Cored deck repair, epoxy or polyester resin?

[Gsailor]

It dries out the moisture is what I was informed. The epoxy flows in any area with a gap, so stops any further flow of water. Always best to ensure no more water enters the deck core, so find the source and reseal.

Thanks.

I did not know antifreeze dried out moisture.

 

[steveeasy]

Oh I dunno, It would seem to be a far quicker & more straightforward job than replacing drooping headlining for instance, which is done all the time.

I’ve heard this drill holes and fill quite a lot as a solution, but having cut off a section of the top deck sandwich to check the problem, I cant see how that can really work properly. It will always leave soggy balsa which will wick to other areas of the deck surely? Anyway, its an idea I have already discarded, as is replacing the core from below. I will be cutting from the top, scraping out all old balsa till I reach drystuff, then replacing with new balsa and repairing. The entire deck will be getting some kind of faux teak on it at a later date so I dont have to manage a pristine finish to the repair.

Sounds like a good plan to me. quite a difficult job from inside. I once found a nice Westerly 33 discuss that was stunning. around the mast the coach roof had gone soft. My plan was the same as yours. did not fall in love with it though.

Steveeasy

 

[Lightwave395]

Interesting.

Out of interest, how much does the export expand?

E.g. Say you were to place a drop the size of a uk pound coin, how much does it expand.

Never come across it in all my decades. Sounds interesting.

Sorry, just seen your response - expansion ratio is 4 times original volume, it's light and it sets rock hard

 

[Keith 66]

Do not use expanding pu builders foam for deck cores, It is cheap crap that absorbs water like a sponge, it is also weak & has no shear strength thus has no place as a structural core.
A well done polyester repair will be as good as the original, better if vinylester resin is used. Both have the added advantage that polyester Gelcoat can be used. Epoxy doesnt like polyester gelcoat & compatibility issues can result.

 

[bergie]

I know epoxy is stronger, but is there any major reason not to use polyester when replacing sections of cored deck?

We used about 15kg of epoxy for re-coring the deck of our 31ft boat. A local boatbuilder was a proponent of sticking to polyester, but we decided to go with epoxy due to better adhesion. But also because we had worked quite a bit with epoxy before.

Important part is getting all the old core out and drying all the surfaces properly.

Some pictures of the process, we did it in some 9-10 sections:
Deck rebuild

 

[steve yates]

I havent actually got any further forward with this, some health issues for my wife have kept me mostly at home. I cant help thinking i may have missed the 4 dry days window I want for the job before it gets cold enough to create issues for resin curing, so I have been researching infra red chicken rearers as a possible solition when I can get back to the job
I’ll report back on how it went and what I used when its finally completed.

 

[Ceirwan]

I would be very cautious about using expanding foam. (The builders type)
Actually, I wouldn't use it at all, the deck is a structural part of the boat & if you are replacing balsa, then the rule of thumb, seems to be to use foam core with a density of 80kg/m3.

Figures don't seem to be exact, but builders foam seems to be around half that. (According to Google)
Possibly there is a use for it to be injected (carefully) into small areas & voids, but for a complete recore, use the proper materials, balsa core or a good foam core.

You can carry out the work with Polyester, Vinylester or Epoxy, as a rule of thumb Polyester < Vinylester < Epoxy. Successful long lasting repairs can be made in either, but epoxy will be more forgiving of preparation, you can also get more working time with a slow hardner. If you're familiar with it & can stand the cost, then the only downside is that you can't gelcoat over it. (If you intended to)

 

[steve yates]

There will be no expanding foam used, and I would prob want to finish it with topcoat/gelcoat.

 

[Wansworth]

Check out “living for sail”….yt vid about just that problem

 

[Refueler]

Do not use expanding pu builders foam for deck cores, It is cheap crap that absorbs water like a sponge, it is also weak & has no shear strength thus has no place as a structural core.

Total rubbish ..... This has been disproved so often ... it is surprising that people still quote this.

Is expanding foam waterproof?.


Product such as PU expansion foam ... Macroflex etc. DOES NOT absorb water once expanded. PU Foam is Closed Cell - specifically for the properties required. It uses moisture to cure - but that is a chemical action. It also does have sufficient structural integrity as a deck core replacement - as it is often a standard material to set windows / door frames in place in addition to the screws / bolts used.
You could put such foam between two boards and then stand on them ... the foam will not crush or significantly deform.
Sheer strength is not required - deck core is under COMPRESSION - not sheer.

I invite you to 'squirt' a sizeable amount - let it expand and then place in a bucket of water after measuring its weight. Leave as long as you like - then take out and check its weight again ... if it absorbs water - which it does not - it would weigh significantly more.

The only environmental effect - is that of colour change.

 

[Refueler]

There will be no expanding foam used, and I would prob want to finish it with topcoat/gelcoat.

If your decision is based on posts here claiming PU foam is not good ... not waterproof - then note - that info is wrong.

 

[boatmike]

I have done this job several times and am just about to do it again on a small section of foredeck. You can use polyester but as you say "I have some" I would question if it is in life still. Polyester ages and degrades. Not worth chancing it my opinion. Epoxy is indeed a better adhesive but more important is to make sure you have proper contact. If as I assume you are working from the outside ( working from the inside up is very difficult and messy) the important thing is to cut out all the affected area outer skin. Remove the old core thoroughly and abrade the inner core before thoroughly cleaning it. Please ignore the advice to drill holes and inject builders foam. The problem you will undoubtedly find is that the existing core is wet and disintegrating. It has to be removed. squirting foam in won't solve the problem. then you either need to arrange a system of heavy weights to ensure the new balsa is properly seated or use a vacuum bag to ensure proper contact between the new balsa and the inner skin. Fully wet out the underside of the balsa and the inner core before laying it down and ensure proper contact all round. The ideal resin to bed the balsa on is crestomer paste. Its expensive though but failing that you can indeed use epoxy but any good thixotropic resin will do the job. I always use vinylester rather than epoxy if I can't get crestomer paste as its also good for laying up the top skin afterwards too and adheres better and has better strength that polyester. Its also lots easier to work with than epoxy. Taper off the edges of the old outer skin and lay up the top skin to join in stages. several layers of close knit weave cloth will do a better job than using chopped strand mat and you can easily lay up gel coat over it and sand and polish to a good finish afterwards. Don't forget to add wax to the gelcoat or cover it with peel ply to exclude the air when curing or it will stay tacky. The most difficult job is matching the gel coat to the existing colour. A bit of an art form I am afraid! Hope this helps. Good luck!

 

[Refueler]

Did anyone suggest drilling holes to inject Builders Foam ??? That would be silly.

 

[Ceirwan]

If your decision is based on posts here claiming PU foam is not good ... not waterproof - then note - that info is wrong.

There's a difference between not good, and not suitable.

Builders foam is very useful stuff, in the right circumustances. Of which a full deck recore is not one.

My first recommendation is generally to replace what was there before, Balsa in most cases, its got great properties & properly sealed & looked after, will outlive most owners. Even mistreated, it lasts a surprisingly long time, my 40 year old MGC still has sound non delammed decks & the previous owners certainly didn't bother epoxy back filling the core in holes etc.

But if someone wants to recore with foam, then far better to use a proper sheet of core material, with known properties and of the correct thickness, expanding foam has many good uses, buoyancy, gap filling, etc.
But a structural core to a deck is not one.

There will be no expanding foam used, and I would prob want to finish it with topcoat/gelcoat.

Better to use a Polyester or Vinylester resin then.
I know there are tests online showing that it adheres, but most professionals I've seen post on Cruiser forum or Sailing Anarchy, all agree that its a bad idea to put gelcoat directly over epoxy, even if it bonds well at first, in time it will fail prematurely.
There is a tie coat you can buy that supposedly links them together, not sure if its available on our side of the pond.

 

[Refueler]

Of which a full deck recore is not one.

Who said a full deck ?? Again - replies that assume what is NOT said.

Of course if you are doing large areas / full deck - then a structural material is to be used. But for limited areas - PU foam is more than adequate.

As to sourcing Balsa .... that is now now so easy in sufficient size / quantity ..... Balsa is subject to serious Environmental controls now and limited supply. Plus what you can get is no longer the quality it was 10 .. 20 .. 30 yrs ago - despite its significant cost increase.

 

[steve yates]

If your decision is based on posts here claiming PU foam is not good ... not waterproof - then note - that info is wrong.

No, simply that i think opening up the deck and replacing the rotted core material would be a better fix than drilling holes and injecting stuff. While that may fill any voids where the core has completely gone, it doesnt replace or fix the core that is simply soaking wet and delaminating. Just seems a more appropriate way to deal with the problem.

 

[steve yates]

Ah, I think I mixed your posts up with someone elses earlier, you are just suggesting pu foam as a full replacement for the damaged section of balsa. Thats fair enough, oug I reallydont fancytrying to get the volume/height correct and consistent across the repair, balsa, resin and glassfibre just seem to be simpler. I already have the balsa, and as its little squares on a membrane, I will be able to follow the curve os the coachroof if required. It was fairly reasonably priced from East coast fibreglass.

 

[Refueler]

Seems some misunderstandings are getting in here ....

Let me be clear :

1. If a full or large area of deck is to have core replaced - then use of original or near original type of material is advised. But its not always possible - so compromises may have to be taken. It also means that for structural integrity and being sure problem is solved - removal of the deck layer is needed to ensure full removal of bad material. This overall is not a simple job and takes care to achieve good final result.

2. Small areas that do not require significant amounts of deck area ... such as where deck fittings have allowed limited water penetration or a crack in deck etc. - can be solved in various ways. Limited removal of top deck layer to ascertain extent of damage ... then removal of bad material - replaced with same or PU foam.
It is even possible to inject resin that coalesces with water to form a secure solid - but this is limited to very small repairs and not for any location required for fittings.

The solution used is based on the size of the repair area(s) ....

 

[B27]

Total rubbish ..... ....
Sheer strength is not required - deck core is under COMPRESSION - not sheer.
...

The basic concept of sandwich structures is that the stiffness comes from the two skins being held apart and not being able to shear relative to each other.

However, the shear strength of 'builder's foam' may be adequate.

It was me who mentioned drilling loads of holes and using builder's foam, I have seen it done very successfully. If you can't get your boat indoors, and you want to leave the surface of the deck intact, working from the underside MAY be worth considering. The boat in question was a race boat with not much 'interior decor' to consider.

 

[Refueler]

The basic concept of sandwich structures is that the stiffness comes from the two skins being held apart and not being able to shear relative to each other.

However, the shear strength of 'builder's foam' may be adequate.

It was me who mentioned drilling loads of holes and using builder's foam, I have seen it done very successfully. If you can't get your boat indoors, and you want to leave the surface of the deck intact, working from the underside MAY be worth considering. The boat in question was a race boat with not much 'interior decor' to consider.

Why would sheer be even considered ??

The reason for core is to avoid the weight penalty of solid GRP ... to use two thin layers of GRP held apart by a core of light material. It is the same principle as the metal I beam ..... two bearers separated by vertical