Resin ‘n Wood: The Basics
A new series that look at using epoxy resin with woodturning.
This episode looks at the basics of what type of resin to use, how to mix it and prevent the bubbles.
G’day and welcome to another new series of mine, This one I’ve called Resin n’ Wood
I have been using resin with my woodturning for a number of years now and have explored a few ideas and these are some of the results.
So with this series I wanted to share with you how I did these and the techniques I used to work with these two mediums. I will also look at some of the problems you may encounter.
But before I do any projects it would be silly not to start with the basics
So with this episode I will cover:
- The different types of resin we can use
- Equipment needed
- What we can use for moulds
- Mixing the resin
- and a bit on some things to avoid
First, what type of resin to choose.
Now this is a bit of can of worms made complicated by brand names and product names.
However, to simplify things, there are only 3 types of resin to choose from: Polyurethane, Polyester and Epoxy.
One thing that is common to all resins is that they have a Part A and Part B. and these get mixed together at a specified ratio which in turn sets off a catalytic reaction that makes the mix go hard. The ratio of A to B will vary from resin to resin and brand to brand so make sure you read the instructions. Its also important to ascertain whether the ratio is measured by volume or weight. SO read ALL the instructions.
Now I use, almost soley, Epoxy resin, so most of this video and future ones will be based on my use this Solid Cast 606, which is an Epoxy Casting resin.
I use Epoxy for 3 important reasons
- It is crystal clear
- It has a good pot life, that is a long working time before it starts to cure
- It adheres to timber better than the other two types of resin.
Polyurethane resin is a great resin for the right job. It can be used to make jewellery and is often used for props in the film industry. One of its characteristics that makes it popular is its cure time. Polyurethane can cure within 15-20 mins but has a very short pot life of about 2 min.
This is good for some applications but for me the short pot life is no good and I have also found the clear Polyurethanes to be inferior in clarity to the Epoxy.
Polyester resin is similar to Epoxy in many ways but has the advantage of being cheaper. I have tried polyester but soon dismissed it for 2 main reasons.
- It has an unpleasant smell that lingers long after the resin has cured and is still very noticeable when it is being turned.
- It doesn’t adhere to timber as well as Epoxy and this was an important factor to me
Another important consideration with Polyester resin is the hardener it uses, called MEKP. This is nasty stuff and has made me very wary of Polyesters. You will need to be careful when using it because it is a severe skin irritant and can cause other health complications.
Now, if either of these three factors is not an issue to you then you will save some dollars by using Polyester. I know a lot of the pen makers use polyester to make their blanks because it is suitable for this purpose. Some pen makers however go for epoxy because epoxy is a harder resin when cured and can be baked to make it even harder.
To confuse matters further you will find if you go to buy resin there are sub groups of each of these three main categories.
For instance, there are doming resins and potting resins and epoxies that are harder than others and some epoxies or polyesters have a tint to them while others are crystal clear. Some resins should only be poured in thin coats where others can be poured in greater mass.
Sometimes they are called fibreglass resin and this could mean it is an epoxy or polyester.
And to make things worse, it is often the case that the person selling you the resin knows very little about it. So my advice is work out which type of resin is best for your needs, polyurethane, Polyester or Epoxy and then go to a store that specialises in this product.
As mentioned earlier, I only use Epoxy resin, in particular this Solid Cast 606 from Solid Solutions in Melbourne Australia. I also stock it. It has a pot life of approx. 2 hours (now that is temperature dependent) is crystal clear and sticks to wood extremely well. It also can be cast on mass but I will talk further about that later on.
This is an important point so don’t miss it.
Now we have our resin organised lets look at the equipment needed and we will start with the mould.
A mould is needed to contain the resin and I use the principle that if it can hold water it will hold resin.
Some of my moulds have been plastic bowls, cups or soft drink cans.
My pepper grinders were moulded up in a pvc pipe. To seal the end I used a piece of timber which not only acted as a plug but also formed the bottom of the grinder.
With a lot of my bowls the mould is the timber itself and I have used masking tape to seal any cracks or grub holes.
Other equipment needed includes
- a mixing jug, which could be plastic, glass ceramic or it could be an recycled can.
- Gloves, try to avoid skin contact.
- Mixing sticks. These should be flat not a dowel so there is enough action created when stirring to mix the 2 parts together. Also consider the shape of the end of your mixing stick. You do need to get down into the bottom corners of your mixing jug so all of A and B are mixed together. This is more important than you might think.
- I have some scales her because this 606 needs to mixed 3:1 by weight. However read the instructions because this varies from brand to brand. Some resins are mixed by volume and there can be different ratios. With Polyester resin the MEKP hardener is used in very small quantities.
- I have masking tape to tape up any cracks. But don’t try to do this once ther is a leak because the tape will not stick to anything that has a coating of resin on it.
- You may need a release agent which you can purchase, often as an aerosol. I use petroleum jelly which I just wipe on to m mould with a rag. The RA prevent the resin from sticking to your mould and helps release the mould from whatever you have cast.
And the last thing you need is some patience. When mixing resin, those that pour and stir their resin slowly, patiently avoid the dreaded bubbles.
I often get asked about the bubbles that everyone seems to get when working with resin and my standard response is that there aren’t any bubbles in the can of resin so they are normally created by the user.
So, we will now look at the mixing of the resin and how to avoid creating bubbles. I am going to use this bowl as for this demo and embed some leaves in resin around the rim.
So this is the mixing process
- Remember what I said earlier on about reading the instructions about mixing ratio. Too little hardener and your mix may never set or cure. Too much and you may end up with a bubbling frothy mess from too much heat being generated. What is important to remember with resin is that there is a catalytic reaction created when the A and B are mixed together which creates heat. Too much hardener creates excessive heat which boils the resin and ruins it. The ambient temperature can also impact on curing. If the temp in your workshop is too low then there is a good chance the resin wont cure. In this case there may be a need to take the project into a warmer room. I tend to be avoiding the other extreme, temp that are too warm. On really warm days I simply don’t mix resin.
- I tend to pour B first and then multiply the quantity by 4 to get my final weight. So, mixing jug on scales, zero scales and start pouring. Now, when pouring A or B make sure you pour it slowly so that you avoid the resin folding in on itself. This is when air is trapped and bubbles created. Another technique I use is to pour the rein down onto the mixing stick which helps prevent the resin folding in on itself.
- Once B is poured Part A goes in. It can be done the other way around, it doesn’t matter which goes in first. Pour carefully.
- I now have to stir the mixture and if this is also done slowly then I won’t fold the mixture in on itself and I won’t create bubbles.
- I have to stir it thoroughly and you can see that initially there is an obvious swirl to it. When this has gone we can stop stirring. I need to make sure that I also scrape around the edges and down the bottom to make sure there is none of either component left unmixed with the other.
Now that I have finished the mixing I am ready to pour it into my mould. This is another time bubbles can be introduced so pour slowly and this won’t happen
How to calculate the quantity needed: I use a few techniques
- I can use some maths and calculate volume which will give me a close idea of quantity needed.
- I could use some rice
But sometimes its difficult to calculate the volume because I am embedding objects so I do more than one pour. In other word I do the first pour which will be less than I need and let it cure over night and then do a top up pour the following day. Providing this 2nd pour is done with 24 hours of the first it will chemically adhere to the first and you won’t see lines between the two layers.
I do this regularly with my grinders.
Another way I overcome this issue is to have a second project ready and pour any excess into it.
The final issue I would like to address deals with the problems you can face when you have a large mass of resin. Remember that the catalytic reaction created when A and B are mixed together creates heat and if you have a large mass of resin then the heat tends to feed of itself, creates more heat and before you know it the resin becomes extremely hot, bubbles and froths and ruins the mix. Its called exotherm.
If I were to mix ½ kg of resin in this mixing jug and leave it to cure I’m sure the exotherm would ruin the mix and perhaps the melt the jug. With my grinders I need 600gms of resin so I overcome exotherm by doing 3 things:
- I do 2 pours
- I break the mass up with gumnuts
- I only mix resin when the ambient temperature allows it. As a guide I would suggest that an ambient temp of anything below 28C (80F) would be safe.
The problem is that there are too many variables to be give you any hard and fast rules so if in doubt err on the side of caution, mix less than you think you need and then do a 2nd pour.