A little fiberglass help please

[rkde]

Hi,

I am currently looking over the internet for the answers but I know this forum has always helped me out in the past and I am sure it can again

As some of you know I am part way through chopping a BIMI (BMW mini) I need to this weekend make a mould of the roof however we all have a concern regarding resin temperature and the roof skin changing shape. Luck for us this weekend is set to be cold...

Can anyone advise me of a cold resin mix? It can take weeks to cure, Ideally days would be nice but no rush, the important factor is almost no heat is produced. Is this possible? I have done grp a few times now and last weekend did some which felt cool to dry.

Any pointers and mix ratios would be greatly appreciated.

Thanks in advanced

 

[the snooper]

as far as i know all resin gets warn due to the chemical reaction, you could put a couple of fans on the other side of the roof if you think it will move due to the heat created

 

[rkde]

cheers, I guess its not the temp so much as ensuring its as low as possible. I just want to be sure I do not heat the roof skin and warp it, I would be very sad!

Got some research to post here for ref too

 

[the snooper]

i dont relly think it will cause enough heat to warp the roof or the fibreglass would ignite if there was that much heat.
it will probably get hotter left out in the sun on a hot day

 

[rkde]

resin and gel coat mix

Slow 1%
Medium 2%
Fast 3%
Stupidly quick 4%

Do not mix less than 1% or more than 4% as curing will be effected.

so 1%,2%,3%,4% hardener to 100% resin depending how you want it to go.

There does seam to be very little information out there or maybe I am not searching well. I also am trying to find cure temperatures but so far nothing, I think I will need to run some test

 

[rkde]

Cheers snooper I agree with you, the issue is because my roof is currently made from 4 cars my body shop guy is having a fit of worry about the whole roof (1 months worth of smoothing) sagging with the heat. I have said it will be fine, his comment of he likes steam coming off the resin made me want to be there so I am researching it to be sure

 

[mart13]

If you use thin layers heat output will be at a minimum even with a strong mix.
A thick layer will cause heat which will speed up the reaction,which will create more heat,which speeds up the reaction,which will create more heat,which speeds up the reaction,which will create more heat,which speeds up the reaction,which will create more heat.......
Did some measurements once and got temps over 150C

Thin is best

Mart

 

[tomsutton529]

I honestly dont think the temperature is going to affect the roof.

 

[troppo]

What you want to do is lay up a couple of thin layers then build in some bracing to prevent the whole frame distorting. cardboard tubes are plenty strong enough once they are impregnated with resin. What you do is lay the tubes on the thin layers and then glass the tubes in place.once you have plenty of reinforcing in place you can add a few thick layers to give the whole thing body and strength. Good luck mate looking forward to seeing pics.

 

[cumbriasteve]

I used to lay up boat moulds and the only time I felt them anything other than slightly warm was when we put them in the sun to cure, I would be amazed if it affected the roof

 

[rkde]

May I ask at what thickness are you calling thin?

I did manage the warp the roof with too much hardener in the filler but I went too much and you could cook on it leant a big lesson there - not to be careless with mixing.

 

[Fergus]

Are you using polyester or epoxy resin?

 

[rkde]

polyester. why?

 

[Fergus]

polyester. why?

From memory the curing process with Epoxy was a lot cooler, it's been a while since I last did any mind.

 

[langy]

I often mould off steel cars and i've never warped any panel. it will be fine.

May I ask at what thickness are you calling thin?

I did manage the warp the roof with too much hardener in the filler but I went too much and you could cook on it leant a big lesson there - not to be careless with mixing.

 

[rkde]

Cheers. This all helps to put my mind at rest

I hope its all going to turn out well!

 

[Ed.]

Using polyester resin, you should on average use no more than 1% MEKP and if you are using Gelcoat/flowcoat then up to 2%, no more. The manufacturer will put in the appropriate amount of Promotor in the resin/gelcoat for the time of year, ie; there will be less promotor in the resin/gelcoat in summer and more in the winter, but the MEKP % shouldn't change. You will only have issues/problems if you had a tin of resin bought in summer and tried to use it in the middle of winter and vice versa. The summer one will just need more promotor in it and not more MEKP in it. There is not a lot you could do if you tried to use the winter one in summer as it will go off very fast and hotter due to the higher temps and the extra promotor in it. If you use the appropriate batch made for the time of the year you shouldn't have dramas.

The only exception to the MEKP % is if you add filler, such as talc to make a "bog" for filling purposes, in which case you could go to 2% in the resin mix, but if you use "microballoons" as the filler , then stick to the 1% as it is a very good insulator and will set very quickly.

I have been glassing for over 40 years and in that time I have not had an issue with excessive curing temps under a covered roof, and by covered, I mean not under a skylight either as UV light will help set it off faster and hotter. In the direct summer sun then that will happen but not under cover. You shouldn't put uncured fibreglass in the direct sunlight, you can after it has gelled and cured but not before. Putting it in the sun or heating it up after it has hardened and set will help it cure/set better.

I have made many moulds off the roofs of vehicles for a pop up camper company I worked for when I was younger, when glassing a mould you should put down 1 layer first then no more than 2-3 layers afterwards otherwise you will get heat build up and more shrinkage, I am currently doing some glasswork in my garage for some live bait tanks and seat bases for my boat. It is currently summer over here and about 30 degrees in the shade, I have been putting down 3 layers of 600GSM at one time and during curing the fibreglass only just gets warm, then again everything in my garage at the moment is warm. As far as curing polyester based resins, it should only take hours, if it doesn't by that time then you have major problems. Hope this helps.

 

[troppo]

Using polyester resin, you should on average use no more than 1% MEKP and if you are using Gelcoat/flowcoat then up to 2%, no more. The manufacturer will put in the appropriate amount of Promotor in the resin/gelcoat for the time of year, ie; there will be less promotor in the resin/gelcoat in summer and more in the winter, but the MEKP % shouldn't change. You will only have issues/problems if you had a tin of resin bought in summer and tried to use it in the middle of winter and vice versa. The summer one will just need more promotor in it and not more MEKP in it. There is not a lot you could do if you tried to use the winter one in summer as it will go off very fast and hotter due to the higher temps and the extra promotor in it. If you use the appropriate batch made for the time of the year you shouldn't have dramas.

The only exception to the MEKP % is if you add filler, such as talc to make a "bog" for filling purposes, in which case you could go to 2% in the resin mix, but if you use "microballoons" as the filler , then stick to the 1% as it is a very good insulator and will set very quickly.

I have been glassing for over 40 years and in that time I have not had an issue with excessive curing temps under a covered roof, and by covered, I mean not under a skylight either as UV light will help set it off faster and hotter. In the direct summer sun then that will happen but not under cover. You shouldn't put uncured fibreglass in the direct sunlight, you can after it has gelled and cured but not before. Putting it in the sun or heating it up after it has hardened and set will help it cure/set better.

I have made many moulds off the roofs of vehicles for a pop up camper company I worked for when I was younger, when glassing a mould you should put down 1 layer first then no more than 2-3 layers afterwards otherwise you will get heat build up and more shrinkage, I am currently doing some glasswork in my garage for some live bait tanks and seat bases for my boat. It is currently summer over here and about 30 degrees in the shade, I have been putting down 3 layers of 600GSM at one time and during curing the fibreglass only just gets warm, then again everything in my garage at the moment is warm. As far as curing polyester based resins, it should only take hours, if it doesn't by that time then you have major problems. Hope this helps.

Somegreat information there Ed, thanks for sharing your years of experience with us, now if we can just get you to do some tutorial vids on various f`glass techniques we can all learn more.
Cheers
Troppo

 

[Ed.]

Thanks Troppo, But that won't happen, I only use it now whenever I absolutely have to, I can't stand the ichyness, the fumes and the mess that working with fibreglass makes. I only work with it if I absolutely have to now, in this particular case I am refitting a GRP boat and needed to make 2 seat bases with a built in live bait tank in each, fortunately I kept the seat base mould from the last boat I built for my self but threw out the live bait tank mould, so made a temp male mould out of a 60lt wheelie bin, did the trick, flipped it over, took the wheels off, put a MDF lid over it sized it to the bottom and then put a flange aound the bin 40cm down the sides, a bit of modeling clay to seal the joints, wax and PVA over the lot and it worked out OK. It doesn't have the polished finish of a proper mould but I don't think that the bait fish will care. There are just a few little jobs left on this boat but once the fibreglassing work is done on this boat, I don't ever want to touch the stuff again. It's nice to have skills that you can call on whenever you need them for doing something different, but welding is much more fun!

 

[rkde]

this is how it went, so far so good

After sleepless nights, and loads of worry the day of making a glass fibre mould of the roof happened today, lots of work have lead to this day and it did seam to go well, the real tell tail sign will be when the mould is cracked off.
So today the gel coat was applied then several layers of mat and resin. Its really looking good and I am very pleased with the progress.

As it stands right now