General Purpose Sealant?

[Bycrick]

I bought some Dow 795 silicone for replacing hatch plastic. There was a leftover tube. Unopened. I decided to use it to caulk around the galley sink. It took several months before it finally set up. It was only a few months past its expiration date. It’s not unusual for "professional" or "industrial" products to have a shorter shelf life than "consumer" products that might have to sit on a shelf for months.

[mikereed100]

Originally Posted by SKMT

Currently, I'm attaching angle moulding to my hardtop as a water collection lip and need to seal the edge. Also need to reseal leaky windows.

For sealing molding to your hardtop, just about anything will work. My choice would be Loctite PL S40. It is a polyurethane with similar properties to GM 5200 at a fraction of the cost. You can buy a cartridge for $6 at Home Depot and not feel bad when the leftover goes off in the tube after a month.



To reseal leaky windows my choice would be Dow 795. It is a structural silicone with good adhesion and, more importantly, 50% elongation, meaning that your windows can move a bit in their frames, as well as expand and contract with temperature change, and not break the seal. Dow 795 is a lot cheaper than Sika 295UV (another good choice) and does not require an expensive primer.


For 'general purpose' I keep a tube of Lifecaulk on the boat for sealing screws and hardware that is not mechanically fastened. For that I keep a couple rolls of butyl tape as, not only does it work great, it is easy to work with and can be kept on the shelf for years.

[CarlF]

I've been slowly moving to Dow 795 for more than window projects. No yellowing or edge peeling in full sun. Very easy to work with a finger - none of the mess of the 3M sealants (4000, 4200, 5200). Great adhesion to aluminum, fiberglass and stainless. It's deigned to hold large panes of glass in tall office buildings with no mechanical fastening. Less expensive than "marine" sealants.

Two cautions:

As mentioned, the expiration date on the tube should be taken seriously.

When joining two materials with different expansion coefficients, it's critical to not squeeze the joint too thin. For windows maintain a 1/4 thickens using foam tape or other standoff.

[coopec43]

I have a leaking deck hatch which I will have to remove and re-install. I'll probably use Sika 291.

I will clean up the hatch and deck and apply the sealant evenly over the deck and hatch. Then bolt up the hatch and tighten the bolts until some of the sealant oozes out. I will then leave the sealant to cure for say 2(?) days and then nip up the bolts (but not too tightly)

Is that the way to go?

[slug]

Originally Posted by coopec43

I have a leaking deck hatch which I will have to remove and re-install. I'll probably use Sika 291.

I will clean up the hatch and deck and apply the sealant evenly over the deck and hatch. Then bolt up the hatch and tighten the bolts until some of the sealant oozes out. I will then leave the sealant to cure for say 2(?) days and then nip up the bolts (but not too tightly)

Is that the way to go?

Don’t know your project

With lewmar hatches it’s common to use no caulking on the flange

Two rows of foam tape , one row on each side of the drilled fastener pattern , staggered joints ..are placed on the hatch flange

The hatch is then placed on deck and only the fasteners and fastener piercings in the deck are caulked with sika of other

I have seen this technique stay watertight for twenty years

This installation required no cleanup of caulk blowout and allows the hatch frame to be easily removed for future service

[slug]

Originally Posted by coopec43

I have a leaking deck hatch which I will have to remove and re-install. I'll probably use Sika 291.

I will clean up the hatch and deck and apply the sealant evenly over the deck and hatch. Then bolt up the hatch and tighten the bolts until some of the sealant oozes out. I will then leave the sealant to cure for say 2(?) days and then nip up the bolts (but not too tightly)

Is that the way to go?

Don’t know your project

With lewmar hatches it’s common to use no caulking on the flange

Two rows of foam tape , one row on each side of the drilled fastener pattern , staggered joints ..are placed on the hatch flange

The hatch is then placed on deck and only the fasteners and fastener piercings in the deck are caulked with sika of other

I have seen this technique stay watertight for twenty

This installation required no cleanup of caulk blowout and allows the hatch frame to be easily removed for future service

[thinwater]

Originally Posted by slug

Loctite is Henkel ... a huge industrial sealant company

I’m sure they have suitable products I just have never used them

3m and Sika market heavily to the marine industry so are widely available on the waterfront

Locktite Marine is carried by Home Depot. Yes, I have tested (boat and test panels) and it is on the same level as Sika and 3M... and the same price.

[coopec43]

Originally Posted by slug

Don’t know your project

With lewmar hatches it’s common to use no caulking on the flange

Two rows of foam tape , one row on each side of the drilled fastener pattern , staggered joints ..are placed on the hatch flange

The hatch is then placed on deck and only the fasteners and fastener piercings in the deck are caulked with sika of other

I have seen this technique stay watertight for twenty

This installation required no cleanup of caulk blowout and allows the hatch frame to be easily removed for future service

Still evaluating ideas. Thanks.

What do you mean by "Two rows of foam tape" Is that butyl tape or is it something different?

[mikereed100]

Originally Posted by coopec43

I have a leaking deck hatch which I will have to remove and re-install. I'll probably use Sika 291.

I will clean up the hatch and deck and apply the sealant evenly over the deck and hatch. Then bolt up the hatch and tighten the bolts until some of the sealant oozes out. I will then leave the sealant to cure for say 2(?) days and then nip up the bolts (but not too tightly)

Is that the way to go?

That used to be the common wisdom. I believe the idea was that you leave enough sealant to form a 'gasket' that you then tighten against, but I believe testing has discredited this approach. Better to just fasten tightly at the first go.

By the way, that would be an excellent application for butyl tape.

[HopCar]

I’ve been using Sudbury sealant the last few years. Good general purpose sealant that sticks to most surfaces including Starboard.

I like to keep some little 1oz tubes in my tool box. That way I don’t need to open a bigger tube that goes bad before I can use it all. If it’s a big job I just buy a bigger tube.

For real men, 5200 is available in 1oz tubes as well. Sorry guys, 5200 is only for real men. 😁

[Sand crab]

Just wanted to add that most of the marine specialty caulks are not in the caulk section at HD. They're in a different place in the paint dept. where the epoxies etc. are. And HD doesn't carry West in case you were wondering.

[slug]

Originally Posted by coopec43

Still evaluating ideas. Thanks.

What do you mean by "Two rows of foam tape" Is that butyl tape or is it something different?

That looks correct

Foam tape perhaps 15 x4 depending on your hatch
One side adhesive

Two rows of tape

Don’t tape to the extreme edge ,, leave 1 mm or so

The tape bulges slightly when compressed

The bulge poking outside the frame looks bad

I don’t know the name or tech spec for the tape because it’s typically supplied with the equipment



Remember ... the fasteners need caulking

Locate and Make the hatch stationary with 4 dry fasteners
Then Go around with the caulk gun and give a squeeze of caulk into each frame hole

Butter up the fastener with caulk and poke thru

Gently torque all fasteners to limit caulk blowout thru the counter sunk hole

Then go around again and finish torque

Be alert down below that you don’t get bog blowout on your bunk