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  #1  
Old 12-19-2009, 07:41 PM
magwas magwas is offline
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epoxy not waterproof?

I have just finished my very first boat model.
I intend to build the real one from stitch and glue plywood, the model has been built from 3mm particleboard.
I have used epoxy to glue, the filler was wheat flour. Used the same to fill holes used to stitch.
I have "painted" it with two layers of epoxy. The paintings were two days apart, and the last was two days ago.
Curing temperature was between 20 and 30 celsius. The coating felt hard, not sticky at all. It did have some minor smell, but I figured it is normal.

There were areas where the first layer did not seem to coat well, because the wood drank it I figure. This is why I have applied the second layer.

I gave it today to the kids to play with in the bath. Warm water, soap and such.

When It came out and dried, some areas looked like they hadn't been coated. Some areas did develop an unevennes because water filling the particles. some white parts (flour filler, remember) had a rough surface, looking like some of the epoxy had washed away.

What could be the cause of all these? I thought that epoxy is absolutely waterproof, and I have to worry about only UV and knocks.

It is a noname epoxy from a Hungarian producer. There comes a booklet with it, which specifically states that it is adequate for filling holes in radiators and such, and for coating boats. I could not find anything about its composition, they do not even use the word "epoxy".
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  #2  
Old 12-19-2009, 09:34 PM
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PAR PAR is offline
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Well, the obvious question is was it really epoxy?

Assuming it was, then you probably didn't have enough on the particle board. It generally takes three good coats to make sure everything is well sealed. The whole surface should be shinny, especially the end grain areas. If they aren't they coat it again.
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  #3  
Old 12-19-2009, 09:36 PM
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Landlubber Landlubber is offline
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Well maybe it was not epoxy....I have never bought a product that was not called epoxy somewhere on the can......
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I am not a complete idiot.......some parts are still missing
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  #4  
Old 12-19-2009, 10:11 PM
magwas magwas is offline
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Quote:
Originally Posted by PAR View Post
Well, the obvious question is was it really epoxy?

Assuming it was, then you probably didn't have enough on the particle board. It generally takes three good coats to make sure everything is well sealed. The whole surface should be shinny, especially the end grain areas. If they aren't they coat it again.
I am a believer, so I believe it is epoxy.
Everything was shiny before the bath...
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  #5  
Old 12-19-2009, 10:25 PM
Submarine Tom Submarine Tom is offline
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Maybe it just needs an hour in a 350F oven and some ice cream.

Why would you use partical board? And flour? And a product that says

nothing about being epoxy on the container?

What materials are you planning to use on the full scale version?

-Tom
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  #6  
Old 12-19-2009, 11:29 PM
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Simply put Magwas, there are only a few possible reasons for this to occur and in spite of your "believing", the product you used may indeed not be suitable 100% solids epoxy.

If moisture got through a barrier coating then the coating wasn't complete or the coating wasn't waterproof. I have repeatedly found that two coats isn't sufficient to insure a waterproof coating, with three being a minimum usually. Also if the epoxy was diluted with solvents, it would dramatically reduce it's waterproof nature.

Can you get a MDS or other product contents sheet for this stuff?
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  #7  
Old 12-20-2009, 02:29 AM
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Herman Herman is offline
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tell us what is on the can, and the brand name. We can find out. Is it made by SPOL?
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  #8  
Old 12-20-2009, 04:43 AM
magwas magwas is offline
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Thank the suggestion about 350F oven and icecream. I do not understand the significance of the latter, however

I used the particleboard because it was the thinest wood I could find.

The reason for flour was that it is easily available, moisture free, homogeneous, small particle size, small bulk density, and feels more "woody" than sand (maybe elasticity have to do something with this).

The reason for this particular product that it was the only one in the local paint shop.

There is no useable information on the can besides a web address. This is the product:
http://www.ablonczy.hu/content.php?cont=9

Reading about other products it is odd that you should add 0.5-1.5ml curing additive for 0.5 dl resin.

One thing is clear however, that 3 coats would the absolute minimum using anything.
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  #9  
Old 12-20-2009, 07:11 AM
apex1
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The flour is swelling too much before the resin kicks, leaving a porous surface. That is impossible to get watertight.
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  #10  
Old 12-20-2009, 07:48 AM
magwas magwas is offline
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Quote:
Originally Posted by apex1 View Post
The flour is swelling too much before the resin kicks, leaving a porous surface. That is impossible to get watertight.
Understood. What do you suggest as a filler?
My main preferences that it should be cheap, readily available, and no need for hassle around.

I do not have the circumstances to produce adequate sawdust, but might be able to obtain it from some carpenter around here. What are the other options?
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  #11  
Old 12-20-2009, 08:22 AM
apex1
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The sawdust from carpenters is too coarse and makes you the same problems as your flour. (but can be used for filling edges / corners.

You have to use something common like silica and/ or chopped cotton fibres. (wear a mask, the silica stuff is nasty on the lungs).

You can get all the common stuff in HU ! Otherwise go to Wien when you´re in the north of "Pannonia".

Regards
Richard
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  #12  
Old 12-20-2009, 08:36 AM
magwas magwas is offline
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Quote:
Originally Posted by apex1 View Post
The sawdust from carpenters is too coarse and makes you the same problems as your flour. (but can be used for filling edges / corners.

You have to use something common like silica and/ or chopped cotton fibres. (wear a mask, the silica stuff is nasty on the lungs).
I am using filler only when filling/gluing, so it will get coated with unfilled resin, so I guess porous surface maybe not such a big issue. However...
I thought I would screen the sawdust before using. What hole size should I aim at? Normal mosquito net, or something finer?
I would like to use something which is easy to handle and not nasty, so silica is out.
Chopped cotton fibres however sounds interesting, never heard about it before. How would I produce some?
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  #13  
Old 12-20-2009, 10:26 AM
apex1
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Quote:
Originally Posted by magwas View Post
I am using filler only when filling/gluing, so it will get coated with unfilled resin, so I guess porous surface maybe not such a big issue. However...
I thought I would screen the sawdust before using. What hole size should I aim at? Normal mosquito net, or something finer?
I would like to use something which is easy to handle and not nasty, so silica is out.
Chopped cotton fibres however sounds interesting, never heard about it before. How would I produce some?
Filling yes. Glueing NO! You cannot use coarse sawdust for glueing. Except you are fine with a terrible result and five times the resin consumption.

You will not go around silica I fear.
The chopped cotton you cannot produce "at home", the filling agent has to be as fine as your flour was (from the consistence it was the right choice).

It is common to use a mix of fillers, cabosil and cotton for example.
There are several builders around the Duna and I remember one at least at the Balaton, they should be able to assist.

I hope you´re not too far away from that.

Regards
Richard
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  #14  
Old 12-20-2009, 10:38 AM
magwas magwas is offline
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Quote:
Originally Posted by apex1 View Post
Filling yes. Glueing NO! You cannot use coarse sawdust for glueing. Except you are fine with a terrible result and five times the resin consumption.
What are the requirements for filling for glueing, and why?
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  #15  
Old 12-20-2009, 02:41 PM
apex1
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Magyar was,

think of it!

Why cant you use a coarse grain filler for glueing???

Sorry if that sounds unpolite, but I have a bit of a problem going through the basics.

And a bigger problem: I´m in bed with pneumonia and 40° C fever.*

Regards
Richard
*but enjoyed it so far...
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