A salutory lesson

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marshon

New Member
I'm soooo frustrated and fu*ked off that I thought I might share the following ......

I'm building a hybrid backpack, I wanted something between a P1 and an AVP style, so I started planning an armature.
I came across this PDO from movieman and thought I could adapt it to my needs.

I assembled the PEP as usual and left out bits / added bits to produce a basic armature.

Three days work with the two outer and two inner coats of resin

...... now .....

I would normally give the internal surfaces an additional coat of resin and rough matt to strengthen it BUT it would be very fiddly and difficult to get into the little nooks and crannies, so I decided to use polyurethane gap filling foam. I've done this before without problems and you normally end up with a light, strong armature. However this time something went VERY wrong! The valve on the foam can stuck open so it dumped all of the foam into the shell. No big deal I thought, just a bit of carving back to do. I left the backpack for 24 hours to cure. When I went back to it, the foam had dried to a nice comforting hard finish, but there appeared to be some still un-cured material that had collected at the base of the back pack. I started to trim back the excess from the surface and a hole about an inch in diameter appeared. I peered in to see that the foam had formed a 1" thick outer cured part and the rest was hollow!

As soon as the air hit the un-cured foam it began to expand. Cool I thought that should fix it! I left it and went make a coffee.......... BANG! (load noise from the workshop). I rush up to see what the noise was ..... the expanding foam had plugged and sealed the 1" hole and then continued to expand until it SPLIT THE RESIN AND THE PEP!

Disaster! Now I have to start again having wasted 3 days work, a can of resin and a can of foam ....... bollox.
 
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Scrapps

New Member
Aww, man. Sorry about that. It was looking great up until that last bit. I know how it goes, having to start from scratch when stuff messes up. Just try not to get discouraged. I'm two days in my own first time pep armor and just praying that nothing goes wrong.
 

papermad

New Member
This is a problem when using spray polyfoam products, they over expand more than you need and the middle's take months to set. Also the cell structure of the foam is unstable and you will find it will shrink back after a few weeks.
The best poly foams for this type of work is the 2 part liquid versions.... but they are not cheap and normal has to be purchased in 10 kilo kits.

I would stick to fibreglass, I tend not to use fibreglass mat on pep items as I find standard glass mat to thick and resin thirsty, I use fibreglass tissue which I get from car repair stores, 1 layer is good but 2 or 3 is very strong and it will work into fine detail. I tend to fibreglass tissue the outside with 1 layer and inside with 1 layer. Because the tissue is so fine you can work the outer layer the get quite a good smooth finish, then I mix a 50/50 mixture of resin and car body filler and apply a skin all over and then sand to a smooth finish... filleing and floors as I go.

With this I have been able to do the items below using pepakura.

photo0174.jpg


Cylon helmet, spray with airbrush chrome paint.

judgehelmet.jpg


Judge Dredd helmet which I made 2 off for last Halloween nightout :D

I am not sure about where you would find fibreglass tissue other than car repair suppliers is a good start, but here in the UK you can buy it off the shelf at halford's stores.

Hope some of this info helps
 

marshon

New Member
This is a problem when using spray polyfoam products, they over expand more than you need and the middle's take months to set. Also the cell structure of the foam is unstable and you will find it will shrink back after a few weeks.
The best poly foams for this type of work is the 2 part liquid versions.... but they are not cheap and normal has to be purchased in 10 kilo kits.

I would stick to fibreglass, I tend not to use fibreglass mat on pep items as I find standard glass mat to thick and resin thirsty, I use fibreglass tissue which I get from car repair stores, 1 layer is good but 2 or 3 is very strong and it will work into fine detail. I tend to fibreglass tissue the outside with 1 layer and inside with 1 layer. Because the tissue is so fine you can work the outer layer the get quite a good smooth finish, then I mix a 50/50 mixture of resin and car body filler and apply a skin all over and then sand to a smooth finish... filleing and floors as I go.

I am not sure about where you would find fibreglass tissue other than car repair suppliers is a good start, but here in the UK you can buy it off the shelf at halford's stores.

Hope some of this info helps
This would have been my nrmal route and I have a load of tissue, but it would be physically difficult to get the tissue into the very deep parts of the PEP. I have hands like bunches of bananas which don't help. Could have added to the outside as you recommend, perhaps that would have been a better solution.
The foam is usually added in layers and allowed to set which stops the hollow/shrinkage problems but the valve had stuck open and wouldn't shut off.

Ah well .....
 

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