Marine Caulking~ Which One Do I Use? 

Used 5200 to seal a jackplate on a high performance hull. Fanatically cleaned gel coat and aluminum, applied a 5/16" bead upon initial installation. A 400lbs engine and a 9" jackplate, the 5200 easily supported the engine with all the bolts removed two years later upon removal. With a hoist, we could lift the 550lbs hull & single axle trailer off the ground on the 5200 bond alone. It's bad serious stuff, so as he said, consider it permanent.

thank you so much for this video brother! I'm working on a 1644 jon boat and wasn't sure about 5200 to help seal rivets...but now I know it will do the job.

Thanks so much for making this video - very well explained. I'm refurbishing a camper high top on an old ford and I need to seal some gaps where a gasket seal or a butyl tape had been. Someone recommended the 3M 4200 to me among various other products but I was a little clueless on the difference in the varieties of sealants, adhesives, silicones, bedding and glazing compounds. So, after watching your video I think the 4000 may be my best bet as it waterproofs well but it doesn't adhere so strongly that it'd be an inconvenience to remove for repair or what have you. P.S. The first person I asked about my project recommended silicone! I'm so glad I didn't take his word for it - now I know silicone's proper application and all the difficulties that go along with it's removal. Thanks!

Thank you for taking the time to clarify the use of these sealants. Very nice shop!

A big thank you for your awesome video.. very well explained. Definitely picking up 3M 4000UV. Have a great summer!

Another great vid Andy, thanks for the info! We're looking for below the best below the waterline bedding/sealant for our (weird) rudder. Thought 5200 would be the play, but now, thanks to you - planning on 4200 👌

Always very instructive videos. Thank you for posting and keep em coming! I use Sikaflex which I have found works well. I think most boat restorers use Sikaflex in Italy and Europe. Greetings from Jens in Italy.

Good advice Andy - great quality video and sound.

I worked for Ericson Yachts for 16 years. We had problems with leaks and tried using 5200 urethane compound, along with some others. The 5200 was a big problem as when a hardware change came through we could not get the part off of the glass without tearing the fiberglass of the hull or deck. The exception would be a hull to deck joint. I would not use it for a bolt on keel as there are cases when keels need to be removed, such as damage or design change. The bedding compound we found was a polysulfide compound such as Life Caulk by BoatLife or others. It makes an excellent long lasting waterproof joint that remains flexible and it can be removed without damaging the boat.

Excellent presentation! well explained and well recorded and very informative.

Thankyou, you just answered my question, the 5200 to re attach the top half of my hydrocycle to the bottom half. I don’t see it needing to be apart ever again after I fix things...

I'm gonna share my secret weapon for removal of deck fittings which are bedded in with 3m 5200. "Steel guitar string". Use the thinnest steel string, (.006"), wrap the ends around two 1 inch diameter wooden dowels for handles. Remove the hardware from the cleat or whatever, and pull the string forcefully between the cleat and the gelcoat. It will part the 5200 like a cheese slicer. No damage. Try it and share with your viewers!

I'm coming rather late to your site but am finding it very helpful. I totally agree with your choice of sealing/bedding materials but have one observation about silicone removal: I believe 3M or some other company makes a softener chemical which greatly facilites the removal of silicone products. Best regards and, obviously, keep up the excellent work.

Excellent information and presentation. Thank you Sir!

We have a small motorhome that I would like to keep in good shape. Winnebago provides a list of the ceiling stay use but they aren’t lasting long and might not be the best choices. I’m assuming that since most of the surfaces are plastic you would recommend the Dow Corning silicone sealer for that and perhaps only use the 3M 4000 as a bed and compound that gets capped with another sealant. There’s another sealant called Geo cell that’s very popular but it seems to have some problems with remaining tacky and attracting dirt. Thanks for the great video, it’s really helpful!

That being said because they are mechanically fastened really any of the compounds I mentioned (other than the silicone) would be a great choice!

Those kind of windows can be a little tricky to seal as there is actually 2 things that need to be addressed. The glass onto the boat then the frames onto the glass. First I would try to use the Dow Corning silicone from my video and glaze around the outside edge of the frames as well as the inside edge where the frame meets the glass. Tape off all edges leaving an 1/8" reveal on each side apply a bead of caulking and smooth over with your finger then pull the tape right away.

Thank you for the information ;). I'm looking to re-bed my deck and transom hardware as well as my rub-rail. I think I'm going to go with the 4000 UV for the deck and transom hardware as it will be semi-exposed to UV. I'm probably going to use the 4200 for the rub-rail because it's not exposed to UV and I would still probably want to be able to remove it to re-do it at some point in the future.

Andy, I already have the frame out and the glass out of frame also, so I will be starting from square one. I need to clean up glass and frame, which is wood. After that, ready to put back together. Thanks

There are a couple of different styles of chainplates; some are for the stays which can be thru-bolted on the hull and the other is for the shrouds which usually are bolted onto an interior bulkhead. There are other ways that this is done, but generally I think that 5200 would be a good use for this as they are something that isn't removed very often (and a little extra bonding strength certainly isn't going to hurt :-) Hope this helps! ~Andy

I really like your videos! What would you recommend to seal tempered glass to the wood frame, these are large windows aprox. 28x40 in the front of the cabin on my Hardin 44 , the glass sets into the frame from the inside and then a wood trim frame is installed around the perimeter of the glass to hold it in. I think I need something that can adhere to the glass but also seal it in, hoping to stay away from silicone due to the clean up factor.The glass is exposed to sunlight most of the time.Thank you!

I found rain gutter silicone to be easy to work with and durable. I used it to seal the rub rail. There is something that sticks to silicon and that is dust, which is the downside to this product.

Great video but I am a little confused I'm going to install a transducer on the back of my boat which will be below the waterline I am not sure which product to use do I just seal around the transducer or do I dip the screws in it also

Great job. Cleared up a bunch for me. Thanks.

Iam confused , cool kind a got it going to be doing hatches n hardware n up grading n got so many more questions as they pop up cool thxs , Scott

Great channel. Thanks for all the great videos ! I am a new boater. Just bought my first older fiberglass boat. There are holes in the transom from a sounder as well as bracket mount (through the transom) . Which sealant would you recommend? Sikaflix? 3m 4200 ? I may need to remove bracket later so would not use 5200. Thank again ....bell rung !

Either one of those would work equally as well. One other suggestion I would offer might be to use one of the Dow Corning Silicones (795 or 791) as you can get those in colors that may match up better to the car :-)

Thank you. Nicely done, as always. But why no mention of butyl tape as a bedding compound for deck hardware? Doesn’t it far exceed the 10-year service life you mentioned for the 3M products?

Hi BWT, first of all congrats for your work! For the last eight years I've been rebuilding an old and initially destroyed 32' sailboat. Unfortunately, I'm in Brazil and we don't find all those incredible things you get in the US. My question is: would Sika 291 work as well as the 3M 4000 UV for resealing my toe rail? Thanks a lot, man!

I just replaced the portlights on my Santana 2023 using the Dow Corning 795. Great suggestion. The smoked Lexan look great with the black 795, Messy but worth the extra effort and time. However, what would be wrong with using Butyl to bed down deck fittings as opposed to 4200? Thanks for your tutorials!!

I always walk away with something useful watching your channel. I can't say that about all channels I watch. Thanks.

I greatly appreciate the class on compounds, especially as I prepare to put 12 plastic portlights back into my boat. I don't understand, however, what you meant about using both silicone and a bedding compound when doing portlights. Not sure how you can use both? Do you mean only using silicone when applying the plastic trim ring to the plastic port frame?

what would work best for stopping the leak along the bow seams on my aluminum Jon boat. there is a keel cap along the middle about 1 1/4 inch wide with a seam along each side of it about 4 ft long. This is a welded modified-V Jon boat with 0.10" thick aluminum. apparently some of the bow's welds or aluminum cracked. The inside of the boat bow is covered with foam encased in aluminum, or I would weld the cracks.

Hi great interesting video, I need a bit help cause i been trying to watch a couple of videos to reinstall the centre window on a Stadline 38. The boat hull is steel. All painted by hampel paints 2 packs. I changed the centre window about 2 years ago. The window is made of perspex. First time i did it with car windscreen sealer and second with wurth product. So summary Need to install a perspex window to a steel frame. Whats best to use. Locally I can only find Dow 791. Watched also your other video where you install the hatch using Dow 795 for the perspex and 4000UV for the frame. The only thing is mine do not have a frame.

Ok, still confused on an application. I'm re doing a Mako 210 fuel tank. What do you suggest I use to reattach coffin cover to deck? 4ooo first then set in cover screws then 4000 uv?

3M seems to be the common sensical approach to caulking, but I was told that some people in Northern Europe caulk folk boats using rotted tree trunk gunk produced from the oak tree. The idea is to intentionally rot a tree trunk in a riverbed nearby for I'm guessing here, 1 year??? and use the rotted core of the tree trunk to produce some kind of black material used to caulk the boat. I'm wondering if it can be combined with other material to produce a really decent caulking material.

Hi great video. Hey i plan to attach the water drain plug housing(In side the boat just below the bottom of the transom of my rib fibreglass boat.Do i use silicon base or 4000 or 5200 as this is going to be a permanent fitting. Thanks and looking forward to your knowledgeable reply.

I want to adhere polycarbonate to gelcoat or fiberglass resin, silicones only? Thanks for your comments Andy?👍🏻

Hi Andy, great stuff as usual. Would 4000 uv be appropriate to use for wood deck seams? Fir deck beams, and be nice if they would stop leaking.

what would you use to fill the pre-existing holes of a rub rail? Also, what would you use to seal the gap between the molds of the hull under the rub rail?

Tough question. I have an inflatable boat all shot out but it still has a few seasons left in it. The cone area in the back the fabric is showing. What’s a good solid sealant that’ll not be sticky when dried but flexible when folded. Thank you.

I have sheets of 3/4" thick Polly. I am wanting to use strips of it as chine guards on the bottom of my fiberglass covered wood Dory. What type of glue/ sealer would you recommend?

thanks for the info. very helpful.

Hi, I just purchase a cat and for transport the removed the windscreen that was attached with screws and black silicone I have managed to remove it all from the glass console and aluminum windscreen frame from what i read here on all different situation advice I'm guess to say that using 4000UV will be correct? Loving the videos it will help a lot now that I own a glass Cat power boat.

I know this might a be about of topic but since ya know so much about sealants and adhesives, could ya help me figure out what would work best to reahear the sole to a boot or shoe? I know it's not boat related, but it needs to be flexible, and be able to stick to rubber.

Very nice video and despite listening to everything about silicone I’m still tempted to use it to fill a small very thin bead along the bottom of my consul because the 4000 UV deteriorated started to crack out and the silicone comes in a gray that matches my consul in my floor gelcoat instead of a bright white I’ll be at Thinline. Any reason I should do this on a bay boat and what about the mildew resistant characteristics of Dowell 795. Thank you

Hello Andy, I just used a 5200 to reseal the connection of the keel and the hull on the sailing boat, but after a short time a lot of bubbles appeared underneath the sealant! What could be the problem? It was sanded nicely and cleaned with acetone before 5200 was applied!

If that doesn't take care of it then you'll need to do a full blown re-seal where you remove the frame and glass and start from square 1. If you end up having to go this route please let me know and I'll give some more detail on this process :-) Good luck!

Thanks for the info Andy. Very helpful, as always. Do you have any experience with butyl rubber for deck hardware, something that stays playable and does not harden or crack?

Which sealant would be best to seal a toe rail to the deck and all other areas of wood to fiberglass? Thanks

Your videos are GREAT! you explain things so well, I am pretty confident I will be able to fix a couple soft spots on my deck this coming spring. I was looking into removing my bow pulpit to get it re-welded and noticed I am getting a lot of leakage at the trough bolts so I will need to start removing things and re bedding them. Im sure it is WAY over due. I plan on using the 3M 4000 UV, but I wanted to know your opinion on butyl tape? thank you again for your videos!

What would you use to place perspex direct without a frame? I am tired of leaking portholes and converting to cut perspex portlights. No frames. Steel hul with epoxy paint.

I'm new to your channel and new to boat ownership. I just bought a 42ft Californian LRC. Basically all the windows need resealed and the fly ridge deck is a little flexible. Any advice you can give us? Thanks 😊

I have an old Coleman pro XL. It is a small pond boat and it has a black rubber or vinyl ‘ring’ around the boat holding the two pieces of the boat together. It is only stapled in which does not help with water getting INSIDE the pontoon part of the boat. I went to bass pro years ago and got some $$$ stuff and it worked GREAT. Don’t remember what it was though. I’m going to try the Dow Corning 791to try to seal that piece. The stuff I got from bass pro is still on there and holding up VERY GOOD but I still need to do the bottom of that ring. What do you recommend?? I used some of the lower grade silicone and now I have to remove and go with something better. Probably something these guys recommend.

Hi Andy, what do you use to clean up silicone from fibreglass and plastic windows? Are you sanding to clean off all the silicone or using a solvent and if a solvent, then what?

hi thx for sharing the info, what would be best for an underwater metal and plastic bond?

As a brand new sailboat owner, love this channel. So do you prefer the 3M bedding compound over butyl tape for hardware, etc. on the deck? I've had a lot of sailors recommending the tape so just curious your thoughts. Thanks again!

1 quick Q; was the glass originally mounted with a type of caulking, something that appeared to be a type of tape or was there some hard / brittle residue left behind on the perimeter of the glass? There are a few different ways these portlights were mounted. Once I know I'll be able to point you in the right direction :-) If it would be possible a quick pic can be sent to my email address. Visit my website About Us --> How To Reach Us :-) Thanks!

I cannot use screws or bolts to mount devices. Need a spacer I can use screws on. Looking for what of bonding sealant? To use? Questions if I may #1 sail boat interior above water line. I need to mount 4x4 inch squares of wood 1x4 pressure treated wood.(if this is exceptable to use) to mount a battery switch or terminal bars. In one case it would Be wood to wood in another case it would be wood to fiberglass. I need the wood block to use screws to hold device on. Or should I do it another way with other than wood. Thank you Mike

Question I have a seam that is filled with Sikaflex now and needs to be pulled out and replaced. What product is best it has to be water tight.

I'm not bedding hardware I'm not putting in polycarbonate. I need to reseal my center console to deck. It was holding my console well with 90% of the screws loose. It appears silicone was used in the past since the remaining product is kinda rubbery and I was able to knife through it quite easily to split the seal. It was holding a lot of force while crashing through the waves. What do you use for this? I will be reinforcing the deck holes and re pilot drilling so the screws and washers get a bite I will also try to through-bolt where I can.

Hey great video. I have a question I was wondering how to get a smooth finish on chop strand

Thanks for this great video!

Just curious your thoughts on the following boat subfloor installation. Looks like a disaster waiting to happen. Thanks!

Love the videos, you clearly put a lot into them - lucky for us! We get a lot out of them. I have a question about caulk. Problem description: I have a catamaran and she is flexible (built that way on purpose). There is a joint between the 'hard bimini' and the coach roof that is about 1/2" wide. The boat came with some horrible caulk that took me forever to remove. I filled it with... 4000? I think. It is pulled away from both sides of the joint and has gotten pretty hard (probably why it pulled apart). Is there something you recommend for filling large joints that will remain flexible in the face of large moving pieces of fiberglass. I do not want to overstate the case, it doesn't flex massively, or even noticeably, but this is a 'lightly built' cat. I understand if you haven't the time for this, but I though I'd take the chance! Thanks again for the videos!

Which 3M product is most similar to Sixaflex 291, and what do you think of the Sixaflex product?

Which compound would you recommend for a drain plug and thur haul drains?

What caulking (white) would you use on a mahogany deck of a Chris Craft type runabout? Thanks

Great video, thanks.

Hi there- thanks for the great video. So I have flush mount deck lights (plexiglass) NOT in a frame, bedded to the deck. As per your video, I'm confused if I should use the bedding (for sealing) or the silicone (for adhering to Plexiglass)? Advice would be appreciated! cheers

Love the guitar intro 🎸

Hi I have a project to reseal a Bomar plastic glass hatch to a metal frame. What would be the proper sealing material to use?

Thanks for the info. What would you recommend for sealing old transducer screw holes that dont go all the way through the transom. It is a 1990 Seaswirl Cuddy

Question here. Why do they use Dow 795 on glass buildings if it's mostly good for plastics and not so uv resistant?

I have a 2006 Sea Pro Walk Around. The Dash plate looks plastic mating to Fiberglass. It is leaking. I need to reseal. Which should I use for this application?

What to use to deal Andersen or Ronstan Bailey's. In other words can I make the gasket from a dealer ? Which one and how to adhere it to stainless steel. It open s to underwater.

3M 4200 may be great, but once opened it cures in the tube in 24 hrs! A pretty major limitation, at least for me who don't do this professionally, just fixing minor things on my boat. Is 4000UV the same?

Nice video. Good info. Thanks

What can I use to remove silicone so I can apply a butyl or a 3M product. How about acetone?

Anybody know the best sealant to apply underwater in the ocean on a boat hull??? I'm currently in Jupiter Florida and got a free 35 ft sailboat I'm just trying to temporarily stop the leak. It's in the hull and I'm looking for a product that maybe someone's use and had success with to dive down and apply under the salt water just to stop the leak temporarily at least or longer term. What would adhere best? The water is dirty as it's in the intercoastal in Jupiter Florida so it's a lot of river water that is about to meet the ocean

Andy, I am redoing a old Carver 2885, It has wood frames around front windows, what would you suggest to use rebedding them? Thanks, enjoy your videos.

I am re-bedding the 3 front windows in my salon on a 35' flybridge. It looks like I'll need to re-bed the tempered glass panels into the frames which I believe are plastic, and then re-bed that entire assembly into the actual boat. Do you recommend silcone from glass to frame, and bedding compound from frame to boat? Both products need to be black in color. I know in the video you discussed using silicone with Lexan but with the glass panels I wasn't sure. Thanks!

what do u recommend for sealing a residential rain gutter ?

What would you use to install a leaning post at a helm

I have a couple of small spots that I need to fix on the bottom side of my boat, I was not looking to repair the fiberglass just cover it with one of the adhesives that you mention in your video. The scuffs are through the gel coat but not the fiberglass. Would using the 5200 work for this application? In the future, I will be getting the bottom re-gel coated but not for some time to come. I was just looking for something that I could cover the scuffs with that would protect the fiberglass and not come off when in the water. Thanks, RG

I love your video! Your the 🐐

Adding wheels to a inflatable boat, if the transom is plastic with metal bolts. What do you use? How about wood transom to metal bolts? Mostly used in freshwater but some saltwater as well.

Silicone for all plastics, or just polycarbonates? I need to repair a sailing dinghy mast that breaks down into three pieces for transport. At the end of each section are black plastic fittings that need replacement. Someone suggested adhesive instead of the original aluminum rivets. The point is to seal it for buoyancy and corrosion protection. I presume they are ABS. I'll try to confirm. Can I use the 4000 UV for that, or is it silicone for all plastics? Thanks for the videos!!

Any idea how to protect exposed silicone seams from weather/uv?

Which would be best to use on the rub-rail?

Andy, on a bronze through hull fitting you would use 3 M 4000 instead of 5200? Good information video. Thanks!

Thanks for sharing

And what about Urethan's, Polymers, Hybrid Polymers, Co-Polymers & Terpolymer's like NPC Solar Seal #900, ChemLink NovaLink, TiteBond Ultimate MP, CP1, Geocel 2300, MasterSeal NP1, SikaFlex & Lexel?

I just thought I'd let you know that boat is beautiful and I have close connections with Kid Rock and he would love that boat! He takes me out in his wood boat that says cowboy on the back!

How do you feel about using Butle tape for bedding hardware?

Hate to say it but probably won't have the opportunity. I don't work much on alum boats (other than painting). But one suggestion I do have for resealing is to look at a product called Gluvit. Sealing seams and rivets is pretty much what this stuff is used for (5200/4200 probably would not be the best choice). There's lots of info on this product, a quick Google search will have you reading for hours :-)

You didn't give any differences between the 4200 and the 4000 UV, yet you prefer the 4000 UV, is there a difference? On a wood boat I want a watertight seal where the garboard plank meets the keel, but have to always consider having to remove that plank in the future. Which is better to use, 4200 or 4000 UV?

What a good info thanks!

Should I use 4000 to caulk between hull and flybridge.

What can I use to repair the bottom front edge of the keel?