Cored deck repair, epoxy or polyester resin?

[steve yates]

I know epoxy is stronger, but is there any major reason not to use polyester when replacing sections of cored deck?
Mainly because I already have some, so saves the expense of buying sufficient epoxy for the job
but also as the boat was built from polyester resin it just seems to make sense to use the same stuff for the repair.
Interested in others thoughts.

 

[Refueler]

OK ... Polyester often has poor bond to itself once one part is old and well cured. You can improve adhesion by cleaning off - I use Oven Cleaner then well washed off ... then brushing acetone to 'soften' the surface.
But you also have to be careful with whatever you used to fill the 'core' part ... as many foams etc are not tolerant of polyester - it can actually eat some foams. You need test if you used foam.

But as long as you really get that old surface clean, softened and keyed and fill material is ok - yes polyester can work. But most people would resort to Epoxy to get a more reliable bond.

The keel repair underway on Superanne ... see my thread ... We actually tested areas with Polyester and Epoxy after various cleaning to make sure we had good bond. We had very good bond of Polyester where strict cleaning and preparation was made - in fact as good as the epoxy. Of course one of the factors is working time and what surface of the resin after application ..... Epoxy is easier in this respect due to longer working time and it flowing out smooth ......
We are using Polyester. With minimum hardener to give increased working time. Ratios are as advised by the Resin Suppliers.

 

[B27]

'Replacing sections of deck'?
That sounds like a big job, a lot of resin?

There's a lot more to doing a proper job than just choosing epoxy because it's a 'better' resin.

 

[steve yates]

Ive got replacement balsa for the core, and the old surface will be well sanded and cleaned.

 

[FairweatherDave]

I have not got experience of working with polyester and haven't much experience with epoxy, but I believe the convention is to repair older polyester boats with epoxy, for reasons refueller hints at. That's what I used on my small cored deck repairs and I would hate to have screwed up. But if I knew someone in the yard with lots of experience training me up with polyester resin maybe....otherwise I would be wary. How large is the area you plan to repair?

 

[Gsailor]

Yes epoxy has better properties with regard to adhesiveness (is that a word?), strength and flexibility, but I found some blisters on the bilge keels of my first cruiser and an old sage told me “the boat was built with polyester...” so I ground out the blisters and repaired with polyester resin.

It worked and for about 5 years I monitored the repair and all was well.

I do not know if this can be extrapolated to a deck and core... I am just telling you of my experience.

If money is no problem, epoxy properly mixed and in correct climate will do a better job (he says after posting his good experience with a polyester resin on a bilge keel...)

I don’t think I have been much help ... unless money is tight... then I say you CAN make polyester suffice.

Edit- I often used epoxy and polyester (too many jobs to recollect) but placed the containers of the goop in an ice bath to give me more working time- once applied, the clock is ticking.

One winter job did require a 60 Watt bulb placed near the repair site overnight to help the epoxy cure- that was on an old catamaran racing dinghy that had been T-boned and I bought it for a mere £25. It was a handful single handed / it flew and hissed in a zephyr of breeze. It was a two man trapeze contraption, but I was the only bloke at my club with a cat and no one would crew with me... multihulls were shunned - their loss my gain.

The cat is now at end of the garden with brambles trying to claim it.

 

[Gsailor]

Coming back to this (insomnia is a pain)

perhaps mix a tiny batch of polyester and test on the materials and see if it sticks to whatever it needs to stick to - if it does the job - you know you are good to go - sorry if I am stating the obvious and you had already planned the above.

 

[B27]

Ive got replacement balsa for the core, and the old surface will be well sanded and cleaned.

Replacing the core is pretty major.

A friend sorted a deck with soggy balsa core by drilling a lot of holes in the underside, raking out the balsa and filling with expanding foam.

If you take the whole of one face off the deck sandwich it may change shape.

 

[Refueler]

The old trick of re-inforcing cored deck / replacing small areas ...... cut out / drill .... then bent nail in drill to destroy the core .... remove the fragmented material .....

If re-inforcing - then fill with chopped strand filled resin .....

If replacing core - builders exterior expanding foam ...

 

[AntarcticPilot]

Replacing the core is pretty major.

A friend sorted a deck with soggy balsa core by drilling a lot of holes in the underside, raking out the balsa and filling with expanding foam.

If you take the whole of one face off the deck sandwich it may change shape.

But the pressure generated by expanding foam may also change the shape.

 

[steve yates]

I have not got experience of working with polyester and haven't much experience with epoxy, but I believe the convention is to repair older polyester boats with epoxy, for reasons refueller hints at. That's what I used on my small cored deck repairs and I would hate to have screwed up. But if I knew someone in the yard with lots of experience training me up with polyester resin maybe....otherwise I would be wary. How large is the area you plan to repair?

There are two sections on the coach roof, one on each side, approx 2ft by 1ft

 

[steve yates]

Replacing the core is pretty major.

A friend sorted a deck with soggy balsa core by drilling a lot of holes in the underside, raking out the balsa and filling with expanding foam.

If you take the whole of one face off the deck sandwich it may change shape.

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.

 

[Refueler]

I have a feeling that "I will be cutting from the top, scraping out all old balsa till I reach drystuff," ..... if any of the wet boats I've surveyed / looked over are to go by ... you may be chasing that wet balsa further than you expect.

I checked out a 33 other day that guy had partially replaced foredeck .... I ran my meter along and not only his new deck - but rest of decks were all sodden.

I honestly have fingers crossed for you and hope its not bad.

 

[srm]

But the pressure generated by expanding foam may also change the shape.

A builder working on my house (in the Azores) used 'zero expansion foam' for some jobs. Stocked by the local builders' merchant.

 

[Refueler]

But the pressure generated by expanding foam may also change the shape.

If its trapped .....

 

[Lightwave395]

I did a couple of small repairs to my balsa cored deck, I cleaned out the damp balsa, cleaned and dried the area and used epoxy foam from East Coast Fibreglass. My surveyor was most happy with the work. I should add that access was relatively easy, the problem had been caused by deck compasses being installed without adequate sealing which gave me a 150mm cutout in the deck to work from

Sicomin PB250 Expanding Epoxy Foam

 

[Gsailor]

I did a couple of small repairs to my balsa cored deck, I cleaned out the damp balsa, cleaned and dried the area and used epoxy foam from East Coast Fibreglass. My surveyor was most happy with the work. I should add that access was relatively easy, the problem had been caused by deck compasses being installed without adequate sealing which gave me a 150mm cutout in the deck to work from

Sicomin PB250 Expanding Epoxy Foam

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.

 

[Concerto]

I would be very wary about using expanding foam as it can blister the deck and it makes the repair worse to fix properly.

When I bought Concerto, the surveyor said part of the central plywood strengthening of the foredeck had a hollow sound when tapped with a hammer. His solution was to drill a series of small holes and syringe in epoxy resin. It took 3 times the amount I expected, but has remained absolutely solid for 10 years now.

This method can also be used in cored areas of deck. If the core is damp, I have read that anti freeze should be injected first and allowed to dry, then epoxy fill.

 

[Gsailor]

I would be very wary about using expanding foam as it can blister the deck and it makes the repair worse to fix properly.

When I bought Concerto, the surveyor said part of the central plywood strengthening of the foredeck had a hollow sound when tapped with a hammer. His solution was to drill a series of small holes and syringe in epoxy resin. It took 3 times the amount I expected, but has remained absolutely solid for 10 years now.

This method can also be used in cored areas of deck. If the core is damp, I have read that anti freeze should be injected first and allowed to dry, then epoxy fill.

Interesting.

Did the article explain what the antifreeze does (except the obvious in cold weather)?

I am trying to visualise how it stops the damp spreading to other bits of the deck core.

 

[Concerto]

Interesting.

Did the article explain what the antifreeze does (except the obvious in cold weather)?

I am trying to visualise how it stops the damp spreading to other bits of the deck core.

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.