Smiths Clear Penetrating Epoxy Sealer ™ (CPES™) is a thin epoxy that penetrates deeply into the surface of wood. It is the original product of Smiths and Co. and has been restoring and protecting timber for over 40 years now. It is also known as Lignu in Scandinavia and MultiWoodPrime for new wood applications and is often abbreviated to CPES.
Why CPES – Clear Penetrating Epoxy Sealer ™?
There is no substitute that performs as well. It is not cheap, but it is significantly cheaper than wood, repainting and maintenance generally. Do it once, do it right.
Clear Penetrating Epoxy Sealer is an epoxy product, supplied as Part A and Part B in two tins. You must mix CPES before use. Mix it in a 1 to 1 ratio; however it is tolerant of minor mix errors. Mix by weight using 98 parts A by weight to 100 parts B for both Cold and Warm formula.
Packaged between the two cans is a very comprehensive instruction leaflet. Please read this prior to use if you are unfamiliar with this product. You can order a copy of that instruction leaflet from us ‘How to restore wood booklet‘.
There is a lot more, written by the inventor, that you can read about the science of clear penetrating epoxy sealer here.
Curing Rot With Clear Penetrating Epoxy Sealer
Clear Penetrating Epoxy Sealer is capable of restoring rotten wood and allowing it to resist further attack by rot. Often used in conjunction with Fill-It for this purpose to restore the original section of the timber.
The marine world loves CPES as the cost of replacing timbers in a wooden boat give a significant incentive to ‘Restore not replace’. It’s extreme marine performance will repair structural or cosmetic timbers in many other environments.
Details on restoration use are found here: how to restore wood. Because Clear Penetrating Epoxy Sealer and Fill-It work so well together, we sell repair kits containing both products at a discounted price too.
Coverage of CPES on rotten timber
Coverage of Clear Penetrating Epoxy Sealer is unfortunately very hard to estimate
On badly rotten timber, which you can crumble to dust with your fingers, you will typically use 2 or more times the volume of rotten timber in CPES to harden your wood dust. You will however end up with a piece of plasticised wood that you could beat someone to death with.
I will often harden wood like this as it can make the restoration of a profile far easier than removing the dust and then filling, even though it is a little more expensive. The solvents can take a long time to evaporate from timber in this state if the sections are large.
Evaluation by Trial
CPES will find rot that you were not even aware of in less rotted timber; the safest way to estimate requirements is to actually try a section of your rotten timber.
If you have a lot to do, I normally recommend you buy a 2 litre pack and use that. Having treated as much as you can with that you will have an accurate idea of how much you will need for the whole job, if it is not sufficient to do the whole job.
Priming Wood to Make Paint and Varnish Last
Clear Penetrating Epoxy Sealer penetrates deeply into timber, especially so at the end grain. This penetration strongly resists the ingress of moisture, protecting joints and end grain particularly thoroughly. It also promotes adhesion of the top coat, which will bond far more strongly to CPES than to the wood itself, thus significantly increasing the life of the top coat and reducing maintenance costs.
See ‘how to prime wood before varnishing‘ for full instructions on its use as a primer. Clear Penetrating Epoxy Sealer can be used without a top coat to achieve a natural surface finish on timber whilst protecting it from the elements, see ‘achieving a natural finish on protected wood‘ for instructions for this application.
Clear Penetrating Epoxy Sealer (CPES) – Coverage on new wood
Clear Penetrating Epoxy Sealer is very often used as the ultimate primer to make paint or varnish finishes that really last.
CPES use on new or sound timber is far easier to estimate. As all timber varies these figures are only estimates:
Treatment is for two coats on NEW timber:
- Softwood or plywood: 5 sq metres / litre
- Hardwood: 10 sq metres / litre
If the wood is old, porous or has suffered significant exposure to sunlight or the elements, it is normally safest to halve these coverage figures (ie you will use double the amount required for new timber).
CPES as a surface finish for interior timbers
Since CPES (like all epoxies) is degraded by UV light – it requires protection with varnish or paint when used outdoors.
Used internally it will last exceptionally well if not exposed to significant UV light. It offers a truly beautiful finish for interior timbers, enhancing the grain whilst protecting from water and staining. Furthermore it is extremely easy and fast to apply.
Clear Penetrating Epoxy Sealer can seal and protect internal doors
Click here for more details on protecting interior timber from staining and water, whilst enhancing the beauty of the timber.
CPES is ideal for worktops, plywood and home made furniture
I recently made a wonderful under stairs winerack, fabricated largely from plywood and Beech kitchen worktop it is all sealed and protected with Smiths CPES.
Curing characteristics: Which Formula CPES?
Clear Penetrating Epoxy Sealer is available in two formulations, a warm weather and a cold weather formulation. We stock and supply both formulations. We recommend Cold Weather Clear Penetrating Epoxy Sealer for use in the UK. Use Warm Weather Clear Penetrating Epoxy Sealer if the temperatures will exceed 25 degrees centigrade and you are priming. Check which temperature CPES you require if you are unsure.
Working With Smiths CPES, Clear Penetrating Epoxy Sealer
Smiths CPES comes in two tins labelled A and B. Mix the two parts 1 part to 1 part by volume prior to use. I find the easiest way is to take a parallel sided jam jar, decide how much you wish to mix, and make marks to suit, say at 4 and 8cm up from the base on the jar. Pour to the marks, and shake thoroughly.
Should you wish to mix Smiths CPES by weight the ratio is 98 parts of A to 100 parts of B. Smiths Clear Penetrating Epoxy Sealer is very forgiving of minor mix errors and the only real penalty will be more of one can left than the other when you have finished the job.
If you like video’s, there is a short one on this page showing the mixing procedure outlined above.
Prior to mixing you will find two metal inserts under the child proof caps. these inserts tightly seal the cans against solvent evaporation. I find these easiest to remove by hammering a small screwdriver through a cap, and prying it out.
Storing Smiths Clear Penetrating Epoxy Sealer
Solvent evaporation is the main means by which CPES ages. Store the cans in a temperature stable environment such as a cellar, with the caps tightly screwed on. 1.9 litre packs will be useable well over a year later, bigger cans even longer. The resins do not go off or set in the cans.
To store mixed CPES for the next coat;
- Lightly cover the container in which you mixed it
- Do not tightly screw the lid back on the jam jar, once the solvents have evaporated the resin is hard to the touch, and will glue the lid back on
- Store in a cool dark place (we do not recommend fridges as sparks can ignite the solvents)
It will remain useable for a surprisingly long time. Brushes likewise will soften again once placed into the container prior to applying the next coat.
Safety with Epoxy Resins
ALL epoxy resins can cause skin sensitisation. Please always wear rubber gloves when working with Clear Penetrating Epoxy Sealer.
The MSDS are available for download on this page, choose the MSDS tab to the left to see them.
Priming for Caulks and similar
Modern polyurethane caulks, such as 3M 5200, will bind extremely strongly to Clear Penetrating Epoxy Sealer, as will the hybrid caulk Everbuild Stixall. This capability can be used to very good effect to achieve permanently sealed boat hulls, and permanent flexible sealed joints in timber framed houses etc.
Smiths CPES is now manufactured in the UK
Make Wood Good are now manufacturing Smiths Clear Penetrating Epoxy Sealer (CPES) in the UK under licence from Smith and Co. of California. This should ensure that supply of the product is far better as our supply line is now more manageable.
Packaging is now Euro compliant, ie fully Reach compliant, and the sizes are now metric rather than Imperial. The product is totally identical to that manufactured in America. We make this same product available to any other European distributors requiring it.
We are moving to European packaging and measures for all CPES variants now.As old stock is run down and new stock appears, the Imperial sizes will be phased out completely.
- A 1 Litre kit replaces the old 2US Pint (0.95l) kit. Identical price
- A 2 Litre kit replaces the old 2US Quart (1.9l) kit. Identical price
- A 10 Litre kit (Supplied as 2 off 5L cans) replaces the old 2US Gallon (7.6l) kit. Increased price
The CW formula is manufactured in the UK and supplied in the new metric packaging since 2019. The 2 US Gallon kit is replaced with a 10 Litre kit supplied as 2 off 5 Litre tins of Smiths CPES.
The WW formula will be packaged inthe UK into metric packaging from the summer of 2021.