Cure for extra slow curing Mold Max 10 rubber?

OdysseySlipways · Post by **OdysseySlipways** » Sat Jan 20, 2007 8:51 pm

Since it has gotten cold out, i have been having a devil of a time trying to getmy molds to set up like they should in 24 hours. thay are now taking uop to 4 days and even then, they still seem to fell not completely cured to the touch.

this is what i have been doing:

I do all of the mold pouring in the basement and then one the pine board (that i set up and do my molds on) and then bring it up to dining room and set in on the radiator for some extra heat (it just makes the surface of the board slightly warm to the touch - not enough to do any damage to the original parts) to help it set up.

it was still taking it 3 to 4 ays to cure.

then i thought, maybe the rubber is too cool sitting in the basement (maybe 65 degrees? have to wear a flannel vest the last few days as it's been a bit chillier that the norm, but then it's been in the single digits witht he wind) as the basement has no heat other than the pipes from the heater. So I would bring the tub of rubber up the moring i was planing to do a pour of molds and sit it next to the radiator to let it get some warmth.

but that didn't seem to help none.

I brought the tub of rubber back up the other day and this time i sat it on the radiator. I also brought up the catalyst and sat it next to the tub on the radiator to see of that might be the problem (cold catalyst).

guess i'll know in the next day or so.

i took the rubber and cat of the radiaor just a little while ago and as soon as i'm done one more plate of food, i'll go down and mix me up a batch.

OdysseySlipways · Post by **OdysseySlipways** » Sun Jan 21, 2007 7:45 am

what a let down..............

I just went and checked the molds this morning and they still have that tacky / gooy feel to them when they are touched.

I thought for sure that warming up the rubber and catalyst would have helped.........

I did get a new tub of rubber the day before. It's still all in the box it was shipped in and it's been sitting ont he radiator to keep it warm.

The current tub of rubber is just about gone, so i'll soon be trying the new tub. if the new tub works just fine and no delay in it's curring, the only thing i cab think of then is something happened to the catalyst with the current batch.

but if anyone has any other thoughts, please chime in...........

Darkov · Post by **Darkov** » Sun Jan 21, 2007 9:58 am

Sounds to me like you didn't mix it up in the right proportions. Shouldn't take that long to cure...even at a cooler temperature.
I also do most of my mold making in the basement...cooler than the rest of the house. I have never had any problems with cure time. I do use the Mold Max Fast Cat so my molds are set up in as litte as 1hr. I don't use it that hot though...mostly in a mix that sets up in 6hrs.
Is it possible that your mold max is old? How cold has it gotten it hasn't frozen has it? Have all the molds you made with this batch of MM been this way? You could possible have gotten a bad batch.

Pete

OdysseySlipways · Post by **OdysseySlipways** » Sun Jan 21, 2007 10:11 am

the mixing is fine, even if i an off by a smidgen, it's forgiving.

now when iwent to go check then just a little while agao again, they felt pretty good. Then about 10 minutes ago, i gave my mother a piece of completely cured rubber to touch and then had her touch the ones i just did and she sais they fell cured - no tackiness.

mind you, i didn't pour the molds until about 11 or 12 last night.

if they are good an solid byt later this afternoon, i'll know it was the catalyst giving me the problem. i all ready will be bringing the mold material back up and sitting upon the radiator again for tomorrows pour.

the only other thing that might be a problem is altitude - i am now in the mountains (Allegheny's sp?) and up on one of the hills (mountain crest) and i know the air is a just a bit thinner (my luck not by much - but how knows).

DX-SFX · Post by **DX-SFX** » Sun Jan 21, 2007 11:53 am

Silicone rubber is inhibited by cold temperatures. It likes warm moist conditions. Bathrooms are great places to cure moulds. In future, try adding a small blob of artist's tube acrylic paint to the rubber. It provides a tiny amount of moisture to the rubber to aid curing and you can use it as a guide to see if the rubber and catalyst is thorougly mixed when you've got a uniform colour.

There is one advantage to a slow cure. The rubber mould tends to last longer (don't ask me why) and it shrinks less.

Don't be hasty to demould too soon. Put those moulds away somewhere warm for another few days and try to forget about them.

OdysseySlipways · Post by **OdysseySlipways** » Sun Jan 21, 2007 12:04 pm

well, the air is a bit dry in the house, but i thought if anything the lack of moisture would be better as it would help dry the surface of the mold.

i could leave the next set of molds int he basment for curing as the basement is a touch damp right now.

as to the color and such, i use a paint stick and stir it up well

can't put the molds away and frget them as I have too many to catch up on (due to this extra slow curing problem).

DX-SFX · Post by **DX-SFX** » Sun Jan 21, 2007 5:45 pm

The temperature is more important. If it got very cold overnight, it would definitely slow things down. The paint trick just helps the curing.

The only alternative to waiting is wasting the rubber you've used, peel it off and start again. That'll probably be dictated by the amount of rubber involved and the cost. To remove uncured rubber if it's still liquid, use enamel thinners/white spirit/Varsol (it's all the same stuff).

OdysseySlipways · Post by **OdysseySlipways** » Sun Jan 21, 2007 5:51 pm

the problem as of right now seems to be the catalyst being too cold as the molds from last night are nice and set up now and i hope to try to get the second half of the molds done tonight.

this would be great if that's all it was (cold catalyst) as i can start getting back on track.

DX-SFX · Post by **DX-SFX** » Mon Jan 22, 2007 4:57 am

Once it's mixed into the rubber, it's one homogenous temperature. Can't you just put the poured mould somewhere warmer for the night?

Joseph Osborn · Post by **Joseph Osborn** » Wed Jan 24, 2007 8:44 pm

For what it's worth; I poured several molds at 10pm last night at room temperature (about 73) and cured them in a pressure pot in a shed overnight (temp went to about 29-30) and when I checked them after 16hrs, they were curing just fine. The rubber is a Shore A 25 Tin-cure from US Composites. I've never had much problem with rubber in the cold. Resin, on the other hand, is a pain in the rear in this weather.