Soft core deck question

[Sfalkner]

Grateful for advice and opinions.
I have a 1974 Alpa 11.50 (Italian) with some spongy/springy patches on the foredeck. When I tap the deck with a ball hammer I get a dull thud in the areas of springiness. I therefore assumed that I had damp in the balsa sandwich core and eventually resolved to fix the problem by removing the top layer of fibreglass, digging out the degraded wet balsa, drying, replacing with Airex foam and re-glassing the top. I had misgivings about doing this as it would be nigh on impossible to match the moulded non-slip pattern which is arranged rather like a teak deck with “planks” of diamond-pattern non-slip about 2” wide separated by smooth “caulking” strips about 1/2” wide.

Today I bit the bullet and made two double cuts with an angle-grinder in the “caulking” strips as a tester. The thin strips of top layer FG were removed leaving an opening about 6” x 1/2” and I was able to dig out some core material with a small screwdriver. To my surprise it was neither balsa nor wet. Rather it was somewhat crumbly foam and quite dry.

Sorry about the long intro. Now to my questions:

What is the foam likely to have been in a boat of this age?
Could the foam have broken down in structure over the 48 years to cause the springiness without ingress of water?
If so, and I were to make frequent cuts as I already have in the “caulking” strips and inject epoxy resin which might then spread sideways under the moulded “planks” might I achieve a sufficiently solid deck and avoid cutting large chunks out which would destroy the moulded “planking” pattern?

Thanks in advance for any thoughts.

 

[Keith-i]

I can imagine foam of that vintage could easily have degraded over time with thermal movement and general flexing from use. Do you think it could be flooded by a thin resin to reinforce it? Perhaps drill holes at 6” intervals and pour in resin.

 

[Neeves]

Depends on the quality of the deck but you can take an impression of the deck, use it as a mould, and make copies (you need a release agent). If you do this, lay down a pigmented gelcoat first for your finished product, presumably white and as close to a match as possible. I've done this - if you come to 'paint' later with a 2 pack then the paint fills the low points leaving the top of the pimples naked, by the time you paint the top of the pimples you have ruined the impression.

Someone might have the answer - but life was too short for me - and I used a not slip coating.

Jonathan

 

[voyager35]

I have repaired ?an area of my foam cored deck that seemed to be a bit soft by drilling small holes that a plastic syringe would fit tightly into and injecting epoxy. this travelled through the void and came out of nearby holes. The deck now feels and sounds solid

 

[Bobc]

As voyager says. Drill lots of small holes in the deck and inject epoxy resin using a syringe.

 

[DownWest]

Just a thought, but Resoltech sell a water based resin in a 1:1 mix ratio, that was originally designed to stiffen up 'soft' wood structures. i.e. minor rot in places where it wasn't too structural and difficult to replace in historic buildings., it flows very easily and gets into spongy stuff.
You don't say where you are? but they have agents in UK.
Here: Advanced technology resins
The stuff is Re. 1010
You could ask their tech services, very friendly. M. P. Calmon esp. Speaks excellent english

 

[Sfalkner]

Thank you, all. I am very encouraged. Keith-i, thanks for confirming that the foam could well have deteriorated over such a long time. The good thing is I do not have to contend with the problem of damp, which I had expected. Jonathan, thanks for your help over replicating the pattern if necessary. I have seen a very good UTube by, I think, Boatworks which confirms your advice. Of course I am hoping not to have to do that by working only on the strips between the moulded pattern. In the end, and I do have to destroy the pattern I agree that I would just go for a thick paint (Kiigrip?) to cover the problem and then get on with sailing! Keith-i, Voyager 35 and Bobc I like your advice and will try this out with lots of holes and injecting epoxy. DownWest, I am in Preveza, Greece, but thanks for your advice re Resoltech’s resin which sounds ideal in order that it flows readily within the sandwich. I will see what easy flowing epoxy I can find here. Again, very many thanks for all your time and advice.
Simon

 

[AntarcticPilot]

A downside of injecting resin is that it will make the structure a lot heavier for no increase in strength. The point of a cored structure is to keep weight down while maintaining structural strength - almost all the load on a deck is taken by the outer layers of the structure; the point of the foam or balsa or whatever is merely to maintain the distance between the inner and outer load-bearing skins. Obviously replacing a very light foam or balsa with resin is going to increase the weight of the structure considerably for little or no increase in strength. The best repair is to cut away one surface or the other and replace the foam (I've seen something called Divynicell, or something like that recommended). But obviously that's a much bigger job!

 

[Sfalkner]

Thank you AntarcticPilot. I realise that the right thing to do is to cut away the top surface, clean out all the deteriorated foam, replace with sheets of new foam and re-glass the top. In fact I brought out sheets of Airex foam and chopped strand matting to Greece to do just that. This was on the assumption that I had water ingress into a balsa core. When I discovered there was broken down foam and no damp, I took the easier route! One question; I am interested in your point about adding weight for no gain, but with the remaining foam material, crumbly though it is, I was hoping that the epoxy would mix with it to form the very link/spacer you describe to join the top and bottom layers and thus increase strength. I have now done a roughly 2’ square with about 40 holes which I have injected. In some cases, as I injected in one hole it came out of another. Would this not indicate the void being filled?

 

[AntarcticPilot]

Thank you AntarcticPilot. I realise that the right thing to do is to cut away the top surface, clean out all the deteriorated foam, replace with sheets of new foam and re-glass the top. In fact I brought out sheets of Airex foam and chopped strand matting to Greece to do just that. This was on the assumption that I had water ingress into a balsa core. When I discovered there was broken down foam and no damp, I took the easier route! One question; I am interested in your point about adding weight for no gain, but with the remaining foam material, crumbly though it is, I was hoping that the epoxy would mix with it to form the very link/spacer you describe to join the top and bottom layers and thus increase strength. I have now done a roughly 2’ square with about 40 holes which I have injected. In some cases, as I injected in one hole it came out of another. Would this not indicate the void being filled?

If the void is entirely filled (and you suggest that it is) , you will have replaced a light weight foam with a solid block of resin. It will be strong enough, but far heavier than the original.

 

[DownWest]

Without pre-empting AP's reply I would not worry too much about a few kg of resin in the deck in the overall scale of things, compared with ripping up the deck and then trying to match the original finish.

Slow typing, AP, but does it matter that much, and, rather than solid resin, a mix of the foam and resin. Not, probably, very well distributed, but OK to go sailing?

 

[Sfalkner]

Thanks AP and Down West. I accept that it will be heavier, and I also accept that it may well not fill the voids everywhere, but if it adds strength (which I think it will) then I will be happy. It will be interesting to apply the famous ball hammer audio test tomorrow, once it has cured!

 

[DownWest]

Thanks AP and Down West. I accept that it will be heavier, and I also accept that it may well not fill the voids everywhere, but if it adds strength (which I think it will) then I will be happy. It will be interesting to apply the famous ball hammer audio test tomorrow, once it has cured!

Wear ear muffs then go sailing...

 

[Restoration man]

The core around my anchor winch is rotten ,I plan on replacing this from underneath, the skin on the outside is much thicker than on the inside so easier to do the repair from inside , and if my fiberglas looks rubbish it doesn’t matter and deck will still look original, My area is very Structual so I wouldn’t want to mess about with injecting stuff , but in your case I’ve heard people drill lots holes from underneath and get an old Allen key stick it in a drill and thread it into the hole run the drill to remove some of the old core, get a vacuum and suck the remains out and then inject west system six10 epoxy, this product is self mixing thickened epoxy that comes in tubes that go onto standard silicone guns

 

[oldbloke]

Honest question. Having found that its not galloping balsa rot, why is it felt necessary to go to these lengths to treat as opposed to leaving alone?

 

[Sfalkner]

RM. I agree that working from underneath makes sense in your case. I have an all in one piece headlining which would make this difficult. I have also heard of the Allen key method. I think after the Allen Key trick, you then blow hot air in to dry before vacuuming out. In my case, I wanted to keep the remnants of the foam to mix with the epoxy to add volume so was happy not to break up the core any more. Good luck with your work and make sure you wear goggles and mask!

Very good question, Oldbloke! I think I just don't much like a bouncy deck and I suspect it would only get worse with time.

I have now drilled and filled about 150 holes. The deck is now solid underfoot, gives quite a good tone with the ball hammer and I have added about 2.5 kg in weight. Therefore, it seems to have been a success. Thanks all.

 

[Stemar]

Well done!