Venting casting resins | Tips & Tricks

After mixing silicone rubber, epoxy casting resin or polyester casting resin, a lot of air can enter the material. These air bubbles can lower the quality of the final casting. So for high quality castings, it is important to vent the resin. Also, for best results, it is recommended to vent epoxy before vacuum injection.

In this information article, we explain how venting resins works!

Supplies for venting resins

Besides the resin used, you will need the following materials to properly vent:

The vacuum pump should be a model that can generate a deep vacuum. Our EVD-VE pumps meet this requirement. These pumps are available in different capacities, from 1.5 m3/h to 21 m3/h. This affects the speed at which sufficient vacuum is achieved to effectively vent.

A second distinction with these pumps is the final vacuum level. EVD-VE pumps are divided into single-acting (the 100 series, EVD-VE 110 to EVD-VE135) and double-acting (the 200 series, from EVD-VE215 to EVD-VE2100). The 100 series reaches a final vacuum of 0.05 mbar (abs) and the 200 series reaches a vacuum of 0.003 mbar (abs). This affects the degree of venting. The 200 series bleeds slightly better, although the 100 series will already be sufficient for normal use. In our videos, an EVD-VE115SV pump was used.

The pumps are available as bare pumps or as pumps with a pressure gauge mounted on the pump and an automatic shut-off valve. These pumps have "SV" after the type designation. For venting, the valve is not important. The pressure gauge is useful but not necessary.

The vacuum vessel should, of course, be large enough to accommodate a mixing cup with sufficient casting material. During degassing, the volume of casting material will increase. This should be taken into account when choosing the dimensions. It strongly depends on the material how much it will increase during degassing. The temperature also affects this. At a higher temperature, the increase in volume will be less because the material can release its air more easily.

Count on the following increases (at 20 degrees):

  • Polyester resin: approx. 4x
  • Epoxy resin: approx. 6x
  • Polyurethane resin: approx. 6x
  • Silicone rubber: approx. 10x

Method for venting resins

 

Step 1: make sure the vacuum pump and vacuum dome are fitted and working. Test this once without resin in the dome, but with a little water. The vacuum pump should be able to boil water at 20 degrees. If this doesn't work, check all connections for leaks. A little Vaseline on the seals, on the tap etc. can work wonders.

Step 2: mix enough resin for your project. Make sure this is very wel mixed, if necessary using the 2 cup method. Make sure the container is large enough to absorb the increase in volume.

Step 3: place the mixing cup in the vacuum dome and close the vacuum dome.

Step 4: switch on the vacuum pump and check that the dome is under vacuum. After a few seconds, the top of the dome is firmly attached to the underside of the dome.

Step 5: wait for the casting resin to start foaming and rising. Keep a close eye on the mixing cup or it will overflow. If this is likely to happen, allow some air in, which will reduce the volume. Allowing air in can be done with the white tap on the dome. Turn it until the (almost invisible) slot matches the tap hole. Do not pull on the white tap out on the dome!

Finally, the resin will suddenly release its air, with large bubbles rising. The volume of the resin will rapidly decrease to almost its initial volume. Depending on the cure time, the resin can be left to rest under vacuum for a further 5 to 10 minutes. Silicone rubber and epoxy resin have sufficient curing time for this. Polyurethane and polyester are often a little faster, so it's important to allow the resin to degas as quickly as possible and to use it immediately after degassing.

Step 6: switch off the pump and turn the tap on the dome so that air is admitted. Wait until the vacuum is completely eliminated and remove the resin from the dome. The resin is now fully vented and ready for use.

 

Product advisor
  • Expert advice
  • Superfast delivery with PostNL
  • Pay after delivery

Products used in this article

Product 1 of the 4

Do it yourself jobs with epoxy (DIY), polyester and PU foam!

Here you can find all 31 related articles on this topic. Mis je informatie om aan de slag te gaan met jouw klus? Neem dan contact met ons op.

Polyester for beginners Polyester for beginners
Polyester is a synthetic resin that hardens after adding a hardener. This process is irreversible, so polyester cannot be melted. Polyester does not rot or ru… More information
Epoxy for beginners Epoxy for beginners
At Polyestershoppen, you will find all the information you need about epoxy for beginners. Would you like to work with epoxy resin but don't you know where to s… More information
Polyester pond making | DIY Polyester pond making | DIY
Making a polyester pond has many advantages and is relatively easy to do yourself. If you make your own pond, you will save a lot of money! With the help of a g… More information
Polyester repair manual Polyester repair manual
Polyester is a material that is easy to repair with materials that are easy to process. An average do-it-yourselfer can easily carry out polyester repairs. On t… More information
Covering an object with polyester Covering an object with polyester
Covering an object with polyester has a number of important advantages: the object is strengthened, becomes water-resistant and is easy to colorize. Coating wit… More information
Covering an object with glass fabric and epoxy Covering an object with glass fabric and epoxy
Do you want to cast an object in epoxy? Then you are in the right place. In this article we explain how you can properly protect an object against external infl… More information
All about reinforcement materials (glass, carbon, aramid All about reinforcement materials (glass, carbon, aramid
When working with polyester and epoxy, reinforcement fibres are often used. There are different fibre materials that are available in different weave types. In… More information
This is how you repair a polyester camper roof! This is how you repair a polyester camper roof!
Over time, (hairline) cracks may appear in the polyester roof of your camper causing roof leaks. Repainting often does not give the desired result, especia… More information
Covering an object with carbon (overlay) Covering an object with carbon (overlay)
Making a carbon overlay with real carbon fabric (carbon) is not difficult. In this article we explain step by step how to achieve optimal results!  Suppli… More information
Finish metal and plastic surfaces with Double Coat DD Paint Finish metal and plastic surfaces with Double Coat DD Paint
You can give a metal or pastic surface a fine finish with Double Coat DD Paint. In this article we explain step by step how to do this. DD Paint is a 2-componen… More information
How do you make colour matching gelcoat? How do you make colour matching gelcoat?
In order to achieve an almost invisible gelcoat, the new gelcoat to be applied must have the exact colour of the surrounding gelcoat. It is often not possible t… More information
This is how you make polyester moulds! This is how you make polyester moulds!
If you want to make multiple polyester products, you can use a mould. You can then work faster and more efficiently. It is important that the mould is of good q… More information
Fix rotten wooden window frames with epoxy Fix rotten wooden window frames with epoxy
This guide will show you how to fix rotten wooden components of your window with epoxy. If you do it right you will no longer see that there has been wood rot!… More information
Finishing concrete countertops and sinks with epoxy Finishing concrete countertops and sinks with epoxy
Epoxy finishing concrete countertops, sinks, water ornaments and garden statues is a good way to get a smooth surface that is waterproof and easy to keep… More information
How to waterproof a wooden hot tub. How to waterproof a wooden hot tub.
Hot tubs are becoming increasingly popular. They offer the opportunity to relax in your own garden. Most hot tubs are made of wood. Wood insulates well and also… More information
Sealing EPS and XPS Styrofoam with polyester or epoxy Sealing EPS and XPS Styrofoam with polyester or epoxy
EPS (Expanded Polystyrene Foam) and XPS (Extruded Polystyrene Foam), better known by the names Styrofoam, Roofmate, insulation board or the like is an inexpensi… More information
Bakelite restoration. Cracks, cracks and missing pieces. Bakelite restoration. Cracks, cracks and missing pieces.
Bakelite is a hard, slightly brittle plastic. It has been widely used for steering wheels of cars and tractors, for radios, household appliances, switchgear and… More information
Repairing a plastic shower tray with polyester or epoxy Repairing a plastic shower tray with polyester or epoxy
Plastic shower trays sometimes become damaged through use, renovations or age. In this article we discuss the most common damages and show you how you can easil… More information
Venting casting resins | Tips & Tricks Venting casting resins | Tips & Tricks
After mixing silicone rubber, epoxy casting resin or polyester casting resin, a lot of air can enter the material. These air bubbles can lower the quality… More information
Polishing epoxy with polishing paste and a drilling machine Polishing epoxy with polishing paste and a drilling machine
A work of art, table or anything else you made out of epoxy resin, may get scratched over time. Epoxy resin scratches quite easilly, this is not a bad thin… More information
DIY | Making a cosplay shield DIY | Making a cosplay shield
How do you make your own beautiful shield that you often see on TV or at cosplay conferences? You can make one out of metal but that is very heavy and not eas… More information
DIY | Building epoxy aquarium and terrarium back walls DIY | Building epoxy aquarium and terrarium back walls
As an aquarium or terrarium fan, you will probably want to make your own back wall. The advantages are that a homemade back wall always fits exactly and looks e… More information
Give your bathroom a makeover with epoxy Give your bathroom a makeover with epoxy
Many Polyestershoppen customers have now renewed their bathrooms using epoxy. You can do various jobs in your bathroom with, for example, our epoxy floor coat… More information
Insulating a van with Froth-Pak PU foam Insulating a van with Froth-Pak PU foam
Do you want to convert a van into a camper van or use it as a refrigerated vehicle? Then you need to insulate the van well to limit the costs of keep the van… More information
Insulating your roof with sprayable Froth-Pak PU foam Insulating your roof with sprayable Froth-Pak PU foam
High energy bills? Time to do something about it! Of course, there are many steps you can take to make your home more energy-friendly. In many old houses or o… More information
How to cover a surfboard with carbon fabric and epoxy How to cover a surfboard with carbon fabric and epoxy
In order to achieve a perfect laminate and ideal fibre to resin ratio, the industry often uses the vacuum wet bagging method. This method involves applying a va… More information
Repair kits manual Repair kits manual
Is your shower tray broken or do you have a crack in your marble floor? Hiring a mechanic is often expensive and why hire a mechanic when you can fix it yoursel… More information
Bonding various materials Bonding various materials
Are you looking for the right products to bond different materials? We have a wide range of professional adhesives for bonding metal, iron, aluminum, wood, plas… More information
Tips and tricks for efficiently operating Froth-Pak insulation foam Tips and tricks for efficiently operating Froth-Pak insulation foam
In this article you can read everything about PU foam from Froth-Pak. We explain to you what the benefits of Froth-Pak are and what you need to process it. We h… More information
Wood stabilisation with Stabicure: the solution for durable and strong wood Wood stabilisation with Stabicure: the solution for durable and strong wood
Stabicure is a revolutionary method in the field of wood stabilisation. It is a process in which wood is impregnated with a special resin, also known as "c… More information
DIY | Make your own epoxy putty DIY | Make your own epoxy putty
Epoxy putty (filler) is a versatile and durable material that is often used to fill cracks, holes and other irregularities in various surfaces. Did you know tha… More information

Do you have a question?

Do you have a specific question? Call one of our specialists for free advice +3185 0220090