oldbutnotslow Posted May 31, 2005 Share Posted May 31, 2005 I’ve made 3 sets of foam seats now and all have wound up shrinking by about 30% making them unusable and bl@@dy uncomfortable. 50/50 mix and well stirred. They come out of the bag fine. Nice and firm only for them to start to shrink within a 3 or 4 days after taping them with B & Q gaffer tape I must be doing something wrong! Any one any suggestions?? Grant 😬 183 BHP of black and stone chip excitement. 😬 here Link to comment Share on other sites More sharing options...
caterhamnut Posted May 31, 2005 Share Posted May 31, 2005 Your not eating a large amount of pies just after making a mould are you? 😬 ...sorry - no help, but BTT. Big update! here 80,000miles in 3 years plus Link to comment Share on other sites More sharing options...
Martin H Posted May 31, 2005 Share Posted May 31, 2005 Don't get out of the seat for the 3-4 days, to ensure it's finished shrinking before taping it up . You could always spend the time driving.... Link to comment Share on other sites More sharing options...
Youngbutnotslow Posted May 31, 2005 Share Posted May 31, 2005 He has already had the pies! 😬 We are wondering if there could be a problem due to a reaction with the adhesive on the tape as one seat covered with "Elephant" tape has not shrunk in the same way. It seems to be worse if you leave the seats in the sun for any length of time. 😳 Matt - see my car here Son of Oldbutnotslow here Link to comment Share on other sites More sharing options...
Nifty Posted May 31, 2005 Share Posted May 31, 2005 Did you want to drive the car again Matt 🤔 *tongue* 😬 😬 Keep off the straight and narrow 😬 Link to comment Share on other sites More sharing options...
sjmmarsh Posted May 31, 2005 Share Posted May 31, 2005 Grant This link suggests changing the mix ratio to prevent shrinking - but it doesn't say by how much: here Steve Link to comment Share on other sites More sharing options...
stephen grant Posted May 31, 2005 Share Posted May 31, 2005 Steve - I've e-mailed them and asked. Will post here with the answer Stephen ps; mine coming along nicely, just a small amount of extra mix to pour in to try to get it all symetrical, but the basic seat is in place. Thanks for all the tips, which worked a treat. Link to comment Share on other sites More sharing options...
deanteam Posted June 1, 2005 Share Posted June 1, 2005 I would suggest increasing the isocyanate (the brown component) by 5 - 10 %. Do a couple of small cup tests to to see if there is an improvement. The anaorak bit ? the polymer is not stiff enough to resist the natural shrinkage of the expansion gas during cooling, or some of the cells are not bursting to release the gas at full expansion (soft foams). Increasing the iso component should cover both these issues. I would also pre-stir the other component to ensure that there is no separation of the mixture. Temperature of the components might be a factor, follow the recommendations. A bodge could be to inject air into the areas that have shrunk opening the cells, this however might result in a softer seat than you need. If the foam is fairly stiff this will not work. Good luck and don't forget to wear the protective clothing. Link to comment Share on other sites More sharing options...
Jason Plato Posted June 1, 2005 Share Posted June 1, 2005 In the link it says "Marcelo played with some left over products and mixed the two parts in different ratios then the one recommended by the manufacture and it turned out to work better" ................. if all else fails read the instructions 😬 😬 😬 Can we have Mike Bees' canoe story 😬 *thumbup* Link to comment Share on other sites More sharing options...
stephen grant Posted June 1, 2005 Share Posted June 1, 2005 Ok, well they e-mailed me back with the following; their manufacturer had recommended a 60%-40% mix. This created shrinkage, so they tried a 50%-50% mix, and that worked fine. If you, like me, are using a product that is supposed to be 50%-50% mixed, this isn't particularly helpful! stephen Link to comment Share on other sites More sharing options...
Rob Walker Posted June 1, 2005 Share Posted June 1, 2005 I had the shrinking problem on my second seat. The conclusion I came to was that the first seat Dave Jackson weighed out the two components 50/50 the second seat was done by volume and guess what the two components have different density/weight. Rob Link to comment Share on other sites More sharing options...
MartinWoodham Posted June 1, 2005 Share Posted June 1, 2005 Grant, I'd suspect the tape as well. I taped my seat only after a week or so - laziness on my part rather than any particular plan - and although it has now started to shrink its taken over a year......and we used exactly the same stuff/ mixed 50:50 by volume on your seat, so they should be the same. Martin Roadsports B If everything's under control you're going too slow (Emmerson Fittipaldi) Link to comment Share on other sites More sharing options...
oldbutnotslow Posted June 1, 2005 Author Share Posted June 1, 2005 As opposed to just throwing the shrunk seat away can it be used as the basis of another? Ie put it into the bag and put mix over it or wont this work? Grant 😬 183 BHP of black and stone chip excitement. 😬 here Link to comment Share on other sites More sharing options...
stephen grant Posted June 1, 2005 Share Posted June 1, 2005 I can't see any reason why that wouldn't work - i've been letting my foam seat set and then incrementally adding little bits of mix, letting it set, etc. I actually mixed my foam 50%/50% by weight, not by volume. It'll be interesting to see if it shrinks. stephen Link to comment Share on other sites More sharing options...
Jason Plato Posted June 1, 2005 Share Posted June 1, 2005 As rob has mentioned above . Weigh the 2 parts of PU foam mix . DO NOT measure out by volume The 2 parts are different density Link to comment Share on other sites More sharing options...
stephen grant Posted June 1, 2005 Share Posted June 1, 2005 Dave - you are, of course, assuming that we are all using the same stuff... Mine says to mix equal weights, but I suppose it's possible that someone elses potion says to mix by equal volume? stephen Link to comment Share on other sites More sharing options...
Rob Walker Posted June 1, 2005 Share Posted June 1, 2005 I would advise against using the shrunk seat as a base as mine continued to srink for at least a year by which time it would only fit a short Quazzimodo Link to comment Share on other sites More sharing options...
Jason Plato Posted June 1, 2005 Share Posted June 1, 2005 yes , I am assuming that the instructions state weight and not volume I use foam from CFS 01209 821028 , 1x 5l pack is plenty for a seat Link to comment Share on other sites More sharing options...
stephen grant Posted June 1, 2005 Share Posted June 1, 2005 So is the conclusion then that the way to avoid having a shrinking seat is to mix 50/50 by weight? I mean, has anyone had the amazing-shrinking-seat problem after using this ratio? stephen Link to comment Share on other sites More sharing options...
deanteam Posted June 1, 2005 Share Posted June 1, 2005 The density of isocyanate is 1.23 and polyol 1.06, very important to get the information whether the instructions mean 50:50 by weight or by volume. Link to comment Share on other sites More sharing options...
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