Smiths Clear Penetrating Epoxy Sealer (CPES)

What Is Clear Penetrating Epoxy Sealer™?

Smiths Clear Penetrating Epoxy Sealer™ (CPES™) is a thin epoxy that will penetrate deeply into the surface of wood. It is the original product of Smiths and Co. and has been restoring and protecting for over 40 years now. It is also known as Lignu in Scandinavia and MultiWoodPrime for new wood applications. It is often abbreviated to CPES.

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. It has to be mixed before use. It is mixed in a 1 to 1 ratio, and is tolerant of minor mix errors. If you wish to mix by weight, both Cold and Warm formula are mixed at 98 parts A by weight to 100 parts B by weight.

Packaged between the two cans is a very comprehensive instruction leaflet. Please read this prior to use if you are unfamiliar with this product.

Smiths clear penetrating epoxy sealer

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. It’s use is well established in the marine world, where the cost of replacing timbers in a wooden boat give a significant incentive to ‘Restore not replace’, however it can be used to good effect to repair structural or cosmetic timbers in many other environments. Details on restoration use are found here. Because Clear Penetrating Epoxy Sealer and Fill-It work so well together, we sell repair kits containing both products at a discounted price too.

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 here 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 here for instructions for this application.

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. For use in the UK Cold Weather Clear Penetrating Epoxy Sealer is recommended, Warm Weather Clear Penetrating Epoxy Sealer should be used if the temperatures will exceed 25 degrees centigrade. Check which temperature CPES you require if you are unsure.

Clear Penetrating Epoxy Sealer CPES working and curing times

Working With Smiths CPES, Clear Penetrating Epoxy Sealer

The two parts of Smiths CPES are supplied in separate tins, and the materials are mixed 1 part to 1 part 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,m say at 4 and 8cm up from the base on the jar. Pour to the marks, and shake gently.

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.

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, and 1.9 litre packs are useable well over a year later, bigger cans even longer. The resins do not go off or set in the cans.

ALL epoxy resins can cause skin sensitisation. Please always wear rubber gloves when working with CPES.

If you have some left over mixed CPES and wish to use it 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), keep it in a cool dark place (fridges are not recommended 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.

Priming for Caulks and similar

Modern polyurethane caulks, such as 3M 5200, will bind extremely strongly to CPES, 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.

More Information

FAQ – Frequently asked questions, with answers, about CPES

Creators Notes – From the pen of Steve Smith

Six simple steps to restoration

Penetration testing with the Rot Doctor – The best vs the Rest

How to create the perfect varnish finish

How to restore rotted wood, the science and the practice

Clear Penetrating Epoxy Sealer Reviews


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