Author:  Created:  Rating: EJSAUNDERS Oct. 12, 2002, 07:21AM   0 Ratings     12345     Water Tension Reducing water tension allows the casting plaster to fill those parts that others cannot reach! It also helps reduce the meniscus effect that can form on slightly less filled molds, or those where the volume of plaster to water is low and allows the water to puddle on top of the cast and keep it damp. The best additive for reducing water tension is a small drop - one or two, more may change the properties of the plaster - of dishwashing detergent (not the powders or tablets that are used in dishwashers though). Other additives such as a small addition of acrylic paint, varnish or flow aid (or Future or Klear acrylic floor polish) can also have a similar effect. Bruce recommends the US Jey Dry brand of dishwashing degreaser (discount coupon available), and for us in the UK, plain Fairy Liquid (about 3-15ml per bucket/bowl of water, depending on container size) works well. Problems with 'Wet Water' Ran the Cid, has been experimenting with the wet water technique and has had some problems. He found that although the wet water eliminates the majority of the large air pockets he gets a lot of little air bubbles. Sometimes he finds an entire section will be riddled with tiny holes, which obviously makes the bricks weaker and looks odd unless your building old, ruined structures.. His 'wet water' technique is to use paint flow air mixed in 1:10 with water in a spray bottle, with Plaster of Paris as his casting material, which is poured into the molds with a spoon. He also noted that ' wet water' seems to make scraping more difficult, because the bricks continue to rise after they have been scraped level. Bruce suggested smacking the excess water out of the molds and if the 'wet water' contains too much soap it will form soap bubbles that will cover over the smaller details. Bruce went on to suggest you can get rid of these air bubbles by giving the molds a good smack against the table top (face down). Myrlyn has also experienced this problem, and thinks that part of the problem is the way he applies the 'wet water'. He wonders if using a spraying mist bottle, rather than the dip bucket method increase the possibility of bubbles in the mixture. I replied that this was indeed the case, and that misting (spraying) the 'wet water' on will create more bubbles, since it atomises the 'wet water' and so actually adds more air. Dipping is unlikely to add bubbles so is the best option, or 'painting' it on with a brush is also a method suggested to decrease the possibility of adding more air bubbles. BMT Gander also uses the dip bucket method and rarely experiences bubble problems. His method is to dip the mold in and give it a good smack. He takes a peek then to see if there are any bubbles in the corners, and if this is the case, then he blows them away before he casts. As for the rising plaster, he also suggests (so did Bruce) that if you hold the scraper at too severe an angle, it will press the plaster down into the mold a bit and afterwards, it'll come back up. He recommends that you do your initial scrape with the scraper more perpendicular, and then do a finish scrape at the more severe angle that doesn't catch on the cavity edges. Tim Hanson also has the problem, and he wondered if it was more related to the type of plaster than the 'wet water'. He wonders if it may be that the more expensive plasters, which have additives that regular Plaster of Paris doesn't may mean it heats up more, therefore causing condensation inside the mold. BMT Gander replied that he doesn't think it's condensation, more the result of a loss of suspension in ambient air. He goes on to say that if you're using the 'glass method' properly, there isn't any air from which to draw the moisture. It might be that you're mixing your Ultracal too thin, or it might be that you're trapping the air with the glass. The one negative thing about the glass method is that there's deliberate waste of plaster. You've got to mound it up to create a seal. You've also got to be careful to maintain a steady pressure. If you press hard, let up, then press hard again, there's a chance of trapping air with the "piston" action. Sageraistlin also has the problem with Ultracal and suggests pounding the mold more, or picking up a corner and letting it drop down which is messy, but effective. Ran the Cid took all these tips back to his workbench and found out that is was too much 'wet water'. After he gave the molds a good smack after spraying the bubbles vanished, and it also eliminate the scraping problems.  Public Comments Please log in to post a comment    You must be a registered member to post comments. You may sign-in Here.

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