit to prevent moisture from getting in. It looks like plumbers putty and would probably work Ok. It is not very cheap though.   

 

I bought 2 tubes of 3M 101 yesterday and will try it out today. I am hoping to get by with one tube and return the other one. I did find some caulking at Ace hardware that I like. Its called Lexel. It's a solvent based butyl rubber sealant that is very elastic. They have some data on their website about the "peal adhesion" on different surfaces. It sound pretty good. The price is about $4.00 / 10oz tube. 

 

Here is a link to the Lexel data sheet: 

http://www.sashcosealants.com/home_improvement/pdffiles/lexel_brochure.pdf 

Andrew, You would like George Buehlers book. He  builds in the "workboat" style, likes locally available lumberyard materials, oil based house paint, galvanized rigging, and concrete ballast. My kind of guy There are a lot of pictures and drawings showing some methods

joel

[Frank Hagan]

Steve , We also used Rector Seal where I worked. It's basically a teflon pipe dope. You can use it on any kind of threads even PVC. The stuff I am familiar  with is kind of thin and is applied with a brush. I dont think it would work well for bedding. The same company also makes another product called Duct Seal. We used it to seal the ends of electrical conduit to prevent moisture from getting in. It looks like plumbers putty and would probably work Ok. It is not very cheap though.   

RectorSeal makes quite a few pipe dopes and joint compounds.  "RectorSeal No. 5" is the gold colored pipe dope and I think what Steve was referring to.  It has an oil base and retains its pliability for quite a while ... years, even.  It is really only for metal pipe though, as it will release stress cracking in ABS plastics pretty quickly (ABS is widely used for things like hatches, cowl vents, etc., on boats).  I don't think it would harm the UHMW plastic, but I couldn't be sure without asking the company about it.  I would opt for another compound, but I'm gun shy about RectorSeal No. 5 due to working in an industry with dozens of ABS products that were destroyed by it.

[PAR]

Nothing really sticks to these dense polyethylene products. Polysulfide (3M 101 or similar) will form a nice gasket, remain flexible and tolerate continuous submersion. The polysulfides are more sealant with less focus on adhesive qualities, where as the polyurethanes (3M 5200, 4200, etc.) are more adhesive in nature with excellent sealant properties. Since nothing really sticks to the stuff, you'll want a sealant and must rely on the fasteners to hold the strip in place.

Even though you've "bonded" the fastener holes (a very good idea on all under LWL holes), moisture can still find a way (it always seems) to get at your keel.

Dolfinite, is a pure bedding compound (sealant only) with no adhesive qualities. It too could be used, but isn't as easy to apply as a tube of goo in a caulking gun. It also doesn't accept paint, so you'll have a seam. The polysulfide and polyurethanes will accept paint, forming even more of a barrier to stave of moisture ingress.

[Joel]

I went ahead and used the 101. Just needed one tube so I guess the cost is not too bad. It does take a long time to dry. I put it on on 07/06. I did not tighten the screws all the way because I didn't want to squeeze all the sealant out of the joint. I was going to tighten the screws yesterday but the 101 is still quite liquid. It said 2-3 weeks cure time on the tube. I guess they meant it

[Hirilonde]

Its a catch-22 concerning when and how much to tighten the screws.  If you wait until the 101 cures you will break the tack of the caulking to the screws during tightening and even though you have a nice gasket water will be much more likely to penetrate into the wood at the screws.  I would lean towards tightening to a snug fit now and then leave it be.

[PAR]

You can speed up the cure by draping moist towels over the area. Of course, don't let them touch or it will smear the caulk and damp not dripping wet towels is all you need.