Feb 27, 2020

Marine Sealantsa selection of popular marine sealants

Over the winter, a many-thousand pound fiberglass, wood or metal shell is held in position by only a few plywood pads, or perhaps by two trailer bunks. In the spring, many of our boats are lifted by two slings into the water, putting enormous pressure on the sides of the hull, causing it to flex and shift. While in the water, the pounding of waves, straining of rigging, driving rain and UV exposure are the norm. It always amazes me how boats hold up under the abuse that we put them through.

To exacerbate the problems above, we’ve created boats about of many types of materials that have to work in concert, together: steel is bedded to wood and fiberglass, rigid porthole frames are set into flexible cabintops, plastic bushings and through-hulls are used extensively, bronze and copper are set at right angles to wood grain – and this is on top of the flexing, twisting and pushing forces that constantly work on a boat. Boat builders, shipwrights, marine techs and owners reconcile all of these contradictory actions in a number of ways – but one of the most overlooked and undervalued is the correct use of sealants. (Note: I’ll use the generic term ‘sealant’ in this article to describe the material used for bedding, bonding and sealing. Another common term is ‘caulking’, which I also tend to use interchangeably).

Hundreds of years ago, gaps in planking aboard wooden clippers were filled using cotton, hemp and tar. Over the years, we’ve made great strides in understanding how wood shrink and expands, and the best methods in compensating for these changes. The era of fiberglass, carbon fibre and Kevlar has seen a number of chemical sealants which are becoming more and more sophisticated and specialized. With the number of options available on the market, how do you decide which to use, and when?

The use of these products is based on a few factors:

The purpose of the repair: Are you bedding, sealing or bonding?

The location of the repair: is it above or below the water line? Is it in a wet or dry area?

The nature of the repair: should the sealant remain flexible, or are rigidity and strength required?

Selection ChartSelection charts and MSDS sheets are the best way to select the right sealant for the job.

Different jobs require different sealants. Lets define a few of these terms:

Bedding: the process that seals water out when installing hardware. Any time a screw or bolt goes into wood or fiberglass, it should be bedded using a sealant.

Sealing: similar to bedding, it is the layer between two parts. The seal may be flexible or rigid. This is done around hatches and portholes, but also around through-hull fittings and deck hardware. The use of a gasket material is also ‘sealing’

Bonding: adhering two parts together: gluing. Often rigidity and strength are called for.

When bedding hardware (such as putting a screw into wood or fiberglass) the purpose is two-fold: First and foremost is to prevent the intrusion of water, rotting the core of the material that the screw is entering. Secondly, it provides a buffer between the two materials as they flex and move at different rates (think of stainless steel deck hardware against fiberglass – the fiberglass will flex much more than the stainless steel).

Bedding compounds like 3M 5200, 4200, Sikaflex 291 and 292 are good choices

Sealing comes in two types: above or below the water line. Sealing is necessary in areas where solid hardware isn’t necessarily used – when installing a through-hull, or a hull-to-deck joint, or between the planks of a wooden boat. Sealing is also done around portholes and hatches.

Sealants like 3M 5200, 4200, Sikaflex 291 and 292 are great for underwater usage. For above the water (on decks) marine-grade silicone products like Butyl tape, 3M Silicone and Boatlife Life Caulk. If an epoxy is needed to combine the benefits of both bonding and sealing, West System’s G-Flex is an option

Bonding can be done above or below the waterline for scarf joints, permanently securing hardware, or as a permanent adhesive. Products like Wood glue, JB Weld, and two-part thickened epoxies (like West System’s Six10) are good choices depending on the application.

Other factors that will affect your choice of sealant are: ease of application and clean-up, price, the flexibility of the cured sealant, and its ability to be taken apart or repaired (3M 5200, as an example, is an excellent sealant both below and above the waterline, but is very difficult to remove once applied). Other factors such as colour availability, cure time, ultimate strength and price.

Taped and Beadthe work area taped off before laying down a bead of sealant during a hatch installation

In terms of application and use, here’s a few tips and tricks to make the job easier:

When sealing around exposed edges, tape is your friend. Use painter’s tape to edge off the areas that you DON’T want the sealant to end up on, but make sure to leave enough of a layer or edge for the sealant to do it’s job.

Press the sealant in place – don’t rely on a surface layer – use a rounded tool or a gloved-finger to press the sealant in any joints, spaces or gaps.

Keep nitrile gloves, garbage bags, acetone and rags handy for clean-up. I find that acetone works very well in removing caulking from fiberglass and gelcoat surfaces. Sealants tend to get into the grain of woods and can be quite difficult to remove – so cover these areas with paper and tape while working. Finally – sealants get everywhere – on clothing and skin. Wear clothes that can get messy, and cover your skin to avoid the mess.

Andrew McDonaldAndrew McDonald is the owner of Lakeside Marine Services – a boat repair/maintenance firm based in Toronto. Andrew has worked in the marine industry for 12 years and is a graduate of the Georgian College ‘Mechanical Techniques - Marine Engine Mechanic’ program.

Questions or comments for Andrew? Email him directly via: This email address is being protected from spambots. You need JavaScript enabled to view it.

Related Articles
Maintenance
  • 09 September 2020
  • By Ethan

Ask Andrew: Blowing Smoke

My Dad is not a mechanical guy. He is educated and well-read, and handy around the house – but not mechanical. When I was 12, I joined a trip to the local mechanic to get our family car...

Maintenance
  • 25 August 2020
  • By Ethan

Ask Andrew – The Bucket

I was cleaning up my workbench the other day. My eyes then scanned across my workbench and fell on ‘the bucket’. Everyone has a one. On a boat, it’s usually in a cockpit lazarette. It’s full of old...

Boat Reviews

  • Prev
The Oceanis Yacht 54, younger sister of the Oceanis 62, embodies the innovation that has always ...
Beneteau announces the launch of the latest addition to the Antares range! With a length overall of ...
I had been looking forward to a sea trial aboard the Greenline 33 because I was hoping it would ...
New at the end of 2019, the 58 Salon Express design features large windows to flood the living ...
No wonder this is one of Regal’s best-selling boats; the Regal 33 Express offers amazing ...
The newest member of Beneteau’s Gran Turismo line is the GT 36 and this yacht brings the style and ...
With a philosophy of quality and 'doing things right Ranger Tugs launches the all new R-25 at the ...
The new Beneteau Swift Trawler 41 renews the spirit of the practical seaworthy cruiser. The ...
The Canadian Yachting test crew last week had the opportunity to run the Bavaria S36 HT at St ...

CY Virtual Video Boat Tours

Virtual Boat ToursWe all love boats and nothing can break us up! So, what better way to spend our time than looking at interesting boats and going aboard in a virtual ride or tour. We have asked our friends at various dealers and manufacturers to help us assemble a one-stop online resource to experience some of the most interesting boats on the market today. Where the CY Team has done a review, we connect you to that expert viewpoint. If you can’t go boating, you can almost experience the thrill via your screen. Not quite the same, but we hope you enjoy our fine tour collection.

 

Read more about the CY Virtual Boat Tours....................

AXOPAR 37 XC

 

Axopar 37 XCWhole new ball game…

 

Set aside your assumptions and expectations for a few minutes while we try to describe the new Axopar 37 XC that made its American debut at the 2020 Miami International Boat Show. This boat represents a whole new ball game in terms of design, performance, seakeeping and functionality. In fact, I’d say it takes a ‘clean sheet of paper’ approach to boating – it’s that different.

Read More about the Axopar 37 XC..................

Destinations

  • Prev
History: right after gym and just before chemistry class. Fifty minutes of naming the prime ...
On May 19, the New York State Canal Corporation today announced an updated opening schedule for the ...
If you have four hours to enjoy a fine tour of one of Canada’s most interesting waterways (let’s ...
Boom & Batten Restaurant is suspended over the water adjacent to the Songhees Walkway and ...
Provincial Boat Havens are those special places to drop anchor in British Columbia’s West Coast and ...
NW Explorations, a Bellingham, Washington-based yacht charter, brokerage, and marine services ...

Exiting Hogs BackBy John Morris

History: right after gym and just before chemistry class. Fifty minutes of naming the prime ministers by date and looking out the window. Who knew it was actually interesting.

And in some ways it hardly matters because the Rideau Waterway is just so amazingly beautiful. Driving your boat through the locks is wonderful fun for kids of all ages (adult kids, too) and the scenery is sensational. The history is a huge bonus however, and worth understanding from both as a political lesson and from an engineering perspective.

Read more about The Rideau...........


Lifestyle

  • Prev
Schooner Cove Yacht Club through their staff Capt. and other volunteers organize cruises so members ...
With things the way they are, a whole new batch of Canadians are discovering that boating is IT! ...
Recently while admiring the boats in Victoria Harbour my eyes locked into a 58ft yacht named ...
The 38.1m / 125' motor yacht, custom built in 1930 by Boeing of Canada and last refitted ...
This interesting shot is one you will remember. It comes to POTW from our pal, photographer and ...
Unknown to us at the time, the quest for VIA-MARA started in 1973 when I saved the back cover of a ...
You will find that many of the yachts travelling up and down the BC Coast have Sea Kayaks on board. ...
The Council of British Columbia Yacht Clubs with over 50 yacht club members has become the voice of ...
Classic boat restoration expert and wooden boat builder Stan Hunter recently sent us this great ...
In Mid June, a floatplane plunged into Constance Bay on the Ottawa River after two planes collide ...

Marine Products

  • Prev
ShockAlarm is a floating, continuously monitoring alarm that protects your family and friends from ...
The Airhead Thrust is an out-of-this-world thrill ride.  Get your wetsuite out and get ready ...
Airhead Recreational Kayak is perfect for cruising boaters at anchor.  Stow it, inflate and ...
To help keep those aboard safe, critical equipment such as the compass must hold up in the rough ...
The Boating HD Marine & Lakes app from Navionics is an excellent resource to help plan your ...
Dive tanks are notoriously difficult to stow on a boat and can be outright dangerous if left ...
Waterways around the world are increasingly becoming choked with plastic trash. To stem the ...
QuenchSea is an up and coming low-cost, portable, manually-powered device that instantly turns ...
The Big Orange Original Filter is connected to the vent line leaving your boats holding tank.  ...
The Cablemaster Model CM-7 is a solid when it comes to handling and storing bulky 50 amp power ...