Nutsabout Posted May 29, 2017 Share Posted May 29, 2017 I tried to use air dry clay from Hobbycraft to make a diorama base, but after it dried overnight it has multiple cracks. Was I using the wrong product, or using the wrong technique? Thoughts please. Thanks Ian.. Link to comment Share on other sites More sharing options...
Will Vale Posted May 30, 2017 Share Posted May 30, 2017 How thick were you putting it on, and what was it on? I've found it helps to spread a thin layer of PVA and apply the clay onto that to help adhesion - then if it cracks it won't come away and you can fill the cracks with more clay (or a slip of clay and water.) Thin layers are much less likely to crack. You can also brush the dried clay with a PVA/water mix to seal it and stop it dusting. HTH, Will Link to comment Share on other sites More sharing options...
Nutsabout Posted May 30, 2017 Author Share Posted May 30, 2017 2 hours ago, Will Vale said: How thick were you putting it on, and what was it on? I've found it helps to spread a thin layer of PVA and apply the clay onto that to help adhesion - then if it cracks it won't come away and you can fill the cracks with more clay (or a slip of clay and water.) Thin layers are much less likely to crack. You can also brush the dried clay with a PVA/water mix to seal it and stop it dusting. HTH, Will Thanks Will, It was on a hardboard backing for a picture frame, I did give the board a coat of PVA first and let that dry. The thickness was mainly 1-2mm to max of about 5mm in places. but it cracked all over, not just the thicker parts. I have tried filling the cracks with slip but where I made track marks etc it looks awful. The clay seemed very wet out of the pack, would letting it dry out a bit first help reduce shrinkage? Assuming I get the base looking ok, would you advise sealing it with PVA before painting or would the paint seal it sufficiently? Ian.. Link to comment Share on other sites More sharing options...
Will Vale Posted May 30, 2017 Share Posted May 30, 2017 That doesn't sound like an excessively thick layer, although I'm pretty sure I had similar problems making a base on a picture frame once. I'll see if I can find if I wrote anything down. On the sealing, I think the PVA is worth it and will probably save you some paint. The dry clay is quite thirsty. Will Link to comment Share on other sites More sharing options...
Thud4444 Posted May 30, 2017 Share Posted May 30, 2017 I've had nothing but bad luck with air dry clay. The high humidity found where I live gives it fits. Have you tried Sculpey? As long as you don't over bake it, it's always worked for me. It's really cheap as well. Link to comment Share on other sites More sharing options...
spruecutter96 Posted May 31, 2017 Share Posted May 31, 2017 (edited) Is it possible that the material that the clay has been applied to has moved, possibly after having absorbed water from the clay itself? Any movement seems the most likely source of the clay cracking.... Hope this is of some help. Chris. Edited May 31, 2017 by spruecutter96 Correcting a typo. 1 Link to comment Share on other sites More sharing options...
Nutsabout Posted May 31, 2017 Author Share Posted May 31, 2017 17 hours ago, Will Vale said: That doesn't sound like an excessively thick layer, although I'm pretty sure I had similar problems making a base on a picture frame once. I'll see if I can find if I wrote anything down. On the sealing, I think the PVA is worth it and will probably save you some paint. The dry clay is quite thirsty. Will I will definitely seal the clay before painting, good point, thanks Will. 17 hours ago, Thud4444 said: I've had nothing but bad luck with air dry clay. The high humidity found where I live gives it fits. Have you tried Sculpey? As long as you don't over bake it, it's always worked for me. It's really cheap as well. I'll try Sculpey next time, thanks. 4 hours ago, spruecutter96 said: Is it possible that the material that the clay has been applied to has moved, possibly after having absorbed water from the clay itself? Any movement seems the most likely source of the clay cracking.... Hope this is of some help. Chris. Possibly, the base was just the cheep hardboard from the back of a picture frame, so although I sealed it with PVA it could have absorbed some water & then dried out. Thanks for your thoughts guys, I really appreciate your time. I think I will strip it off and start again. Ian.. Link to comment Share on other sites More sharing options...
spruecutter96 Posted May 31, 2017 Share Posted May 31, 2017 No problem at all, Ian. I hope the second attempt is much more successful for you. Cheers. Chris. Link to comment Share on other sites More sharing options...
Black Knight Posted May 31, 2017 Share Posted May 31, 2017 The cracking is simply the clay shrinking as the water evaporates out of it. Sculpey or Fimo is ok, but it has its draw backs, like having to bake it at 130* for 30 minutes or so - can the base be baked? I now use the tile grout from a £1 shop. Put on in thin layers it doesn't crack and is dry inside a couple of hours Link to comment Share on other sites More sharing options...
Nutsabout Posted May 31, 2017 Author Share Posted May 31, 2017 2 hours ago, Black Knight said: The cracking is simply the clay shrinking as the water evaporates out of it. Sculpey or Fimo is ok, but it has its draw backs, like having to bake it at 130* for 30 minutes or so - can the base be baked? I now use the tile grout from a £1 shop. Put on in thin layers it doesn't crack and is dry inside a couple of hours Thanks, might give that a go, but cost might be prohibitive Link to comment Share on other sites More sharing options...
Badder Posted June 1, 2017 Share Posted June 1, 2017 Using such a thin hardboard base seems to me to be a major factor.... it will expand and warp with the moisture from the clay, then shrink and move again as it dries. Rather than waste what you may have left, try it on a chipboard base of 1cm thick. You can always find a deep picture frame and make the chipboard base to fit. If the thicker base doesn't work then refer to advice given above. Rearguards, Badder Link to comment Share on other sites More sharing options...
Nutsabout Posted June 1, 2017 Author Share Posted June 1, 2017 7 hours ago, Badder said: Using such a thin hardboard base seems to me to be a major factor.... it will expand and warp with the moisture from the clay, then shrink and move again as it dries. Rather than waste what you may have left, try it on a chipboard base of 1cm thick. You can always find a deep picture frame and make the chipboard base to fit. If the thicker base doesn't work then refer to advice given above. Rearguards, Badder Thanks Badder, Looking at the base again, after calming down a bit, I think your right, the cheep hardboard does seem water damaged. Ian.. Link to comment Share on other sites More sharing options...
BIG X Posted June 1, 2017 Share Posted June 1, 2017 Have you considered something less porous such as acrylic / styrene / corex / foamex sheeting - not massively expensive and available in a range of thicknesses - just a thought. 1 Link to comment Share on other sites More sharing options...
dcrfan Posted June 6, 2017 Share Posted June 6, 2017 I regularly use air drying clay and have not had cracking problem (but not used on hardboard). As other have advised, I first seal and surface (I often place over cardboard) with PVA to stop it pulling moisture out of the clay too quick. Once it is dry I recoat with PVA to hold clay. Don't let it dry out too quick such as in centrally heated house - I place out in garage and in summer place cloth over the top to slow evaporation. Paul Link to comment Share on other sites More sharing options...
Nutsabout Posted June 6, 2017 Author Share Posted June 6, 2017 14 hours ago, dcrfan said: I regularly use air drying clay and have not had cracking problem (but not used on hardboard). As other have advised, I first seal and surface (I often place over cardboard) with PVA to stop it pulling moisture out of the clay too quick. Once it is dry I recoat with PVA to hold clay. Don't let it dry out too quick such as in centrally heated house - I place out in garage and in summer place cloth over the top to slow evaporation. Paul Thanks Paul, I'll try again. Ian.. Link to comment Share on other sites More sharing options...
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