I never expected that

[toesup]

I just put my hull plug (foam / glass) outside in the sun (California, 70 degrees) to dry after another coat of primer....

Its been there about 1/2 an hour and I've just checked it to find its split... 2 splits about 2" long...

I never expected that to happen... :eek::eek::eek::censored:

[Shaun Hendricks]

That sux. Is it clear through the glass or just the primer?

(What kind of Foam did you use?)

[toesup]

That sux. Is it clear through the glass or just the primer?

(What kind of Foam did you use?)

It looks as if its through the glass back to the foam....

Its the blue Dow foam...

I'm guessing the grey primer soaked up the heat and expanded the foam?..

:censored::censored::censored::censored: it...

[Umi_Ryuzuki]

Interesting... I suppose foam is closed cell air pockets and it probably has
some expansion properties...

Ah,... here it is...
Coefficient of Linear Thermal Expansion,
ASTM D696, in/in•°F (mm/m•°C) 3.5 x 10-5 (6.3 x 10-2) This means something...

Does this mean it will expand 0.0143 inches for every inch of foam at 70°?

1" ÷ 1"•70° = 1÷70 = 0.014286 inch expansion per inch.
so over 10 inches, you could get a tenth of an inch expansion at 70°

PDF Dow insulation properties (http://www.dow.com/PublishedLiterature/dh_011b/0901b8038011b57b.pdf?filepath=styrofoam/pdfs/noreg/178-00300.pdf&fromPage=GetDoc)

[mb1387]

I may be way off but I have found that if rush the primer it reacts with glass thats not fully cured and makes alot of heat

[toesup]

Interesting... I suppose foam is closed cell air pockets and it probably has
some expansion properties...

Thanks Umi.. that is an interesting explanation... DONT try this at home eh...

I may be way off but I have found that if rush the primer it reacts with glass thats not fully cured and makes alot of heat

The glass has been on the foam for something like 2 months.. and i have just gotten round to painting it. I think that should be long enough..

[fooman2008]

What kind of primer did you use? I know that some kinds of primer don't have very much 'flex' for the hull to expand and contract (hello those who've ever painted over GM primer on a 70's vette, we discovered to use primer meant for boats) check your primer perhaps when it got into the sun the hull expanded a little.
Foo

[steveciambrone]

If it went through the glass, then how many layers and what weight of glass did you use? The resin should not make a difference.

Steve

[toesup]

If it went through the glass, then how many layers and what weight of glass did you use? The resin should not make a difference.



One layer of cloth.. 0.75oz... and three layers of resin (West Systems)

[der kapitan]

Toes, this has me scratching my head---. :confused:

I've done a LOT of plugs, using various materials and primers, and have never had anything like that happen. :eek:

[Tachikaze]

I have seen the same thing happen on a balsa hull set out in the sun.

[steveciambrone]

One layer of cloth.. 0.75oz... and three layers of resin (West Systems)

You need more glass, .075 is too light and not strong enough to even overcome the effect of the foam expanding due to heat. Which is really not much.

I would strip the primer sand well and add three layers of .075. Or one layer of 1.5oz and a finish layer of .075oz. Only one coat of resin after that to fill any weave. Then sand and prime.

I am assuming you are keeping most of the foam in place for floatation, other wise i would add more layers of 1.5oz.

If it is just a plug then you can afford to make it heavy.

Thanks
Steve

[Aerominded]

Bummer. :(

Kap, you use 1.5 oz mat on your plugs, yes?

[der kapitan]

Bummer. :(
Kap, you use 1.5 oz mat on your plugs, yes?
Aero, yes, I use 1 1/2 oz mat exclusively, sometimes doubling it in spots, and do the finish filling with Bondo. ;)

Steve Ciambrone is right in that if it's only a plug, it won't matter if it's heavier. :)

BTW, I still have most of the plugs I've made over the years, and except for some minor refinishing, they could be reused---. :D

[Shaun Hendricks]

I know some use the lighter glass to fit curves better. Will 1.5 oz mat bend and curve as well as .75 oz fabric?

[der kapitan]

I know some use the lighter glass to fit curves better. Will 1.5 oz mat bend and curve as well as .75 oz fabric?
Shaun, the 1 1/2 oz. mat will conform very nicely to virtually any shape, provided you crumple the material a bit to break the sizeing before laying it down. However, I do use layers of 3/4 oz. mat for sharp outside corners. ;)

I avoid using fabric because it does not conform to surfaces as well as mat. :p