Clear Penetrating Epoxy Sealer (CPES)


Clear Penetrating Epoxy Sealer™ (Smiths CPES™) is a thin epoxy that will penetrate deeply into the surface of wood. It is the ultimate primer for wood to make paint or varnish stick. CPES restores strength to rotten wood and waterproofs all wood.

(35 customer reviews)

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.


This is the Make Wood Good American site. From here we can ship pallets worldwide but parcels only surface (UPS), meaning US and Canada, or via freight-consolidators to Hawaii, Puerto Rico and the Caribbean islands.

If you need to ship parcels to Europe, visit one of our European sites by clicking the closest of the two European flags on the header.

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.

Coverage of Clear Penetrating Epoxy Sealer (CPES) on new wood

Clear Penetrating Epoxy Sealer is very often used as the ultimate primer to make paint or varnish finishes that really last.

varnish primed with clear penetrating epoxy sealer to make it last on exterior wood

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

beautiful sealed oak interior 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.

finished under stairs winerack store

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 cold conditions. 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.

Clear Penetrating Epoxy Sealer CPES working and curing times

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 in the UK into metric packaging from the summer of 2021.

More Information

Clear Penetrating Epoxy Sealer Performance Testing

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

Additional information

Weight N/A
Dimensions N/A

Cold, Warm


5 Litre, 0.95 Litre – 2 US Pint, 1.9 Litre – 2 US Quart, 7.6 Litre – 2 US Gallons, 38 Litres – 10 US Gallons


Smiths Clear Penetrating Epoxy Sealer (CPES) MSDS

Cold Weather Formula MSDS



Warm Weather Formula MSDS



35 reviews for Clear Penetrating Epoxy Sealer (CPES)

  1. Amanda Rofe (verified owner)

    I used this to repair the rotting wood on the rafters and fascia of an old house. It saved me a lot of money in replacing the wood. Tha, and Smith’s filler, are the best products on the market by far.

  2. Piero Dalle Pezze (verified owner)

    I bought 1L of CPES for sealing my adjustable chair which is used outdoors next to my dobsonian telescope. The sealer was easy to apply. The first coat was left to dry for 3 days, although 2 were probably sufficient. I applied a second coat to work as a primer for the varnish, as described in the instruction guide. I am very pleased with the result. Hope it last long.

  3. David Angove (verified owner)

    Ah! CPES
    The time had come for a (much needed) mainetance session of the mahogany wheelhouse on our boat – the wheelhouse keeps all the bad weather out – but it was paying the price as joints were shrinking and slight traces of decomposition were appearing.
    A couple of treatments with CPES, and then three coats of my preferred ‘varnish’, and the timber looks, and feels, excellent.
    Time will always tell the durability of course, but I have sufficient CPES left in the tins for another 65 treatments, so I have absolutely no doubt that the wheelhouse shall last longer than me!
    Thank you Steve, your service is excellent too.

  4. Stephen Dakin (verified owner)

    Hello Michelle and Steve , I would just like to say how marvellous this product is . I thought that the slabs of lightening struck oak ,that had been felled and left laying on the ground for twenty years had gone past the point of no return , but two treatments of this product has made it solid and even the rot holes have been solidified .
    Thanks again .
    Phil Chandler

  5. Oldblue (verified owner)

    Really good for outdoor wood. Had a pair of shed doors that were becoming unusable in the wet. During a dry spell, treated them with CPES paying particular attention to the end grain, and this winter they have been really stable – amazing given the amount of rain we have had. Excellent product.

  6. Leigh Puddifoot (verified owner)

    Seems ok for the moment but only time will tell how good the product is.
    Extremely helpful people to deal with.

  7. Norman Finlayson (verified owner)

    Have used CPES for over two years,it is excellent for priming and sealing all sorts of wood ply etc ashore or afloat, way ahead of anything else I have tried before. Very happy with all the products.

  8. pjcampbell123 (verified owner)

    Originally used this product twenty years ago on an old (1950) cedar strip boat in Canada. The boat is still in fabulous condition with only a little wipe down with linseed oil every spring. Great product. Tried to get CPES in the UK without avail, until now. Well done Makewoodgood. I am currently using it on an old garden bench. Great stuff

  9. justinbrea (verified owner)

    Have bought a number of litres of this product and used it for wood restoration of cedar hot tub, water proofing marine ply, stabilising window frames. It has great properties of transforming spongy rotting wood into solid workable material. Use with filler for larger repairs.

  10. cyril.bannister (verified owner)

    Bought this to treat the entire woodwork on a 30+ year old boat, using a professional to take back to bare wood. The end result is very attractive to look at and based on my previous experience with epoxy products on boats will be extremely strong so resistant to the odd scrape and hard wearing. Would recommend to anyone who is fed up with the defecencies of just using varnish whatever the quality

  11. ian1bond

    Easy to use, and does the job – CPES is now a “must have” for all my joinery repair projects. I’ve used it with the Fill-It epoxy filler, and for priming new wood where I’ve spliced in repairs. It’s an excellent primer for the Stand Oil paint that I’m using to decorate doors and windows.

  12. chrisringrose (verified owner)

    An excellent product for rotten windows that needed repair, not replacement. Wood has turned solid in a short time, allowing filler to be added and (hopefully) a long lasting repair. Straightforwards to use if instructions followed. Having tested this on my first window, I’m now onto my next order!

  13. Craig Horner

    solid. I’ve used a 1 litre pack on about 16feet of wooden joists (6″x3) which if probably a bit much. However, they are now shiny and hard isn’t the word for it. I’ve tried to scratch it and knock it, there’s no impact. I’ve also had a good bounce on them and they’re more rigid than the others. Make sure you wash the brush or seal it in plastic bag as it’ll be useless tomorrow!

  14. Ray Carter

    Deck Repair. I used 3 products to repair the delaminating deck on my 33 year old boat. Rain water had found its way into the balsa sandwich between the grp layers and soaked and partially rotted some of the wood. This required drilling numerous holes in the affected part of the deck. After allowing a few weeks for the balsa core to dry out I used a syringe to inject CPES into the affected area to consolidate the wooden core and protect from rot. Layup and laminating epoxy with added silica was then injected to fill any voids. Finally Fill-It was used to fill and fair the holes. I then painted the deck with anti-slip paint. This process seems to have done the trick. The deck is strong and stable. It just remains to be seen if the repair stands the test of time. I found all 3 products extremely easy to work with.

  15. Duncan Reynolds

    Indoor Planters. Instead of lining all my orangery planters with plastic, I decided to use CPES. It was very easy to apply, and so far has worked brilliantly. My planters are on a wall inside, so I did not want water dripping down the wall from my automatic watering system. So far so good, I do keep checking the underside of each planter, and to this point no water is seeping through at all. I should just mention that I did apply a silicone sealant to the joints between each wals and the floor first as well as the CPES. Whilst I was applying the CPES I had a question about multiple coats. I posted the question, and within hours had received a phone call and was talked through exactly what to do. So all in all, for the product and the customer service, I would heartily recommend CPES.

  16. Steve

    Smiths CPES. I can only comment on the short term at this stage. Steve is a very helpful chap – call him with any questions and he always gets back to you. I used CPES on the teak frame on my boats superstructure prior to varnishing, and it has worked a treat. Very happy. Also has worked wonders on repairing some marine ply parts of the superstructure. Recommend both the product (though expensive for sure) and the vendor – top people.

  17. Bob

    Yacht rebuild. Have used CPES as a primer prior to painting on ply interior refit of small yacht. Application is simple and effective, a couple of coats sealed the good quality exterior ply I am using. Paint took well to the sealed wood. Obviously yet to see if it helps the wood last longer in the marine environment. Will update when I know!

  18. Simon Lyon

    Yachts. I use CPES as a primer on new wood prior to varnishing with Epiphanes. The CPES is a doddle to use, I use medication measuring cups to achieve the correct mix and just paint it on, it goes on like water. Keep applying until you achieve a shiny surface then apply the varnish before the primer fully dries. I have used this method on many wooden items on my boat, whether used inside or out and have had fantastic results and good longevity of the coating. I use CPES on new items as well as recoating old ones, it is expensive initialy but will reduce the amount of time, money and effort needed to keep wood looking good in the future.

  19. alasdair ramsay

    tannin pull. Used the product to stop tannin pull in exterior white oak doors. Seems to have worked very well but cannot rate it yet until I see what the worst of the weather can do over the winter. Will get back in the spring hopefully with a 5 * rating

  20. Mick Nash

    It is a lifesaver. This is my third batch of CPES. I will not start any restoration project on my wooden boat without first making sure I have a plentiful supply. It is a lifesaver.

  21. ken marshall

    Home timbers. I had very prompt and good advice for seriously deteriorated varnished house timbers. I applied the two pack a couple of weeks ago and have varnished over. I did not need to apply thinned product as is usual. I have applied four coats and the result looks solid and good. I need some time to be certain that the Epoxy it fulfils its promises

  22. Peter T Markham

    CPES. The stuff we brought from you worked very well in curing our soft deck on our Kelly Peterson 44. We are delighted how easy it was when we worked out how to go about doing it. I am ordering some more CPES to do a few more patches. we had plenty of the resin, thinners, and filler left.
    Had we had it done professionally it would have cost thousands of pounds not £225!!

  23. Chris

    CPES. Useful for special applications but rather expensive for regular use.

  24. Rob

    Cpes. Great product that works, just feel it’s a little too expensive.

  25. Chris NMarsay

    CPES. Useful product for special applications

  26. Travis

    Smiths Clear Penetrating Epoxy Sealer (CPES). Well I purchased this to help me carry out repairs on my wooden fishing boat. It seems perfect for my application. I had some wood rot that had penetrated the surface on oak and teak.. This was dug out and I dried the goodish wood as much as possble treated with rot killer then soaked the wood with the epoxy mix, left it for a week to cure. It makes a good hard rough base to then fill with normal expoxy and filler mix. I used it on different types of wood, always digging out as much of the loose stuff as possible.Results look great, only time will tell if it is still good in a year or two. I will try to remember to report back.
    The guy on the phone could not have been more helpful. Total oldschool specialist. Brilliant service and advice. Fingers crossed this has saved me a fortune and a load of work replacing planks.
    Regards, Travis.

  27. Janewood

    Great product. Customer service and delivery excellent and speedy.

    Simple product to use. Enters wood very easily. Saved several thousand pounds in dismantling a roof to replace lightly rotted roof apex beam- what’s not to like/ Absolutely solid now.

  28. Paul

    CPES. I’m writing this review based on the fact I keep ordering the product!!! Why? Well I’m restoring a 1934 Dunkirk little ship and found that CPES is an effective sealer and forms a good bonding surface in which to apply other products to like resins. It does toughen the timber as stated although you need a lot of it to effectively do this, weaker areas benefit from the application and I feel more confident about the timber not rottinging when I apply resins inside and out on the hull. I have decided to use CPES throught the boat although it’s expensive and only available in small qtys which is a bit frustrating, I feel it’s worth it on such a restoration.

  29. Travis

    Epoxy as a wood finisjh. I forgot to add, I sanded an area of teak decking that always weathers bad. Got back to good wood. I coated the teak in 2 coats of the epoxy and it brought the wood back to its former glory looking better than any varnish or wood oil that I hve previoulsy tried. It looks really hard wearing and has soaked into the wood rather than sitting on the surface. I have high hopes of this lasting well. Great product. The fumes blow your mind, but its workth it!

  30. Mick Nash

    Wonderful Stuff. Wonderful stuff. After removing the rotten gunwales from Escaper I had to be sure that the teak covering boards were rot free and suitable for accepting screws. The CPES penetrated the full depth of the wood and set rock hard. Job done

  31. Kjell Inge Hanson

    CPES Wonderstuff. Hi. Have used CPES from top to bottom and also inside on my 1949 Century Seamaid which I just restored. I must say, this is truly a wonderful stuff. Had some soft spots but they are gone for good. I stain the boats first and then use 3-4 coats of CPES before varnish. Also used it on the deck and mahogany cabin on my 1947 40 feet Chris Craft DCEB. I will also use it on my 55 feet Shain Trimmership from 1950 which I also will restore next year. Again, wonderful stuff! Kjell from Kristiansund, Norway

  32. Chris Marsay

    CPES. Did the job of consolidating rotten hardwood with a complex profile well. Be patient, it takes as much as a week for the solvent to evaporate and the resin to harden, even in summer.

  33. Bob Carter

    Garden Railway: Sealing Plywood Edges. I used the product to seal the cut edges of the marine ply boards I employed in constructing my garden railway. Only time will tell how durable the boards now are, but the product was easy to use, and seems to have penetrated and filled the wood effectively.

  34. pär

    Sweet. it works as it should
    the wood gets back strength so you do not need to replace the unnecessary wood


  35. Tom Hickock

    deck boards. I have recently used the resin on a set replacement deckboaeds for my narrowboat. it was easy to use and seems to penetrate well. check with me n a couple of years and I will tell you better then how it lasts

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