Sail Life - Expanding epoxy foam for the rudder, and more sanding - DIY sailboat repair 

Everyone needs a Mr. Cement Boat Guy. Once again very good presentation.

One video in the future should love you to introduce us to all these smart people you mention each week who you consult regularly between episodes .Would make a pretty dan spiffy 20 minutes meeting these experts! And a lot of fun!!

I have the highest respect for Mads and all of his projects. He's a perfectionist. In fact, he is the Yoda of boat refitting and repair. Don't believe me? Close your eyes and listen to Mads speak. He even sounds like Yoda. Help you, he will.

If you haven't already assembled the rudder you might consider having the rudder shaft magnafluxed before putting it all together. This test will be able to look inside the metal and find any stress cracks within it. It would be another safeguard of knowing that a accidental grounding didn't do any structural damage. It's a common procedure on aircraft parts and hardware. I had all my wing, and landing gear bolts checked using this procedure. Just another layer of comfort. Chances are it's 100% fine but the piece of mind is worth the testing. It doesn't cost that much to have it done. Just my 10 cents suggestion. Thanks for sharing the adventure.

You need to get the little triangle sanding attachment for your oscillating tool. It will allow you to get into those tight spaces

Twenty-five thumbs up for vids from you and also Just About Sailing vids!CHEERS from Westcoast Canada!!!

Just about sailing is a top-notch sailing DiY video channel. Keep Flying!

"The pain of sanding & fairing is temporary, a spiffy dodger is forever" . That would make a great TShirt!

When I was much younger I worked in a boat shop where the owner hand built a Flying Dutchman (21' racing sailboat) out of mahogany. It looked magnificent. He decided to add flotation by pouring pu foam under the fore deck. The stuff expanded and literally pushed the entire mahogany deck off the hull.

I think the best way to set up for a pour of expanding epoxy is to assemble the rudder in your 2 part shells and secure it all vertically how you want it to be, drill some release holes at top and pour from top and you can pour onto both sides of metal of rudder. And if you don't finish with one pour, you can mix more up and top it off later too.

To pour the rudder, I would place the stock parallel to the ground with the aft edge pointed down. Then, a few holes in the forward edge to pour into and relieve pressure. This would allow the foam to expand upward; any out ward push should be converted to upward force since the easy route for expansion until you get a lot closer to the forward edge is toward the forward edge (more open air rather than fibreglass walls). Your bonding experiment suggests that you should be able to pour in layers to avoid massive heat build up (perhaps an experiment: pour a layer, let it expand, pour another layer, let it set, check results; then a second experiment pour a layer, let it harden, pour another layer let is set, check results).

Hi Mads, For sure have the rudder blade upright for the pour and in the moulds for support, this does not mean the rudder shaft must be vertical, the shaft could be horizontal near the floor and still the blade is upright making the depth of pour less than if the shaft were vertical. Make a box to suit the orientation with enough room to install some anti-swelling braces and still have air circulate freely around the moulds so you can heat the whole insides of the box with circulated hot air later to make it set hard. For actual pouring make provision for funnel/s that remains in place until cut off later like a sand casting and for exits use the gap in the top of the mould so the level in the funnel will always exceed the level in the exits to ensure filling. Seal the bottom and ends gaps of the mould with sticking tape. Strap the mould together with ratchet straps plus the box braces. Due the low pressure of the expanding foam there may be a depth at which the foam cannot expand against its own weight, checkable, so maybe a few pours required but unlikely, especially with blade upright + shaft horizontal, this orientation is also less top heavy than with shaft vertical. If more than one pour need to know the adhesion to a previous pour, checkable, nice to know beforehand anyway in case. best of luck but seems quite straight forward, the epoxy foam is re-assuringly predictable. The steel core will act as a heat sink to prevent melt down runaway. I like the new standard of ocean stainless to be painted after passivation although perhaps overkill for the shaft unless the epoxy foam is permeable to some percent.

What you could try to fill the rudder is to get a container, (something like an empty alhambra water bottle) that could be sealed airtight at the top with a Schrader type tire valve in the sealing cap, and a hose barb fitted through the bottom. Then drill a fill hole on the bottom of the assembled rudder shell on either side of the rudder stock, and a weep hole on either side at the top, and pour the foam epoxy mixture into the container, seal it, and inject it through a hose to the bottom holes till the mixture comes out the top holes with a bicycle pump, or similar air pressure device.

I worked for Ericson Yachts (sailboat mfg) for 15 years. We used polyurethane foam for insulation for all of our iceboxes. It works great, except you have to be careful as to how you do the pour so you have room for it to expand around the FRP icebox part, which is built into the cabinet part, such that you have room for it to expand without causing cabinet bulkheads to be deformed by the expanding foam.

Pour it in with the rudder in a vehicle position and have an escape hole to allow it to flow up and out. It will not have any problem communicating through the holes and only a small area at the top that might not be perfect. If it’s horizontal could be many area not filled. When your all done you can “sound “ it and tell where the voids are.

Hi Mads, I am very impressed with that epoxy foam! Already thinking where to use it. About the dodger: most pro paintshops have a dirty little secret for pinholes: polyester fairing compound.Yes, the stuff from the hardware store. Its totally o.k. to fill pinholes above the waterline. I aplly it with a flexible steel spatula using enough pressure to leave zero exess arround the pinhole. that way there is zero sanding and its very quick+painless.

Mads, Excellent video. I loved the experiments. I am hoping that someone watching this will be inspired to start a video channel focussing only on different foam expanding tests. I'd watch that! I was told that the 'dough' in the old rudder is slate dust mixed with some sort of polyurethane resin. I tested a block of it vs. a block of the expanded epoxy foam (by immersing both in a closed box) and found that neither soaked up any water. Can't wait to see the next bit of the rudder process. Cheers, Paul

Hi Mads I coated underwater stainless on my yacht with West epoxy 105 to protect from high salt content in tropics so far 35 years and going good. I advise coated your rudder stock with same not only will,it protect from salt water ingress that you will get at some point but the foam will adhere to the expoxy coated stainless better . Also from experience of surfboard manufacturing when pouring expanding foam you will to drill holes in rudder to allow air escape as foam expands to prevent voids in foam.

Nice foaming experience. Nice to see some has the patience to perform this task👍👍

Hi Mads!. One trick concerning those pinholes on the dodger. Sometimes when only really small fixes need to be made and preferably quickly, I use 5-minute epoxy glue or even 90sec epoxy glue. Both can be thickened with fillers and usually extremely small quantity of filler is enough. These glues are of course sold in very small packages which become horrendously expensive in large quantities. From the products that I can find locally, Ive found Pacer Z-Poxy 5min glue to be "reasonably" priced 22€/236g package. So ONLY when few millilitres are needed its nice to be able to carry on with the project still on the same day. Just an idea....

Trusses, gussets or whatever they are called - it is good you welded those in. Coming together nicely

Hi Mads perhaps making something like supports on the inside of the shells to secure the rudderstock is staying centered in the molds is in order..? As it is now, the foam can push it around and the stock could end up sitting to one side inside. Also noticeable from your experiment with flow is that the void present in the sample is situated where the AIR got trapped, so keep in mind to drill/leave pinhole size holes in any corners and places where this might happen.. Could be done by simply pushing a needle/nail through the newly laid up glass you join the shells with, and removing it at the right time (when the resin is not flowing to close the gap, but also not hardened sufficiently to hold on to the nail)

Siting on the patio with a gin & tonic, and Sail Life in hand, you really got to love Sunday's. Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, SailLifeday, oh ya

I have used expanding foam like the PU you tried. My Bayliner factory foam in the Port and Starboard Stern ares was waterlogged after 30 years of service. After cutting out all the old foam and letting it dry out for a couple of days. I glassed in marine plywood to cover the access holes I made. I then drilled a couple 1" holes for expansion. I raised the bow up as high as I could get while on the trailer. Then added the foam. It was cool seeing the progress of the expansion as it flowed uphill and popped out of the holes.. A day later I trimmed the excess foam and glassed up the holes. I had never worked with foam before. I was completely satisfied with how it turned out. Getting rid of all that waterlogged foam made my boat sit level in the water and it gets up on plain so much faster. Keep up the good work. Your going to have a beautiful boat when she is done.

I'm new to your channel (As of 24 hours ago) and I am really enjoying watching what you've been doing (Up to about 10 video's watched so far). You explain things so clearly about your processes which is really refreshing. Your editing and production skills are fantastic, thanks so much for taking time sharing all your experiences. 😀🙏

You're doing the right thing by experimenting. I used to work at a place that made commercial refrigerators and I've seen expanding foam buckle 16ga stainless steel. Experiment with it until you're confident that you understand how it behaves!

somewhat extensive is a complete understatement but ok Mads long as you make it Spiffy #11!

Feel like I've just been through a physics lesson that I almost understood. You'd make a great teacher/lecturer in a different life. Thank you for taking the time to record and edit your journey it's most appreciated.

Hej Mads.. Godt arbejde som altid.. Elsker den måde du tilgår dine projekter.. Måske vi på et tidspunkt kan få rundtur på cement-båden.. kunne være cool hvis han også havde en kanal for der findes ikke så meget om cement både. Håber at alt flasker sig i den næste uge😉

Will, Mads. If next week is a "thumb twiddle week" and its warm. Why not relax and take Obelix for a spin.

I'd really like to see a water saturation test on the epoxy vs. PU. (weigh the sample, put it under water for a day/week, lift, shake, weigh again). There's a "controversy" here about PU-filled plastic (abs) boats, apparently while PU doesn't normally absorb water, many complain about them getting waterlogged..

Mads, I think you got the best solution to the rudder. Thanks for showing the foam in action, was hoping you would show the action, seems nice and easy to work with. I will put that info away for future use. It's also not likely to absorb water like PU. Rudder vertical looks like the way to fill, a couple of 12mm holes on the top one for for a fill straw hose attached to a funnel and one to let the air out. If the flow down the straw is too slow could always attach your vacuum pump the air outlet hole to speed things up. Could also consider twot fill straws -L&R. Possibly consider doing two lifts, 3/4 full and a top off of 1/4, use the first lift measurement to figure how much to add for the second lift. Stainless steel gets it's corrosion resistance from a layer of chrome oxide on the metal surface. Machining and welding disturb this coating, the material must go through a passivation process to restore the coating. This removes any residual iron (that can rust) from the surface leaving higher chrome content at the outer boundary layer and reforms the oxide. Been a while since I studied this but I believe they use a bath of Nitric acid to etch away the iron leaving the chromium. Likely the bath contains other additives like dichromates or citric acid to reform the oxide layer. Good luck with the foam pour. Please show us how that foam sands. Craig

Thanks Mads for the video. Watching the epoxy foam versus the pu foam was interesting. I have never used the expanding 2 part foams just the spray foam from cans but I would be tempted to place the rudder with the shaft at the bottom and the trailing edge at the top with holes along the trailing edge to pour in the foam from the top. The rudder stock would act as a heat sink and you could pour along both sides of the plates as Grant Myers mentions below. Looking forward to seeing how you do. Take care and have a great week.

Your joyous moment of Monday Madness is so dear to me. Thank you so much.

Enjoy learning from your comments and work experiments.

I LIKE that expanding epoxy! REALLY like how when next to a Smooth Surface, it cures nice and Smooth, also, which one would think will help it Resist Moisture. Little gussets on the rudder stock an EXCELLENT idea. I wonder how well the expanding epoxy foam Insulates against temperature and Sound.....And Do a Fire test on it, Mads, see if it's Flammable, i.e. does it Go Up like a bucketful of Gasoline, or does it just smoulder....And maybe Noxious Fumes when burning.?

Your channel is too good. I can't believe I ended up subbing to a third boat building channel.

You should have those plates shot blasted and the shaft where no bearings will be. I would add more welds with the tabs to those plates Once it's blasted you can drop the whole thing anodized. Then you can finish the rudder, all metal will degrade you can rest assured that once you encapsulate those plates unless you strike something underwater it will last just as long as a new one.

Hope this hasn’t already been covered by others comments. But I have some serious concerns about filling just one side of the rudder expecting enough material will go through your drilled holes to the other side. Yes a lot will no doubt migrate, but as the viscosity thickens, you could be left with some voids on the one side. I would try to feed both sides at once if practical. I also like the idea of keeping the rudder immersed in a sand drum to prevent bulges, as suggested by another. The problem, you just don’t know how the flow is going through those holes. It would be different if it was under vacuum and being pulled through the holes. Best...misstuffy

Thank you for another excellent video Mads. As far laying up the expanding foam, I would pour the expanding into the 1/2 of the shell, then put the rudder shaft in, then add more foam on top of the rudder shaft plates (to ensure even conformity) then bolt the other 1/2 of the rudder mold. I find that placing the mold on an angle (30º-45ºwith a hole drilled at the top allows foam to slowly fill all voids and produces an even density. I hope this makes sense and I look forward to seeing you have any new tricks :)

Dont forget your oscillating multi tool has a sanding pad too. Good luck with the hull.

Mads - what is your thinking on using epoxy for the rib strengthening in the boat? I get that epoxy is stronger than polyester, but not much stronger than vinylester. The hull would have been laid up in polyester I imagine (if it was epoxy then that is impressive - and expensive!). Epoxy is nicer to work with due to the solvents involved, but cost wise it is much more expensive than polyester. Given you are mainly relying on the increased section inertia of the new ribs by virtue of increasing wall thickness, then I reckon (as an Engineer), that the stiffness increase you will get will not be greatly different between the two resin systems. I realise you are well underway now and have the materials, but I almost always try to keep resin systems the same when I am repairing structures.

Can make a suggestion about the floor frames while you are waiting for it to be moved that you drill some weep holes in the frames and heat it to drive the moisture out of the plywwod.

I'm sure you can find an R factor for each foam, but an experiment of a small box with epoxy foam on one side and PU foam on another to see the insulating effects of both could fill a 20 minute slot if no other projects are ready for next week. I look forward to your videos each week. Thanks Mads.

Omigosh! Mads, you truly are a Mads Scientist!

Learn something every day - have had some insulation/flotation experience with expanding PU and didn't think you'd have a show with epoxy foam but super impressed with the experimental results - some new thoughts for a current DIY boat restoration. Cheers and thanks as always

I have seen some video of guys pouring PU foam between the deck and the hull of fiberglass power boats for flotation. Yes, the expansion is unbelievable ! You need very strong walls and a couple of "vents" for the foam. PU foam is the devil if you ever have to remove it.

Hi, just did a similar job with a part of my rudder. Partly based on the video from andy of boatworks. I thought his epoxy foam looked different than mine. I used an epoxy foam of 250kg/m3. This really worked out fine. I suggest you to put your mold with rudderstock positioned vertical and make different batches of epoxy foam which you poor from the top. Let it it expand and hard, than you can poor a second, third etc batch in it untill its full. Afterthat follow andys video for finishing Worked out for me

If anything, there will be glorious, glorious sanding involved!

Did you see Boat Works Rudder repair? Andy left one side off and filled with foam, shaped and glassed the open side. Looked great when he was done.

I'm relieved that you've sent the dodger for painting. I continue to love your videos, Mads. Thank you.

I hate to beat a dead horse, but considering the positive test results of the epoxy foam I would be on a 'seek an destroy' mission to remove the wet core from the structural members and replacing it with the epoxy foam before glassing it over. I remember that you tested multiple areas and that it is not wet everywhere, so you could just use a deep plunge router bit to attack those areas from the top or the sides with your trim router. I think its worth the extra steps and peace of mind that the wet ply isn't in there for eternity turning into a funky chemical soup underneath the new laminate. My bet is that only about 30% of the structural grid has wet spots.

Well done, as usual. I love the whole concept of DIY from an engineering perspective. Keep it up.

With the additional time you now have waiting for Athena to be moved around. What if you attempted to remove the old plywood in the structural members by drilling 2-3'' holes and essentially scraping and vacuuming out the debris? Then you could fill all the structural member voids with expanding foam and never have to worry about that pesky rotten plywood ever again. Just a thought to make it extra spiffy!

I Vote vertical, mix x amount and pour in, let it foam, add some more, kinda multiple stages - multiple lifts, at least this is generally the best way with complex PU foam fills. You don't need to wait for the foam to cure, just for it to mostly foam up then add more, rinse and repeat! Air vents holes are a must if you want it to get into any corners too! You can get slower low pressure expanding PU foams too, but in industry most of it is used in semi closed molds than can withhold the pressure. This also makes the bubles smaller and makes it a lot better insulator. Free expanded foam would have nothing like the insulation value of the good sheets of the same stuff cured under pressure.

In order to sand those small corner areas on your steel rudder try using the sanding attachment (foot) that came with your multi-tool.

Hi Mads, Did you watch "Just AboutSailing" channel? He did a very similar test when he replaced his rudder with quite comprehensive Foam tests. Might have been interesting to compare notes.

wow its rock solid, immagine if you put some short chopped carbon to add even more strength? OMG

A spiffy dodger is forever. Words to live by.

Mads - how about assembling the rudder and use vacuum (connected to a hole at the top of the rudder) to draw in the mixed epoxy foam (through A hole in the bottom). Once drawn in both holes will act as vents.

Sand blasting is the BEST way to get into corners and crevices.

I'm a bit confused. A few videos back you discussed PU vs epoxy foam vs PVC sheet foam and you told us you chose the PVC foam sheet. PU was out due to mechanical properties and epoxy foam was out due to outrageous cost. What changed? BTW, I would not recommend PU/ISO as insulation where it will be exposed to moisture. It absorbs moisture and when it does, the insulation value takes a serious dive. Expanded or extruded polystyrene are a better choice. This has been heavily studied by the building science folks and manufacturers like Dow Chemical. In applications like below-grade insulation where they will encounter groundwater, these are the products recommended. In testing up to 15 years, EPS absorbed the least water. Sure, your galley (hopefully) won't be submerged, but condensation or incidental water are a concern. The inner skin of a cold box will naturally be below the dew point at all times. Household refrigerators/freezers typically use EPS as well for this reason. FWIW, I'm with Nigal Calder on my ideal cold box given today's materials. Vacuum panels _plus_ 4 inch / 100 mm of EPS for a refridgerator or 6 inches / 150 mm of EPS for a freezer. Vacuum panels are amazing but if/when they ever fail, they're much less than amazing. Belt and bracers approach ensures you're not screwed when that happens.

A company that I worked for uses PU as an insulator in custom environmental chambers. It is a very good filler.andnleaves zero voidsnif done correctly and is quick. We have measured it to over 50ins quality and use it in chamber from -40c to +70c. Also almost every walk in cooler.in the world has this PU as an insulator and bonding agent for the panels whether they be steel, aluminum, plastic or stainless..

Wonderful education watching you. Thank you.

You mentioned painting and installing the dodger soon. You may want to hold off on that until you finish interior work. You may find it gets in the way of loading larger stuff through the companionway. Just my 2 cents. I really enjoy your videos.

PU off-gasses chemical fumes for several years. Typically exposure is minimal because rooms are bigger than the volume of gas is able to significantly effect. However in a boat, rooms are smaller. Off gassing is usually worse around certain type of timber as some timber is treated with a specific preservative that interacts with the foaming chemistry. I'm afraid the extent of my knowledge goes no further. It's something to consider for somebody building a smallish sailboat that might or might not be using cedar or pine as wall planking. Cutting already expanded foam and using it to fill spaces as insulation is several orders of magnitude better as a choice for sail boat use.

Attach an uneven or bent stick into your power drill, hold drill against mould after pouring to vibrate the bubbles upwards ?

Spiffy morning. I wake up and have a Patreon notice that Sail Life has posted a video!! Sunday morning coffee and a new video.

Just from the looks the old material in the rudder could be "eternit". In German that is "Faserzement" which i would translate to "fibre cement". But that is just from the looks ;)

It would be great if you could force your mixed epoxy foam through a small hose down into the bottom of the rudder. This would help avoid entrapped air and would allow for a better pour. Maybe sacrifice a new, cheap grease gun.

Can you show us more of the detail about how you try to prevent pinholes in your faring compound?

According to another boatbuilder/repair guy (BoatworksToday on RU-vid) he reckons the stuff in the rudder should be 16lb foam, which is heavy and hard, almost like cement. The stuff you're using seems light...

Very cool! I like the epoxy foam!

Happy Sunday 👌The paint shop will take care of the pinholes, with filler before paint.

No a spiffy dodger is only spiffy until the first scratch, dent, blemish! Lol. I think we need a new shirt made "perfection is the enemy of something something".

If it comes to twiddling, id like to see more of the welding the toe rail.

I am curious what the buoyancy of this foam is. How much weight per cubic inch can this foam float? I don’t know if I am expressing the question correctly but in essence I’m wondering how much the foam helps to keep the aft of the boat afloat. Does it at least zero out the weight of the rudder stock?

Well done great video once again very interesting

Hi Mads , what is the influence of water on both products ?

Madds Expanding epoxy foam can be made from MAS standard low vis resin and fast hardener along with cab o sil just mix all together with a power drill

Hi Mads , I don't like the idea of filling the rudder with an expanding epoxy foam from the top. Very hard to ensure you get it to fill properly and the shaft area is the mosts critical for water intrusion and strength. (It will also add 5-10psi head pressure to deal with) I suggest you stand with shaft side down and with the back edge Up , you must also do it while in the mold too. But how to get material in? Well you won't like it but cut some holes in the mold edge so you can pour thru holes in the edge . Since you will eventually be glassing over the joint on the exterior that will take care of the holes. You can repair the mold later if somebody else wants to reuse it. But 2 or 3 holes is probably all you will need. And just big enough for the tip of a couple of plastic funnels. ( alternatively fill from the top and lay it down before expansion but that's complicated). Having said that , as I suggest previously you should fill each half first, allow to cure ,then glue halves together , much easier and you know what is going on. The post curing is going to be a big problem too........ Also as somebody else said regular fast curing 'automotive body putty ' is the product to use for the pin holes. That what the paint shop will do after spraying with primer. Cheers Warren

Another excellent blog as usual keep up the good work brother Reef Runner out

Any bets on how long after Ava moves until they introduce a tiny deck hand to the crew and announce they bought a catamaran to refit

Enjoyed...as always

hi, where did you buy the sicomin PB 250 - its un-gettable in the USA

With regards to void free foam grow, perhaps largen the holes in the ruder plate to 100mm each to alwo for better travel of foam, from on side to another. And perhaps you can vibrate the foam whe its is still squishi like...

I am no expert and even less of a boatbuilder, but here are some of my thoughts: -When PU foam is in contact with the water, it is diffusing into the foam. So be careful with PU on the boat it even absorbs humidity. -a good solution to filling the rudder could be in the vertical position (i.e. to avoid trapped air pockets) using several smaller batches of foam so it will not run out through gaps between the skins.

If you stood the rudder mold up vertically, in an empty 55-gallon drum (or shipping barrel, whatever) surrounded by well-packed sand, wouldn't that do to hold it from distortion and absorb a lot of heat? Especially if the sand was dampened?

That foam looks like amazing stuff, thanks for sharing.

Take us sailing on Oblex next video if you run out of projects!

I have foamed in a old rowing boat once snd used sl little bit too much pu foam. It gave a loud bang and the inner and outer shell of the boat came apart. There is a lot of pressure behind that. Had to scrap that boat.

Ahhhh it's all so mysterious! What will we be doing next Sunday. Thank you for the epoxy foam experiment. Good fun.

Don't forget to fill the space in the molds that you forgot to fill before making your shells.

Thank you, great video as always.

Hi Mads, if you apply liberal amounts of talcum powder to your exposed skin before sanding fiberglass the itching shouldn't be as bad.

Pin holes are where manual mixing your filler comes in handy, you can go over your work with a soupy mix that will fill all the pin holes. Of course you then have to watch out for runs. There's always a trade offs.

Still want to see a Tiki 38 for his next boat! Ava, lots more room and a washer/dryer and dishwasher, too.

On that one test piece you had a void looked to me that might have been air perhaps you need an air vent?

Does the expanding epoxy only cure hard if heated?

Now as you know I am a landlubber and know nothing about boat, fibreglass, etc. But people were suggesting about the waterlogged wood in the floor of the boat. Is there anyway that you could inject the epoxy foam to make a new core?