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Help with covering and waterproofing polystyrene foam ‘floats’


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Evening all.

Help required covering polystyrene foam floats.

I have tried to get to the bottom of this but there seem to be so many options.

Fibre glass cloth using epoxy resin.

Fibre glass cloth using resin (don’t want to go down this option!)

Fibre glass using waterproof pva

or

Brown paper using epoxy

Brown paper using pva glue.

or 

Light balsa…. As above.

 

I realise using the brown paper method involves shrinkage so doing curved concave and convex surfaces will not work?

 

No idea where to start.

Any suggestions?

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Depends on the model, if it's a lightweight foamy I leave the floats uncovered.

 

But on heavier models I've balsa skinned them and then glass clothed them. Last floatplane I built was a flying boat, I glass clothed the fuselage using Poly C and just coated the blue foam wing floats with a few coats of Poly C and then painted them.

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12 hours ago, Frank Skilbeck said:

Depends on the model, if it's a lightweight foamy I leave the floats uncovered.

 

But on heavier models I've balsa skinned them and then glass clothed them. Last floatplane I built was a flying boat, I glass clothed the fuselage using Poly C and just coated the blue foam wing floats with a few coats of Poly C and then painted them.

Thanks Frank.

Good advise. I have a foamy model Tundra from Hobby King that has foam floats and that’s the L plate water plane for the larger model.

The floats I want to cover are already starting to put on weight so hence the question regarding covering.

Also the issue of balsa on the underside compound curves keeps me awake at night!

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58 minutes ago, Richard Thornton 2 said:

 

The floats I want to cover are already starting to put on weight

It does depend on the nature of the way the polystyrene is moulded but it should be fully water proof.

One of the worst things you can do with polystyrene with a water immersion situation is to paint it. Unless the paint oil based and several layer thick the paint will not be fully water proof so over time water will get in and lodge in the poly styrene cells with no way of ever drying out.

In other words any covering of foam has to be fully water proof in its own right. The total weight of the end result could be significantly heavier than the original foam.

In some respects a hollow float is better than a solid foam one in that if it does leak then it is at least possible to get the water out again.   

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1 hour ago, Learner said:

Foam floats that are designed for artfs are fine uncovered. 

Very good point.

So let me be more specific, the floats are not for an ARTF.

They are light ply formers, hard wood stringers and foam white polystyrene infills to give the shape and support to the loaded areas ie underside.

A picture says a 1000 words but having looked at the photo I took, my model seems to have gone backwards in construction rather than forwards.

Each stage needs general arrangement, to a degree, prior to final completion, finished coatings and re assembly.

I have a dreadful habit of doing things twice. First time seems to be to get things in the right place, then take it all to pieces, modify it to look more scale like before putting it all back together.

 

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14 minutes ago, Simon Chaddock said:

It does depend on the nature of the way the polystyrene is moulded but it should be fully water proof.

One of the worst things you can do with polystyrene with a water immersion situation is to paint it. Unless the paint oil based and several layer thick the paint will not be fully water proof so over time water will get in and lodge in the poly styrene cells with no way of ever drying out.

In other words any covering of foam has to be fully water proof in its own right. The total weight of the end result could be significantly heavier than the original foam.

In some respects a hollow float is better than a solid foam one in that if it does leak then it is at least possible to get the water out again.   

 

Good point 

 

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Nice model!

Having now seen your photos, and the construction method to this point, it's too far in to go backwards. 

I would cover them with a proper waterproof covering, i.e. fibreglass cloth and wbp or epoxy resin as you prefer working with, and doing a through job of. I would think the difference in weight that this method might offer is of less importance at this size.

 

If i bought this plane today in this condition i would: (i.e. using materials/methods i am familiar with)

not bother skinning with balsa,

i would spackle the foam to get the surface smooth enough

I would then cover with glass cloth and epoxy,

and then i would paint.

 

 

 

 

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1 hour ago, Dale Bradly said:

Nice model!

Having now seen your photos, and the construction method to this point, it's too far in to go backwards. 

I would cover them with a proper waterproof covering, i.e. fibreglass cloth and wbp or epoxy resin as you prefer working with, and doing a through job of. I would think the difference in weight that this method might offer is of less importance at this size.

 

If i bought this plane today in this condition i would: (i.e. using materials/methods i am familiar with)

not bother skinning with balsa,

i would spackle the foam to get the surface smooth enough

I would then cover with glass cloth and epoxy,

and then i would paint.

 

 

 

 

Thats the way i am leaning towards.

Many thanks and the use of epoxy means the house doesn’t stick for weeks and I don’t melt the polystyrene 

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2 hours ago, Dale Bradly said:

Nice model!

Having now seen your photos, and the construction method to this point, it's too far in to go backwards. 

I would cover them with a proper waterproof covering, i.e. fibreglass cloth and wbp or epoxy resin as you prefer working with, and doing a through job of. I would think the difference in weight that this method might offer is of less importance at this size.

 

If i bought this plane today in this condition i would: (i.e. using materials/methods i am familiar with)

not bother skinning with balsa,

i would spackle the foam to get the surface smooth enough

I would then cover with glass cloth and epoxy,

and then i would paint.

 

 

 

 

Question, what WBP glue do you use.

I had some from work years ago, powder form and it was fantastic but it was only an eggcup full.

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36 minutes ago, Simon Chaddock said:

Richard

That looks like it is going to be a spectacualr model.

With that form of float construction a full glass cloth/Epoxy covering is the only practical option. Just be careful about the finished weight. Those are big floats.  

They are massive floats but are the correct size for the model, or put another way, line up with the photos I have.

I am really concerned about the weight but being a Tiger Moth, should cope….fingers crossed

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I’ve covered a few floats with fiberglass cloth and epoxy resin before, and it worked out great for me. I tried brown paper and PVA glue once, but it was a real hassle with all the shrinkage and didn’t last as long. If you’re aiming for something durable and smooth, the fiberglass and epoxy method is definitely the way to go. Just be sure to get all the bubbles out and let it cure fully for the best results!

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24 minutes ago, Yaho said:

I’ve covered a few floats with fiberglass cloth and epoxy resin before, and it worked out great for me. I tried brown paper and PVA glue once, but it was a real hassle with all the shrinkage and didn’t last as long. If you’re aiming for something durable and smooth, the fiberglass and epoxy method is definitely the way to go. Just be sure to get all the bubbles out and let it cure fully for the best results!

Many thanks Yaho

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You might want to consider skinning the forward section of the floats (ahead of the step) with 1/64" birch ply. Floats can take a bit of a battering in this area when running the model back to the edge of the lake.

 

I've recently completed a set of hot-wire cut floats and skinned them in poplar veneer with glass-cloth over the top. I found the poplar ply to be a bit soft but with a distinct, harder grain in places. I'm thinking that over the winter I will strip the lower front section of the skinning and replace it with 1/64" ply. Not cheap but I think it is worth it for better damage resistance.

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5 minutes ago, Nick Cripps said:

You might want to consider skinning the forward section of the floats (ahead of the step) with 1/64" birch ply. Floats can take a bit of a battering in this area when running the model back to the edge of the lake.

 

I've recently completed a set of hot-wire cut floats and skinned them in poplar veneer with glass-cloth over the top. I found the poplar ply to be a bit soft but with a distinct, harder grain in places. I'm thinking that over the winter I will strip the lower front section of the skinning and replace it with 1/64" ply. Not cheap but I think it is worth it for better damage resistance.

Thanks Nick. That’s what I was really concerned with the original concept with these floats. It’s a large model, it’s has weight. It needs added speed to take off on water and water at this speed is ‘hard’.

Hence the backing with polystyrene which gives strength in both longitudinal and compressive areas

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  • 1 month later...

Looks good Richard. I have found that floats can take quite a beating so glassing is a good option. I have also found that floats can be less drag than what you would expect and also can add stability if set up correctly. I see that the mounting looks strong. The floats also make the aircraft so much bigger when handling, almost like 2 extra fuselages and also the amount of work!   

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1 hour ago, Chris Freeman 3 said:

Looks good Richard. I have found that floats can take quite a beating so glassing is a good option. I have also found that floats can be less drag than what you would expect and also can add stability if set up correctly. I see that the mounting looks strong. The floats also make the aircraft so much bigger when handling, almost like 2 extra fuselages and also the amount of work!   

Thats good to know Chris, about the handling. The pilot who owns the full sized aircraft mentioned that it was quite a stable platform but took some turning as the plane ‘weather cocked’ in any breeze.

Re the 3 fuselages, I fully agree and it’s only when you’re getting the shiny coats on that all the lumps and bumps appear. 

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