A little caulk help please!

Discussion in 'Materials' started by Customride, May 30, 2008.

  1. Customride
    Joined: May 2008
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    Customride jtrutkus@mns.com

    I am building a 17 foot twin cockpit runabout. Where I’m stuck is caulking the decking. It is Mahogany planked that I have stained and have eight coats of varnish on it. Now I started to caulk it and two things are happening. The first thing is it is shrinking a lot and second is when I pull the tape off (caulk is Still soft) it is leaving little peeks and its rough. How do you get those beautiful y smooth white caulk line without messing up that nice varnish job??????
    What type of caulk works the best and how do I do it?

    Todd pic's 036.JPG

    Todd pic's 037.JPG
  2. DanishBagger
    Joined: Feb 2006
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    DanishBagger Never Again

    Listen, someone who knows will likely answer you when they have the time and if they feel like it. It's no use spamming all over the forums – on the contrary it might prove counterproductive.

    Edit: What's worse is that your four threads are withing a time span of three and a half hours. Sheesh! You expect people to come running whenever you need some help?
  3. Gypsie
    Joined: Apr 2005
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    Gypsie Randall Future by Design

  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Two part polysulfide is far better than any single part goo, including the DeckTec 100 stuff listed, which they don't really describe in their tech sheet. I suspect it's a single part polyurethane or polysulfide, which they could easily say without jeopardizing their patent, but instead they refer to previous formulations of other polymers, with no mention of it's basic components.

    Polysulfide (two part) is the hands down preferred deck seam caulking.

    I've elected to stay out of the discussion until now, as I fear you may be in for a disappointing day.

    Typically the deck is caulked to raw wood or sometimes (depending on wood species and caulk used) to a primed groove. This permits the wood to move as moisture content changes, but it (the caulk) remains attached, preventing moisture ingress. After the seams are goo'd up, the whole deck is sanded clean and finished to desired result.

    Now you have a finished deck and are about to apply caulk to the finish, which relies solely on the varnish's ability to stick to wood to keep moisture out. Do you see the rub? A good quality varnish will resist about 70 - 74% of moisture vapor transmission (what causes wood to swell and contract) and it's also preventing the caulk from getting a good grip on the wood, forming the flexible seal it's intended to provide.

    Lightly sand the deck surface to remove a couple of coats of varnish and add some "tooth" to the surface. Clean out the seams and use a two part polysulfide such as BoatLife "Life-Calk Deck Seam Sealant" type P #1046 (quart). On mahogany you can use it straight, but on oily woods such as teak or pitch pine, then use BoatLife "Life-Calk Primer" #1059.

    You'll have to wait some time to let this stuff cure good, or the sanding will smear around a bunch of yet cured caulk. I usually wait a few weeks.
  5. Gypsie
    Joined: Apr 2005
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    Gypsie Randall Future by Design

    Par you had better get your facts right before condemning a recommended product, can you come up with a tech sheet for your "two part polysulfide" equal to the MSP 100?
  6. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member


    I would suggest that PAR is writing from years long experience, how long have you used MSP100 or any other of the Fixtech products?

    He is certainly correct as a general statement, two pack is superior to single pack.

    I too have used the Fixtech products (5 minutes ago in fact), and really like them, but here we are not product loyal in general discussions, many people swear by Sika, many people also swear at Sika, your product is in the "same boat".......to us workinh with the ****, it is all irrelevant, we are only interested in results, and the two packs have proven their substance for many years.
    1 person likes this.

  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Gypsie, I usually verify my facts when necessary and I wasn't condemning any particular product, but merely stating a well understood reality. I was a little miffed with FiXTech's product technical information, which lists the material as a similar version of a previously produced polymer. This is overly protective and vague (of the manufacture), especially considering the sensitivity of long chain polymer molecules to moderate chemical changes (as if someone would use a tech sheet to duplicate this material). This same trend also appears in there other product's tech sheets, suggesting their legal department has handed down an edict.

    These single part (I'm assuming is it's a polysulfide, judging by it's physical properties) caulks are have other "habits" that should be taken into consideration as well, the biggest is the length of full cure which can be over a month in reasonable weather, longer in poor.

    If I've insulted your favorite goo Gypsie, then take heart that it wasn't an intentional act on my part. On the other hand I don't see anything in my previous post that suggests I was. Hopefully this was nothing more then misinterpreted syntax.
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